Merge remote-tracking branch 'origin/main' into feature/140

backend/.rspec

@@ -0,0 +1 @@
+--require spec_helper

backend/Gemfile

@@ -46,6 +46,8 @@ group :development, :test do
 
   # Omakase Ruby styling [https://github.com/rails/rubocop-rails-omakase/]
   gem "rubocop-rails-omakase", require: false
+
+  gem 'factory_bot_rails'
 end
 
 
@@ -63,3 +65,7 @@ gem 'diff-lcs'
 gem 'dotenv-rails'
 
 gem 'whenever', require: false
+
+gem 'discard'
+
+gem "rspec-rails", "~> 8.0", :groups => [:development, :test]

backend/Gemfile.lock

@@ -90,6 +90,8 @@ GEM
     crass (1.0.6)
     date (3.4.1)
     diff-lcs (1.6.2)
+    discard (1.4.0)
+      activerecord (>= 4.2, < 9.0)
     dotenv (3.1.8)
     dotenv-rails (3.1.8)
       dotenv (= 3.1.8)
@@ -97,6 +99,11 @@ GEM
     drb (2.2.1)
     ed25519 (1.4.0)
     erubi (1.13.1)
+    factory_bot (6.5.6)
+      activesupport (>= 6.1.0)
+    factory_bot_rails (6.5.1)
+      factory_bot (~> 6.5)
+      railties (>= 6.1.0)
     ffi (1.17.2-aarch64-linux-gnu)
     ffi (1.17.2-aarch64-linux-musl)
     ffi (1.17.2-arm-linux-gnu)
@@ -296,6 +303,23 @@ GEM
       io-console (~> 0.5)
     rexml (3.4.1)
     rouge (3.30.0)
+    rspec-core (3.13.6)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.5)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.7)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-rails (8.0.2)
+      actionpack (>= 7.2)
+      activesupport (>= 7.2)
+      railties (>= 7.2)
+      rspec-core (~> 3.13)
+      rspec-expectations (~> 3.13)
+      rspec-mocks (~> 3.13)
+      rspec-support (~> 3.13)
+    rspec-support (3.13.6)
     rss (0.3.1)
       rexml
     rubocop (1.75.6)
@@ -420,7 +444,9 @@ DEPENDENCIES
   bootsnap
   brakeman
   diff-lcs
+  discard
   dotenv-rails
+  factory_bot_rails
   gollum
   image_processing (~> 1.14)
   jwt
@@ -430,6 +456,7 @@ DEPENDENCIES
   puma (>= 5.0)
   rack-cors
   rails (~> 8.0.2)
+  rspec-rails (~> 8.0)
   rubocop-rails-omakase
   sprockets-rails
   sqlite3 (>= 2.1)

backend/app/controllers/application_controller.rb

@@ -11,4 +11,15 @@ class ApplicationController < ActionController::API
     code = request.headers['X-Transfer-Code'] || request.headers['HTTP_X_TRANSFER_CODE']
     @current_user = User.find_by(inheritance_code: code)
   end
+
+  def bool? key, default: false
+    return default if params[key].nil?
+
+    s = params[key].to_s.strip.downcase
+    if default
+      !(s.in?(['0', 'false', 'off', 'no']))
+    else
+      s.in?(['', '1', 'true', 'on', 'yes'])
+    end
+  end
 end

backend/app/controllers/ip_addresses_controller.rb

@@ -1,20 +0,0 @@
-class IpAddressesController < ApplicationController
-  def index
-    @ip_addresses = IpAddress.all
-
-    render json: @ip_addresses
-  end
-
-  def show
-    render json: @ip_address
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/nico_tag_relation_controller.rb

@@ -1,16 +0,0 @@
-class NicoTagRelationController < ApplicationController
-  def index
-  end
-
-  def show
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/nico_tags_controller.rb

@@ -1,9 +1,13 @@
 class NicoTagsController < ApplicationController
+  TAG_JSON = { only: [:id, :category, :post_count], methods: [:name, :has_wiki] }.freeze
+
   def index
     limit = (params[:limit] || 20).to_i
     cursor = params[:cursor].presence
 
-    q = Tag.nico_tags.includes(:linked_tags).order(updated_at: :desc)
+    q = Tag.nico_tags
+           .includes(:tag_name, linked_tags: :tag_name)
+           .order(updated_at: :desc)
     q = q.where('tags.updated_at < ?', Time.iso8601(cursor)) if cursor
 
     tags = q.limit(limit + 1)
@@ -15,7 +19,9 @@ class NicoTagsController < ApplicationController
     end
 
     render json: { tags: tags.map { |tag|
-      tag.as_json(include: :linked_tags)
+      tag.as_json(TAG_JSON).merge(linked_tags: tag.linked_tags.map { |lt|
+        lt.as_json(TAG_JSON)
+      })
     }, next_cursor: }
   end
 
@@ -30,12 +36,11 @@ class NicoTagsController < ApplicationController
 
     linked_tag_names = params[:tags].to_s.split(' ')
     linked_tags = Tag.normalise_tags(linked_tag_names, with_tagme: false)
-    return head :bad_request if linked_tags.filter { |t| t.category == 'nico' }.present?
+    return head :bad_request if linked_tags.any? { |t| t.category == 'nico' }
 
     tag.linked_tags = linked_tags
-    tag.updated_at = Time.now
     tag.save!
 
-    render json: tag.linked_tags, status: :ok
+    render json: tag.linked_tags.map { |t| t.as_json(TAG_JSON) }, status: :ok
   end
 end

backend/app/controllers/post_tags_controller.rb

@@ -1,16 +0,0 @@
-class PostTagsController < ApplicationController
-  def index
-  end
-
-  def show
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/posts_controller.rb

@@ -1,29 +1,42 @@
-require 'open-uri'
-require 'nokogiri'
-
-
 class PostsController < ApplicationController
-  # GET /posts
+  Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
+
   def index
-    limit = params[:limit].presence&.to_i
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
     cursor = params[:cursor].presence
 
-    created_at = ('COALESCE(posts.original_created_before - INTERVAL 1 SECOND,' +
-                  'posts.original_created_from,' +
-                  'posts.created_at)')
-    q = filtered_posts.order(Arel.sql("#{ created_at } DESC"))
-    q = q.where("#{ created_at } < ?", Time.iso8601(cursor)) if cursor
+    page = 1 if page < 1
+    limit = 1 if limit < 1
+
+    offset = (page - 1) * limit
 
-    posts = limit ? q.limit(limit + 1) : q
+    sort_sql =
+        'COALESCE(posts.original_created_before - INTERVAL 1 SECOND,' +
+        'posts.original_created_from,' +
+        'posts.created_at)'
+    q =
+        filtered_posts
+        .preload(tags: :tag_name)
+        .with_attached_thumbnail
+        .select("posts.*, #{ sort_sql } AS sort_ts")
+        .order(Arel.sql("#{ sort_sql } DESC"))
+    posts = (
+        if cursor
+          q.where("#{ sort_sql } < ?", Time.iso8601(cursor)).limit(limit + 1)
+        else
+          q.limit(limit).offset(offset)
+        end).to_a
 
     next_cursor = nil
-    if limit && posts.size > limit
-      next_cursor = posts.last.created_at.iso8601(6)
+    if cursor && posts.length > limit
+      next_cursor = posts.last.read_attribute('sort_ts').iso8601(6)
       posts = posts.first(limit)
     end
 
     render json: { posts: posts.map { |post|
-      post.as_json(include: { tags: { only: [:id, :name, :category, :post_count] } }).tap do |json|
+      post.as_json(include: { tags: { only: [:id, :category, :post_count],
+                                      methods: [:name, :has_wiki] } }).tap do |json|
         json['thumbnail'] =
             if post.thumbnail.attached?
               rails_storage_proxy_url(post.thumbnail, only_path: false)
@@ -31,58 +44,69 @@ class PostsController < ApplicationController
               nil
             end
       end
-    }, next_cursor: }
+    }, count: if filtered_posts.group_values.present?
+      filtered_posts.count.size
+    else
+      filtered_posts.count
+    end, next_cursor: }
   end
 
   def random
-    post = filtered_posts.order('RAND()').first
+    post = filtered_posts.preload(tags: :tag_name).order('RAND()').first
     return head :not_found unless post
 
     viewed = current_user&.viewed?(post) || false
 
     render json: (post
-                  .as_json(include: { tags: { only: [:id, :name, :category, :post_count] } })
+                  .as_json(include: { tags: { only: [:id, :category, :post_count],
+                                              methods: [:name, :has_wiki] } })
                   .merge(viewed:))
   end
 
-  # GET /posts/1
   def show
-    post = Post.includes(:tags).find(params[:id])
+    post = Post.includes(tags: :tag_name).find(params[:id])
     return head :not_found unless post
 
     viewed = current_user&.viewed?(post) || false
 
-    render json: (post
-                  .as_json(include: { tags: { only: [:id, :name, :category, :post_count] } })
-                  .merge(related: post.related(limit: 20), viewed:))
+    json = post.as_json
+    json['tags'] = build_tag_tree_for(post.tags)
+    json['related'] = post.related(limit: 20)
+    json['viewed'] = viewed
+
+    render json:
   end
 
-  # POST /posts
   def create
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.member?
 
-    # TODO: URL が正規のものがチェック，不正ならエラー
-    # TODO: URL は必須にする（タイトルは省略可）．
     # TODO: サイトに応じて thumbnail_base 設定
-    title = params[:title]
+    title = params[:title].presence
     url = params[:url]
     thumbnail = params[:thumbnail]
     tag_names = params[:tags].to_s.split(' ')
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
 
-    post = Post.new(title:, url:, thumbnail_base: '', uploaded_user: current_user,
+    post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
                     original_created_from:, original_created_before:)
     post.thumbnail.attach(thumbnail)
     if post.save
       post.resized_thumbnail!
-      post.tags = Tag.normalise_tags(tag_names)
-      render json: post.as_json(include: { tags: { only: [:id, :name, :category, :post_count] } }),
+      tags = Tag.normalise_tags(tag_names)
+      tags = Tag.expand_parent_tags(tags)
+      sync_post_tags!(post, tags)
+
+      post.reload
+      render json: post.as_json(include: { tags: { only: [:id, :category, :post_count],
+                                                   methods: [:name, :has_wiki] } }),
              status: :created
     else
       render json: { errors: post.errors.full_messages }, status: :unprocessable_entity
     end
+  rescue Tag::NicoTagNormalisationError
+    head :bad_request
   end
 
   def viewed
@@ -99,48 +123,162 @@ class PostsController < ApplicationController
     head :no_content
   end
 
-  # PATCH/PUT /posts/1
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.member?
 
-    title = params[:title]
+    title = params[:title].presence
     tag_names = params[:tags].to_s.split(' ')
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
 
     post = Post.find(params[:id].to_i)
-    tags = post.tags.where(category: 'nico').to_a +
-           Tag.normalise_tags(tag_names, with_tagme: false)
-    if post.update(title:, tags:, original_created_from:, original_created_before:)
-      render json: post.as_json(include: { tags: { only: [:id, :name, :category, :post_count] } }),
-             status: :ok
+    if post.update(title:, original_created_from:, original_created_before:)
+      tags = post.tags.where(category: 'nico').to_a +
+             Tag.normalise_tags(tag_names, with_tagme: false)
+      tags = Tag.expand_parent_tags(tags)
+      sync_post_tags!(post, tags)
+
+      post.reload
+      json = post.as_json
+      json['tags'] = build_tag_tree_for(post.tags)
+      render json:, status: :ok
     else
       render json: post.errors, status: :unprocessable_entity
     end
+  rescue Tag::NicoTagNormalisationError
+    head :bad_request
   end
 
-  # DELETE /posts/1
-  def destroy
+  def changes
+    id = params[:id]
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
+
+    page = 1 if page < 1
+    limit = 1 if limit < 1
+
+    offset = (page - 1) * limit
+
+    pts = PostTag.with_discarded
+    pts = pts.where(post_id: id) if id.present?
+    pts = pts.includes(:post, { tag: :tag_name }, :created_user, :deleted_user)
+
+    events = []
+    pts.each do |pt|
+      events << Event.new(
+          post:         pt.post,
+          tag:          pt.tag.as_json(only: [:id, :category], methods: [:name, :has_wiki]),
+          user:         pt.created_user && { id: pt.created_user.id, name: pt.created_user.name },
+          change_type:  'add',
+          timestamp:    pt.created_at)
+
+      if pt.discarded_at
+        events << Event.new(
+            post:         pt.post,
+            tag:          pt.tag.as_json(only: [:id, :category], methods: [:name, :has_wiki]),
+            user:         pt.deleted_user && { id: pt.deleted_user.id, name: pt.deleted_user.name },
+            change_type:  'remove',
+            timestamp:    pt.discarded_at)
+      end
+    end
+    events.sort_by!(&:timestamp)
+    events.reverse!
+
+    render json: { changes: events.slice(offset, limit).as_json, count: events.size }
   end
 
   private
 
   def filtered_posts
-    tag_names = params[:tags]&.split(' ')
+    tag_names = params[:tags].to_s.split(' ')
     match_type = params[:match]
-    tag_names.present? ? filter_posts_by_tags(tag_names, match_type) : Post.all
+    if tag_names.present?
+      filter_posts_by_tags(tag_names, match_type)
+    else
+      Post.all
+    end
   end
 
   def filter_posts_by_tags tag_names, match_type
-    posts = Post.joins(:tags)
+    tag_names = TagName.canonicalise(tag_names)
+
+    posts = Post.joins(tags: :tag_name)
+
     if match_type == 'any'
-      posts = posts.where(tags: { name: tag_names }).distinct
+      posts.where(tag_names: { name: tag_names }).distinct
     else
-      tag_names.each do |tag|
-        posts = posts.where(id: Post.joins(:tags).where(tags: { name: tag }))
+      posts.where(tag_names: { name: tag_names })
+           .group('posts.id')
+           .having('COUNT(DISTINCT tag_names.id) = ?', tag_names.uniq.size)
+    end
+  end
+
+  def sync_post_tags! post, desired_tags
+    desired_tags.each do |t|
+      t.save! if t.new_record?
+    end
+
+    desired_ids = desired_tags.map(&:id).to_set
+    current_ids = post.tags.pluck(:id).to_set
+
+    to_add = desired_ids - current_ids
+    to_remove = current_ids - desired_ids
+
+    Tag.where(id: to_add).find_each do |tag|
+      begin
+        PostTag.create!(post:, tag:, created_user: current_user)
+      rescue ActiveRecord::RecordNotUnique
+        ;
       end
     end
-    posts.distinct
+
+    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+      pt.discard_by!(current_user)
+    end
+  end
+
+  def build_tag_tree_for tags
+    tags = tags.to_a
+    tag_ids = tags.map(&:id)
+
+    implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
+
+    children_ids_by_parent = Hash.new { |h, k| h[k] = [] }
+    implications.each do |imp|
+      children_ids_by_parent[imp.parent_tag_id] << imp.tag_id
+    end
+
+    child_ids = children_ids_by_parent.values.flatten.uniq
+
+    root_ids = tag_ids - child_ids
+
+    tags_by_id = tags.index_by(&:id)
+
+    memo = { }
+
+    build_node = -> tag_id, path do
+      tag = tags_by_id[tag_id]
+      return nil unless tag
+
+      if path.include?(tag_id)
+        return tag.as_json(only: [:id, :category, :post_count],
+                           methods: [:name, :has_wiki]).merge(children: [])
+      end
+
+      if memo.key?(tag_id)
+        return memo[tag_id]
+      end
+
+      new_path = path + [tag_id]
+      child_ids = children_ids_by_parent[tag_id] || []
+
+      children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
+
+      memo[tag_id] = tag.as_json(only: [:id, :category, :post_count],
+                                 methods: [:name, :has_wiki]).merge(children:)
+    end
+
+    root_ids.filter_map { |id| build_node.call(id, []) }
   end
 end

backend/app/controllers/settings_controller.rb

@@ -1,16 +0,0 @@
-class SettingsController < ApplicationController
-  def index
-  end
-
-  def show
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/tag_aliases_controller.rb

@@ -1,16 +0,0 @@
-class TagAliasesController < ApplicationController
-  def index
-  end
-
-  def show
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/tag_children_controller.rb

@@ -0,0 +1,27 @@
+class TagChildrenController < ApplicationController
+  def create
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.admin?
+
+    parent_id = params[:parent_id]
+    child_id = params[:child_id]
+    return head :bad_request if parent_id.blank? || child_id.blank?
+
+    Tag.find(parent_id).children << Tag.find(child_id) rescue nil
+
+    head :no_content
+  end
+
+  def destroy
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.admin?
+
+    parent_id = params[:parent_id]
+    child_id = params[:child_id]
+    return head :bad_request if parent_id.blank? || child_id.blank?
+
+    Tag.find(parent_id).children.delete(Tag.find(child_id)) rescue nil
+
+    head :no_content
+  end
+end

backend/app/controllers/tags_controller.rb

@@ -1,46 +1,100 @@
 class TagsController < ApplicationController
   def index
     post_id = params[:post]
-    tags = if post_id.present?
-             Tag.joins(:posts).where(posts: { id: post_id })
-           else
-             Tag.all
-           end
-    render json: tags
+
+    tags =
+        if post_id.present?
+          Tag.joins(:posts).where(posts: { id: post_id })
+        else
+          Tag.all
+        end
+
+    render json: tags.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
   end
 
   def autocomplete
     q = params[:q].to_s.strip
     return render json: [] if q.blank?
 
-    tags = (Tag
-            .where('(category = ? AND name LIKE ?) OR name LIKE ?',
-                   'nico', "nico:#{ q }%", "#{ q }%")
-            .order('post_count DESC, name ASC')
-            .limit(20))
-    render json: tags
+    with_nico = bool?(:nico, default: true)
+    present_only = bool?(:present, default: true)
+
+    alias_rows =
+        TagName
+        .where('name LIKE ?', "#{ q }%")
+        .where.not(canonical_id: nil)
+        .pluck(:canonical_id, :name)
+
+    matched_alias_by_tag_name_id = { }
+    canonical_ids = []
+
+    alias_rows.each do |canonical_id, alias_name|
+      canonical_ids << canonical_id
+      matched_alias_by_tag_name_id[canonical_id] ||= alias_name
+    end
+
+    base = Tag.joins(:tag_name).includes(:tag_name)
+    base = base.where('tags.post_count > 0') if present_only
+
+    canonical_hit =
+        base
+        .where(((with_nico ? '(tags.category = ? AND tag_names.name LIKE ?) OR ' : '') +
+                'tag_names.name LIKE ?'),
+               *(with_nico ? ['nico', "nico:#{ q }%"] : []), "#{ q }%")
+
+    tags =
+        if canonical_ids.present?
+          canonical_hit.or(base.where(tag_name_id: canonical_ids.uniq))
+        else
+          canonical_hit
+        end
+
+    tags = tags.order(Arel.sql('post_count DESC, tag_names.name')).limit(20).to_a
+
+    render json: tags.map { |tag|
+      tag.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
+          .merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
+    }
   end
 
   def show
-    tag = Tag.find(params[:id])
-    render json: tag
+    tag = Tag.find_by(id: params[:id])
+    if tag
+      render json: tag.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
+    else
+      head :not_found
+    end
   end
 
   def show_by_name
-    tag = Tag.find_by(name: params[:name])
+    name = params[:name].to_s.strip
+    return head :bad_request if name.blank?
+
+    tag = Tag.joins(:tag_name).includes(:tag_name).find_by(tag_names: { name: })
     if tag
-      render json: tag
+      render json: tag.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
     else
       head :not_found
     end
   end
 
-  def create
-  end
-
   def update
-  end
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.member?
+
+    name = params[:name].presence
+    category = params[:category].presence
+
+    tag = Tag.find(params[:id])
+
+    if name.present?
+      tag.tag_name.update!(name:)
+    end
+
+    if category.present?
+      tag.update!(category:)
+    end
 
-  def destroy
+    render json: tag.as_json(methods: [:name])
   end
 end

backend/app/controllers/user_ips_controller.rb

@@ -1,16 +0,0 @@
-class UserIpsController < ApplicationController
-  def index
-  end
-
-  def show
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/user_post_views_controller.rb

@@ -1,16 +0,0 @@
-class UserPostViewsController < ApplicationController
-  def index
-  end
-
-  def show
-  end
-
-  def create
-  end
-
-  def update
-  end
-
-  def destroy
-  end
-end

backend/app/controllers/users_controller.rb

@@ -18,6 +18,8 @@ class UsersController < ApplicationController
   end
 
   def renew
+    return head :unauthorized unless current_user
+
     user = current_user
     user.inheritance_code = SecureRandom.uuid
     user.save!

backend/app/controllers/wiki_pages_controller.rb

@@ -1,35 +1,66 @@
 class WikiPagesController < ApplicationController
+  rescue_from Wiki::Commit::Conflict, with: :render_wiki_conflict
+
   def index
-    wiki_pages = WikiPage.all
+    title = params[:title].to_s.strip
+    return render json: WikiPage.all.as_json(methods: [:title]) if title.blank?
 
-    render json: wiki_pages
+    q = WikiPage.joins(:tag_name).includes(:tag_name)
+        .where('tag_names.name LIKE ?', "%#{ WikiPage.sanitize_sql_like(title) }%")
+    render json: q.limit(20).as_json(methods: [:title])
   end
 
   def show
-    render_wiki_page_or_404 WikiPage.find(params[:id])
+    page = WikiPage.find_by(id: params[:id])
+    render_wiki_page_or_404 page
   end
 
   def show_by_title
-    render_wiki_page_or_404 WikiPage.find_by(title: params[:title])
+    title = params[:title].to_s.strip
+    page = WikiPage.joins(:tag_name)
+                   .includes(:tag_name)
+                   .find_by(tag_names: { name: title })
+    render_wiki_page_or_404 page
+  end
+
+  def exists
+    if WikiPage.exists?(id: params[:id])
+      head :no_content
+    else
+      head :not_found
+    end
+  end
+
+  def exists_by_title
+    title = params[:title].to_s.strip
+    if WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
+      head :no_content
+    else
+      head :not_found
+    end
   end
 
   def diff
     id = params[:id]
-    from = params[:from]
+    return head :bad_request if id.blank?
+
+    from = params[:from].presence
     to = params[:to].presence
-    return head :bad_request if id.blank? || from.blank?
 
-    wiki_page_from = WikiPage.find(id)
-    wiki_page_to = WikiPage.find(id)
-    wiki_page_from.sha = from
-    wiki_page_to.sha = to
+    page = WikiPage.find(id)
+
+    from_rev = from && page.wiki_revisions.find(from)
+    to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
+    if ((from_rev && !(from_rev.content?)) || !(to_rev&.content?))
+      return head :unprocessable_entity
+    end
 
-    diffs = Diff::LCS.sdiff(wiki_page_from.body, wiki_page_to.body)
+    diffs = Diff::LCS.sdiff(from_rev&.body&.lines || [], to_rev.body.lines)
     diff_json = diffs.map { |change|
       case change.action
       when ?=
         { type: 'context', content: change.old_element }
-      when ?|
+      when ?!
         [{ type: 'removed', content: change.old_element },
          { type: 'added', content: change.new_element }]
       when ?+
@@ -39,23 +70,32 @@ class WikiPagesController < ApplicationController
       end
     }.flatten.compact
 
-    render json: { wiki_page_id:  wiki_page_from.id,
-                   title:         wiki_page_from.title,
-                   older_sha:     wiki_page_from.sha,
-                   newer_sha:     wiki_page_to.sha,
-                   diff:          diff_json }
+    render json: { wiki_page_id:      page.id,
+                   title:             page.title,
+                   older_revision_id: from_rev&.id,
+                   newer_revision_id: to_rev.id,
+                   diff:              diff_json }
   end
 
   def create
     return head :unauthorized unless current_user
-    return head :forbidden unless ['admin', 'member'].include?(current_user.role)
+    return head :forbidden unless current_user.member?
+
+    title = params[:title]&.strip
+    body = params[:body].to_s
+
+    return head :unprocessable_entity if title.blank? || body.blank?
+
+    page = WikiPage.new(title:, created_user: current_user, updated_user: current_user)
 
-    wiki_page = WikiPage.new(title: params[:title], created_user: current_user, updated_user: current_user)
-    if wiki_page.save
-      wiki_page.set_body params[:body], user: current_user
-      render json: wiki_page, status: :created
+    if page.save
+      message = params[:message].presence
+      Wiki::Commit.content!(page:, body:, created_user: current_user, message:)
+
+      render json: page.as_json(methods: [:title]), status: :created
     else
-      render json: { errors: wiki_page.errors.full_messages }, status: :unprocessable_entity
+      render json: { errors: page.errors.full_messages },
+             status: :unprocessable_entity
     end
   end
 
@@ -63,73 +103,82 @@ class WikiPagesController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.member?
 
-    title = params[:title]
-    body = params[:body]
+    title = params[:title]&.strip
+    body = params[:body].to_s
 
     return head :unprocessable_entity if title.blank? || body.blank?
 
-    wiki_page = WikiPage.find(params[:id])
-    wiki_page.title = title
-    wiki_page.updated_user = current_user
-    wiki_page.set_body(body, user: current_user)
-    wiki_page.save!
+    page = WikiPage.find(params[:id])
+    base_revision_id = page.current_revision.id
+
+    if params[:title].present? && params[:title].strip != page.title
+      return head :unprocessable_entity
+    end
+
+    message = params[:message].presence
+    Wiki::Commit.content!(page:,
+                          body:,
+                          created_user: current_user,
+                          message:,
+                          base_revision_id:)
 
     head :ok
   end
 
   def search
-    title = params[:title]&.strip
-
-    q = WikiPage.all
-    q = q.where('title LIKE ?', "%#{ WikiPage.sanitize_sql_like(title) }%") if title.present?
-
-    render json: q.limit(20)
+    index
   end
 
   def changes
-    id = params[:id]
-    log = if id.present?
-            wiki.page("#{ id }.md")&.versions
-          else
-            wiki.repo.log('main', nil)
-          end
-    return render json: [] unless log
-
-    render json: log.map { |commit|
-      wiki_page = WikiPage.find(commit.message.split(' ')[1].to_i)
-      wiki_page.sha = commit.id
-
-      next nil if wiki_page.sha.blank?
-
-      user = User.find(commit.author.name.to_i)
-
-      { sha:          wiki_page.sha,
-        pred:         wiki_page.pred,
-        succ:         wiki_page.succ,
-        wiki_page:    wiki_page && { id: wiki_page.id, title: wiki_page.title },
-        user:         user && { id: user.id, name: user.name },
-        change_type:  commit.message.split(' ')[0].downcase[0...(-1)],
-        timestamp:    commit.authored_date }
+    id = params[:id].presence
+    q = WikiRevision.includes(:wiki_page, :created_user).order(id: :desc)
+    q = q.where(wiki_page_id: id) if id
+
+    render json: q.limit(200).map { |rev|
+      { revision_id:  rev.id,
+        pred:         rev.base_revision_id,
+        succ:         nil,
+        wiki_page:    { id: rev.wiki_page_id, title: rev.wiki_page.title },
+        user:         { id: rev.created_user.id, name: rev.created_user.name },
+        kind:         rev.kind,
+        message:      rev.message,
+        timestamp:    rev.created_at }
     }.compact
   end
 
   private
 
-  WIKI_PATH = Rails.root.join('wiki').to_s
+  def render_wiki_page_or_404 page
+    return head :not_found unless page
 
-  def wiki
-    @wiki ||= Gollum::Wiki.new(WIKI_PATH)
-  end
+    rev = find_revision(page)
+    return head :not_found unless rev
+
+    if rev.redirect?
+      return (
+          redirect_to wiki_page_by_title_path(title: rev.redirect_page.title),
+                      status: :moved_permanently)
+    end
+
+    body = rev.body
+    revision_id = rev.id
+    pred = page.pred_revision_id(revision_id)
+    succ = page.succ_revision_id(revision_id)
+    updated_at = rev.created_at
 
-  def render_wiki_page_or_404 wiki_page
-    return head :not_found unless wiki_page
+    render json: page.as_json(methods: [:title])
+                     .merge(body:, revision_id:, pred:, succ:, updated_at:)
+  end
 
-    wiki_page.sha = params[:version].presence
+  def find_revision page
+    if params[:version].present?
+      page.wiki_revisions.find_by(id: params[:version])
+    else
+      page.current_revision
+    end
+  end
 
-    body = wiki_page.body
-    sha = wiki_page.sha
-    pred = wiki_page.pred
-    succ = wiki_page.succ
-    render json: wiki_page.as_json.merge(body:, sha:, pred:, succ:)
+  def render_wiki_conflict err
+    render json: { error: 'conflict', message: err.message }, status: :conflict
   end
 end

backend/app/models/nico_tag_relation.rb

@@ -6,6 +6,7 @@ class NicoTagRelation < ApplicationRecord
   validates :tag_id, presence: true
 
   validate :nico_tag_must_be_nico
+  validate :tag_mustnt_be_nico
 
   private
 

backend/app/models/post.rb

@@ -1,21 +1,25 @@
-require 'mini_magick'
-
-
 class Post < ApplicationRecord
+  require 'mini_magick'
+
   belongs_to :parent, class_name: 'Post', optional: true, foreign_key: 'parent_id'
   belongs_to :uploaded_user, class_name: 'User', optional: true
-  has_many :post_tags, dependent: :destroy
-  has_many :tags, through: :post_tags
-  has_many :user_post_views, dependent: :destroy
-  has_many :post_similarities_as_post,
-           class_name: 'PostSimilarity',
-           foreign_key: :post_id
-  has_many :post_similarities_as_target_post,
-           class_name: 'PostSimilarity',
-           foreign_key: :target_post_id
+
+  has_many :post_tags, dependent: :destroy, inverse_of: :post
+  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
+  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
+  has_many :tags, through: :active_post_tags
+
+  has_many :user_post_views, dependent: :delete_all
+  has_many :post_similarities, dependent: :delete_all
+
   has_one_attached :thumbnail
 
+  before_validation :normalise_url
+
+  validates :url, presence: true, uniqueness: true
+
   validate :validate_original_created_range
+  validate :url_must_be_http_url
 
   def as_json options = { }
     super(options).merge({ thumbnail: thumbnail.attached? ?
@@ -27,18 +31,12 @@ class Post < ApplicationRecord
   end
 
   def related(limit: nil)
-    ids_with_cos =
-        post_similarities_as_post.select(:target_post_id, :cos)
-                                 .map { |ps| [ps.target_post_id, ps.cos] } +
-        post_similarities_as_target_post.select(:post_id, :cos)
-                                        .map { |ps| [ps.post_id, ps.cos] }
-
-    sorted = ids_with_cos.sort_by { |_, cos| -cos }
-
-    ids = sorted.map(&:first)
-    ids = ids.first(limit) if limit
+    ids = post_similarities.select(:target_post_id).order(cos: :desc)
+    ids = ids.limit(limit) if limit
+    ids = ids.pluck(:target_post_id)
+    return [] if ids.empty?
 
-    Post.where(id: ids).index_by(&:id).values_at(*ids)
+    Post.where(id: ids).order(Arel.sql("FIELD(id, #{ ids.join(',') })"))
   end
 
   def resized_thumbnail!
@@ -67,4 +65,33 @@ class Post < ApplicationRecord
       errors.add :original_created_before, 'オリジナルの作成日時の順番がをかしぃです．'
     end
   end
+
+  def url_must_be_http_url
+    begin
+      u = URI.parse(url)
+    rescue URI::InvalidURIError
+      errors.add(:url, 'URL が不正です．')
+      return
+    end
+
+    if !(u in URI::HTTP) || u.host.blank?
+      errors.add(:url, 'URL が不正です．')
+      return
+    end
+  end
+
+  def normalise_url
+    return if url.blank?
+
+    self.url = url.strip
+
+    u = URI.parse(url)
+    return unless u in URI::HTTP
+
+    u.host = u.host.downcase if u.host
+    u.path = u.path.sub(/\/\Z/, '') if u.path.present?
+    self.url = u.to_s
+  rescue URI::InvalidURIError
+    ;
+  end
 end

backend/app/models/post_similarity.rb

@@ -1,4 +1,6 @@
 class PostSimilarity < ApplicationRecord
-  belongs_to :post, class_name: 'Post', foreign_key: 'post_id'
-  belongs_to :target_post, class_name: 'Post', foreign_key: 'target_post_id'
+  self.primary_key = :post_id, :target_post_id
+
+  belongs_to :post
+  belongs_to :target_post, class_name: 'Post'
 end

backend/app/models/post_tag.rb

@@ -1,7 +1,29 @@
 class PostTag < ApplicationRecord
+  include Discard::Model
+
+  before_destroy do
+    raise ActiveRecord::ReadOnlyRecord, '消さないでください．'
+  end
+
   belongs_to :post
   belongs_to :tag, counter_cache: :post_count
+  belongs_to :created_user, class_name: 'User', optional: true
+  belongs_to :deleted_user, class_name: 'User', optional: true
 
   validates :post_id, presence: true
   validates :tag_id, presence: true
+  validates :post_id, uniqueness: {
+      scope: :tag_id,
+      conditions: -> { where(discarded_at: nil) } }
+
+  def discard_by! deleted_user
+    return self if discarded?
+
+    transaction do
+      update!(discarded_at: Time.current, deleted_user:)
+      Tag.where(id: tag_id).update_all('post_count = GREATEST(post_count - 1, 0)')
+    end
+
+    self
+  end
 end

backend/app/models/tag.rb

@@ -1,72 +1,138 @@
 class Tag < ApplicationRecord
-  has_many :post_tags, dependent: :destroy
-  has_many :posts, through: :post_tags
-  has_many :tag_aliases, dependent: :destroy
+  class NicoTagNormalisationError < ArgumentError
+    ;
+  end
+
+  has_many :post_tags, inverse_of: :tag
+  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
+  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
+  has_many :posts, through: :active_post_tags
 
   has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
   has_many :linked_tags, through: :nico_tag_relations, source: :tag
 
-  has_many :reversed_nico_tag_relations, class_name: 'NicoTagRelation',
-                                         foreign_key: :tag_id,
-                                         dependent: :destroy
+  has_many :reversed_nico_tag_relations,
+           class_name: 'NicoTagRelation', foreign_key: :tag_id, dependent: :destroy
   has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
-  enum :category, { deerjikist:  'deerjikist',
-                    meme:        'meme',
-                    character:   'character',
-                    general:     'general',
-                    material:    'material',
-                    nico:        'nico',
-                    meta:        'meta' }
+  has_many :tag_implications, foreign_key: :parent_tag_id, dependent: :destroy
+  has_many :children, through: :tag_implications, source: :tag
+
+  has_many :reversed_tag_implications,
+           class_name: 'TagImplication', foreign_key: :tag_id, dependent: :destroy
+  has_many :parents, through: :reversed_tag_implications, source: :parent_tag
+
+  has_many :tag_similarities, dependent: :delete_all
+
+  belongs_to :tag_name
+  delegate :name, to: :tag_name, allow_nil: true
+  validates :tag_name, presence: true
+
+  enum :category, deerjikist:  'deerjikist',
+                  meme:        'meme',
+                  character:   'character',
+                  general:     'general',
+                  material:    'material',
+                  nico:        'nico',
+                  meta:        'meta'
 
-  validates :name, presence: true, length: { maximum: 255 }
   validates :category, presence: true, inclusion: { in: Tag.categories.keys }
 
   validate :nico_tag_name_must_start_with_nico
+  validate :tag_name_must_be_canonical
 
   scope :nico_tags, -> { where(category: :nico) }
 
   CATEGORY_PREFIXES = {
-      'gen:'  => 'general',
-      'djk:'  => 'deerjikist',
-      'meme:' => 'meme',
-      'chr:'  => 'character',
-      'mtr:'  => 'material',
-      'meta:' => 'meta' }.freeze
+      'gen:'  => :general,
+      'djk:'  => :deerjikist,
+      'meme:' => :meme,
+      'chr:'  => :character,
+      'mtr:'  => :material,
+      'meta:' => :meta }.freeze
+
+  def name= val
+    (self.tag_name ||= build_tag_name).name = val
+  end
+
+  def has_wiki
+    tag_name&.wiki_page.present?
+  end
 
   def self.tagme
-    @tagme ||= Tag.find_or_initialize_by(name: 'タグ希望') do |tag|
-      tag.category = 'meta'
-    end
+    @tagme ||= find_or_create_by_tag_name!('タグ希望', category: :meta)
   end
 
   def self.bot
-    @bot ||= Tag.find_or_initialize_by(name: 'bot操作') do |tag|
-      tag.category = 'meta'
-    end
+    @bot ||= find_or_create_by_tag_name!('bot操作', category: :meta)
   end
 
-  def self.normalise_tags tag_names, with_tagme: true
+  def self.normalise_tags tag_names, with_tagme: true, deny_nico: true
+    if deny_nico && tag_names.any? { |n| n.start_with?('nico:') }
+      raise NicoTagNormalisationError 
+    end
+
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.start_with?(p) } || ['', nil]
-      name.delete_prefix!(pf)
-      Tag.find_or_initialize_by(name:).tap do |tag|
+      name = TagName.canonicalise(name.delete_prefix(pf)).first
+      find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         if cat && tag.category != cat
-          tag.category = cat
-          tag.save!
+          tag.update!(category: cat)
         end
       end
     end
+
     tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
-    tags.uniq
+    tags.uniq(&:id)
+  end
+
+  def self.expand_parent_tags tags
+    return [] if tags.blank?
+
+    seen = Set.new
+    result = []
+    stack = tags.compact.dup
+
+    until stack.empty?
+      tag = stack.pop
+      next unless tag
+
+      tag.parents.each do |parent|
+        next if seen.include?(parent.id)
+
+        seen << parent.id
+        result << parent
+        stack << parent
+      end
+    end
+
+    (result + tags).uniq { |t| t.id }
+  end
+
+  def self.find_or_create_by_tag_name! name, category:
+    tn = TagName.find_or_create_by!(name: name.to_s.strip)
+    tn = tn.canonical if tn.canonical_id?
+
+    Tag.find_or_create_by!(tag_name_id: tn.id) do |t|
+      t.category = category
+    end
+  rescue ActiveRecord::RecordNotUnique
+    retry
   end
 
   private
 
   def nico_tag_name_must_start_with_nico
-    if ((category == 'nico' && !(name.start_with?('nico:'))) || 
-        (category != 'nico' && name.start_with?('nico:')))
+    n = name.to_s
+    if ((category == 'nico' && !(n.start_with?('nico:'))) || 
+        (category != 'nico' && n.start_with?('nico:')))
       errors.add :name, 'ニコニコ・タグの命名規則に反してゐます．'
     end
   end
+
+  def tag_name_must_be_canonical
+    if tag_name&.canonical_id?
+      errors.add :tag_name, 'tag_names へは実体を示す必要があります．'
+    end
+  end
 end

backend/app/models/tag_alias.rb

@@ -1,6 +0,0 @@
-class TagAlias < ApplicationRecord
-  belongs_to :tag
-
-  validates :tag_id, presence: true
-  validates :name, presence: true, length: { maximum: 255 }, uniqueness: true
-end

backend/app/models/tag_implication.rb

@@ -0,0 +1,17 @@
+class TagImplication < ApplicationRecord
+  belongs_to :tag, class_name: 'Tag'
+  belongs_to :parent_tag, class_name: 'Tag'
+
+  validates :tag_id, presence: true, uniqueness: { scope: :parent_tag_id }
+  validates :parent_tag_id, presence: true
+
+  validate :parent_tag_mustnt_be_itself
+
+  private
+
+  def parent_tag_mustnt_be_itself
+    if parent_tag == tag
+      errors.add :parent_tag_id, '親タグは子タグと同一であってはなりません．'
+    end
+  end
+end

backend/app/models/tag_name.rb

@@ -0,0 +1,42 @@
+class TagName < ApplicationRecord
+  has_one :tag
+  has_one :wiki_page
+
+  belongs_to :canonical, class_name: 'TagName', optional: true
+  has_many :aliases, class_name: 'TagName', foreign_key: :canonical_id
+
+  validates :name, presence: true, length: { maximum: 255 }, uniqueness: true
+
+  validate :canonical_must_be_canonical
+  validate :alias_name_must_not_have_prefix
+  validate :canonical_must_not_be_present_with_tag_or_wiki_page
+
+  def self.canonicalise names
+    names = Array(names).map { |n| n.to_s.strip }.reject(&:blank?)
+    return [] if names.blank?
+
+    tns = TagName.includes(:canonical).where(name: names).index_by(&:name)
+
+    names.map { |name| tns[name]&.canonical&.name || name }.uniq
+  end
+
+  private
+
+  def canonical_must_be_canonical
+    if canonical&.canonical_id?
+      errors.add :canonical, 'canonical は実体を示す必要があります．'
+    end
+  end
+
+  def alias_name_must_not_have_prefix
+    if canonical_id? && name.to_s.include?(':')
+      errors.add :name, 'エーリアス名にプレフィクスを含むことはできません．'
+    end
+  end
+
+  def canonical_must_not_be_present_with_tag_or_wiki_page
+    if canonical_id? && (tag || wiki_page)
+      errors.add :canonical, 'タグもしくは Wiki の参照がある名前はエーリアスになれません．'
+    end
+  end
+end

backend/app/models/tag_similarity.rb

@@ -0,0 +1,6 @@
+class TagSimilarity < ApplicationRecord
+  self.primary_key = :tag_id, :target_tag_id
+
+  belongs_to :tag
+  belongs_to :target_tag, class_name: 'Tag'
+end

backend/app/models/user_ip.rb

@@ -1,4 +1,6 @@
 class UserIp < ApplicationRecord
+  self.primary_key = :user_id, :ip_address_id
+
   belongs_to :user
   belongs_to :ip_address
 

backend/app/models/user_post_view.rb

@@ -1,4 +1,6 @@
 class UserPostView < ApplicationRecord
+  self.primary_key = :user_id, :post_id
+
   belongs_to :user
   belongs_to :post
 

backend/app/models/wiki_line.rb

@@ -0,0 +1,15 @@
+class WikiLine < ApplicationRecord
+  has_many :wiki_revision_lines, dependent: :restrict_with_exception
+
+  validates :sha256, presence: true, uniqueness: true, length: { is: 64 }
+  validates :body, presence: true
+
+  def self.upsert_by_body! body
+    sha = Digest::SHA256.hexdigest(body)
+    now = Time.current
+
+    upsert({ sha256: sha, body:, created_at: now, updated_at: now })
+
+    find_by!(sha256: sha)
+  end
+end

backend/app/models/wiki_page.rb

@@ -1,80 +1,59 @@
-require 'gollum-lib'
+require 'set'
 
 
 class WikiPage < ApplicationRecord
-  belongs_to :tag, optional: true
-  belongs_to :created_user, class_name: 'User', foreign_key: 'created_user_id'
-  belongs_to :updated_user, class_name: 'User', foreign_key: 'updated_user_id'
+  has_many :wiki_revisions, dependent: :destroy
+  belongs_to :created_user, class_name: 'User'
+  belongs_to :updated_user, class_name: 'User'
 
-  validates :title, presence: true, length: { maximum: 255 }, uniqueness: true
+  has_many :redirected_from_revisions,
+           class_name: 'WikiRevision',
+           foreign_key: :redirect_page_id,
+           dependent: :nullify
 
-  def as_json options = { }
-    self.sha = nil
-    super options
-  end
+  belongs_to :tag_name
+  validates :tag_name, presence: true
 
-  def sha= val
-    if val.present?
-      @sha = val
-      @page = wiki.page("#{ id }.md", @sha)
-    else
-      @page = wiki.page("#{ id }.md")
-      @sha = @page.versions.first.id
-    end
-    vers = @page.versions
-    idx = vers.find_index { |ver| ver.id == @sha }
-    if idx
-      @pred = vers[idx + 1]&.id
-      @succ = idx.positive? ? vers[idx - 1].id : nil
-      @updated_at = vers[idx].authored_date
-    else
-      @sha = nil
-      @pred = nil
-      @succ = nil
-      @updated_at = nil
-    end
-    @sha
+  def title
+    tag_name.name
   end
 
-  def sha
-    @sha
+  def title= val
+    (self.tag_name ||= build_tag_name).name = val
   end
 
-  def pred
-    @pred
+  def current_revision
+    wiki_revisions.order(id: :desc).first
   end
 
-  def succ
-    @succ
+  def body
+    rev = current_revision
+    rev.body if rev&.content?
   end
 
-  def updated_at
-    @updated_at
-  end
+  def resolve_redirect limit: 10
+    page = self
+    visited = Set.new
 
-  def body
-    sha = nil unless @page
-    @page&.raw_data&.force_encoding('UTF-8')
-  end
+    limit.times do
+      return page if visited.include?(page.id)
+
+      visited.add(page.id)
+
+      rev = page.current_revision
+      return page if !(rev&.redirect?) || !(rev.redirect_page)
 
-  def set_body content, user:
-    commit_info = { name:   user.id.to_s,
-                    email:  'dummy@example.com' }
-    page = wiki.page("#{ id }.md")
-    if page
-      commit_info[:message] = "Updated #{ id }"
-      wiki.update_page(page, id.to_s, :markdown, content, commit_info)
-    else
-      commit_info[:message] = "Created #{ id }"
-      wiki.write_page(id.to_s, :markdown, content, commit_info)
+      page = rev.redirect_page
     end
-  end
 
-  private
+    page
+  end
 
-  WIKI_PATH = Rails.root.join('wiki').to_s
+  def pred_revision_id revision_id
+    wiki_revisions.where('id < ?', revision_id).order(id: :desc).limit(1).pick(:id)
+  end
 
-  def wiki
-    @wiki ||= Gollum::Wiki.new(WIKI_PATH)
+  def succ_revision_id revision_id
+    wiki_revisions.where('id > ?', revision_id).order(id: :asc).limit(1).pick(:id)
   end
 end

backend/app/models/wiki_revision.rb

@@ -0,0 +1,55 @@
+class WikiRevision < ApplicationRecord
+  belongs_to :wiki_page
+  belongs_to :base_revision, class_name: 'WikiRevision', optional: true
+  belongs_to :created_user, class_name: 'User'
+  belongs_to :redirect_page, class_name: 'WikiPage', optional: true
+
+  has_many :wiki_revision_lines, dependent: :delete_all
+  has_many :wiki_lines, through: :wiki_revision_lines
+
+  enum :kind, { content: 0, redirect: 1 }
+
+  validates :kind, presence: true
+  validates :lines_count, numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :tree_sha256, length: { is: 64 }, allow_nil: true
+
+  validate :kind_consistency
+
+  def body
+    return unless content?
+
+    wiki_revision_lines
+        .includes(:wiki_line)
+        .order(:position)
+        .map { |rev| rev.wiki_line.body }
+        .join("\n")
+  end
+
+  private
+
+  def kind_consistency
+    if content?
+      if tree_sha256.blank?
+        errors.add(:tree_sha256, '種類がページの場合は必須です．') 
+      end
+
+      if redirect_page_id.present?
+        errors.add(:redirect_page_id, '種類がページの場合は空である必要があります．')
+      end
+    end
+
+    if redirect?
+      if redirect_page_id.blank?
+        errors.add(:redirect_page_id, '種類がリダイレクトの場合は必須です．')
+      end
+
+      if tree_sha256.present?
+        errors.add(:tree_sha256, '種類がリダイレクトの場合は空である必要があります．')
+      end
+
+      if lines_count.to_i > 0
+        errors.add(:lines_count, '種類がリダイレクトの場合は 0 である必要があります．')
+      end
+    end
+  end
+end

backend/app/models/wiki_revision_line.rb

@@ -0,0 +1,8 @@
+class WikiRevisionLine < ApplicationRecord
+  belongs_to :wiki_revision
+  belongs_to :wiki_line
+
+  validates :position, presence: true,
+                       numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :position, uniqueness: { scope: :wiki_revision_id }
+end

backend/app/services/similarity/calc.rb

@@ -0,0 +1,106 @@
+module Similarity
+  class Calc
+    def self.call model, tgt
+      similarity_model = "#{ model.name }Similarity".constantize
+
+      # 最大保存件数
+      n = 20
+
+      similarity_model.delete_all
+
+      posts = model.includes(tgt).select(:id).to_a
+
+      tag_ids = { }
+      tag_cnts = { }
+
+      posts.each do |p|
+        arr = p.public_send(tgt).map(&:id).sort
+        tag_ids[p.id] = arr
+        tag_cnts[p.id] = arr.size
+      end
+
+      intersection_size = -> a, b do
+        i = 0
+        j = 0
+        cnt = 0
+        while i < a.size && j < b.size
+          a_i = a[i]
+          b_j = b[j]
+          if a_i == b_j
+            cnt += 1
+            i += 1
+            j += 1
+          elsif a_i < b_j
+            i += 1
+          else
+            j += 1
+          end
+        end
+        cnt
+      end
+
+      push_topk = -> list, cos, target_id do
+        return if list.size >= n && cos <= list[-1][0]
+
+        idx = nil
+        list.each_with_index do |(c, tid), i|
+          if tid == target_id
+            idx = i
+            break
+          end
+        end
+        if idx
+          return if cos <= list[idx][0]
+          list.delete_at(idx)
+        end
+
+        insert_at = list.size
+        list.each_with_index do |(c, _), i|
+          if cos > c
+            insert_at = i
+            break
+          end
+        end
+        list.insert(insert_at, [cos, target_id])
+        list.pop if list.size > n
+      end
+
+      top = Hash.new { |h, key| h[key] = [] }
+
+      ids = posts.map(&:id)
+      ids.each_with_index do |post_id, i|
+        a = tag_ids[post_id]
+        a_cnt = tag_cnts[post_id]
+
+        ((i + 1)...ids.size).each do |j|
+          target_id = ids[j]
+          b = tag_ids[target_id]
+          b_cnt = tag_cnts[target_id]
+
+          norm = Math.sqrt(a_cnt * b_cnt)
+          cos = norm.zero? ? 0.0 : intersection_size.(a, b).fdiv(norm)
+
+          push_topk.(top[post_id], cos, target_id)
+          push_topk.(top[target_id], cos, post_id)
+        end
+      end
+
+      buf = []
+      flush = -> do
+        return if buf.empty?
+        similarity_model.insert_all!(buf)
+        buf.clear
+      end
+
+      top.each do |post_id, list|
+        list.each do |cos, target_post_id|
+          buf << { "#{ model.name.underscore }_id".to_sym => post_id,
+                   "target_#{ model.name.underscore }_id".to_sym => target_post_id,
+                   cos: }
+          flush.call if buf.size >= 1_000
+        end
+      end
+      flush.call
+    end
+  end
+end

backend/app/services/wiki/commit.rb

@@ -0,0 +1,122 @@
+require 'digest'
+
+
+module Wiki
+  class Commit
+    class Conflict < StandardError
+      ;
+    end
+
+    def self.content! page:, body:, created_user:, message: nil, base_revision_id: nil
+      new(page:, created_user:).content!(body:, message:, base_revision_id:)
+    end
+
+    def self.redirect! page:, redirect_page:, created_user:, message: nil, base_revision_id: nil
+      new(page:, created_user:).redirect!(redirect_page:, message:, base_revision_id:)
+    end
+
+    def initialize page:, created_user:
+      @page = page
+      @created_user = created_user
+    end
+
+    def content! body:, message:, base_revision_id:
+      normalised = normalise_body(body)
+      lines = split_lines(normalised)
+
+      line_shas = lines.map { |line| Digest::SHA256.hexdigest(line) }
+      tree_sha = Digest::SHA256.hexdigest(line_shas.join(','))
+
+      line_id_by_sha = upsert_lines!(lines, line_shas)
+      line_ids = line_shas.map { |sha| line_id_by_sha.fetch(sha) }
+
+      ActiveRecord::Base.transaction do
+        @page.lock!
+
+        if base_revision_id.present?
+          current_id = @page.wiki_revisions.maximum(:id)
+          if current_id && current_id != base_revision_id.to_i
+            raise Conflict,
+                "競合が発生してゐます（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
+          end
+        end
+
+        rev = WikiRevision.create!(
+            wiki_page:        @page,
+            base_revision_id:,
+            created_user:     @created_user,
+            kind:             :content,
+            redirect_page_id: nil,
+            message:,
+            lines_count:      lines.length,
+            tree_sha256:      tree_sha)
+
+        rows = line_ids.each_with_index.map do |line_id, pos|
+          { wiki_revision_id: rev.id, wiki_line_id: line_id, position: pos }
+        end
+        WikiRevisionLine.insert_all!(rows)
+
+        rev
+      end
+    end
+
+    def redirect! redirect_page:, message:, base_revision_id:
+      ActiveRecord::Base.transaction do
+        @page.lock!
+
+        if base_revision_id.present?
+          current_id = @page.wiki_revisions.maximum(:id)
+          if current_id && current_id != base_revision_id.to_i
+            raise Conflict,
+                "競合が発生してゐます（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
+          end
+        end
+
+        WikiRevision.create!(
+            wiki_page:        @page,
+            base_revision_id:,
+            created_user:     @created_user,
+            kind:             :redirect,
+            redirect_page:,
+            message:,
+            lines_count:      0,
+            tree_sha256:      nil)
+      end
+    end
+
+    private
+
+    def normalise_body body
+      s = body.to_s
+      s.gsub!("\r\n", "\n")
+      s.encode('UTF-8', invalid: :replace, undef: :replace, replace: '🖕')
+    end
+
+    def split_lines body
+      body.split("\n")
+    end
+
+    def upsert_lines! lines, line_shas
+      now = Time.current
+
+      id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+
+      missing_rows = []
+      line_shas.each_with_index do |sha, i|
+        next if id_by_sha.key?(sha)
+
+        missing_rows << { sha256:     sha,
+                          body:       lines[i],
+                          created_at: now,
+                          updated_at: now }
+      end
+
+      if missing_rows.any?
+        WikiLine.upsert_all(missing_rows)
+        id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+      end
+
+      id_by_sha
+    end
+  end
+end

backend/config/application.rb

@@ -11,6 +11,9 @@ module Backend
     # Initialize configuration defaults for originally generated Rails version.
     config.load_defaults 8.0
 
+    config.i18n.available_locales = [:ja, :en]
+    config.i18n.default_locale = :ja
+
     # Please, add to the `ignore` list any other `lib` subdirectories that do
     # not contain `.rb` files, or that should not be reloaded or eager loaded.
     # Common ones are `templates`, `generators`, or `middleware`, for example.

backend/config/locales/en.yml

@@ -28,4 +28,8 @@
 #       enabled: "ON"
 
 en:
-  hello: "Hello world"
+  activerecord:
+    errors:
+      messages:
+        record_invalid: "Validation failed: %{errors}"
+        taken: 'イキスギ!'

backend/config/locales/ja.yml

@@ -0,0 +1,2 @@
+ja:
+  hello: 'ぬ゛〜゛ん゛'

backend/config/routes.rb

@@ -1,45 +1,57 @@
 Rails.application.routes.draw do
-  get 'tags/nico', to: 'nico_tags#index'
-  put 'tags/nico/:id', to: 'nico_tags#update'
-  get 'tags/autocomplete', to: 'tags#autocomplete'
-  get 'tags/name/:name', to: 'tags#show_by_name'
-  get 'posts/random', to: 'posts#random'
-  post 'posts/:id/viewed', to: 'posts#viewed'
-  delete 'posts/:id/viewed', to: 'posts#unviewed'
-  get 'preview/title', to: 'preview#title'
-  get 'preview/thumbnail', to: 'preview#thumbnail'
-  get 'wiki/title/:title', to: 'wiki_pages#show_by_title'
-  get 'wiki/search', to: 'wiki_pages#search'
-  get 'wiki/changes', to: 'wiki_pages#changes'
-  get 'wiki/:id/diff', to: 'wiki_pages#diff'
-  get 'wiki/:id', to: 'wiki_pages#show'
-  get 'wiki', to: 'wiki_pages#index'
-  post 'wiki', to: 'wiki_pages#create'
-  put 'wiki/:id', to: 'wiki_pages#update'
-  post 'users/code/renew', to: 'users#renew'
-
-  resources :posts
-  resources :ip_addresses
-  resources :nico_tag_relations
-  resources :post_tags
-  resources :settings
-  resources :tag_aliases
-  resources :tags
-  resources :user_ips
-  resources :user_post_views
-  resources :users, only: [:create, :update] do
+  resources :nico_tags, path: 'tags/nico', only: [:index, :update]
+
+  scope 'tags/:parent_id/children', controller: :tag_children do
+    post ':child_id', action: :create
+    delete ':child_id', action: :destroy
+  end
+
+  resources :tags, only: [:index, :show, :update] do
     collection do
-      post :verify
-      get :me
+      get :autocomplete
+      get 'name/:name', action: :show_by_name
     end
   end
 
-  # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html
+  scope :preview, controller: :preview do
+    get :title
+    get :thumbnail
+  end
 
-  # Reveal health status on /up that returns 200 if the app boots with no exceptions, otherwise 500.
-  # Can be used by load balancers and uptime monitors to verify that the app is live.
-  # get "up" => "rails/health#show", as: :rails_health_check
+  resources :wiki_pages, path: 'wiki', only: [:index, :show, :create, :update] do
+    collection do
+      get :search
+      get :changes
+
+      scope :title do
+        get ':title/exists', action: :exists_by_title
+        get ':title', action: :show_by_title
+      end
+    end
+
+    member do
+      get :exists
+      get :diff
+    end
+  end
 
-  # Defines the root path route ("/")
-  # root "posts#index"
+  resources :posts, only: [:index, :show, :create, :update] do
+    collection do
+      get :random
+      get :changes
+    end
+
+    member do
+      post :viewed
+      delete :viewed, action: :unviewed
+    end
+  end
+
+  resources :users, only: [:create, :update] do
+    collection do
+      post :verify
+      get :me
+      post 'code/renew', action: :renew
+    end
+  end
 end

backend/db/migrate/20251009222200_create_tag_implications.rb

@@ -0,0 +1,9 @@
+class CreateTagImplications < ActiveRecord::Migration[8.0]
+  def change
+    create_table :tag_implications do |t|
+      t.references :tag, null: false, foreign_key: { to_table: :tags }
+      t.references :parent_tag, null: false, foreign_key: { to_table: :tags }
+      t.timestamps
+    end
+  end
+end

backend/db/migrate/20251011200300_add_discard_to_post_tags.rb

@@ -0,0 +1,36 @@
+class AddDiscardToPostTags < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+        pt1
+      FROM
+        post_tags pt1
+        INNER JOIN
+          post_tags pt2
+          ON
+            pt1.post_id = pt2.post_id
+            AND pt1.tag_id = pt2.tag_id
+            AND pt1.id > pt2.id
+      ;
+    SQL
+
+    add_column :post_tags, :discarded_at, :datetime
+    add_index :post_tags, :discarded_at
+
+    add_column :post_tags, :is_active, :boolean,
+               as: 'discarded_at IS NULL', stored: true
+
+    add_column :post_tags, :active_unique_key, :string,
+               as: "CASE WHEN discarded_at IS NULL THEN CONCAT(post_id, ':', tag_id) ELSE NULL END",
+               stored: true
+
+    add_index :post_tags, :active_unique_key, unique: true, name: 'idx_post_tags_active_unique'
+
+    add_index :post_tags, [:post_id, :discarded_at]
+    add_index :post_tags, [:tag_id, :discarded_at]
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20251210123200_add_unique_index_to_tag_implications.rb

@@ -0,0 +1,27 @@
+class AddUniqueIndexToTagImplications < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+        ti1
+      FROM
+        tag_implications ti1
+        INNER JOIN
+          tag_implications ti2
+          ON
+            ti1.tag_id = ti2.tag_id
+            AND ti1.parent_tag_id = ti2.parent_tag_id
+            AND ti1.id > ti2.id
+      ;
+    SQL
+
+    add_index :tag_implications, [:tag_id, :parent_tag_id],
+              unique: true,
+              name: 'index_tag_implications_on_tag_id_and_parent_tag_id'
+  end
+
+  def down
+    # NOTE: 重複削除は復元されなぃ．
+    remove_index :tag_implications,
+                 name: 'index_tag_implications_on_tag_id_and_parent_tag_id'
+  end
+end

backend/db/migrate/20251229012100_remove_tag_from_wiki_pages.rb

@@ -0,0 +1,5 @@
+class RemoveTagFromWikiPages < ActiveRecord::Migration[7.0]
+  def change
+    remove_reference :wiki_pages, :tag, if_exists: true
+  end
+end

backend/db/migrate/20251229020700_create_wiki_lines.rb

@@ -0,0 +1,11 @@
+class CreateWikiLines < ActiveRecord::Migration[7.0]
+  def change
+    create_table :wiki_lines do |t|
+      t.string :sha256, null: false, limit: 64
+      t.text :body, null: false
+      t.timestamps
+    end
+
+    add_index :wiki_lines, :sha256, unique: true
+  end
+end

backend/db/migrate/20251229021000_create_wiki_revisions.rb

@@ -0,0 +1,19 @@
+class CreateWikiRevisions < ActiveRecord::Migration[7.0]
+  def change
+    create_table :wiki_revisions do |t|
+      t.references :wiki_page, null: false, foreign_key: true
+      t.references :base_revision, foreign_key: { to_table: :wiki_revisions }
+      t.references :created_user, null: false, foreign_key: { to_table: :users }
+      t.integer :kind, null: false, default: 0  # 0: content, 1: redirect
+      t.references :redirect_page, foreign_key: { to_table: :wiki_pages }
+      t.string :message
+      t.integer :lines_count, null: false, default: 0
+      t.string :tree_sha256, limit: 64
+      t.timestamps
+    end
+
+    add_index :wiki_revisions, :tree_sha256
+    add_index :wiki_revisions, [:wiki_page_id, :id]
+    add_index :wiki_revisions, :kind
+  end
+end

backend/db/migrate/20251229022100_create_wiki_revision_lines.rb

@@ -0,0 +1,12 @@
+class CreateWikiRevisionLines < ActiveRecord::Migration[7.0]
+  def change
+    create_table :wiki_revision_lines do |t|
+      t.references :wiki_revision, null: false, foreign_key: true
+      t.integer :position, null: false
+      t.references :wiki_line, null: false, foreign_key: true
+    end
+
+    add_index :wiki_revision_lines, [:wiki_revision_id, :position], unique: true
+    add_index :wiki_revision_lines, [:wiki_revision_id, :wiki_line_id]
+  end
+end

backend/db/migrate/20251230143400_make_thumbnail_base_nullable_in_posts.rb

@@ -0,0 +1,27 @@
+class MakeThumbnailBaseNullableInPosts < ActiveRecord::Migration[7.0]
+  def up
+    change_column_null :posts, :thumbnail_base, true
+
+    execute <<~SQL
+      UPDATE
+        posts
+      SET
+        thumbnail_base = NULL
+      WHERE
+        thumbnail_base = ''
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      UPDATE
+        posts
+      SET
+        thumbnail_base = ''
+      WHERE
+        thumbnail_base IS NULL
+    SQL
+
+    change_column_null :posts, :thumbnail_base, false
+  end
+end

backend/db/migrate/20260107034300_make_title_nullable_in_posts.rb

@@ -0,0 +1,28 @@
+class MakeTitleNullableInPosts < ActiveRecord::Migration[7.0]
+  def up
+    change_column_null :posts, :title, true
+
+    execute <<~SQL
+      UPDATE
+        posts
+      SET
+        title = NULL
+      WHERE
+        title = ''
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      UPDATE
+        posts
+      SET
+        title = ''
+      WHERE
+        title IS NULL
+    SQL
+
+    change_column_null :posts, :title, false
+  end
+end
+

backend/db/migrate/20260111180600_create_tag_names.rb

@@ -0,0 +1,10 @@
+class CreateTagNames < ActiveRecord::Migration[7.0]
+  def change
+    create_table :tag_names do |t|
+      t.string :name, limit: 255, null: false
+      t.references :canonical, null: true, foreign_key: { to_table: :tag_names }, index: true
+      t.timestamps
+    end
+    add_index :tag_names, :name, unique: true
+  end
+end

backend/db/migrate/20260111192600_add_tag_name_to_tags.rb

@@ -0,0 +1,42 @@
+class AddTagNameToTags < ActiveRecord::Migration[7.0]
+  class Tag < ApplicationRecord
+    self.table_name = 'tags'
+  end
+
+  class TagName < ApplicationRecord
+    self.table_name = 'tag_names'
+  end
+
+  def up
+    add_reference :tags, :tag_name, null: true, foreign_key: true, index: false, after: :id
+    add_index :tags, :tag_name_id, unique: true
+
+    Tag.find_each do |tag|
+      name = tag.read_attribute(:name)
+      tn = TagName.find_or_create_by!(name:) do |r|
+        r.canonical_id = nil
+      end
+      tag.update_columns(tag_name_id: tn.id)
+    end
+
+    change_column_null :tags, :tag_name_id, false
+
+    remove_column :tags, :name
+  end
+
+  def down
+    add_column :tags, :name, :string, limit: 255, null: true, after: :id
+
+    Tag.find_each do |tag|
+      tag_name_id = tag.read_attribute(:tag_name_id)
+      name = TagName.find(tag_name_id).read_attribute(:name)
+      tag.update_columns(name:)
+    end
+
+    change_column_null :tags, :name, false
+
+    remove_foreign_key :tags, column: :tag_name_id
+    remove_index :tags, :tag_name_id
+    remove_column :tags, :tag_name_id
+  end
+end

backend/db/migrate/20260111204400_add_tag_name_to_wiki_pages.rb

@@ -0,0 +1,42 @@
+class AddTagNameToWikiPages < ActiveRecord::Migration[7.0]
+  class WikiPage < ApplicationRecord
+    self.table_name = 'wiki_pages'
+  end
+
+  class TagName < ApplicationRecord
+    self.table_name = 'tag_names'
+  end
+
+  def up
+    add_reference :wiki_pages, :tag_name, null: true, foreign_key: true, index: false, after: :id
+    add_index :wiki_pages, :tag_name_id, unique: true
+
+    WikiPage.find_each do |page|
+      name = page.read_attribute(:title)
+      tn = TagName.find_or_create_by!(name:) do |r|
+        r.canonical_id = nil
+      end
+      page.update_columns(tag_name_id: tn.id)
+    end
+
+    change_column_null :wiki_pages, :tag_name_id, false
+
+    remove_column :wiki_pages, :title
+  end
+
+  def down
+    add_column :wiki_pages, :title, :string, limit: 255, null: true, after: :id
+
+    WikiPage.find_each do |page|
+      tag_name_id = page.read_attribute(:tag_name_id)
+      title = TagName.find(tag_name_id).read_attribute(:name)
+      page.update_columns(title:)
+    end
+
+    change_column_null :wiki_pages, :title, false
+
+    remove_foreign_key :wiki_pages, column: :tag_name_id
+    remove_index :wiki_pages, :tag_name_id
+    remove_column :wiki_pages, :tag_name_id
+  end
+end

backend/db/migrate/20260112111800_drop_tag_aliases.rb

@@ -0,0 +1,9 @@
+class DropTagAliases < ActiveRecord::Migration[7.0]
+  def up
+    drop_table :tag_aliases
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20260118144400_add_unique_index_to_url_in_posts.rb

@@ -0,0 +1,6 @@
+class AddUniqueIndexToUrlInPosts < ActiveRecord::Migration[7.1]
+  def change
+    change_column :posts, :url, :string, limit: 768
+    add_index :posts, :url, unique: true, name: 'index_posts_on_url'
+  end
+end

backend/db/migrate/20260121024000_change_post_similarities_to_composite_pk.rb

@@ -0,0 +1,43 @@
+class ChangePostSimilaritiesToCompositePk < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      ALTER TABLE
+        post_similarities
+          MODIFY COLUMN id BIGINT NOT NULL
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        post_similarities
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    remove_column :post_similarities, :id
+
+    execute <<~SQL
+      ALTER TABLE
+        post_similarities
+          ADD PRIMARY KEY (post_id, target_post_id)
+      ;
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      ALTER TABLE
+        post_similarities
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        post_similarities
+          ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT FIRST
+        , ADD PRIMARY KEY (id)
+      ;
+    SQL
+  end
+end

backend/db/migrate/20260121024800_change_tag_similarities_to_composite_pk.rb

@@ -0,0 +1,43 @@
+class ChangeTagSimilaritiesToCompositePk < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      ALTER TABLE
+        tag_similarities
+          MODIFY COLUMN id BIGINT NOT NULL
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        tag_similarities
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    remove_column :tag_similarities, :id
+
+    execute <<~SQL
+      ALTER TABLE
+        tag_similarities
+          ADD PRIMARY KEY (tag_id, target_tag_id)
+      ;
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      ALTER TABLE
+        tag_similarities
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        tag_similarities
+          ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT FIRST
+        , ADD PRIMARY KEY (id)
+      ;
+    SQL
+  end
+end

backend/db/migrate/20260121213900_add_index_to_post_similarities.rb

@@ -0,0 +1,9 @@
+class AddIndexToPostSimilarities < ActiveRecord::Migration[8.0]
+  def change
+    remove_index :post_similarities, name: 'index_post_similarities_on_post_id'
+
+    add_index :post_similarities, [:post_id, :cos],
+              order: { cos: :desc },
+              name: 'index_post_similarities_on_post_id_and_cos'
+  end
+end

backend/db/migrate/20260121225600_add_index_to_tag_similarities.rb

@@ -0,0 +1,9 @@
+class AddIndexToTagSimilarities < ActiveRecord::Migration[8.0]
+  def change
+    remove_index :tag_similarities, name: 'index_tag_similarities_on_tag_id'
+
+    add_index :tag_similarities, [:tag_id, :cos],
+              order: { cos: :desc },
+              name: 'index_tag_similarities_on_tag_id_and_cos'
+  end
+end

backend/db/migrate/20260126124100_add_unique_index_to_ip_addresses.rb

@@ -0,0 +1,3 @@
+class AddUniqueIndexToIpAddresses < ActiveRecord::Migration[8.0]
+  add_index :ip_addresses, :ip_address, unique: true, name: 'index_ip_addresses_on_ip_address'
+end

backend/db/migrate/20260127000900_change_user_ips_to_composite_pk.rb

@@ -0,0 +1,47 @@
+class ChangeUserIpsToCompositePk < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      ALTER TABLE
+        user_ips
+          MODIFY COLUMN id BIGINT NOT NULL
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        user_ips
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    remove_column :user_ips, :id
+
+    execute <<~SQL
+      ALTER TABLE
+        user_ips
+          ADD PRIMARY KEY (user_id, ip_address_id)
+      ;
+    SQL
+
+    remove_index :user_ips, name: 'index_user_ips_on_user_id'
+  end
+
+  def down
+    execute <<~SQL
+      ALTER TABLE
+        user_ips
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        user_ips
+          ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT FIRST
+        , ADD PRIMARY KEY (id)
+      ;
+    SQL
+
+    add_index :user_ips, :user_id, name: 'index_user_ips_on_user_id'
+  end
+end

backend/db/migrate/20260127005300_change_user_post_views_to_composite_pk.rb

@@ -0,0 +1,47 @@
+class ChangeUserPostViewsToCompositePk < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      ALTER TABLE
+        user_post_views
+          MODIFY COLUMN id BIGINT NOT NULL
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        user_post_views
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    remove_column :user_post_views, :id
+
+    execute <<~SQL
+      ALTER TABLE
+        user_post_views
+          ADD PRIMARY KEY (user_id, post_id)
+      ;
+    SQL
+
+    remove_index :user_post_views, name: 'index_user_post_views_on_user_id'
+  end
+
+  def down
+    execute <<~SQL
+      ALTER TABLE
+        user_post_views
+          DROP PRIMARY KEY
+      ;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        user_post_views
+          ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT FIRST
+        , ADD PRIMARY KEY (id)
+      ;
+    SQL
+
+    add_index :user_post_views, :user_id, name: 'index_user_post_views_on_user_id'
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
+ActiveRecord::Schema[8.0].define(version: 2026_01_27_005300) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -44,6 +44,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
     t.boolean "banned", default: false, null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["ip_address"], name: "index_ip_addresses_on_ip_address", unique: true
   end
 
   create_table "nico_tag_relations", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -55,11 +56,11 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
     t.index ["tag_id"], name: "index_nico_tag_relations_on_tag_id"
   end
 
-  create_table "post_similarities", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "post_similarities", primary_key: ["post_id", "target_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "target_post_id", null: false
     t.float "cos", null: false
-    t.index ["post_id"], name: "index_post_similarities_on_post_id"
+    t.index ["post_id", "cos"], name: "index_post_similarities_on_post_id_and_cos", order: { cos: :desc }
     t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
   end
 
@@ -84,9 +85,9 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
   end
 
   create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "title", null: false
-    t.string "url", limit: 2000, null: false
-    t.string "thumbnail_base", limit: 2000, null: false
+    t.string "title"
+    t.string "url", limit: 768, null: false
+    t.string "thumbnail_base", limit: 2000
     t.bigint "parent_id"
     t.bigint "uploaded_user_id"
     t.datetime "created_at", null: false
@@ -95,6 +96,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
     t.datetime "updated_at", null: false
     t.index ["parent_id"], name: "index_posts_on_parent_id"
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
+    t.index ["url"], name: "index_posts_on_url", unique: true
   end
 
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -106,55 +108,56 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
     t.index ["user_id"], name: "index_settings_on_user_id"
   end
 
-  create_table "tag_aliases", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "tag_id", null: false
-    t.string "name", null: false
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["tag_id"], name: "index_tag_aliases_on_tag_id"
-  end
-
   create_table "tag_implications", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "parent_tag_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["parent_tag_id"], name: "index_tag_implications_on_parent_tag_id"
+    t.index ["tag_id", "parent_tag_id"], name: "index_tag_implications_on_tag_id_and_parent_tag_id", unique: true
     t.index ["tag_id"], name: "index_tag_implications_on_tag_id"
   end
 
-  create_table "tag_similarities", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "tag_names", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "name", null: false
+    t.bigint "canonical_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["canonical_id"], name: "index_tag_names_on_canonical_id"
+    t.index ["name"], name: "index_tag_names_on_name", unique: true
+  end
+
+  create_table "tag_similarities", primary_key: ["tag_id", "target_tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "target_tag_id", null: false
     t.float "cos", null: false
-    t.index ["tag_id"], name: "index_tag_similarities_on_tag_id"
+    t.index ["tag_id", "cos"], name: "index_tag_similarities_on_tag_id_and_cos", order: { cos: :desc }
     t.index ["target_tag_id"], name: "index_tag_similarities_on_target_tag_id"
   end
 
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "name", null: false
+    t.bigint "tag_name_id", null: false
     t.string "category", default: "general", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
+    t.index ["tag_name_id"], name: "index_tags_on_tag_name_id", unique: true
   end
 
-  create_table "user_ips", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "user_ips", primary_key: ["user_id", "ip_address_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "user_id", null: false
     t.bigint "ip_address_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["ip_address_id"], name: "index_user_ips_on_ip_address_id"
-    t.index ["user_id"], name: "index_user_ips_on_user_id"
   end
 
-  create_table "user_post_views", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "user_post_views", primary_key: ["user_id", "post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "user_id", null: false
     t.bigint "post_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["post_id"], name: "index_user_post_views_on_post_id"
-    t.index ["user_id"], name: "index_user_post_views_on_user_id"
   end
 
   create_table "users", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -166,18 +169,55 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
     t.datetime "updated_at", null: false
   end
 
+  create_table "wiki_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "sha256", limit: 64, null: false
+    t.text "body", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["sha256"], name: "index_wiki_lines_on_sha256", unique: true
+  end
+
   create_table "wiki_pages", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "title", null: false
-    t.bigint "tag_id"
+    t.bigint "tag_name_id", null: false
     t.bigint "created_user_id", null: false
     t.bigint "updated_user_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["created_user_id"], name: "index_wiki_pages_on_created_user_id"
-    t.index ["tag_id"], name: "index_wiki_pages_on_tag_id"
+    t.index ["tag_name_id"], name: "index_wiki_pages_on_tag_name_id", unique: true
     t.index ["updated_user_id"], name: "index_wiki_pages_on_updated_user_id"
   end
 
+  create_table "wiki_revision_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_revision_id", null: false
+    t.integer "position", null: false
+    t.bigint "wiki_line_id", null: false
+    t.index ["wiki_line_id"], name: "index_wiki_revision_lines_on_wiki_line_id"
+    t.index ["wiki_revision_id", "position"], name: "index_wiki_revision_lines_on_wiki_revision_id_and_position", unique: true
+    t.index ["wiki_revision_id", "wiki_line_id"], name: "index_wiki_revision_lines_on_wiki_revision_id_and_wiki_line_id"
+    t.index ["wiki_revision_id"], name: "index_wiki_revision_lines_on_wiki_revision_id"
+  end
+
+  create_table "wiki_revisions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.bigint "base_revision_id"
+    t.bigint "created_user_id", null: false
+    t.integer "kind", default: 0, null: false
+    t.bigint "redirect_page_id"
+    t.string "message"
+    t.integer "lines_count", default: 0, null: false
+    t.string "tree_sha256", limit: 64
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["base_revision_id"], name: "index_wiki_revisions_on_base_revision_id"
+    t.index ["created_user_id"], name: "index_wiki_revisions_on_created_user_id"
+    t.index ["kind"], name: "index_wiki_revisions_on_kind"
+    t.index ["redirect_page_id"], name: "index_wiki_revisions_on_redirect_page_id"
+    t.index ["tree_sha256"], name: "index_wiki_revisions_on_tree_sha256"
+    t.index ["wiki_page_id", "id"], name: "index_wiki_revisions_on_wiki_page_id_and_id"
+    t.index ["wiki_page_id"], name: "index_wiki_revisions_on_wiki_page_id"
+  end
+
   add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
   add_foreign_key "active_storage_variant_records", "active_storage_blobs", column: "blob_id"
   add_foreign_key "nico_tag_relations", "tags"
@@ -191,16 +231,23 @@ ActiveRecord::Schema[8.0].define(version: 2025_11_26_231500) do
   add_foreign_key "posts", "posts", column: "parent_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
-  add_foreign_key "tag_aliases", "tags"
   add_foreign_key "tag_implications", "tags"
   add_foreign_key "tag_implications", "tags", column: "parent_tag_id"
+  add_foreign_key "tag_names", "tag_names", column: "canonical_id"
   add_foreign_key "tag_similarities", "tags"
   add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
+  add_foreign_key "tags", "tag_names"
   add_foreign_key "user_ips", "ip_addresses"
   add_foreign_key "user_ips", "users"
   add_foreign_key "user_post_views", "posts"
   add_foreign_key "user_post_views", "users"
-  add_foreign_key "wiki_pages", "tags"
+  add_foreign_key "wiki_pages", "tag_names"
   add_foreign_key "wiki_pages", "users", column: "created_user_id"
   add_foreign_key "wiki_pages", "users", column: "updated_user_id"
+  add_foreign_key "wiki_revision_lines", "wiki_lines"
+  add_foreign_key "wiki_revision_lines", "wiki_revisions"
+  add_foreign_key "wiki_revisions", "users", column: "created_user_id"
+  add_foreign_key "wiki_revisions", "wiki_pages"
+  add_foreign_key "wiki_revisions", "wiki_pages", column: "redirect_page_id"
+  add_foreign_key "wiki_revisions", "wiki_revisions", column: "base_revision_id"
 end

backend/lib/tasks/calc_post_similarities.rake

@@ -1,28 +1,6 @@
 namespace :post_similarity do
   desc '関聯投稿テーブル作成'
   task calc: :environment do
-    dot = -> a, b { (a.keys & b.keys).sum { |k| a[k] * b[k] } }
-    norm = -> v { Math.sqrt(v.values.sum { |e| e * e }) }
-    cos = -> a, b do
-      na = norm.(a)
-      nb = norm.(b)
-      if na.zero? || nb.zero?
-        0.0
-      else
-        dot.(a, b) / na / nb
-      end
-    end
-
-    posts = Post.includes(:tags).to_a
-    posts.each_with_index do |post, i|
-      existence_of_tags = post.tags.index_with(1)
-      ((i + 1)...posts.size).each do |j|
-        target_post = posts[j]
-        existence_of_target_tags = target_post.tags.index_with(1)
-        PostSimilarity.find_or_initialize_by(post:, target_post:).tap { |ps|
-          ps.cos = cos.(existence_of_tags, existence_of_target_tags)
-        }.save!
-      end
-    end
+    Similarity::Calc.call(Post, :tags)
   end
 end

backend/lib/tasks/calc_tag_similarities.rake

@@ -0,0 +1,6 @@
+namespace :tag_similarity do
+  desc '関聯タグ・テーブル作成'
+  task calc: :environment do
+    Similarity::Calc.call(Tag, :posts)
+  end
+end

backend/lib/tasks/migrate_wiki.rake

@@ -0,0 +1,74 @@
+namespace :wiki do
+  desc 'Wiki 移行'
+  task migrate: :environment do
+    require 'digest'
+    require 'gollum-lib'
+
+    wiki = Gollum::Wiki.new(Rails.root.join('wiki').to_s)
+
+    WikiPage.where.missing(:wiki_revisions).find_each do |wiki_page|
+      page = wiki.page("#{ wiki_page.id }.md")
+      next unless page
+
+      versions = page.versions
+      next if versions.blank?
+
+      base_revision_id = nil
+      versions.reverse_each do |version|
+        pg = wiki.page("#{ wiki_page.id }.md", version.id)
+        raw = pg&.raw_data
+        next unless raw
+
+        lines = raw.force_encoding('UTF-8').split("\n")
+
+        line_shas = lines.map { |l| Digest::SHA256.hexdigest(l) }
+        tree_sha = Digest::SHA256.hexdigest(line_shas.join(','))
+
+        at = version.authored_date
+
+        line_id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+
+        missing_rows = []
+        line_shas.each_with_index do |sha, i|
+          next if line_id_by_sha.key?(sha)
+
+          missing_rows << { sha256:     sha,
+                            body:       lines[i],
+                            created_at: at,
+                            updated_at: at }
+        end
+
+        if missing_rows.any?
+          WikiLine.upsert_all(missing_rows)
+          line_id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+        end
+        line_ids = line_shas.map { |sha| line_id_by_sha.fetch(sha) }
+
+        rev = nil
+        ActiveRecord::Base.transaction do
+          wiki_page.lock!
+
+          rev = WikiRevision.create!(
+              wiki_page:,
+              base_revision_id:,
+              created_user_id:  (Integer(version.author.name) rescue 2),
+              kind:             :content,
+              redirect_page_id: nil,
+              message:          nil,
+              lines_count:      lines.length,
+              tree_sha256:      tree_sha,
+              created_at:       at,
+              updated_at:       at)
+
+          rows = line_ids.each_with_index.map do |line_id, pos|
+            { wiki_revision_id: rev.id,
+              wiki_line_id:     line_id,
+              position:         pos }
+          end
+          WikiRevisionLine.insert_all!(rows)
+        end
+        base_revision_id = rev.id
+      end
+    end
+  end
+end

backend/lib/tasks/sync_nico.rake

@@ -4,13 +4,34 @@ namespace :nico do
     require 'open3'
     require 'open-uri'
     require 'nokogiri'
+    require 'set'
 
-    fetch_thumbnail = -> url {
+    fetch_thumbnail = -> url do
       html = URI.open(url, read_timeout: 60, 'User-Agent' => 'Mozilla/5.0').read
       doc = Nokogiri::HTML(html)
 
       doc.at('meta[name="thumbnail"]')&.[]('content').presence
-    }
+    end
+
+    def sync_post_tags! post, desired_tag_ids, current_ids: nil
+      current_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      desired_ids = desired_tag_ids.compact.to_set
+
+      to_add = desired_ids - current_ids
+      to_remove = current_ids - desired_ids
+
+      Tag.where(id: to_add.to_a).find_each do |tag|
+        begin
+          PostTag.create!(post:, tag:)
+        rescue ActiveRecord::RecordNotUnique
+          ;
+        end
+      end
+
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+        pt.discard_by!(nil)
+      end
+    end
 
     mysql_user = ENV['MYSQL_USER']
     mysql_pass = ENV['MYSQL_PASS']
@@ -19,43 +40,55 @@ namespace :nico do
         { 'MYSQL_USER' => mysql_user, 'MYSQL_PASS' => mysql_pass },
         'python3', "#{ nizika_nico_path }/get_videos.py")
 
-    if status.success?
-      data = JSON.parse(stdout)
-      data.each do |datum|
-        post = Post.where('url LIKE ?', '%nicovideo.jp%').find { |post|
-          post.url =~ %r{#{ Regexp.escape(datum['code']) }(?!\d)}
-        }
-        unless post
-          title = datum['title']
-          url = "https://www.nicovideo.jp/watch/#{ datum['code'] }"
-          thumbnail_base = fetch_thumbnail.(url) || '' rescue ''
-          post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil)
-          if thumbnail_base.present?
-            post.thumbnail.attach(
-                io:           URI.open(thumbnail_base),
-                filename:     File.basename(URI.parse(thumbnail_base).path),
-                content_type: 'image/jpeg')
-          end
-          post.save!
-          post.resized_thumbnail!
+    abort unless status.success?
+
+    data = JSON.parse(stdout)
+    data.each do |datum|
+      code = datum['code']
+      post = Post.where('url REGEXP ?', "nicovideo\\.jp/watch/#{ Regexp.escape(code) }([^0-9]|$)")
+                 .first
+      unless post
+        title = datum['title']
+        url = "https://www.nicovideo.jp/watch/#{ code }"
+        thumbnail_base = fetch_thumbnail.(url) rescue nil
+        post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil)
+        if thumbnail_base.present?
+          post.thumbnail.attach(
+              io:           URI.open(thumbnail_base),
+              filename:     File.basename(URI.parse(thumbnail_base).path),
+              content_type: 'image/jpeg')
         end
+        post.save!
+        post.resized_thumbnail!
+        sync_post_tags!(post, [Tag.tagme.id])
+      end
+
+      kept_ids = PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      kept_non_nico_ids = post.tags.where.not(category: 'nico').pluck(:id).to_set
 
-        current_tags = post.tags.where(category: 'nico').pluck(:name).sort
-        new_tags = datum['tags'].map { |tag| "nico:#{ tag }" }.sort
-        if current_tags != new_tags
-          post.tags.destroy(post.tags.where(name: current_tags))
-          tags_to_add = []
-          new_tags.each do |name|
-            tag = Tag.find_or_initialize_by(name:) do |t|
-              t.category = 'nico'
-            end
-            tags_to_add.concat([tag] + tag.linked_tags)
-          end
-          tags_to_add << Tag.tagme if post.tags.size < 10
-          tags_to_add << Tag.bot
-          post.tags = (post.tags + tags_to_add).uniq
+      desired_nico_ids = []
+      desired_non_nico_ids = []
+      datum['tags'].each do |raw|
+        name = "nico:#{ raw }"
+        tag = Tag.find_or_create_by_tag_name!(name, category: 'nico')
+        desired_nico_ids << tag.id
+        unless tag.id.in?(kept_ids)
+          linked_ids = tag.linked_tags.pluck(:id)
+          desired_non_nico_ids.concat(linked_ids)
+          desired_nico_ids.concat(linked_ids)
         end
       end
+      desired_nico_ids.uniq!
+
+      desired_all_ids = kept_non_nico_ids.to_a + desired_nico_ids
+      desired_non_nico_ids.concat(kept_non_nico_ids.to_a)
+      desired_non_nico_ids.uniq!
+      if kept_non_nico_ids.to_set != desired_non_nico_ids.to_set
+        desired_all_ids << Tag.bot.id
+      end
+      desired_all_ids.uniq!
+
+      sync_post_tags!(post, desired_all_ids, current_ids: kept_ids)
     end
   end
 end

backend/spec/factories/tag_names.rb

@@ -0,0 +1,5 @@
+FactoryBot.define do
+  factory :tag_name do
+    name { "tag-#{SecureRandom.hex(4)}" }
+  end
+end

backend/spec/factories/tags.rb

@@ -0,0 +1,12 @@
+FactoryBot.define do
+  factory :tag do
+    category { 'general' }
+    post_count { 0 }
+    association :tag_name
+
+    trait :nico do
+      category { 'nico' }
+      tag_name { association(:tag_name, name: "nico:#{ SecureRandom.hex(4) }") }
+    end
+  end
+end

backend/spec/factories/users.rb

@@ -0,0 +1,15 @@
+FactoryBot.define do
+  factory :user do
+    name { "test-user" }
+    inheritance_code { SecureRandom.uuid }
+    role { "guest" }
+
+    trait :member do
+      role { "member" }
+    end
+
+    trait :admin do
+      role { 'admin' }
+    end
+  end
+end

backend/spec/factories/wiki_pages.rb

@@ -0,0 +1,7 @@
+FactoryBot.define do
+  factory :wiki_page do
+    title { "TestPage" }
+    association :created_user, factory: :user
+    association :updated_user, factory: :user
+  end
+end

backend/spec/rails_helper.rb

@@ -0,0 +1,90 @@
+# This file is copied to spec/ when you run 'rails generate rspec:install'
+require 'spec_helper'
+ENV['RAILS_ENV'] ||= 'test'
+require_relative '../config/environment'
+# Prevent database truncation if the environment is production
+abort("The Rails environment is running in production mode!") if Rails.env.production?
+# Uncomment the line below in case you have `--require rails_helper` in the `.rspec` file
+# that will avoid rails generators crashing because migrations haven't been run yet
+# return unless Rails.env.test?
+require 'rspec/rails'
+Dir[Rails.root.join('spec/support/**/*.rb')].each do |f|
+  require f
+end
+
+# Add additional requires below this line. Rails is not loaded until this point!
+
+# Requires supporting ruby files with custom matchers and macros, etc, in
+# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
+# run as spec files by default. This means that files in spec/support that end
+# in _spec.rb will both be required and run as specs, causing the specs to be
+# run twice. It is recommended that you do not name files matching this glob to
+# end with _spec.rb. You can configure this pattern with the --pattern
+# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
+#
+# The following line is provided for convenience purposes. It has the downside
+# of increasing the boot-up time by auto-requiring all files in the support
+# directory. Alternatively, in the individual `*_spec.rb` files, manually
+# require only the support files necessary.
+#
+# Rails.root.glob('spec/support/**/*.rb').sort_by(&:to_s).each { |f| require f }
+
+# Ensures that the test database schema matches the current schema file.
+# If there are pending migrations it will invoke `db:test:prepare` to
+# recreate the test database by loading the schema.
+# If you are not using ActiveRecord, you can remove these lines.
+begin
+  ActiveRecord::Migration.maintain_test_schema!
+rescue ActiveRecord::PendingMigrationError => e
+  abort e.to_s.strip
+end
+RSpec.configure do |config|
+  config.before do
+    I18n.locale = :en
+  end
+
+  config.include TestRecords
+  config.include RakeTaskHelper
+
+  # FactoryBot の create / create_list を使へるやぅにする
+  config.include FactoryBot::Syntax::Methods
+
+  # request spec で helper 使へるやぅにする
+  config.include AuthHelper, type: :request
+  config.include JsonHelper, type: :request
+
+  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
+  config.fixture_paths = [
+    Rails.root.join('spec/fixtures')
+  ]
+
+  # If you're not using ActiveRecord, or you'd prefer not to run each of your
+  # examples within a transaction, remove the following line or assign false
+  # instead of true.
+  config.use_transactional_fixtures = true
+
+  # You can uncomment this line to turn off ActiveRecord support entirely.
+  # config.use_active_record = false
+
+  # RSpec Rails uses metadata to mix in different behaviours to your tests,
+  # for example enabling you to call `get` and `post` in request specs. e.g.:
+  #
+  #     RSpec.describe UsersController, type: :request do
+  #       # ...
+  #     end
+  #
+  # The different available types are documented in the features, such as in
+  # https://rspec.info/features/8-0/rspec-rails
+  #
+  # You can also this infer these behaviours automatically by location, e.g.
+  # /spec/models would pull in the same behaviour as `type: :model` but this
+  # behaviour is considered legacy and will be removed in a future version.
+  #
+  # To enable this behaviour uncomment the line below.
+  # config.infer_spec_type_from_file_location!
+
+  # Filter lines from Rails gems in backtraces.
+  config.filter_rails_from_backtrace!
+  # arbitrary gems may also be filtered via:
+  # config.filter_gems_from_backtrace("gem name")
+end

backend/spec/requests/nico_tags_spec.rb

@@ -0,0 +1,38 @@
+require 'rails_helper'
+
+
+RSpec.describe 'NicoTags', type: :request do
+  describe 'GET /tags/nico' do
+    it 'returns tags and next_cursor when overflowing limit' do
+      create_list(:tag, 21, :nico)
+      get '/tags/nico', params: { limit: 20 }
+      expect(response).to have_http_status(:ok)
+      expect(json['tags'].size).to eq(20)
+      expect(json['next_cursor']).to be_present
+    end
+  end
+
+  describe 'PATCH /tags/nico/:id' do
+    let(:member) { create(:user, :member) }
+    let(:nico_tag) { create(:tag, :nico) }
+
+    it '401 when not logged in' do
+      sign_out
+      patch "/tags/nico/#{nico_tag.id}", params: { tags: 'a b' }
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it '403 when not member' do
+      sign_in_as(create(:user, role: 'guest'))
+      patch "/tags/nico/#{nico_tag.id}", params: { tags: 'a b' }
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it '400 when target is not nico category' do
+      sign_in_as(member)
+      non_nico = create(:tag, :general)
+      patch "/tags/nico/#{non_nico.id}", params: { tags: 'a b' }
+      expect(response).to have_http_status(:bad_request)
+    end
+  end
+end

backend/spec/requests/posts_spec.rb

@@ -0,0 +1,393 @@
+require 'rails_helper'
+require 'set'
+
+
+RSpec.describe 'Posts API', type: :request do
+  # create / update で thumbnail.attach は走るが、
+  # resized_thumbnail! が MiniMagick 依存でコケやすいので request spec ではスタブしとくのが無難。
+  before do
+    allow_any_instance_of(Post).to receive(:resized_thumbnail!).and_return(true)
+  end
+
+  def dummy_upload
+    # 中身は何でもいい（加工処理はスタブしてる）
+    Rack::Test::UploadedFile.new(StringIO.new('dummy'), 'image/jpeg', original_filename: 'dummy.jpg')
+  end
+
+  let!(:tag_name) { TagName.create!(name: 'spec_tag') }
+  let!(:tag)      { Tag.create!(tag_name: tag_name, category: 'general') }
+
+  let!(:post_record) do
+    Post.create!(title: 'spec post', url: 'https://example.com/spec').tap do |p|
+      PostTag.create!(post: p, tag: tag)
+    end
+  end
+
+  describe "GET /posts" do
+    let!(:user) { create_member_user! }
+
+    let!(:tag_name) { TagName.create!(name: "spec_tag") }
+    let!(:tag) { Tag.create!(tag_name:, category: "general") }
+    let!(:tag_name2) { TagName.create!(name: 'unko') }
+    let!(:tag2) { Tag.create!(tag_name: tag_name2, category: 'deerjikist') }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
+
+    let!(:hit_post) do
+      Post.create!(uploaded_user: user, title: "hello spec world",
+                   url: 'https://example.com/spec2').tap do |p|
+        PostTag.create!(post: p, tag:)
+      end
+    end
+
+    let!(:miss_post) do
+      Post.create!(uploaded_user: user, title: "unrelated title",
+                   url: 'https://example.com/spec3').tap do |p|
+        PostTag.create!(post: p, tag: tag2)
+      end
+    end
+
+    it "returns posts with tag name in JSON" do
+      get "/posts"
+
+      expect(response).to have_http_status(:ok)
+      posts = json.fetch("posts")
+
+      # 全postの全tagが name を含むこと
+      expect(posts).not_to be_empty
+      posts.each do |p|
+        expect(p['tags']).to be_an(Array)
+        p['tags'].each do |t|
+          expect(t).to include('name', 'category', 'has_wiki')
+        end
+      end
+      expect(json['count']).to be_an(Integer)
+
+      # spec_tag を含む投稿が存在すること
+      all_tag_names = posts.flat_map { |p| p["tags"].map { |t| t["name"] } }
+      expect(all_tag_names).to include("spec_tag")
+    end
+
+    context "when q is provided" do
+      it "filters posts by q (hit case)" do
+        get "/posts", params: { tags: "spec_tag" }
+
+        expect(response).to have_http_status(:ok)
+        posts = json.fetch('posts')
+        ids = posts.map { |p| p['id'] }
+
+        expect(ids).to include(hit_post.id)
+        expect(ids).not_to include(miss_post.id)
+        expect(json['count']).to be_an(Integer)
+
+        posts.each do |p|
+          expect(p['tags']).to be_an(Array)
+          p['tags'].each do |t|
+            expect(t).to include('name', 'category', 'has_wiki')
+          end
+        end
+      end
+
+      it "filters posts by q (hit case by alias)" do
+        get "/posts", params: { tags: "manko" }
+
+        expect(response).to have_http_status(:ok)
+        posts = json.fetch('posts')
+        ids = posts.map { |p| p['id'] }
+
+        expect(ids).to include(hit_post.id)
+        expect(ids).not_to include(miss_post.id)
+        expect(json['count']).to be_an(Integer)
+
+        posts.each do |p|
+          expect(p['tags']).to be_an(Array)
+          p['tags'].each do |t|
+            expect(t).to include('name', 'category', 'has_wiki')
+          end
+        end
+      end
+
+      it "returns empty posts when nothing matches" do
+        get "/posts", params: { tags: "no_such_keyword_12345" }
+
+        expect(response).to have_http_status(:ok)
+        expect(json.fetch("posts")).to eq([])
+        expect(json.fetch('count')).to eq(0)
+      end
+    end
+  end
+
+  describe 'GET /posts/:id' do
+    subject(:request) { get "/posts/#{post_id}" }
+
+    context 'when post exists' do
+      let(:post_id) { post_record.id }
+
+      it 'returns post with tag tree + related + viewed' do
+        request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to include('id' => post_record.id)
+        expect(json).to have_key('tags')
+        expect(json['tags']).to be_an(Array)
+
+        # show は build_tag_tree_for を使うので、tags はツリー形式（children 付き）
+        node = json['tags'][0]
+        expect(node).to include('id', 'name', 'category', 'post_count', 'children', 'has_wiki')
+        expect(node['name']).to eq('spec_tag')
+
+        expect(json).to have_key('related')
+        expect(json['related']).to be_an(Array)
+
+        expect(json).to have_key('viewed')
+        expect([true, false]).to include(json['viewed'])
+      end
+    end
+
+    context 'when post does not exist' do
+      let(:post_id) { 999_999_999 }
+
+      it 'returns 404' do
+        request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'POST /posts' do
+    let(:member) { create(:user, :member) }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
+
+    it '401 when not logged in' do
+      sign_out
+      post '/posts', params: { title: 't', url: 'https://example.com/x', tags: 'a', thumbnail: dummy_upload }
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it '403 when not member' do
+      sign_in_as(create(:user, role: 'guest'))
+      post '/posts', params: { title: 't', url: 'https://example.com/x', tags: 'a', thumbnail: dummy_upload }
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it '201 and creates post + tags when member' do
+      sign_in_as(member)
+
+      post '/posts', params: {
+        title: 'new post',
+        url: 'https://example.com/new',
+        tags: 'spec_tag', # 既存タグ名を投げる
+        thumbnail: dummy_upload
+      }
+
+      expect(response).to have_http_status(:created)
+      expect(json).to include('id', 'title', 'url')
+
+      # tags が name を含むこと（API 側の serialization が正しいこと）
+      expect(json).to have_key('tags')
+      expect(json['tags']).to be_an(Array)
+      expect(json['tags'][0]).to have_key('name')
+    end
+
+    it '201 and creates post + tags when member and tags have aliases' do
+      sign_in_as(member)
+
+      post '/posts', params: {
+        title: 'new post',
+        url: 'https://example.com/new',
+        tags: 'manko', # 既存タグ名を投げる
+        thumbnail: dummy_upload
+      }
+
+      expect(response).to have_http_status(:created)
+      expect(json).to include('id', 'title', 'url')
+
+      # tags が name を含むこと（API 側の serialization が正しいこと）
+      names = json.fetch('tags').map { |t| t['name'] }
+      expect(names).to include('spec_tag')
+      expect(names).not_to include('manko')
+    end
+
+    context "when nico tag already exists in tags" do
+      before do
+        Tag.find_or_create_by!(tag_name: TagName.find_or_create_by!(name: 'nico:nico_tag'),
+                               category: 'nico')
+      end
+
+      it 'return 400' do
+        sign_in_as(member)
+
+        post '/posts', params: {
+            title: 'new post',
+            url: 'https://example.com/nico_tag',
+            tags: 'nico:nico_tag',
+            thumbnail: dummy_upload }
+
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+
+    context 'when url is blank' do
+      it 'returns 422' do
+        sign_in_as(member)
+
+        post '/posts', params: {
+            title: 'new post',
+            url: '   ',
+            tags: 'spec_tag', # 既存タグ名を投げる
+            thumbnail: dummy_upload }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+
+    context 'when url is invalid' do
+      it 'returns 422' do
+        sign_in_as(member)
+
+        post '/posts', params: {
+          title: 'new post',
+          url: 'ぼざクリタグ広場',
+          tags: 'spec_tag', # 既存タグ名を投げる
+          thumbnail: dummy_upload
+        }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+  end
+
+  describe 'PUT /posts/:id' do
+    let(:member) { create(:user, :member) }
+
+    it '401 when not logged in' do
+      sign_out
+      put "/posts/#{post_record.id}", params: { title: 'updated', tags: 'spec_tag' }
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it '403 when not member' do
+      sign_in_as(create(:user, role: 'guest'))
+      put "/posts/#{post_record.id}", params: { title: 'updated', tags: 'spec_tag' }
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it '200 and updates title + resync tags when member' do
+      sign_in_as(member)
+
+      # 追加で別タグも作って、更新時に入れ替わることを見る
+      tn2 = TagName.create!(name: 'spec_tag_2')
+      Tag.create!(tag_name: tn2, category: 'general')
+
+      put "/posts/#{post_record.id}", params: {
+        title: 'updated title',
+        tags: 'spec_tag_2'
+      }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to have_key('tags')
+      expect(json['tags']).to be_an(Array)
+
+      # show と同様、update 後レスポンスもツリー形式
+      names = json['tags'].map { |n| n['name'] }
+      expect(names).to include('spec_tag_2')
+    end
+
+    context "when nico tag already exists in tags" do
+      before do
+        Tag.find_or_create_by!(tag_name: TagName.find_or_create_by!(name: 'nico:nico_tag'),
+                               category: 'nico')
+      end
+
+      it 'return 400' do
+        sign_in_as(member)
+
+        put "/posts/#{ post_record.id }", params: {
+            title: 'updated title',
+            tags: 'nico:nico_tag' }
+
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+  end
+
+  describe 'GET /posts/random' do
+    it '404 when no posts' do
+      PostTag.delete_all
+      Post.delete_all
+      get '/posts/random'
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it '200 and returns viewed boolean' do
+      get '/posts/random'
+      expect(response).to have_http_status(:ok)
+      expect(json).to have_key('viewed')
+      expect([true, false]).to include(json['viewed'])
+    end
+  end
+
+  describe 'GET /posts/changes' do
+    let(:member) { create(:user, :member) }
+
+    it 'returns add/remove events (history) for a post' do
+      # add
+      tn2 = TagName.create!(name: 'spec_tag2')
+      tag2 = Tag.create!(tag_name: tn2, category: 'general')
+      pt = PostTag.create!(post: post_record, tag: tag2, created_user: member)
+
+      # remove (discard)
+      pt.discard_by!(member)
+
+      get '/posts/changes', params: { id: post_record.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('changes', 'count')
+      expect(json['changes']).to be_an(Array)
+      expect(json['count']).to be >= 2
+
+      types = json['changes'].map { |e| e['change_type'] }.uniq
+      expect(types).to include('add')
+      expect(types).to include('remove')
+    end
+  end
+
+  describe 'POST /posts/:id/viewed' do
+    let(:user) { create(:user) }
+
+    it '401 when not logged in' do
+      sign_out
+      post "/posts/#{ post_record.id }/viewed"
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it '204 and marks viewed when logged in' do
+      sign_in_as(user)
+      post "/posts/#{ post_record.id }/viewed"
+      expect(response).to have_http_status(:no_content)
+
+      expect(user.reload.viewed?(post_record)).to be(true)
+    end
+  end
+
+  describe 'DELETE /posts/:id/viewed' do
+    let(:user) { create(:user) }
+
+    it '401 when not logged in' do
+      sign_out
+      delete "/posts/#{ post_record.id }/viewed"
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it '204 and unmarks viewed when logged in' do
+      sign_in_as(user)
+
+      # 先に viewed 付けてから外す
+      user.viewed_posts << post_record
+
+      delete "/posts/#{ post_record.id }/viewed"
+      expect(response).to have_http_status(:no_content)
+
+      expect(user.reload.viewed?(post_record)).to be(false)
+    end
+  end
+end

backend/spec/requests/preview_spec.rb

@@ -0,0 +1,28 @@
+require "rails_helper"
+
+
+RSpec.describe "Preview", type: :request do
+  describe "GET /preview/title" do
+    it "401 unless logged in" do
+      sign_out
+      get "/preview/title", params: { url: "example.com" }
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it "400 when url blank" do
+      sign_in_as(create(:user))
+      get "/preview/title", params: { url: "" }
+      expect(response).to have_http_status(:bad_request)
+    end
+
+    it "returns parsed title (stubbing URI.open)" do
+      sign_in_as(create(:user))
+      fake_html = "<html><head><title>  Hello  </title></head></html>"
+      allow(URI).to receive(:open).and_return(StringIO.new(fake_html))
+
+      get "/preview/title", params: { url: "example.com" }
+      expect(response).to have_http_status(:ok)
+      expect(json["title"]).to eq("Hello")
+    end
+  end
+end

backend/spec/requests/tag_children_spec.rb

@@ -0,0 +1,134 @@
+# spec/requests/tag_children_spec.rb
+require "rails_helper"
+
+RSpec.describe "TagChildren", type: :request do
+  let!(:parent) { create(:tag) }
+  let!(:child)  { create(:tag) }
+
+  # ここは君のUser factoryに合わせて調整
+  let(:user) { create_member_user! }
+  let(:admin) { create_admin_user! }
+
+  # current_user を ApplicationController でスタブ
+  def stub_current_user(user_or_nil)
+    allow_any_instance_of(ApplicationController)
+      .to receive(:current_user)
+      .and_return(user_or_nil)
+  end
+
+  describe "POST /tag_children" do
+    subject(:do_request) do
+      post "/tags/#{ parent_id }/children/#{ child_id }"
+    end
+
+    context "when not logged in" do
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it "returns 401" do
+        stub_current_user(nil)
+        do_request
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context "when logged in but not admin" do
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it "returns 403" do
+        stub_current_user(user)
+        do_request
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context "when admin and params are present" do
+      before { stub_current_user(admin) }
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it "returns 204 and adds child to parent.children" do
+        expect(parent.children).not_to include(child)
+
+        expect { do_request }
+          .to change { parent.reload.children.ids.include?(child.id) }
+          .from(false).to(true)
+
+        expect(response).to have_http_status(:no_content)
+      end
+    end
+
+    context "when Tag.find raises (invalid ids) it still returns 204" do
+      before { stub_current_user(admin) }
+
+      let(:parent_id) { -1 }
+      let(:child_id) { -1 }
+
+      it "returns 204 (rescue nil)" do
+        do_request
+        expect(response).to have_http_status(:no_content)
+      end
+    end
+  end
+
+  describe "DELETE /tag_children" do
+    subject(:do_request) do
+      delete "/tags/#{ parent_id }/children/#{ child_id }"
+    end
+
+    context "when not logged in" do
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it "returns 401" do
+        stub_current_user(nil)
+        do_request
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context "when logged in but not admin" do
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it "returns 403" do
+        stub_current_user(user)
+        do_request
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context "when admin and params are present" do
+      before do
+        stub_current_user(admin)
+        parent.children << child
+      end
+
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it "returns 204 and removes child from parent.children" do
+        expect(parent.reload.children).to include(child)
+
+        expect { do_request }
+          .to change { parent.reload.children.ids.include?(child.id) }
+          .from(true).to(false)
+
+        expect(response).to have_http_status(:no_content)
+      end
+    end
+
+    context "when Tag.find raises (invalid ids) it still returns 204" do
+      before { stub_current_user(admin) }
+
+      let(:parent_id) { -1 }
+      let(:child_id) { -1 }
+
+      it "returns 204 (rescue nil)" do
+        do_request
+        expect(response).to have_http_status(:no_content)
+      end
+    end
+  end
+end

backend/spec/requests/tags_spec.rb

@@ -0,0 +1,198 @@
+require 'cgi'
+require 'rails_helper'
+
+
+RSpec.describe 'Tags API', type: :request do
+  let!(:tn) { TagName.create!(name: 'spec_tag') }
+  let!(:tag) { Tag.create!(tag_name: tn, category: :general) }
+  let!(:alias_tn) { TagName.create!(name: 'unko', canonical: tn) }
+  let!(:post) { Post.create!(url: 'https://example.com/unkounkounko') }
+  let!(:post_tag) { PostTag.create!(post:, tag:) }
+  let!(:tn2) { TagName.create!(name: 'unknown') }
+  let!(:tag2) { Tag.create!(tag_name: tn2, category: :general) }
+
+  describe 'GET /tags' do
+    it 'returns tags with name' do
+      get '/tags'
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to be_an(Array)
+      expect(json).not_to be_empty
+      expect(json[0]).to have_key('name')
+      expect(json.map { |t| t['name'] }).to include('spec_tag')
+    end
+  end
+
+  describe 'GET /tags/:id' do
+    subject(:request) do
+      get "/tags/#{ tag_id }"
+    end
+
+    let(:tag_id) { tag.id }
+
+    context 'when tag exists' do
+      it 'returns tag with name' do
+        request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to include(
+            'id'        => tag.id,
+            'name'      => 'spec_tag',
+            'category'  => 'general')
+      end
+    end
+
+    context 'when tag does not exist' do
+      let(:tag_id) { 9_999_999 }
+
+      it 'returns 404' do
+        request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'GET /tags/autocomplete' do
+    it 'returns matching tags by q' do
+      get '/tags/autocomplete', params: { q: 'spec' }
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to be_an(Array)
+      expect(json.map { |t| t['name'] }).to include('spec_tag')
+      t = json.find { |t| t['name'] == 'spec_tag' }
+      expect(t).to have_key('matched_alias')
+      expect(t['matched_alias']).to be(nil)
+    end
+
+    it 'returns matching canonical tags by q with aliases' do
+      get '/tags/autocomplete', params: { q: 'unk' }
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to be_an(Array)
+      expect(json.map { |t| t['name'] }).to include('spec_tag')
+      t = json.find { |t| t['name'] == 'spec_tag' }
+      expect(t['matched_alias']).to eq('unko')
+      expect(json.map { |t| t['name'] }).not_to include('unknown')
+    end
+  end
+
+  describe 'GET /tags/name/:name' do
+    it 'returns tag by name' do
+      get "/tags/name/#{ CGI.escape('spec_tag') }"
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to have_key('id')
+      expect(json).to have_key('name')
+      expect(json['id']).to eq(tag.id)
+      expect(json['name']).to eq('spec_tag')
+    end
+
+    it 'returns 404 when not found' do
+      get "/tags/name/#{ CGI.escape('nope') }"
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  # member? を持つ user を想定（Factory 側で trait 作ってもOK）
+  let(:member_user) { create(:user) }
+  let(:non_member_user) { create(:user) }
+
+  def stub_current_user(user)
+    allow_any_instance_of(ApplicationController).to receive(:current_user).and_return(user)
+  end
+
+  before do
+    allow(member_user).to receive(:member?).and_return(true)
+    allow(non_member_user).to receive(:member?).and_return(false)
+  end
+
+  describe "PATCH /tags/:id" do
+    context "未ログイン" do
+      before { stub_current_user(nil) }
+
+      it "401 を返す" do
+        patch "/tags/#{tag.id}", params: { name: "new" }
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context "ログインしてゐるが member でない" do
+      before { stub_current_user(non_member_user) }
+
+      it "403 を返す" do
+        patch "/tags/#{tag.id}", params: { name: "new" }
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context "member" do
+      before { stub_current_user(member_user) }
+
+      it "name だけ更新できる" do
+        patch "/tags/#{tag.id}", params: { name: "new" }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+        expect(tag.name).to eq("new")
+        expect(tag.category).to eq("general")
+
+        json = JSON.parse(response.body)
+        expect(json["id"]).to eq(tag.id)
+        expect(json["name"]).to eq("new")
+        expect(json["category"]).to eq("general")
+      end
+
+      it "category だけ更新できる" do
+        patch "/tags/#{tag.id}", params: { category: "meme" }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+        expect(tag.name).to eq("spec_tag")
+        expect(tag.category).to eq("meme")
+      end
+
+      it "空文字は presence により無視され、更新は走らない（値が変わらない）" do
+        patch "/tags/#{tag.id}", params: { name: "", category: "   " }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+        expect(tag.name).to eq("spec_tag")
+        expect(tag.category).to eq("general")
+      end
+
+      it "両方更新できる" do
+        patch "/tags/#{tag.id}", params: { name: "n", category: "meta" }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+        expect(tag.name).to eq("n")
+        expect(tag.category).to eq("meta")
+      end
+
+      it "存在しない id だと RecordNotFound になる（通常は 404）" do
+        # Rails 設定次第で例外がそのまま上がる/404になる
+        # APIなら rescue_from で 404 にしてることが多いので、その場合は 404 を期待。
+        patch "/tags/999999999", params: { name: "x" }
+
+        expect(response.status).to be_in([404, 500])
+      end
+
+      it "バリデーションで update! が失敗したら（通常は 422 か 500）" do
+        patch "/tags/#{tag.id}", params: { name: 'new', category: 'nico' }
+
+        # rescue_from の実装次第で変はる:
+        # - RecordInvalid を 422 にしてるなら 422
+        # - 未処理なら 500
+        expect(response.status).to be_in([422, 500])
+      end
+    end
+  end
+end

backend/spec/requests/users_spec.rb

@@ -0,0 +1,110 @@
+require "rails_helper"
+
+
+RSpec.describe "Users", type: :request do
+  describe "POST /users" do
+    it "creates guest user and returns code" do
+      post "/users"
+      expect(response).to have_http_status(:ok)
+      expect(json["code"]).to be_present
+      expect(json["user"]["role"]).to eq("guest")
+    end
+  end
+
+  describe "POST /users/code/renew" do
+    it "returns 401 when not logged in" do
+      sign_out
+      post "/users/code/renew"
+      expect(response).to have_http_status(:unauthorized)
+    end
+  end
+
+  describe "PUT /users/:id" do
+    let(:user) { create(:user, name: "old-name", role: "guest") }
+
+    it "returns 401 when current_user id mismatch" do
+      sign_in_as(create(:user))
+      put "/users/#{user.id}", params: { name: "new-name" }
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it "returns 400 when name is blank" do
+      sign_in_as(user)
+      put "/users/#{user.id}", params: { name: "   " }
+      expect(response).to have_http_status(:bad_request)
+    end
+
+    it "updates name and returns 201 with user slice" do
+      sign_in_as(user)
+      put "/users/#{user.id}", params: { name: "new-name" }
+
+      expect(response).to have_http_status(:created)
+      expect(json["id"]).to eq(user.id)
+      expect(json["name"]).to eq("new-name")
+
+      user.reload
+      expect(user.name).to eq("new-name")
+    end
+  end
+
+  describe "POST /users/verify" do
+    it "returns valid:false when code not found" do
+      post "/users/verify", params: { code: "nope" }
+      expect(response).to have_http_status(:ok)
+      expect(json["valid"]).to eq(false)
+    end
+
+    it "creates IpAddress and UserIp, and returns valid:true with user slice" do
+      user = create(:user, inheritance_code: SecureRandom.uuid, role: "guest")
+
+      # request.remote_ip を固定
+      allow_any_instance_of(ActionDispatch::Request).to receive(:remote_ip).and_return("203.0.113.10")
+
+      expect {
+        post "/users/verify", params: { code: user.inheritance_code }
+      }.to change(UserIp, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json["valid"]).to eq(true)
+      expect(json["user"]["id"]).to eq(user.id)
+      expect(json["user"]["inheritance_code"]).to eq(user.inheritance_code)
+      expect(json["user"]["role"]).to eq("guest")
+
+      # ついでに IpAddress もできてることを確認（ipの保存形式がバイナリでも count で見れる）
+      expect(IpAddress.count).to be >= 1
+    end
+
+    it "is idempotent for same user+ip (does not create duplicate UserIp)" do
+      user = create(:user, inheritance_code: SecureRandom.uuid, role: "guest")
+      allow_any_instance_of(ActionDispatch::Request).to receive(:remote_ip).and_return("203.0.113.10")
+
+      post "/users/verify", params: { code: user.inheritance_code }
+      expect(response).to have_http_status(:ok)
+
+      expect {
+        post "/users/verify", params: { code: user.inheritance_code }
+      }.not_to change(UserIp, :count)
+
+      expect(response).to have_http_status(:ok)
+      expect(json["valid"]).to eq(true)
+    end
+  end
+
+  describe "GET /users/me" do
+    it "returns 404 when code not found" do
+      get "/users/me", params: { code: "nope" }
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it "returns user slice when found" do
+      user = create(:user, inheritance_code: SecureRandom.uuid, name: "me", role: "guest")
+      get "/users/me", params: { code: user.inheritance_code }
+
+      expect(response).to have_http_status(:ok)
+      expect(json["id"]).to eq(user.id)
+      expect(json["name"]).to eq("me")
+      expect(json["inheritance_code"]).to eq(user.inheritance_code)
+      expect(json["role"]).to eq("guest")
+    end
+  end
+end

backend/spec/requests/wiki_spec.rb

@@ -0,0 +1,426 @@
+require 'cgi'
+require 'rails_helper'
+require 'securerandom'
+
+
+RSpec.describe 'Wiki API', type: :request do
+  let!(:user) { create_member_user! }
+
+  let!(:tn) { TagName.create!(name: 'spec_wiki_title') }
+  let!(:page) do
+    WikiPage.create!(tag_name: tn, created_user: user, updated_user: user).tap do |p|
+      Wiki::Commit.content!(page: p, body: 'init', created_user: user, message: 'init')
+    end
+  end
+
+  describe 'GET /wiki' do
+    it 'returns wiki pages with title' do
+      get '/wiki'
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to be_an(Array)
+      expect(json).not_to be_empty
+
+      expect(json[0]).to have_key('title')
+      expect(json.map { |p| p['title'] }).to include('spec_wiki_title')
+    end
+  end
+
+  describe 'GET /wiki/:id' do
+    subject(:request) do
+      get "/wiki/#{ page_id }"
+    end
+
+    let(:page_id) { page.id }
+
+    context 'when wiki page exists' do
+      it 'returns wiki page with title' do
+        request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to include(
+            'id'        => page.id,
+            'title'     => 'spec_wiki_title')
+      end
+    end
+
+    context 'when wiki page does not exist' do
+      let(:page_id) { 9_999_999 }
+
+      it 'returns 404' do
+        request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'POST /wiki' do
+    let(:endpoint) { '/wiki' }
+
+    let(:member) { create(:user, role: 'member') }
+    let(:guest) { create(:user, role: 'guest') }
+
+    def auth_headers(user)
+      { 'X-Transfer-Code' => user.inheritance_code }
+    end
+
+    context 'when not logged in' do
+      it 'returns 401' do
+        post endpoint, params: { title: 'Test', body: 'Hello' }
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      it 'returns 403' do
+        post endpoint, params: { title: 'Test', body: 'Hello' }, headers: auth_headers(guest)
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when params invalid' do
+      it 'returns 422 when title blank' do
+        post endpoint, params: { title: '', body: 'Hello' }, headers: auth_headers(member)
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+
+      it 'returns 422 when body blank' do
+        post endpoint, params: { title: 'Test', body: '' }, headers: auth_headers(member)
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+
+    context 'when success' do
+      it 'creates wiki_page and first content revision' do
+        expect do
+          post endpoint, params: { title: 'TestPage', body: "a\nb\nc", message: 'init' },
+                         headers: auth_headers(member)
+        end
+            .to change(WikiPage, :count).by(1)
+            .and change(WikiRevision, :count).by(1)
+
+        expect(response).to have_http_status(:created)
+
+        page_id = json.fetch('id')
+        expect(json.fetch('title')).to eq('TestPage')
+
+        page = WikiPage.find(page_id)
+        rev = page.current_revision
+        expect(rev).to be_present
+        expect(rev).to be_content
+        expect(rev.message).to eq('init')
+
+        # body が復元できること
+        expect(page.body).to eq("a\nb\nc")
+
+        # 行数とリレーションの整合
+        expect(rev.lines_count).to eq(3)
+        expect(rev.wiki_revision_lines.order(:position).pluck(:position)).to eq([0, 1, 2])
+        expect(rev.wiki_lines.pluck(:body)).to match_array(%w[a b c])
+      end
+
+      it 'reuses existing WikiLine rows by sha256' do
+        # 先に同じ行を作っておく
+        WikiLine.create!(sha256: Digest::SHA256.hexdigest('a'), body: 'a', created_at: Time.current, updated_at: Time.current)
+
+        post endpoint,
+             params: { title: 'Reuse', body: "a\na" },
+             headers: auth_headers(member)
+
+        page = WikiPage.find(JSON.parse(response.body).fetch('id'))
+        rev = page.current_revision
+        expect(rev.lines_count).to eq(2)
+
+        # "a" の WikiLine が増殖しない（1行のはず）
+        expect(WikiLine.where(body: 'a').count).to eq(1)
+      end
+    end
+  end
+
+  describe 'PUT /wiki/:id' do
+    let(:member) { create(:user, role: 'member', inheritance_code: SecureRandom.hex(16)) }
+    let(:guest)  { create(:user, role: 'guest',  inheritance_code: SecureRandom.hex(16)) }
+
+    def auth_headers(user)
+      { 'X-Transfer-Code' => user.inheritance_code }
+    end
+
+    #let!(:page) { create(:wiki_page, title: 'TestPage') }
+    let!(:page) do
+      build(:wiki_page, title: 'TestPage').tap do |p|
+        puts p.errors.full_messages unless p.valid?
+        p.save!
+      end
+    end
+
+    before do
+      # 初期版を 1 つ作っておく（更新が“2版目”になるように）
+      Wiki::Commit.content!(page: page, body: "a\nb", created_user: member, message: 'init')
+    end
+
+    context 'when not logged in' do
+      it 'returns 401' do
+        put "/wiki/#{page.id}", params: { title: 'TestPage', body: 'x' }
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      it 'returns 403' do
+        put "/wiki/#{page.id}",
+            params: { title: 'TestPage', body: 'x' },
+            headers: auth_headers(guest)
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when params invalid' do
+      it 'returns 422 when body blank' do
+        put "/wiki/#{page.id}",
+            params: { title: 'TestPage', body: '' },
+            headers: auth_headers(member)
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+
+      it 'returns 422 when title mismatched (if you forbid rename here)' do
+        put "/wiki/#{page.id}",
+            params: { title: 'OtherTitle', body: 'x' },
+            headers: auth_headers(member)
+        # 君の controller 例だと title 変更は 422 にしてた
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+
+    context 'when success' do
+      it 'creates new revision and returns 200' do
+        current_id = page.wiki_revisions.maximum(:id)
+
+        expect do
+          put "/wiki/#{page.id}",
+              params: { title: 'TestPage', body: "x\ny", message: 'edit', base_revision_id: current_id },
+              headers: auth_headers(member)
+        end.to change(WikiRevision, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        page.reload
+        rev = page.current_revision
+        expect(rev).to be_content
+        expect(rev.message).to eq('edit')
+        expect(page.body).to eq("x\ny")
+        expect(rev.base_revision_id).to eq(current_id)
+      end
+    end
+
+    # TODO: コンフリクト未実装のため，実装したらコメント外す．
+    # context 'when conflict' do
+    #   it 'returns 409 when base_revision_id mismatches' do
+    #     # 先に別ユーザ（同じ member でもOK）が 1 回更新して先頭を進める
+    #     Wiki::Commit.content!(page: page, body: "zzz", created_user: member, message: 'other edit')
+    #     page.reload
+
+    #     stale_id = page.wiki_revisions.order(:id).first.id # わざと古い id
+    #     put "/wiki/#{page.id}",
+    #         params: { title: 'TestPage', body: 'x', base_revision_id: stale_id },
+    #         headers: auth_headers(member)
+
+    #     expect(response).to have_http_status(:conflict)
+    #     json = JSON.parse(response.body)
+    #     expect(json['error']).to eq('conflict')
+    #   end
+    # end
+
+    context 'when page not found' do
+      it 'returns 404' do
+        put "/wiki/99999999",
+            params: { title: 'X', body: 'x' },
+            headers: auth_headers(member)
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'GET /wiki/title/:title' do
+    it 'returns wiki page by title' do
+      get "/wiki/title/#{CGI.escape('spec_wiki_title')}"
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to have_key('id')
+      expect(json).to have_key('title')
+      expect(json['id']).to eq(page.id)
+      expect(json['title']).to eq('spec_wiki_title')
+    end
+
+    it 'returns 404 when not found' do
+      get "/wiki/title/#{ CGI.escape('nope') }"
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'GET /wiki/search' do
+    before do
+      # 追加で検索ヒット用
+      TagName.create!(name: 'spec_wiki_title_2')
+      WikiPage.create!(tag_name: TagName.find_by!(name: 'spec_wiki_title_2'),
+                       created_user: user, updated_user: user)
+
+      TagName.create!(name: 'unrelated_title')
+      WikiPage.create!(tag_name: TagName.find_by!(name: 'unrelated_title'),
+                       created_user: user, updated_user: user)
+    end
+
+    it 'returns up to 20 pages filtered by title like' do
+      get "/wiki/search?title=#{CGI.escape('spec_wiki')}"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to be_an(Array)
+
+      titles = json.map { |p| p['title'] }
+      expect(titles).to include('spec_wiki_title', 'spec_wiki_title_2')
+      expect(titles).not_to include('unrelated_title')
+    end
+
+    it 'returns all when title param is blank' do
+      get "/wiki/search?title=#{CGI.escape('')}"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to be_an(Array)
+      expect(json.map { |p| p['title'] }).to include('spec_wiki_title')
+    end
+  end
+
+  describe 'GET /wiki/changes' do
+    let!(:rev1) do
+      Wiki::Commit.content!(page: page, body: "a\nb", created_user: user, message: 'r1')
+      page.current_revision
+    end
+
+    let!(:rev2) do
+      Wiki::Commit.content!(page: page, body: "a\nc", created_user: user, message: 'r2')
+      page.current_revision
+    end
+
+    it 'returns latest revisions (optionally filtered by page id)' do
+      get "/wiki/changes?id=#{page.id}"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to be_an(Array)
+      expect(json).not_to be_empty
+
+      top = json.first
+      expect(top).to include(
+        'revision_id' => rev2.id,
+        'pred' => rev2.base_revision_id,
+        'succ' => nil,
+        'kind' => 'content',
+        'message' => 'r2'
+      )
+      expect(top['wiki_page']).to include('id' => page.id, 'title' => 'spec_wiki_title')
+      expect(top['user']).to include('id' => user.id, 'name' => user.name)
+      expect(top).to have_key('timestamp')
+
+      # order desc をざっくり担保
+      ids = json.map { |x| x['revision_id'] }
+      expect(ids).to eq(ids.sort.reverse)
+    end
+
+    it 'returns empty array when page has no revisions and filtered by id' do
+      # 別ページを作って revision 無し
+      tn2 = TagName.create!(name: 'spec_no_rev')
+      p2 = WikiPage.create!(tag_name: tn2, created_user: user, updated_user: user)
+
+      get "/wiki/changes?id=#{p2.id}"
+      expect(response).to have_http_status(:ok)
+      expect(json).to eq([])
+    end
+  end
+
+  describe 'GET /wiki/title/:title/exists' do
+    it 'returns 204 when exists' do
+      get "/wiki/title/#{CGI.escape('spec_wiki_title')}/exists"
+      expect(response).to have_http_status(:no_content)
+      expect(response.body).to be_empty
+    end
+
+    it 'returns 404 when not exists' do
+      get "/wiki/title/#{CGI.escape('nope')}/exists"
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'GET /wiki/:id/exists' do
+    it 'returns 204 when exists' do
+      get "/wiki/#{page.id}/exists"
+      expect(response).to have_http_status(:no_content)
+      expect(response.body).to be_empty
+    end
+
+    it 'returns 404 when not exists' do
+      get "/wiki/99999999/exists"
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'GET /wiki/:id/diff' do
+    let!(:rev_a) do
+      Wiki::Commit.content!(page: page, body: "a\nb\nc", created_user: user, message: 'A')
+      page.current_revision
+    end
+
+    let!(:rev_b) do
+      Wiki::Commit.content!(page: page, body: "a\nx\nc", created_user: user, message: 'B')
+      page.current_revision
+    end
+
+    it 'returns diff json between revisions' do
+      get "/wiki/#{page.id}/diff?from=#{rev_a.id}&to=#{rev_b.id}"
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to include(
+        'wiki_page_id' => page.id,
+        'title' => 'spec_wiki_title',
+        'older_revision_id' => rev_a.id,
+        'newer_revision_id' => rev_b.id
+      )
+      expect(json['diff']).to be_an(Array)
+      # ざっくり「b が消えて x が増えた」が含まれることを確認
+      types = json['diff'].map { |x| x['type'] }
+      expect(types).to include('removed', 'added').or include('removed').and include('added')
+    end
+
+    it 'uses latest as "to" when to is omitted' do
+      get "/wiki/#{page.id}/diff?from=#{rev_a.id}"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['older_revision_id']).to eq(rev_a.id)
+      expect(json['newer_revision_id']).to eq(page.current_revision.id)
+    end
+
+    it 'returns 422 when "to" is redirect revision' do
+      # redirect revision を作る
+      tn2 = TagName.create!(name: 'redirect_target')
+      target = WikiPage.create!(tag_name: tn2, created_user: user, updated_user: user)
+
+      Wiki::Commit.redirect!(page: page, redirect_page: target, created_user: user, message: 'redir')
+      redirect_rev = page.current_revision
+      expect(redirect_rev).to be_redirect
+
+      get "/wiki/#{page.id}/diff?from=#{rev_a.id}&to=#{redirect_rev.id}"
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'returns 422 when "from" is redirect revision' do
+      tn2 = TagName.create!(name: 'redirect_target2')
+      target = WikiPage.create!(tag_name: tn2, created_user: user, updated_user: user)
+
+      Wiki::Commit.redirect!(page: page, redirect_page: target, created_user: user, message: 'redir2')
+      redirect_rev = page.current_revision
+
+      get "/wiki/#{page.id}/diff?from=#{redirect_rev.id}&to=#{rev_b.id}"
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+  end
+end

backend/spec/spec_helper.rb

@@ -0,0 +1,94 @@
+# This file was generated by the `rails generate rspec:install` command. Conventionally, all
+# specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
+# The generated `.rspec` file contains `--require spec_helper` which will cause
+# this file to always be loaded, without a need to explicitly require it in any
+# files.
+#
+# Given that it is always loaded, you are encouraged to keep this file as
+# light-weight as possible. Requiring heavyweight dependencies from this file
+# will add to the boot time of your test suite on EVERY test run, even for an
+# individual file that may not need all of that loaded. Instead, consider making
+# a separate helper file that requires the additional dependencies and performs
+# the additional setup, and require it from the spec files that actually need
+# it.
+#
+# See https://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+RSpec.configure do |config|
+  # rspec-expectations config goes here. You can use an alternate
+  # assertion/expectation library such as wrong or the stdlib/minitest
+  # assertions if you prefer.
+  config.expect_with :rspec do |expectations|
+    # This option will default to `true` in RSpec 4. It makes the `description`
+    # and `failure_message` of custom matchers include text for helper methods
+    # defined using `chain`, e.g.:
+    #     be_bigger_than(2).and_smaller_than(4).description
+    #     # => "be bigger than 2 and smaller than 4"
+    # ...rather than:
+    #     # => "be bigger than 2"
+    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
+  end
+
+  # rspec-mocks config goes here. You can use an alternate test double
+  # library (such as bogus or mocha) by changing the `mock_with` option here.
+  config.mock_with :rspec do |mocks|
+    # Prevents you from mocking or stubbing a method that does not exist on
+    # a real object. This is generally recommended, and will default to
+    # `true` in RSpec 4.
+    mocks.verify_partial_doubles = true
+  end
+
+  # This option will default to `:apply_to_host_groups` in RSpec 4 (and will
+  # have no way to turn it off -- the option exists only for backwards
+  # compatibility in RSpec 3). It causes shared context metadata to be
+  # inherited by the metadata hash of host groups and examples, rather than
+  # triggering implicit auto-inclusion in groups with matching metadata.
+  config.shared_context_metadata_behavior = :apply_to_host_groups
+
+# The settings below are suggested to provide a good initial experience
+# with RSpec, but feel free to customize to your heart's content.
+=begin
+  # This allows you to limit a spec run to individual examples or groups
+  # you care about by tagging them with `:focus` metadata. When nothing
+  # is tagged with `:focus`, all examples get run. RSpec also provides
+  # aliases for `it`, `describe`, and `context` that include `:focus`
+  # metadata: `fit`, `fdescribe` and `fcontext`, respectively.
+  config.filter_run_when_matching :focus
+
+  # Allows RSpec to persist some state between runs in order to support
+  # the `--only-failures` and `--next-failure` CLI options. We recommend
+  # you configure your source control system to ignore this file.
+  config.example_status_persistence_file_path = "spec/examples.txt"
+
+  # Limits the available syntax to the non-monkey patched syntax that is
+  # recommended. For more details, see:
+  # https://rspec.info/features/3-12/rspec-core/configuration/zero-monkey-patching-mode/
+  config.disable_monkey_patching!
+
+  # Many RSpec users commonly either run the entire suite or an individual
+  # file, and it's useful to allow more verbose output when running an
+  # individual spec file.
+  if config.files_to_run.one?
+    # Use the documentation formatter for detailed output,
+    # unless a formatter has already been configured
+    # (e.g. via a command-line flag).
+    config.default_formatter = "doc"
+  end
+
+  # Print the 10 slowest examples and example groups at the
+  # end of the spec run, to help surface which specs are running
+  # particularly slow.
+  config.profile_examples = 10
+
+  # Run specs in random order to surface order dependencies. If you find an
+  # order dependency and want to debug it, you can fix the order by providing
+  # the seed, which is printed after each run.
+  #     --seed 1234
+  config.order = :random
+
+  # Seed global randomization in this process using the `--seed` CLI option.
+  # Setting this allows you to use `--seed` to deterministically reproduce
+  # test failures related to randomization by passing the same `--seed` value
+  # as the one that triggered the failure.
+  Kernel.srand config.seed
+=end
+end

backend/spec/support/auth_helper.rb

@@ -0,0 +1,11 @@
+module AuthHelper
+  def sign_in_as(user)
+    allow_any_instance_of(ApplicationController)
+      .to receive(:current_user).and_return(user)
+  end
+
+  def sign_out
+    allow_any_instance_of(ApplicationController)
+      .to receive(:current_user).and_return(nil)
+  end
+end

backend/spec/support/json_helper.rb

@@ -0,0 +1,5 @@
+module JsonHelper
+  def json
+    JSON.parse(response.body)
+  end
+end

backend/spec/support/rake.rb

@@ -0,0 +1,21 @@
+require "rake"
+
+
+module RakeTaskHelper
+  # Railsの rake task を一度だけロードする
+  def load_rails_tasks!
+    return if defined?(@rails_tasks_loaded) && @rails_tasks_loaded
+    @rails_tasks_loaded = true
+
+    Rake.application = Rake::Application.new
+    Rails.application.load_tasks
+  end
+
+  def run_rake_task(full_name)
+    load_rails_tasks!
+
+    task = Rake::Task[full_name]  # ここは rake[...] じゃなくて良い
+    task.reenable
+    task.invoke
+  end
+end

backend/spec/support/test_records.rb

@@ -0,0 +1,15 @@
+module TestRecords
+  def create_member_user!
+    User.create!(name: 'spec user',
+                 inheritance_code: SecureRandom.hex(16),
+                 role: 'member',
+                 banned: false)
+  end
+
+  def create_admin_user!
+    User.create!(name: 'spec admin',
+                 inheritance_code: SecureRandom.hex(16),
+                 role: 'admin',
+                 banned: false)
+  end
+end

backend/spec/tasks/nico_sync_spec.rb

@@ -0,0 +1,86 @@
+require "rails_helper"
+
+
+RSpec.describe "nico:sync" do
+  def stub_python(json_array)
+    status = instance_double(Process::Status, success?: true)
+    allow(Open3).to receive(:capture3).and_return([json_array.to_json, "", status])
+  end
+
+  def create_tag!(name, category:)
+    tn = TagName.find_or_create_by!(name: name.to_s.strip)
+    Tag.find_or_create_by!(tag_name_id: tn.id) { |t| t.category = category }
+  end
+
+  def link_nico_to_tag!(nico_tag, tag)
+    # NicoTagRelation がある前提（君の model からそう見える）
+    NicoTagRelation.create!(nico_tag_id: nico_tag.id, tag_id: tag.id)
+  end
+
+  it "既存 post を見つけて、nico tag と linked tag を追加し、差分が出たら bot を付ける" do
+    # 既存 post（正規表現で拾われるURL）
+    post = Post.create!(title: "old", url: "https://www.nicovideo.jp/watch/sm9", uploaded_user: nil)
+
+    # 既存の非nicoタグ（kept_non_nico_ids）
+    kept_general = create_tag!("spec_kept", category: "general")
+    PostTag.create!(post: post, tag: kept_general)
+
+    # 追加される linked tag を準備（nico tag に紐付く一般タグ）
+    linked = create_tag!("spec_linked", category: "general")
+    nico = create_tag!("nico:AAA", category: "nico")
+    link_nico_to_tag!(nico, linked)
+
+    # bot / tagme は task 内で使うので作っておく（Tag.bot/tagme がある前提）
+    Tag.bot
+    Tag.tagme
+
+    # pythonの出力（AAA が付く）
+    stub_python([{ "code" => "sm9", "title" => "t", "tags" => ["AAA"] }])
+
+    # 外部HTTPは今回「既存 post なので呼ばれない」はずだが、念のため塞ぐ
+    allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
+
+    run_rake_task("nico:sync")
+
+    post.reload
+    active_tag_names = post.tags.joins(:tag_name).pluck("tag_names.name")
+
+    expect(active_tag_names).to include("spec_kept")
+    expect(active_tag_names).to include("nico:AAA")
+    expect(active_tag_names).to include("spec_linked")
+
+    # 差分が出るので bot が付く（kept_non_nico_ids != desired_non_nico_ids）
+    expect(active_tag_names).to include("bot操作")
+  end
+
+  it "既存 post にあった古い nico tag は active から外され、履歴として discard される" do
+    post = Post.create!(title: "old", url: "https://www.nicovideo.jp/watch/sm9", uploaded_user: nil)
+
+    # 旧nicoタグ（今回の同期結果に含まれない）
+    old_nico = create_tag!("nico:OLD", category: "nico")
+    old_pt = PostTag.create!(post: post, tag: old_nico)
+    expect(old_pt.discarded_at).to be_nil
+
+    # 今回は NEW のみ欲しい
+    new_nico = create_tag!("nico:NEW", category: "nico")
+
+    # bot/tagme 念のため
+    Tag.bot
+    Tag.tagme
+
+    stub_python([{ "code" => "sm9", "title" => "t", "tags" => ["NEW"] }])
+    allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
+
+    run_rake_task("nico:sync")
+
+    # OLD は active から外れる（discarded_at が入る）
+    old_pts = PostTag.where(post_id: post.id, tag_id: old_nico.id).order(:id).to_a
+    expect(old_pts.last.discarded_at).to be_present
+
+    # NEW は active にいる
+    post.reload
+    active_names = post.tags.joins(:tag_name).pluck("tag_names.name")
+    expect(active_names).to include("nico:NEW")
+    expect(active_names).not_to include("nico:OLD")
+  end
+end

backend/spec/tasks/post_similarity_calc_spec.rb

@@ -0,0 +1,34 @@
+require 'rails_helper'
+
+
+RSpec.describe 'post_similarity:calc' do
+  include RakeTaskHelper
+
+  it 'calls Similarity::Calc with Post and :tags' do
+    # 必要最低限のデータ
+    t1 = Tag.create!(name: "t1")
+    t2 = Tag.create!(name: "t2")
+    t3 = Tag.create!(name: "t3")
+
+    p1 = Post.create!(url: "https://example.com/1")
+    p2 = Post.create!(url: "https://example.com/2")
+    p3 = Post.create!(url: "https://example.com/3")
+
+    # kept スコープが絡むなら、PostTag がデフォで kept になる前提
+    PostTag.create!(post: p1, tag: t1)
+    PostTag.create!(post: p1, tag: t2)
+
+    PostTag.create!(post: p2, tag: t1)
+    PostTag.create!(post: p2, tag: t3)
+
+    PostTag.create!(post: p3, tag: t3)
+
+    expect { run_rake_task("post_similarity:calc") }
+      .to change { PostSimilarity.count }.from(0)
+
+    ps = PostSimilarity.find_by!(post_id: p1.id, target_post_id: p2.id)
+    ps_rev = PostSimilarity.find_by!(post_id: p2.id, target_post_id: p1.id)
+    expect(ps_rev.cos).to eq(ps.cos)
+  end
+end
+

backend/spec/tasks/tag_similarity_calc_spec.rb

@@ -0,0 +1,34 @@
+require 'rails_helper'
+
+
+RSpec.describe 'tag_similarity:calc' do
+  include RakeTaskHelper
+
+  it 'calls Similarity::Calc with Tag and :posts' do
+    # 必要最低限のデータ
+    t1 = Tag.create!(name: "t1")
+    t2 = Tag.create!(name: "t2")
+    t3 = Tag.create!(name: "t3")
+
+    p1 = Post.create!(url: "https://example.com/1")
+    p2 = Post.create!(url: "https://example.com/2")
+    p3 = Post.create!(url: "https://example.com/3")
+
+    # kept スコープが絡むなら、PostTag がデフォで kept になる前提
+    PostTag.create!(post: p1, tag: t1)
+    PostTag.create!(post: p1, tag: t2)
+
+    PostTag.create!(post: p2, tag: t1)
+    PostTag.create!(post: p2, tag: t3)
+
+    PostTag.create!(post: p3, tag: t3)
+
+    expect { run_rake_task("tag_similarity:calc") }
+      .to change { TagSimilarity.count }.from(0)
+
+    ps = TagSimilarity.find_by!(tag_id: t1.id, target_tag_id: t2.id)
+    ps_rev = TagSimilarity.find_by!(tag_id: t2.id, target_tag_id: t1.id)
+    expect(ps_rev.cos).to eq(ps.cos)
+  end
+end
+

frontend/package-lock.json

@@ -9,6 +9,9 @@
       "version": "0.0.0",
       "license": "ISC",
       "dependencies": {
+        "@dnd-kit/core": "^6.3.1",
+        "@dnd-kit/modifiers": "^9.0.0",
+        "@dnd-kit/utilities": "^3.2.2",
         "@fontsource-variable/noto-sans-jp": "^5.2.9",
         "@radix-ui/react-dialog": "^1.1.14",
         "@radix-ui/react-switch": "^1.2.5",
@@ -18,6 +21,7 @@
         "camelcase-keys": "^9.1.3",
         "class-variance-authority": "^0.7.1",
         "clsx": "^2.1.1",
+        "framer-motion": "^12.23.26",
         "humps": "^2.0.1",
         "lucide-react": "^0.511.0",
         "markdown-it": "^14.1.0",
@@ -31,6 +35,7 @@
         "react-youtube": "^10.1.0",
         "remark-gfm": "^4.0.1",
         "tailwind-merge": "^3.3.0",
+        "unist-util-visit-parents": "^6.0.1",
         "zustand": "^5.0.8"
       },
       "devDependencies": {
@@ -372,6 +377,59 @@
         "node": ">=6.9.0"
       }
     },
+    "node_modules/@dnd-kit/accessibility": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/@dnd-kit/accessibility/-/accessibility-3.1.1.tgz",
+      "integrity": "sha512-2P+YgaXF+gRsIihwwY1gCsQSYnu9Zyj2py8kY5fFvUM1qm2WA2u639R6YNVfU4GWr+ZM5mqEsfHZZLoRONbemw==",
+      "license": "MIT",
+      "dependencies": {
+        "tslib": "^2.0.0"
+      },
+      "peerDependencies": {
+        "react": ">=16.8.0"
+      }
+    },
+    "node_modules/@dnd-kit/core": {
+      "version": "6.3.1",
+      "resolved": "https://registry.npmjs.org/@dnd-kit/core/-/core-6.3.1.tgz",
+      "integrity": "sha512-xkGBRQQab4RLwgXxoqETICr6S5JlogafbhNsidmrkVv2YRs5MLwpjoF2qpiGjQt8S9AoxtIV603s0GIUpY5eYQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@dnd-kit/accessibility": "^3.1.1",
+        "@dnd-kit/utilities": "^3.2.2",
+        "tslib": "^2.0.0"
+      },
+      "peerDependencies": {
+        "react": ">=16.8.0",
+        "react-dom": ">=16.8.0"
+      }
+    },
+    "node_modules/@dnd-kit/modifiers": {
+      "version": "9.0.0",
+      "resolved": "https://registry.npmjs.org/@dnd-kit/modifiers/-/modifiers-9.0.0.tgz",
+      "integrity": "sha512-ybiLc66qRGuZoC20wdSSG6pDXFikui/dCNGthxv4Ndy8ylErY0N3KVxY2bgo7AWwIbxDmXDg3ylAFmnrjcbVvw==",
+      "license": "MIT",
+      "dependencies": {
+        "@dnd-kit/utilities": "^3.2.2",
+        "tslib": "^2.0.0"
+      },
+      "peerDependencies": {
+        "@dnd-kit/core": "^6.3.0",
+        "react": ">=16.8.0"
+      }
+    },
+    "node_modules/@dnd-kit/utilities": {
+      "version": "3.2.2",
+      "resolved": "https://registry.npmjs.org/@dnd-kit/utilities/-/utilities-3.2.2.tgz",
+      "integrity": "sha512-+MKAJEOfaBe5SmV6t34p80MMKhjvUz0vRrvVJbPT0WElzaOJ/1xs+D+KDv+tD/NE5ujfrChEcshd4fLn0wpiqg==",
+      "license": "MIT",
+      "dependencies": {
+        "tslib": "^2.0.0"
+      },
+      "peerDependencies": {
+        "react": ">=16.8.0"
+      }
+    },
     "node_modules/@esbuild/aix-ppc64": {
       "version": "0.25.4",
       "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.25.4.tgz",
@@ -3602,6 +3660,33 @@
         "url": "https://github.com/sponsors/rawify"
       }
     },
+    "node_modules/framer-motion": {
+      "version": "12.23.26",
+      "resolved": "https://registry.npmjs.org/framer-motion/-/framer-motion-12.23.26.tgz",
+      "integrity": "sha512-cPcIhgR42xBn1Uj+PzOyheMtZ73H927+uWPDVhUMqxy8UHt6Okavb6xIz9J/phFUHUj0OncR6UvMfJTXoc/LKA==",
+      "license": "MIT",
+      "dependencies": {
+        "motion-dom": "^12.23.23",
+        "motion-utils": "^12.23.6",
+        "tslib": "^2.4.0"
+      },
+      "peerDependencies": {
+        "@emotion/is-prop-valid": "*",
+        "react": "^18.0.0 || ^19.0.0",
+        "react-dom": "^18.0.0 || ^19.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@emotion/is-prop-valid": {
+          "optional": true
+        },
+        "react": {
+          "optional": true
+        },
+        "react-dom": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/fsevents": {
       "version": "2.3.3",
       "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.3.tgz",
@@ -5245,6 +5330,21 @@
         "node": ">=16 || 14 >=14.17"
       }
     },
+    "node_modules/motion-dom": {
+      "version": "12.23.23",
+      "resolved": "https://registry.npmjs.org/motion-dom/-/motion-dom-12.23.23.tgz",
+      "integrity": "sha512-n5yolOs0TQQBRUFImrRfs/+6X4p3Q4n1dUEqt/H58Vx7OW6RF+foWEgmTVDhIWJIMXOuNNL0apKH2S16en9eiA==",
+      "license": "MIT",
+      "dependencies": {
+        "motion-utils": "^12.23.6"
+      }
+    },
+    "node_modules/motion-utils": {
+      "version": "12.23.6",
+      "resolved": "https://registry.npmjs.org/motion-utils/-/motion-utils-12.23.6.tgz",
+      "integrity": "sha512-eAWoPgr4eFEOFfg2WjIsMoqJTW6Z8MTUCgn/GZ3VRpClWBdnbjryiA3ZSNLyxCTmCQx4RmYX6jX1iWHbenUPNQ==",
+      "license": "MIT"
+    },
     "node_modules/ms": {
       "version": "2.1.3",
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",

frontend/package.json

@@ -11,6 +11,9 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@dnd-kit/core": "^6.3.1",
+    "@dnd-kit/modifiers": "^9.0.0",
+    "@dnd-kit/utilities": "^3.2.2",
     "@fontsource-variable/noto-sans-jp": "^5.2.9",
     "@radix-ui/react-dialog": "^1.1.14",
     "@radix-ui/react-switch": "^1.2.5",
@@ -20,6 +23,7 @@
     "camelcase-keys": "^9.1.3",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "framer-motion": "^12.23.26",
     "humps": "^2.0.1",
     "lucide-react": "^0.511.0",
     "markdown-it": "^14.1.0",
@@ -33,7 +37,8 @@
     "react-youtube": "^10.1.0",
     "remark-gfm": "^4.0.1",
     "tailwind-merge": "^3.3.0",
-    "zustand": "^5.0.8"
+    "zustand": "^5.0.8",
+    "unist-util-visit-parents": "^6.0.1"
   },
   "devDependencies": {
     "@eslint/js": "^9.25.0",

frontend/scripts/generate-sitemap.js

@@ -19,7 +19,6 @@ const fetchPosts = async tagName => (await axios.get (`${ API_BASE_URL }/posts`,
     { params: { ...(tagName && { tags:  tagName,
                                  match: 'all',
                                  limit: '20' }) } })).data.posts
-const fetchPostIds = async () => (await fetchPosts ()).map (post => post.id)
 
 const fetchTags = async () => (await axios.get (`${ API_BASE_URL }/tags`)).data
 const fetchTagNames = async () => (await fetchTags ()).map (tag => tag.name)
@@ -33,7 +32,7 @@ const createPostListOutlet = async tagName => `
         <div class="flex gap-4"><a href="#" class="font-bold">広場</a></div>
         <div class="mt-2">
           <div class="flex flex-wrap gap-6 p-4">
-            ${ (await fetchPosts (tagName)).map (post => `
+            ${ (await fetchPosts (tagName)).slice (0, 20).map (post => `
                 <a class="w-40 h-40 overflow-hidden rounded-lg shadow-md hover:shadow-lg"
                    href="/posts/${ post.id }">
                   <img alt="${ post.title }"
@@ -42,7 +41,7 @@ const createPostListOutlet = async tagName => `
                        fetchpriority="high"
                        decoding="async"
                        class="object-none w-full h-full"
-                       src="${ post.url }" />
+                       src="${ post.thumbnail }" />
                 </a>`).join ('') }
           </div>
         </div>

frontend/src/App.tsx

@@ -10,6 +10,7 @@ import { API_BASE_URL } from '@/config'
 import NicoTagListPage from '@/pages/tags/NicoTagListPage'
 import NotFound from '@/pages/NotFound'
 import PostDetailPage from '@/pages/posts/PostDetailPage'
+import PostHistoryPage from '@/pages/posts/PostHistoryPage'
 import PostListPage from '@/pages/posts/PostListPage'
 import PostNewPage from '@/pages/posts/PostNewPage'
 import ServiceUnavailable from '@/pages/ServiceUnavailable'
@@ -89,6 +90,7 @@ export default (() => {
 	      <Route path="/posts" element={<PostListPage/>}/>
 	      <Route path="/posts/new" element={<PostNewPage user={user}/>}/>
 	      <Route path="/posts/:id" element={<PostDetailRoute user={user}/>}/>
+	      <Route path="/posts/changes" element={<PostHistoryPage/>}/>
 	      <Route path="/tags/nico" element={<NicoTagListPage user={user}/>}/>
 	      <Route path="/wiki" element={<WikiSearchPage/>}/>
 	      <Route path="/wiki/:title" element={<WikiDetailPage/>}/>

frontend/src/components/DraggableDroppableTagRow.tsx

@@ -0,0 +1,93 @@
+import { useDraggable, useDroppable } from '@dnd-kit/core'
+import { CSS } from '@dnd-kit/utilities'
+import { useRef } from 'react'
+
+import TagLink from '@/components/TagLink'
+import { cn } from '@/lib/utils'
+
+import type { CSSProperties, FC, MutableRefObject } from 'react'
+
+import type { Tag } from '@/types'
+
+type Props = {
+    tag:              Tag
+    nestLevel:        number
+    pathKey:          string
+    parentTagId?:     number
+    suppressClickRef: MutableRefObject<boolean> }
+
+
+export default (({ tag, nestLevel, pathKey, parentTagId, suppressClickRef }: Props) => {
+  const dndId = `tag-node:${ pathKey }`
+
+  const downPosRef = useRef<{ x: number; y: number } | null> (null)
+  const armedRef = useRef (false)
+
+  const armEatNextClick = () => {
+    if (armedRef.current)
+      return
+
+    armedRef.current = true
+    suppressClickRef.current = true
+
+    const handler = (ev: MouseEvent) => {
+      ev.preventDefault ()
+      ev.stopPropagation ()
+      armedRef.current = false
+      suppressClickRef.current = false
+    }
+
+    addEventListener ('click', handler, { capture: true, once: true })
+  }
+
+  const { attributes,
+	  listeners,
+	  setNodeRef: setDragRef,
+	  transform,
+	  isDragging: dragging } = useDraggable ({ id:    dndId,
+						   data:  { kind:   'tag',
+							    tagId:  tag.id,
+							    parentTagId } })
+
+  const { setNodeRef: setDropRef, isOver: over } = useDroppable ({
+      id:   dndId,
+      data: { kind: 'tag', tagId: tag.id } })
+
+  const style: CSSProperties = { transform:   CSS.Translate.toString (transform),
+				 visibility:  dragging ? 'hidden' : 'visible' }
+
+  return (
+      <div
+	  onPointerDownCapture={e => {
+	    downPosRef.current = { x: e.clientX, y: e.clientY }
+	  }}
+	  onPointerMoveCapture={e => {
+	    const p = downPosRef.current
+	    if (!(p))
+	      return
+	    const dx = e.clientX - p.x
+	    const dy = e.clientY - p.y
+	    if (dx * dx + dy * dy >= 9)
+	      armEatNextClick ()
+	  }}
+	  onPointerUpCapture={() => {
+	    downPosRef.current = null
+	  }}
+	  onClickCapture={e => {
+	    if (suppressClickRef.current)
+	      {
+		e.preventDefault ()
+		e.stopPropagation ()
+	      }
+	  }}
+	  ref={node => {
+	    setDragRef (node)
+	    setDropRef (node)
+	  }}
+	  style={style}
+	  className={cn ('rounded select-none', over && 'ring-2 ring-offset-2')}
+	  {...attributes}
+	  {...listeners}>
+	<TagLink tag={tag} nestLevel={nestLevel}/>
+      </div>)
+}) satisfies FC<Props>

frontend/src/components/PostEditForm.tsx

@@ -1,6 +1,6 @@
 import axios from 'axios'
 import toCamel from 'camelcase-keys'
-import { useState } from 'react'
+import { useEffect, useState } from 'react'
 
 import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
@@ -10,7 +10,23 @@ import { API_BASE_URL } from '@/config'
 
 import type { FC } from 'react'
 
-import type { Post } from '@/types'
+import type { Post, Tag } from '@/types'
+
+
+const tagsToStr = (tags: Tag[]): string => {
+  const result: Tag[] = []
+
+  const walk = (tag: Tag) => {
+    const { children, ...rest } = tag
+    result.push (rest)
+    children?.forEach (walk)
+  }
+
+  tags.filter (t => t.category !== 'nico').forEach (walk)
+
+  return [...(new Set (result.map (t => t.name)))].join (' ')
+}
+
 
 type Props = { post:    Post
 	       onSave:  (newPost: Post) => void }
@@ -22,10 +38,7 @@ export default (({ post, onSave }: Props) => {
   const [originalCreatedFrom, setOriginalCreatedFrom] =
       useState<string | null> (post.originalCreatedFrom)
   const [title, setTitle] = useState (post.title)
-  const [tags, setTags] = useState<string> (post.tags
-					    .filter (t => t.category !== 'nico')
-					    .map (t => t.name)
-					    .join (' '))
+  const [tags, setTags] = useState<string> ('')
 
   const handleSubmit = async () => {
     const res = await axios.put (
@@ -43,6 +56,10 @@ export default (({ post, onSave }: Props) => {
 	      originalCreatedBefore:  data.originalCreatedBefore } as Post)
   }
 
+  useEffect (() => {
+    setTags(tagsToStr (post.tags))
+  }, [post])
+
   return (
       <div className="max-w-xl pt-2 space-y-4">
 	{/* タイトル */}

frontend/src/components/PostEmbed.tsx

@@ -1,3 +1,4 @@
+import { useState } from 'react'
 import YoutubeEmbed from 'react-youtube'
 
 import NicoViewer from '@/components/NicoViewer'
@@ -39,10 +40,28 @@ export default (({ post }: Props) => {
     }
   }
 
+  const [framed, setFramed] = useState (false)
+
   return (
-      <a href={post.url} target="_blank">
-	<img src={post.thumbnailBase || post.thumbnail}
-	     alt={post.url}
-	     className="mb-4 w-full"/>
-      </a>)
+      <>
+	{framed
+	 ? (
+	    <iframe
+		src={post.url}
+		title={post.title || post.url}
+		width={640}
+		height={360}/>)
+	 : (
+	    <div>
+	      <a href="#" onClick={e => {
+		e.preventDefault ()
+		setFramed (confirm ('未確認の外部ページを表示します。\n'
+				    + '悪意のあるスクリプトが実行される可能性があります。\n'
+				    + '表示しますか?'))
+		return
+	      }}>
+		外部ページを表示
+	      </a>
+	    </div>)}
+      </>)
 }) satisfies FC<Props>

frontend/src/components/PostFormTagsArea.tsx

@@ -60,7 +60,8 @@ export default (({ tags, setTags }: Props) => {
     const { start, end, token } = getTokenAt (v, pos)
     setBounds ({ start, end })
     const res = await axios.get (`${ API_BASE_URL }/tags/autocomplete`, { params: { q: token } })
-    setSuggestions (toCamel (res.data as any, { deep: true }) as Tag[])
+    const data = toCamel (res.data as any, { deep: true }) as Tag[]
+    setSuggestions (data.filter (t => t.postCount > 0))
     setSuggestionsVsbl (suggestions.length > 0)
   }
 

frontend/src/components/TagDetailSidebar.tsx

@@ -1,24 +1,280 @@
-import { useEffect, useState } from 'react'
+import { DndContext,
+	 DragOverlay,
+	 MouseSensor,
+	 TouchSensor,
+	 useDroppable,
+	 useSensor,
+	 useSensors } from '@dnd-kit/core'
+import { restrictToWindowEdges } from '@dnd-kit/modifiers'
+import axios from 'axios'
+import toCamel from 'camelcase-keys'
+import { AnimatePresence, motion } from 'framer-motion'
+import { useEffect, useRef, useState } from 'react'
+import { Link } from 'react-router-dom'
 
+import DraggableDroppableTagRow from '@/components/DraggableDroppableTagRow'
 import TagLink from '@/components/TagLink'
 import TagSearch from '@/components/TagSearch'
 import SectionTitle from '@/components/common/SectionTitle'
 import SubsectionTitle from '@/components/common/SubsectionTitle'
 import SidebarComponent from '@/components/layout/SidebarComponent'
+import { toast } from '@/components/ui/use-toast'
+import { API_BASE_URL } from '@/config'
 import { CATEGORIES } from '@/consts'
 
-import type { FC } from 'react'
+import type { DragEndEvent } from '@dnd-kit/core'
+import type { FC, MutableRefObject, ReactNode } from 'react'
 
 import type { Category, Post, Tag } from '@/types'
 
 type TagByCategory = { [key in Category]: Tag[] }
 
+
+const renderTagTree = (
+    tag:              Tag,
+    nestLevel:        number,
+    path:             string,
+    suppressClickRef: MutableRefObject<boolean>,
+    parentTagId?:     number,
+): ReactNode[] => {
+  const key = `${ path }-${ tag.id }`
+
+  const self = (
+      <motion.li
+	  key={key}
+	  layout
+	  transition={{ duration: .2, ease: 'easeOut' }}
+	  className="mb-1">
+	<DraggableDroppableTagRow
+	    tag={tag}
+	    nestLevel={nestLevel}
+	    pathKey={key}
+	    parentTagId={parentTagId}
+	    suppressClickRef={suppressClickRef}/>
+      </motion.li>)
+
+  return [
+      self,
+      ...((tag.children
+	   ?.sort ((a, b) => a.name < b.name ? -1 : 1)
+	   .flatMap (child => renderTagTree (child, nestLevel + 1, key, suppressClickRef, tag.id)))
+	  ?? [])]
+}
+
+
+const isDescendant = (
+    root:     Tag,
+    targetId: number,
+): boolean => {
+  if (!(root.children))
+    return false
+
+  for (const c of root.children)
+    {
+      if (c.id === targetId)
+	return true
+      if (isDescendant (c, targetId))
+	return true
+    }
+
+  return false
+}
+
+
+const findTag = (
+    byCat:  TagByCategory,
+    id:     number,
+): Tag | undefined => {
+  const walk = (nodes: Tag[]): Tag | undefined => {
+    for (const t of nodes)
+      {
+	if (t.id === id)
+	  return t
+
+	const found = t.children ? walk (t.children) : undefined
+	if (found)
+	  return found
+      }
+
+    return undefined
+  }
+
+  for (const cat of Object.keys (byCat) as (keyof typeof byCat)[])
+    {
+      const found = walk (byCat[cat] ?? [])
+      if (found)
+	return found
+    }
+
+  return undefined
+}
+
+
+const buildTagByCategory = (post: Post): TagByCategory => {
+  const tagsTmp = { } as TagByCategory
+
+  for (const tag of post.tags)
+    {
+      if (!(tag.category in tagsTmp))
+	tagsTmp[tag.category] = []
+
+      tagsTmp[tag.category].push (tag)
+    }
+
+  for (const cat of Object.keys (tagsTmp) as (keyof typeof tagsTmp)[])
+    tagsTmp[cat].sort ((a, b) => a.name < b.name ? -1 : 1)
+
+  return tagsTmp
+}
+
+
+const changeCategory = async (
+    tagId:    number,
+    category: Category,
+): Promise<void> => {
+  await axios.patch (
+      `${ API_BASE_URL }/tags/${ tagId }`,
+      { category },
+      { headers: { 'X-Transfer-Code': localStorage.getItem ('user_code') ?? '' } })
+}
+
+
+const DropSlot = ({ cat }: { cat: Category }) => {
+  const { setNodeRef, isOver: over } = useDroppable ({
+      id:   `slot:${ cat }`,
+      data: { kind: 'slot', cat } })
+
+  return (
+      <li ref={setNodeRef} className="h-1">
+	{over && <div className="h-0.5 w-full rounded bg-sky-400"/>}
+      </li>)
+}
+
+
 type Props = { post: Post | null }
 
 
 export default (({ post }: Props) => {
+  const [activeTagId, setActiveTagId] = useState<number | null> (null)
+  const [dragging, setDragging] = useState (false)
+  const [saving, setSaving] = useState (false)
   const [tags, setTags] = useState ({ } as TagByCategory)
 
+  const suppressClickRef = useRef (false)
+
+  const sensors = useSensors (
+      useSensor (MouseSensor, { activationConstraint: { distance: 6 } }),
+      useSensor (TouchSensor, { activationConstraint: { delay: 250, tolerance: 8 } }))
+
+  const reloadTags = async (): Promise<void> => {
+    if (!(post))
+      return
+
+    const res = await axios.get (
+	`${ API_BASE_URL }/posts/${ post.id }`,
+	{ headers: { 'X-Transfer-Code': localStorage.getItem ('user_code') ?? '' } })
+    const data = toCamel (res.data as any, { deep: true }) as Post
+
+    setTags (buildTagByCategory (data))
+  }
+
+  const onDragEnd = async (e: DragEndEvent) => {
+    if (saving)
+      return
+
+    const activeKind = e.active.data.current?.kind
+    if (activeKind !== 'tag')
+      return
+
+    const childId: number | undefined = e.active.data.current?.tagId
+    const fromParentId: number | undefined = e.active.data.current?.parentTagId
+
+    const overKind = e.over?.data.current?.kind
+
+    if (childId == null || !(overKind))
+      return
+
+    const child = findTag (tags, childId)
+
+    try
+    {
+      setSaving (true)
+
+      switch (overKind)
+      {
+      case 'tag':
+	{
+	  const parentId: number | undefined = e.over?.data.current?.tagId
+	  if (parentId == null || childId === parentId)
+	    return
+
+	  const parent = findTag (tags, parentId)
+
+	  if (!(child)
+	      || !(parent)
+	      || isDescendant (child, parentId))
+	    return
+
+	  if (fromParentId != null)
+	    {
+	      await axios.delete (
+		  `${ API_BASE_URL }/tags/${ fromParentId }/children/${ childId }`,
+		  { headers: { 'X-Transfer-Code': localStorage.getItem ('user_code') ?? '' } })
+	    }
+
+	  await axios.post (
+	      `${ API_BASE_URL }/tags/${ parentId }/children/${ childId }`,
+	      { },
+	      { headers: { 'X-Transfer-Code': localStorage.getItem ('user_code') ?? '' } })
+
+	  await reloadTags ()
+	  toast ({
+	      title: '上位タグ対応追加',
+	      description: `《${ child?.name }》を《${ parent?.name }》の子タグに設定しました．` })
+
+	  break
+	}
+
+      case 'slot':
+	{
+	  const cat: Category | undefined = e.over?.data.current?.cat
+	  if (!(cat) || !(child))
+	    return
+
+	  if (child.category !== cat)
+	    await changeCategory (childId, cat)
+
+	  if (fromParentId != null)
+	    {
+	      await axios.delete (
+		  `${ API_BASE_URL }/tags/${ fromParentId }/children/${ childId }`,
+		  { headers: { 'X-Transfer-Code': localStorage.getItem ('user_code') ?? '' } })
+	    }
+
+	  const fromParent = fromParentId == null ? null : findTag (tags, fromParentId)
+
+	  await reloadTags ()
+	  toast ({
+	      title: '上位タグ対応解除',
+	      description: (
+		  fromParent
+		  ? `《${ child.name }》を《${ fromParent.name }》の子タグから外しました．`
+		  : `《${ child.name }》のカテゴリを変更しました．`) })
+
+	  break
+	}
+      }
+    }
+    catch
+    {
+      toast ({ title: '上位タグ対応失敗', description: '独裁者である必要があります．' })
+    }
+    finally
+    {
+      setSaving (false)
+    }
+  }
+
   const categoryNames: Record<Category, string> = {
       deerjikist: 'ニジラー',
       meme:       '原作・ネタ元・ミーム等',
@@ -50,58 +306,103 @@ export default (({ post }: Props) => {
   return (
       <SidebarComponent>
 	<TagSearch/>
-	{CATEGORIES.map ((cat: Category) => cat in tags && (
-	    <div className="my-3" key={cat}>
-	      <SubsectionTitle>{categoryNames[cat]}</SubsectionTitle>
-	      <ul>
-		{tags[cat].map (tag => (
-		    <li key={tag.id} className="mb-1">
-		      <TagLink tag={tag}/>
-		    </li>))}
-	      </ul>
-	    </div>))}
-	{post && (
-	    <div>
-	      <SectionTitle>情報</SectionTitle>
-	      <ul>
-		<li>Id.: {post.id}</li>
-		{/* TODO: uploadedUser の取得を対応したらコメント外す */}
-		{/*
-		<li>
-		  <>耕作者: </>
-		  {post.uploadedUser
-		   ? (
-		      <Link to={`/users/${ post.uploadedUser.id }`}>
-			{post.uploadedUser.name || '名もなきニジラー'}
-		      </Link>)
-		   : 'bot操作'}
-		</li>
-		*/}
-		<li>耕作日時: {(new Date (post.createdAt)).toLocaleString ()}</li>
-		<li>
-		  <>リンク: </>
-		  <a
-		      className="break-all"
-		      href={post.url}
-		      target="_blank"
-		      rel="noopener noreferrer nofollow">
-		    {post.url}
-		  </a>
-		</li>
-		<li>
-		  {/* TODO: 表示形式きしょすぎるので何とかする */}
-		  <>オリジナルの投稿日時: </>
-		  {!(post.originalCreatedFrom) && !(post.originalCreatedBefore)
-		   ? '不明'
-		   : (
-		      <>
-			{post.originalCreatedFrom
-			 && `${ (new Date (post.originalCreatedFrom)).toLocaleString () } 以降 `}
-			{post.originalCreatedBefore
-			 && `${ (new Date (post.originalCreatedBefore)).toLocaleString () } より前`}
-		      </>)}
-		</li>
-	      </ul>
-	    </div>)}
+	<DndContext
+	    sensors={sensors}
+	    onDragStart={e => {
+	      if (e.active.data.current?.kind === 'tag')
+		setActiveTagId (e.active.data.current?.tagId ?? null)
+	      setDragging (true)
+	      suppressClickRef.current = true
+	      document.body.style.userSelect = 'none'
+	      getSelection?.()?.removeAllRanges?.()
+	      addEventListener ('click', e => {
+		e.preventDefault ()
+		e.stopPropagation ()
+		suppressClickRef.current = false
+	      }, { capture: true, once: true })
+	    }}
+	    onDragCancel={() => {
+	      setActiveTagId (null)
+	      setDragging (false)
+	      document.body.style.userSelect = ''
+	      suppressClickRef.current = false
+	    }}
+	    onDragEnd={async e => {
+	      setActiveTagId (null)
+	      setDragging (false)
+	      await onDragEnd (e)
+	      document.body.style.userSelect = ''
+	    }}
+	    modifiers={[restrictToWindowEdges]}>
+	  <motion.div key={post?.id ?? 0} layout>
+	    {CATEGORIES.map ((cat: Category) => ((tags[cat] ?? []).length > 0 || dragging) && (
+		<motion.div layout className="my-3" key={cat}>
+		  <SubsectionTitle>{categoryNames[cat]}</SubsectionTitle>
+
+		  <motion.ul layout>
+		    <AnimatePresence initial={false}>
+		      {(tags[cat] ?? []).flatMap (tag => (
+			  renderTagTree (tag, 0, `cat-${ cat }`, suppressClickRef, undefined)))}
+		      <DropSlot cat={cat}/>
+		    </AnimatePresence>
+		  </motion.ul>
+		</motion.div>))}
+	    {post && (
+		<div>
+		  <SectionTitle>情報</SectionTitle>
+		  <ul>
+		    <li>Id.: {post.id}</li>
+		    {/* TODO: uploadedUser の取得を対応したらコメント外す */}
+		    {/*
+		    <li>
+		      <>耕作者: </>
+		      {post.uploadedUser
+		       ? (
+			  <Link to={`/users/${ post.uploadedUser.id }`}>
+			    {post.uploadedUser.name || '名もなきニジラー'}
+			  </Link>)
+		       : 'bot操作'}
+		    </li>
+		    */}
+		    <li>耕作日時: {(new Date (post.createdAt)).toLocaleString ()}</li>
+		    <li>
+		      <>リンク: </>
+		      <a
+			  className="break-all"
+			  href={post.url}
+			  target="_blank"
+			  rel="noopener noreferrer nofollow">
+			{post.url}
+		      </a>
+		    </li>
+		    <li>
+		      {/* TODO: 表示形式きしょすぎるので何とかする */}
+		      <>オリジナルの投稿日時: </>
+		      {!(post.originalCreatedFrom) && !(post.originalCreatedBefore)
+		       ? '不明'
+		       : (
+			  <>
+			    {post.originalCreatedFrom
+			     && `${ (new Date (post.originalCreatedFrom)).toLocaleString () } 以降 `}
+			    {post.originalCreatedBefore
+			     && `${ (new Date (post.originalCreatedBefore)).toLocaleString () } より前`}
+			  </>)}
+		    </li>
+		    <li>
+		      <Link to={`/posts/changes?id=${ post.id }`}>履歴</Link>
+		    </li>
+		  </ul>
+		</div>)}
+	  </motion.div>
+
+	  <DragOverlay adjustScale={false}>
+	    <div className="pointer-events-none">
+	      {activeTagId != null && (() => {
+		const tag = findTag (tags, activeTagId)
+		return tag && <TagLink tag={tag}/>
+	      }) ()}
+	    </div>
+	  </DragOverlay>
+	</DndContext>
       </SidebarComponent>)
 }) satisfies FC<Props>

frontend/src/components/TagLink.tsx

@@ -1,6 +1,9 @@
+import axios from 'axios'
+import { useEffect, useState } from 'react'
 import { Link } from 'react-router-dom'
 
 import PrefetchLink from '@/components/PrefetchLink'
+import { API_BASE_URL } from '@/config'
 import { LIGHT_COLOUR_SHADE, DARK_COLOUR_SHADE, TAG_COLOUR } from '@/consts'
 import { cn } from '@/lib/utils'
 
@@ -9,6 +12,7 @@ import type { ComponentProps, FC, HTMLAttributes } from 'react'
 import type { Tag } from '@/types'
 
 type CommonProps = { tag:         Tag
+		     nestLevel?:  number
 		     withWiki?:   boolean
 		     withCount?:  boolean
 		     prefetch?:   boolean }
@@ -23,11 +27,41 @@ type Props = PropsWithLink | PropsWithoutLink
 
 
 export default (({ tag,
+		   nestLevel = 0,
 		   linkFlg   = true,
 		   withWiki  = true,
 		   withCount = true,
 		   prefetch  = false,
 		   ...props }: Props) => {
+  const [havingWiki, setHavingWiki] = useState (true)
+
+  const wikiExists = async (tag: Tag) => {
+    if ('hasWiki' in tag)
+      {
+	setHavingWiki (tag.hasWiki)
+	return
+      }
+
+    const tagName = (tag as Tag).name
+
+    try
+    {
+      await axios.get (`${ API_BASE_URL }/wiki/title/${ encodeURIComponent (tagName) }/exists`)
+      setHavingWiki (true)
+    }
+    catch
+    {
+      setHavingWiki (false)
+    }
+  }
+
+  useEffect (() => {
+    if (!(linkFlg) || !(withWiki))
+      return
+
+    wikiExists (tag)
+  }, [tag.name, linkFlg, withWiki])
+
   const spanClass = cn (
       `text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE }`,
       `dark:text-${ TAG_COLOUR[tag.category] }-${ DARK_COLOUR_SHADE }`)
@@ -40,11 +74,33 @@ export default (({ tag,
       <>
 	{(linkFlg && withWiki) && (
 	    <span className="mr-1">
-	      <Link to={`/wiki/${ encodeURIComponent (tag.name) }`}
-		    className={linkClass}>
-		?
-	      </Link>
+	      {havingWiki
+	       ? (
+		  <Link to={`/wiki/${ encodeURIComponent (tag.name) }`}
+			className={linkClass}>
+		    ?
+		  </Link>)
+	       : (
+		  <Link to={`/wiki/${ encodeURIComponent (tag.name) }`}
+			className="animate-[wiki-blink_.25s_steps(2,end)_infinite]
+				   dark:animate-[wiki-blink-dark_.25s_steps(2,end)_infinite]"
+			title={`${ tag.name } Wiki が存在しません．`}>
+		    !
+		  </Link>)}
+	    </span>)}
+	{nestLevel > 0 && (
+	    <span
+		className="ml-1 mr-1"
+		style={{ paddingLeft: `${ (nestLevel - 1) }rem` }}>
+	      ↳
 	    </span>)}
+	{tag.matchedAlias != null && (
+	    <>
+	      <span className={spanClass} {...props}>
+		{tag.matchedAlias}
+	      </span>
+	      <> → </>
+	    </>)}
 	{linkFlg
 	 ? (
 	    prefetch

frontend/src/components/TagSearch.tsx

@@ -1,4 +1,5 @@
 import axios from 'axios'
+import toCamel from 'camelcase-keys'
 import React, { useEffect, useState } from 'react'
 import { useNavigate, useLocation } from 'react-router-dom'
 
@@ -31,8 +32,8 @@ export default (() => {
       }
 
     const res = await axios.get (`${ API_BASE_URL }/tags/autocomplete`, { params: { q } })
-    const data = res.data as Tag[]
-    setSuggestions (data)
+    const data = toCamel (res.data, { deep: true }) as Tag[]
+    setSuggestions (data.filter (t => t.postCount > 0))
     if (suggestions.length > 0)
       setSuggestionsVsbl (true)
   }

frontend/src/components/TagSearchBox.tsx

@@ -1,3 +1,4 @@
+import TagLink from '@/components/TagLink'
 import { cn } from '@/lib/utils'
 
 import type { FC } from 'react'
@@ -22,8 +23,7 @@ export default (({ suggestions, activeIndex, onSelect }: Props) => {
 		className={cn ('px-3 py-2 cursor-pointer hover:bg-gray-300 dark:hover:bg-gray-700', 
 			       i === activeIndex && 'bg-gray-300 dark:bg-gray-700')}
 		onMouseDown={() => onSelect (tag)}>
-	      {tag.name}
-	      {<span className="ml-2 text-sm text-gray-400">{tag.postCount}</span>}
+	      <TagLink tag={tag} linkFlg={false} withWiki={false}/>
 	    </li>))}
       </ul>)
 }) satisfies FC<Props>

frontend/src/components/TagSidebar.tsx

@@ -1,4 +1,5 @@
 import axios from 'axios'
+import { AnimatePresence, motion } from 'framer-motion'
 import { useEffect, useState } from 'react'
 import { useLocation, useNavigate } from 'react-router-dom'
 
@@ -8,7 +9,6 @@ import SectionTitle from '@/components/common/SectionTitle'
 import SidebarComponent from '@/components/layout/SidebarComponent'
 import { API_BASE_URL } from '@/config'
 import { CATEGORIES } from '@/consts'
-import { cn } from '@/lib/utils'
 
 import type { FC, MouseEvent } from 'react'
 
@@ -59,47 +59,71 @@ export default (({ posts, onClick }: Props) => {
     setTags (tagsTmp)
   }, [posts])
 
+  const TagBlock = (
+      <>
+	<SectionTitle>タグ</SectionTitle>
+	<ul>
+	  {CATEGORIES.flatMap (cat => cat in tags ? (
+	      tags[cat].map (tag => (
+		  <li key={tag.id} className="mb-1">
+		    <TagLink tag={tag} prefetch onClick={onClick}/>
+		  </li>))) : [])}
+	</ul>
+	<SectionTitle>関聯</SectionTitle>
+	{posts.length > 0 && (
+	    <a href="#"
+	       onClick={ev => {
+		 ev.preventDefault ()
+		 void ((async () => {
+		   try
+		   {
+		     const { data } = await axios.get (`${ API_BASE_URL }/posts/random`,
+			 { params: { tags:  tagsQuery.split (' ').filter (e => e !== '').join (' '),
+				     match: (anyFlg ? 'any' : 'all') } })
+		     navigate (`/posts/${ (data as Post).id }`)
+		   }
+		   catch
+		   {
+		     ;
+		   }
+		 }) ())
+	       }}>
+	      ランダム
+	    </a>)}
+      </>)
+
   return (
       <SidebarComponent>
 	<TagSearch/>
-	<div className={cn (!(tagsVsbl) && 'hidden', 'md:block mt-4')}>
-	  <SectionTitle>タグ</SectionTitle>
-	  <ul>
-	    {CATEGORIES.flatMap (cat => cat in tags ?
-		tags[cat].map (tag => (
-		    <li key={tag.id} className="mb-1">
-		      <TagLink tag={tag} prefetch onClick={onClick}/>
-		    </li>)) : [])}
-	  </ul>
-	  <SectionTitle>関聯</SectionTitle>
-	  {posts.length > 0 && (
-	      <a href="#"
-		 onClick={ev => {
-		   ev.preventDefault ()
-		   void ((async () => {
-		     try
-		     {
-		       const { data } = await axios.get (`${ API_BASE_URL }/posts/random`,
-			   { params: { tags:  tagsQuery.split (' ').filter (e => e !== '').join (' '),
-				       match: (anyFlg ? 'any' : 'all') } })
-		       navigate (`/posts/${ (data as Post).id }`)
-		     }
-		     catch
-		     {
-		       ;
-		     }
-		   }) ())
-		 }}>
-		ランダム
-	      </a>)}
+
+	<div className="hidden md:block mt-4">
+	  {TagBlock}
 	</div>
+
+	<AnimatePresence initial={false}>
+	  {tagsVsbl && (
+	      <motion.div
+		  key="sptags"
+		  className="md:hidden mt-4"
+		  variants={{ hidden:   { clipPath: 'inset(0 0 100% 0)',
+					  height:   0 },
+			      visible:  { clipPath: 'inset(0 0 0% 0)',
+					  height:   'auto'} }}
+		  initial="hidden"
+		  animate="visible"
+		  exit="hidden"
+		  transition={{ duration: .2, ease: 'easeOut' }}>
+		{TagBlock}
+	      </motion.div>)}
+	</AnimatePresence>
+
 	<a href="#"
 	   className="md:hidden block my-2 text-center text-sm
 		      text-gray-500 hover:text-gray-400
 		      dark:text-gray-300 dark:hover:text-gray-100"
 	   onClick={ev => {
 	     ev.preventDefault ()
-	     setTagsVsbl (!(tagsVsbl))
+	     setTagsVsbl (v => !(v))
 	   }}>
 	  {tagsVsbl ? '▲▲▲ タグ一覧を閉じる ▲▲▲' : '▼▼▼ タグ一覧を表示 ▼▼▼'}
 	</a>

frontend/src/components/TopNav.tsx

@@ -1,6 +1,7 @@
 import axios from 'axios'
 import toCamel from 'camelcase-keys'
-import { Fragment, useState, useEffect } from 'react'
+import { AnimatePresence, motion } from 'framer-motion'
+import { Fragment, useEffect, useLayoutEffect, useRef, useState } from 'react'
 import { Link, useLocation } from 'react-router-dom'
 
 import Separator from '@/components/MenuSeparator'
@@ -19,6 +20,28 @@ type Props = { user: User | null }
 export default (({ user }: Props) => {
   const location = useLocation ()
 
+  const dirRef = useRef<(-1) | 1> (1)
+  const itemsRef = useRef<(HTMLAnchorElement | null)[]> ([])
+  const navRef = useRef<HTMLDivElement | null> (null)
+
+  const measure = () => {
+    const nav = navRef.current
+    const el = itemsRef.current[activeIdx]
+    if (!(nav) || !(el) || activeIdx < 0)
+      return
+
+    const navRect = nav.getBoundingClientRect ()
+    const elRect = el.getBoundingClientRect ()
+
+    setHl ({ left:    elRect.left - navRect.left,
+	     width:   elRect.width,
+	     visible: true })
+  }
+
+  const [hl, setHl] = useState<{ left: number; width: number; visible: boolean }> ({
+      left:     0,
+      width:    0,
+      visible:  false })
   const [menuOpen, setMenuOpen] = useState (false)
   const [openItemIdx, setOpenItemIdx] = useState (-1)
   const [postCount, setPostCount] = useState<number | null> (null)
@@ -30,6 +53,7 @@ export default (({ user }: Props) => {
       { name: '広場', to: '/posts', subMenu: [
 	  { name: '一覧', to: '/posts' },
 	  { name: '投稿追加', to: '/posts/new' },
+	  { name: '耕作履歴', to: '/posts/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:広場' }] },
       { name: 'タグ', to: '/tags', subMenu: [
 	  { name: 'タグ一覧', to: '/tags', visible: false },
@@ -52,6 +76,32 @@ export default (({ user }: Props) => {
 	  { name: 'お前', to: `/users/${ user?.id }`, visible: false },
 	  { name: '設定', to: '/users/settings', visible: Boolean (user) }] }]
 
+  const activeIdx = menu.findIndex (item => location.pathname.startsWith (item.base || item.to))
+
+  const prevActiveIdxRef = useRef<number> (activeIdx)
+
+  if (activeIdx !== prevActiveIdxRef.current)
+    {
+      dirRef.current = activeIdx > prevActiveIdxRef.current ? 1 : -1
+      prevActiveIdxRef.current = activeIdx
+    }
+
+  const dir = dirRef.current
+
+  useLayoutEffect (() => {
+    if (activeIdx < 0)
+      return
+
+    const raf = requestAnimationFrame (measure)
+    const onResize = () => requestAnimationFrame (measure)
+
+    addEventListener ('resize', onResize)
+    return () => {
+      cancelAnimationFrame (raf)
+      removeEventListener ('resize', onResize)
+    }
+  }, [activeIdx])
+
   useEffect (() => {
     const unsubscribe = WikiIdBus.subscribe (setWikiId)
     return () => unsubscribe ()
@@ -97,16 +147,26 @@ export default (({ user }: Props) => {
 	      ぼざクリ タグ広場
 	    </Link>
 
-	    {menu.map ((item, i) => (
-		<Link key={i}
-		      to={item.to}
-		      className={cn ('hidden md:flex h-full items-center',
-				     (location.pathname.startsWith (item.base || item.to)
-				      ? 'bg-yellow-200 dark:bg-red-950 px-4 font-bold'
-				      : 'px-2'))}>
-		  {item.name}
-		</Link>
-	    ))}
+	    <div ref={navRef} className="relative hidden md:flex h-full items-center">
+	      <div aria-hidden
+		   className={cn ('absolute top-1/2 -translate-y-1/2 h-full',
+				  'bg-yellow-200 dark:bg-red-950',
+				  'transition-[transform,width] duration-200 ease-out')}
+		   style={{ width:      hl.width,
+			    transform:  `translate(${ hl.left }px, -50%)`,
+			    opacity:    hl.visible ? 1 : 0 }}/>
+
+	      {menu.map ((item, i) => (
+		  <Link key={i}
+			to={item.to}
+			ref={el => {
+			  itemsRef.current[i] = el
+			}}
+			className={cn ('relative z-10 flex h-full items-center px-5',
+				       (i === openItemIdx) && 'font-bold')}>
+		    {item.name}
+		  </Link>))}
+	    </div>
 	  </div>
 
 	  <TopNavUser user={user}/>
@@ -123,49 +183,101 @@ export default (({ user }: Props) => {
 	  </a>
 	</nav>
 
-	<div className="hidden md:flex bg-yellow-200 dark:bg-red-950
-			items-center w-full min-h-[40px] px-3">
-	  {menu.find (item => location.pathname.startsWith (item.base || item.to))?.subMenu
-	   .filter (item => item.visible ?? true)
-	   .map ((item, i) => 'component' in item ? item.component : (
-	      <Link key={i}
-		    to={item.to}
-		    className="h-full flex items-center px-3">
-		{item.name}
-	      </Link>))}
+	<div className="relative hidden md:flex bg-yellow-200 dark:bg-red-950
+			items-center w-full min-h-[40px] overflow-hidden">
+	  <AnimatePresence initial={false} custom={dir}>
+	    <motion.div
+		key={activeIdx}
+		custom={dir}
+		variants={{ enter: (d: -1 | 1) => ({ y: d * 24, opacity: 0 }),
+			    centre: { y: 0, opacity: 1 },
+			    exit: (d: -1 | 1) => ({ y: (-d) * 24, opacity: 0 }) }}
+		className="absolute inset-0 flex items-center px-3"
+		initial="enter"
+		animate="centre"
+		exit="exit"
+		transition={{ duration: .2, ease: 'easeOut' }}>
+	      {(menu[activeIdx]?.subMenu ?? [])
+	       .filter (item => item.visible ?? true)
+	       .map ((item, i) => (
+		  'component' in item
+		  ? <Fragment key={`c-${ i }`}>{item.component}</Fragment>
+		  : (
+		      <Link key={`l-${ i }`}
+			    to={item.to}
+			    className="h-full flex items-center px-3">
+			{item.name}
+		      </Link>)))}
+	    </motion.div>
+	  </AnimatePresence>
 	</div>
 
-	<div className={cn (menuOpen ? 'flex flex-col md:hidden' : 'hidden',
-			    'bg-yellow-200 dark:bg-red-975 items-start')}>
-	  <Separator/>
-	  {menu.map ((item, i) => (
-	      <Fragment key={i}>
-		<Link to={i === openItemIdx ? item.to : '#'}
-		      className={cn ('w-full min-h-[40px] flex items-center pl-8',
-				     ((i === openItemIdx)
-				      && 'font-bold bg-yellow-50 dark:bg-red-950'))}
-		      onClick={ev => {
-			if (i !== openItemIdx)
-			  {
-			    ev.preventDefault ()
-			    setOpenItemIdx (i)
-			  }
-		      }}>
-		  {item.name}
-		</Link>
-		{i === openItemIdx && (
-		    item.subMenu
-		    .filter (subItem => subItem.visible ?? true)
-		    .map ((subItem, j) => 'component' in subItem ? subItem.component : (
-			<Link key={j}
-			      to={subItem.to}
-			      className="w-full min-h-[36px] flex items-center pl-12
-					 bg-yellow-50 dark:bg-red-950">
-			  {subItem.name}
-			</Link>)))}
-	      </Fragment>))}
-	  <TopNavUser user={user} sp/>
-	  <Separator/>
-	</div>
+	<AnimatePresence initial={false}>
+	  {menuOpen && (
+	      <motion.div
+		  key="spmenu"
+		  className={cn ('flex flex-col md:hidden',
+				 'bg-yellow-200 dark:bg-red-975 items-start')}
+		  variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
+					height:   0 },
+			      open:   { clipPath: 'inset(0 0 0% 0)',
+					height:   'auto' } }}
+		  initial="closed"
+		  animate="open"
+		  exit="closed"
+		  transition={{ duration: .2, ease: 'easeOut' }}>
+		<Separator/>
+		{menu.map ((item, i) => (
+		    <Fragment key={i}>
+		      <Link to={i === openItemIdx ? item.to : '#'}
+			    className={cn ('w-full min-h-[40px] flex items-center pl-8',
+					   ((i === openItemIdx)
+					    && 'font-bold bg-yellow-50 dark:bg-red-950'))}
+			    onClick={ev => {
+			      if (i !== openItemIdx)
+				{
+				  ev.preventDefault ()
+				  setOpenItemIdx (i)
+				}
+			    }}>
+			{item.name}
+		      </Link>
+
+		      <AnimatePresence initial={false}>
+			{i === openItemIdx && (
+			    <motion.div
+				key={`sp-sub-${ i }`}
+				className="w-full bg-yellow-50 dark:bg-red-950"
+				variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
+						      height:   0,
+						      opacity:  0 },
+					    open:   { clipPath: 'inset(0 0 0% 0)',
+						      height:   'auto',
+						      opacity:  1 } }}
+				initial="closed"
+				animate="open"
+				exit="closed"
+				transition={{ duration: .2, ease: 'easeOut' }}>
+			      {item.subMenu
+			       .filter (subItem => subItem.visible ?? true)
+			       .map ((subItem, j) => (
+				  'component' in subItem
+				  ? (
+				      <Fragment key={`sp-c-${ i }-${ j }`}>
+					{subItem.component}
+				      </Fragment>)
+				  : (
+				      <Link key={`sp-l-${ i }-${ j }`}
+					    to={subItem.to}
+					    className="w-full min-h-[36px] flex items-center pl-12">
+					{subItem.name}
+				      </Link>)))}
+			    </motion.div>)}
+		      </AnimatePresence>
+		    </Fragment>))}
+		<TopNavUser user={user} sp/>
+		<Separator/>
+	      </motion.div>)}
+	</AnimatePresence>
       </>)
 }) satisfies FC<Props>

frontend/src/components/WikiBody.tsx

@@ -1,6 +1,6 @@
 import axios from 'axios'
 import toCamel from 'camelcase-keys'
-import { useEffect, useState } from 'react'
+import { useEffect, useMemo, useState } from 'react'
 import ReactMarkdown from 'react-markdown'
 import { Link } from 'react-router-dom'
 import remarkGFM from 'remark-gfm'
@@ -8,6 +8,7 @@ import remarkGFM from 'remark-gfm'
 import SectionTitle from '@/components/common/SectionTitle'
 import SubsectionTitle from '@/components/common/SubsectionTitle'
 import { API_BASE_URL } from '@/config'
+import remarkWikiAutoLink from '@/lib/remark-wiki-autolink'
 
 import type { FC } from 'react'
 import type { Components } from 'react-markdown'
@@ -34,17 +35,16 @@ const mdComponents = { h1:  ({ children }) => <SectionTitle>{children}</SectionT
 
 export default (({ title, body }: Props) => {
   const [pageNames, setPageNames] = useState<string[]> ([])
-  const [realBody, setRealBody] = useState<string> ('')
 
-  useEffect (() => {
-    if (!(body))
-      return
+  const remarkPlugins = useMemo (
+      () => [() => remarkWikiAutoLink (pageNames), remarkGFM], [pageNames])
 
+  useEffect (() => {
     void (async () => {
       try
       {
 	const res = await axios.get (`${ API_BASE_URL }/wiki`)
-	const data = toCamel (res.data as any, { deep: true }) as WikiPage[]
+	const data: WikiPage[] = toCamel (res.data as any, { deep: true })
 	setPageNames (data.map (page => page.title).sort ((a, b) => b.length - a.length))
       }
       catch
@@ -54,52 +54,8 @@ export default (({ title, body }: Props) => {
     }) ()
   }, [])
 
-  useEffect (() => {
-    setRealBody ('')
-  }, [body])
-
-  useEffect (() => {
-    if (!(body))
-      return
-
-    const matchIndices = (target: string, keyword: string) => {
-      const indices: number[] = []
-      let pos = 0
-      let idx
-      while ((idx = target.indexOf (keyword, pos)) >= 0)
-	{
-	  indices.push (idx)
-	  pos = idx + keyword.length
-	}
-
-      return indices
-    }
-
-    const linkIndices = (text: string, names: string[]): [string, [number, number]][] => {
-      const result: [string, [number, number]][] = []
-
-      names.forEach (name => {
-	matchIndices (text, name).forEach (idx => {
-	  const start = idx
-	  const end = idx + name.length
-	  const overlaps = result.some (([, [st, ed]]) => start < ed && end > st)
-	  if (!(overlaps))
-	    result.push ([name, [start, end]])
-	})
-      })
-
-      return result.sort (([, [a]], [, [b]]) => b - a)
-    }
-
-    setRealBody (
-	linkIndices (body, pageNames).reduce ((acc, [name, [start, end]]) => (
-	    acc.slice (0, start)
-	    + `[${ name }](/wiki/${ encodeURIComponent (name) })`
-	    + acc.slice (end)), body))
-  }, [body, pageNames])
-
   return (
-      <ReactMarkdown components={mdComponents} remarkPlugins={[remarkGFM]}>
-	{realBody || `このページは存在しません。[新規作成してください](/wiki/new?title=${ encodeURIComponent (title) })。`}
+      <ReactMarkdown components={mdComponents} remarkPlugins={remarkPlugins}>
+	{body || `このページは存在しません。[新規作成してください](/wiki/new?title=${ encodeURIComponent (title) })。`}
       </ReactMarkdown>)
 }) satisfies FC<Props>

frontend/src/components/common/Pagination.tsx

@@ -0,0 +1,79 @@
+import { Link, useLocation } from 'react-router-dom'
+
+import type { FC } from 'react'
+
+type Props = { page:          number
+	       totalPages:    number
+	       siblingCount?: number }
+
+
+const range = (start: number, end: number): number[] =>
+    [...Array (end - start + 1).keys ()].map (i => start + i)
+
+
+const getPages = (
+    page:         number,
+    total:        number,
+    siblingCount: number,
+): (number | '…')[] => {
+  if (total <= 1)
+    return [1]
+
+  const first = 1
+  const last = total
+
+  const left = Math.max (page - siblingCount, first)
+  const right = Math.min (page + siblingCount, last)
+
+  const pages: (number | '…')[] = []
+
+  pages.push (first)
+
+  if (left > first + 1)
+    pages.push ('…')
+
+  const midStart = Math.max (left, first + 1)
+  const midEnd = Math.min (right, last - 1)
+  pages.push (...range (midStart, midEnd))
+
+  if (right < last - 1)
+    pages.push ('…')
+
+  if (last !== first)
+    pages.push (last)
+
+  return pages.filter ((v, i, arr) => i === 0 || v !== arr[i - 1])
+}
+
+
+export default (({ page, totalPages, siblingCount = 4 }) => {
+  const location = useLocation ()
+
+  const buildTo = (p: number) => {
+    const qs = new URLSearchParams (location.search)
+    qs.set ('page', String (p))
+    return `${ location.pathname }?${ qs.toString () }`
+  }
+
+  const pages = getPages (page, totalPages, siblingCount)
+
+  return (
+      <nav className="mt-4 flex justify-center" aria-label="Pagination">
+	<div className="flex items-center gap-2">
+	  {(page > 1)
+	   ? <Link to={buildTo (page - 1)} aria-label="前のページ">&lt;</Link>
+	   : <span aria-hidden>&lt;</span>}
+
+	  {pages.map ((p, idx) => (
+	      (p === '…')
+	      ? <span key={`dots-${ idx }`}>…</span>
+	      : ((p === page)
+		 ? <span key={p} className="font-bold" aria-current="page">{p}</span>
+		 : <Link key={p} to={buildTo (p)}>{p}</Link>)))}
+
+	  {(page < totalPages)
+	   ? <Link to={buildTo (page + 1)} aria-label="次のページ">&gt;</Link>
+	   : <span aria-hidden>&gt;</span>}
+	</div>
+      </nav>)
+}) satisfies FC<Props>