Merge branch 'main' into feature/100

backend/Gemfile

@@ -63,3 +63,5 @@ gem 'diff-lcs'
 gem 'dotenv-rails'
 
 gem 'whenever', require: false
+
+gem 'discard'

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)
@@ -420,6 +422,7 @@ DEPENDENCIES
   bootsnap
   brakeman
   diff-lcs
+  discard
   dotenv-rails
   gollum
   image_processing (~> 1.14)

backend/app/controllers/posts_controller.rb

@@ -1,8 +1,6 @@
-require 'open-uri'
-require 'nokogiri'
-
-
 class PostsController < ApplicationController
+  Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
+
   # GET /posts
   def index
     limit = params[:limit].presence&.to_i
@@ -52,9 +50,12 @@ class PostsController < ApplicationController
 
     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
@@ -77,7 +78,9 @@ class PostsController < ApplicationController
     post.thumbnail.attach(thumbnail)
     if post.save
       post.resized_thumbnail!
-      post.tags = Tag.normalise_tags(tag_names)
+      tags = Tag.normalise_tags(tag_names)
+      tags = Tag.expand_parent_tags(tags)
+      sync_post_tags!(post, tags)
       render json: post.as_json(include: { tags: { only: [:id, :name, :category, :post_count] } }),
              status: :created
     else
@@ -110,10 +113,14 @@ class PostsController < ApplicationController
     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)
-    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)
+      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
@@ -123,12 +130,54 @@ class PostsController < ApplicationController
   def destroy
   end
 
+  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, :created_user, :deleted_user)
+
+    events = []
+    pts.each do |pt|
+      events << Event.new(
+          post:         pt.post,
+          tag:          pt.tag,
+          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,
+            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(' ')
     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
@@ -142,4 +191,70 @@ class PostsController < ApplicationController
     end
     posts.distinct
   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
+
+    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, :name, :category, :post_count]).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, :name, :category, :post_count]).merge(children:)
+    end
+
+    root_ids.filter_map { |id| build_node.call(id, []) }
+  end
 end

backend/app/controllers/users_controller.rb

@@ -6,12 +6,15 @@ class UsersController < ApplicationController
   end
 
   def verify
+    ip_bin = IPAddr.new(request.remote_ip).hton
+    ip_address = IpAddress.find_or_create_by!(ip_address: ip_bin)
+
     user = User.find_by(inheritance_code: params[:code])
-    render json: if user
-                   { valid: true, user: user.slice(:id, :name, :inheritance_code, :role) }
-                 else
-                   { valid: false }
-                 end
+    return render json: { valid: false } unless user
+
+    UserIp.find_or_create_by!(user:, ip_address:)
+
+    render json: { valid: true, user: user.slice(:id, :name, :inheritance_code, :role) }
   end
 
   def renew

backend/app/models/post.rb

@@ -1,11 +1,13 @@
-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 :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: :destroy
   has_many :post_similarities_as_post,
            class_name: 'PostSimilarity',

backend/app/models/post_tag.rb

@@ -1,7 +1,25 @@
 class PostTag < ApplicationRecord
+  include Discard::Model
+
   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

@@ -1,6 +1,8 @@
 class Tag < ApplicationRecord
-  has_many :post_tags, dependent: :destroy
-  has_many :posts, through: :post_tags
+  has_many :post_tags, dependent: :delete_all, 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 :tag_aliases, dependent: :destroy
 
   has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
@@ -11,6 +13,14 @@ class Tag < ApplicationRecord
                                          dependent: :destroy
   has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
+  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
+
   enum :category, { deerjikist:  'deerjikist',
                     meme:        'meme',
                     character:   'character',
@@ -35,13 +45,13 @@ class Tag < ApplicationRecord
       'meta:' => 'meta' }.freeze
 
   def self.tagme
-    @tagme ||= Tag.find_or_initialize_by(name: 'タグ希望') do |tag|
+    @tagme ||= Tag.find_or_create_by!(name: 'タグ希望') do |tag|
       tag.category = 'meta'
     end
   end
 
   def self.bot
-    @bot ||= Tag.find_or_initialize_by(name: 'bot操作') do |tag|
+    @bot ||= Tag.find_or_create_by!(name: 'bot操作') do |tag|
       tag.category = 'meta'
     end
   end
@@ -57,10 +67,33 @@ class Tag < ApplicationRecord
         end
       end
     end
-    tags << Tag.tagme if with_tagme && tags.size < 20 && tags.none?(Tag.tagme)
+    tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
     tags.uniq
   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
+
   private
 
   def nico_tag_name_must_start_with_nico

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/user.rb

@@ -8,7 +8,6 @@ class User < ApplicationRecord
 
   has_many :posts
   has_many :settings
-  has_many :ip_addresses
   has_many :user_ips, dependent: :destroy
   has_many :ip_addresses, through: :user_ips
   has_many :user_post_views, dependent: :destroy

backend/config/routes.rb

@@ -4,6 +4,7 @@ Rails.application.routes.draw do
   get 'tags/autocomplete', to: 'tags#autocomplete'
   get 'tags/name/:name', to: 'tags#show_by_name'
   get 'posts/random', to: 'posts#random'
+  get 'posts/changes', to: 'posts#changes'
   post 'posts/:id/viewed', to: 'posts#viewed'
   delete 'posts/:id/viewed', to: 'posts#unviewed'
   get 'preview/title', to: 'preview#title'

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/20251126231500_rename_ip_adress_column_to_ip_addresses.rb

@@ -0,0 +1,5 @@
+class RenameIpAdressColumnToIpAddresses < ActiveRecord::Migration[8.0]
+  def change
+    rename_column :ip_addresses, :ip_adress, :ip_address
+  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/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_09_09_075500) do
+ActiveRecord::Schema[8.0].define(version: 2025_12_10_123200) 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
@@ -40,7 +40,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_09_075500) do
   end
 
   create_table "ip_addresses", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.binary "ip_adress", limit: 16, null: false
+    t.binary "ip_address", limit: 16, null: false
     t.boolean "banned", default: false, null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
@@ -70,9 +70,16 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_09_075500) do
     t.bigint "deleted_user_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.datetime "discarded_at"
+    t.virtual "is_active", type: :boolean, as: "(`discarded_at` is null)", stored: true
+    t.virtual "active_unique_key", type: :string, as: "(case when (`discarded_at` is null) then concat(`post_id`,_utf8mb4':',`tag_id`) else NULL end)", stored: true
+    t.index ["active_unique_key"], name: "idx_post_tags_active_unique", unique: true
     t.index ["created_user_id"], name: "index_post_tags_on_created_user_id"
     t.index ["deleted_user_id"], name: "index_post_tags_on_deleted_user_id"
+    t.index ["discarded_at"], name: "index_post_tags_on_discarded_at"
+    t.index ["post_id", "discarded_at"], name: "index_post_tags_on_post_id_and_discarded_at"
     t.index ["post_id"], name: "index_post_tags_on_post_id"
+    t.index ["tag_id", "discarded_at"], name: "index_post_tags_on_tag_id_and_discarded_at"
     t.index ["tag_id"], name: "index_post_tags_on_tag_id"
   end
 
@@ -107,6 +114,16 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_09_075500) do
     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|
     t.bigint "tag_id", null: false
     t.bigint "target_tag_id", null: false
@@ -176,6 +193,8 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_09_075500) do
   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_similarities", "tags"
   add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
   add_foreign_key "user_ips", "ip_addresses"

backend/lib/tasks/link_nico.rake

@@ -1,12 +0,0 @@
-namespace :nico do
-  desc 'ニコタグ連携'
-  task link: :environment do
-    Post.find_each do |post|
-      tags = post.tags.where(category: 'nico')
-      tags.each do |tag|
-        post.tags.concat(tag.linked_tags) if tag.linked_tags.present?
-      end
-      post.tags = post.tags.to_a.uniq
-    end
-  end
-end

backend/lib/tasks/sync_nico.rake

@@ -5,12 +5,32 @@ namespace :nico do
     require 'open-uri'
     require 'nokogiri'
 
-    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
+      desired_ids = desired_tag_ids.compact.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.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 +39,57 @@ 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|
+      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!
+        sync_post_tags!(post, [Tag.tagme.id])
+      end
+
+      kept_tags = post.tags.reload
+      kept_non_nico_ids = kept_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 < 20
-          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_initialize_by(name:) do |t|
+          t.category = 'nico'
         end
+        tag.save! if tag.new_record?
+        desired_nico_ids << tag.id
+        unless tag.in?(kept_tags)
+          desired_non_nico_ids.concat(tag.linked_tags.pluck(:id))
+          desired_nico_ids.concat(tag.linked_tags.pluck(:id))
+        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)
     end
   end
 end

frontend/package-lock.json

@@ -17,6 +17,7 @@
         "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",
@@ -3573,6 +3574,33 @@
         "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",
@@ -5216,6 +5244,21 @@
         "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

@@ -19,6 +19,7 @@
     "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",

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

@@ -9,6 +9,7 @@ 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'
@@ -79,6 +80,7 @@ export default (() => {
 	    <Route path="/posts" element={<PostListPage/>}/>
 	    <Route path="/posts/new" element={<PostNewPage user={user}/>}/>
 	    <Route path="/posts/:id" element={<PostDetailPage 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/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/TagDetailSidebar.tsx

@@ -1,3 +1,4 @@
+import { AnimatePresence, motion } from 'framer-motion'
 import { useEffect, useState } from 'react'
 
 import TagLink from '@/components/TagLink'
@@ -7,12 +8,37 @@ import SubsectionTitle from '@/components/common/SubsectionTitle'
 import SidebarComponent from '@/components/layout/SidebarComponent'
 import { CATEGORIES } from '@/consts'
 
-import type { FC } from 'react'
+import type { FC, ReactNode } from 'react'
 
 import type { Category, Post, Tag } from '@/types'
 
 type TagByCategory = { [key in Category]: Tag[] }
 
+
+const renderTagTree = (
+    tag:        Tag,
+    nestLevel:  number,
+    path:       string,
+): ReactNode[] => {
+  const key = `${ path }-${ tag.id }`
+
+  const self = (
+      <motion.li
+	  key={key}
+	  layout
+	  transition={{ duration: .2, ease: 'easeOut' }}
+	  className="mb-1">
+	<TagLink tag={tag} nestLevel={nestLevel}/>
+      </motion.li>)
+
+  return [self,
+	  ...((tag.children
+	       ?.sort ((a, b) => a.name < b.name ? -1 : 1)
+	       .flatMap (child => renderTagTree (child, nestLevel + 1, key)))
+	      ?? [])]
+}
+
+
 type Props = { post: Post | null }
 
 
@@ -50,58 +76,60 @@ 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
-			 && `${ (new Date (post.originalCreatedBefore)).toLocaleString () } より前`}
-		      </>)}
-		</li>
-	      </ul>
-	    </div>)}
+	<motion.div key={post?.id ?? 0} layout>
+	  {CATEGORIES.map ((cat: Category) => cat in tags && (
+	      <motion.div layout className="my-3" key={cat}>
+		<SubsectionTitle>{categoryNames[cat]}</SubsectionTitle>
+
+		<motion.ul layout>
+		  <AnimatePresence initial={false}>
+		    {tags[cat].map (tag => renderTagTree (tag, 0, `cat-${ 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>
+		</ul>
+	      </div>)}
+	</motion.div>
       </SidebarComponent>)
 }) satisfies FC<Props>

frontend/src/components/TagLink.tsx

@@ -8,6 +8,7 @@ import type { ComponentProps, FC, HTMLAttributes } from 'react'
 import type { Tag } from '@/types'
 
 type CommonProps = { tag:         Tag
+		     nestLevel?:  number
 		     withWiki?:   boolean
 		     withCount?:  boolean }
 
@@ -21,6 +22,7 @@ type Props = PropsWithLink | PropsWithoutLink
 
 
 export default (({ tag,
+		   nestLevel = 0,
 		   linkFlg   = true,
 		   withWiki  = true,
 		   withCount = true,
@@ -42,6 +44,12 @@ export default (({ tag,
 		?
 	      </Link>
 	    </span>)}
+	{nestLevel > 0 && (
+	    <span
+		className="ml-1 mr-1"
+		style={{ paddingLeft: `${ (nestLevel - 1) }rem` }}>
+	      ↳
+	    </span>)}
 	{linkFlg
 	 ? (
 	    <Link to={`/posts?${ (new URLSearchParams ({ tags: tag.name })).toString () }`}

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 } from 'react'
 
@@ -58,47 +58,71 @@ export default (({ posts }: 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}/>
+		  </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}/>
-		    </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/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>

frontend/src/pages/posts/PostHistoryPage.tsx

@@ -0,0 +1,90 @@
+import axios from 'axios'
+import toCamel from 'camelcase-keys'
+import { useEffect, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { Link, useLocation } from 'react-router-dom'
+
+import TagLink from '@/components/TagLink'
+import PageTitle from '@/components/common/PageTitle'
+import Pagination from '@/components/common/Pagination'
+import MainArea from '@/components/layout/MainArea'
+import { API_BASE_URL, SITE_TITLE } from '@/config'
+
+import type { FC } from 'react'
+
+import type { PostTagChange } from '@/types'
+
+
+export default (() => {
+  const [changes, setChanges] = useState<PostTagChange[]> ([])
+  const [totalPages, setTotalPages] = useState<number> (0)
+
+  const location = useLocation ()
+  const query = new URLSearchParams (location.search)
+  const id = query.get ('id')
+  const page = Number (query.get ('page') ?? 1)
+  const limit = Number (query.get ('limit') ?? 20)
+
+  useEffect (() => {
+    void (async () => {
+      const res = await axios.get (`${ API_BASE_URL }/posts/changes`,
+				   { params: { ...(id && { id }),
+					       ...(page && { page }),
+					       ...(limit && { limit }) } })
+      const data = toCamel (res.data as any, { deep: true }) as {
+	  changes:  PostTagChange[]
+	  count:    number }
+      setChanges (data.changes)
+      setTotalPages (Math.trunc ((data.count - 1) / limit))
+    }) ()
+  }, [location.search])
+
+  return (
+      <MainArea>
+	<Helmet>
+	  <title>{`耕作履歴 | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<PageTitle>
+	  耕作履歴
+	  {Boolean (id) && <>: 投稿 {<Link to={`/posts/${ id }`}>#{id}</Link>}</>}
+	</PageTitle>
+
+	<table className="table-auto w-full border-collapse">
+	  <thead>
+	    <tr>
+	      <th className="p-2 text-left">投稿</th>
+	      <th className="p-2 text-left">変更</th>
+	      <th className="p-2 text-left">日時</th>
+	    </tr>
+	  </thead>
+	  <tbody>
+	    {changes.map (change => (
+		<tr key={`${ change.timestamp }-${ change.post.id }-${ change.tag.id }`}>
+		  <td>
+		    <Link to={`/posts/${ change.post.id }`}>
+		      <img src={change.post.thumbnail || change.post.thumbnailBase || undefined}
+			   alt={change.post.title || change.post.url}
+			   title={change.post.title || change.post.url || undefined}
+			   className="w-40"/>
+		    </Link>
+		  </td>
+		  <td>
+		    <TagLink tag={change.tag} withWiki={false} withCount={false}/>
+		    {`を${ change.changeType === 'add' ? '追加' : '削除' }`}
+		  </td>
+		  <td>
+		    {change.user ? (
+			<Link to={`/users/${ change.user.id }`}>
+			  {change.user.name}
+			</Link>) : 'bot 操作'}
+		    <br/>
+		    {change.timestamp}
+		  </td>
+		</tr>))}
+	  </tbody>
+	</table>
+
+	<Pagination page={page} totalPages={totalPages}/>
+      </MainArea>)
+}) satisfies FC

frontend/src/types.ts

@@ -1,7 +1,7 @@
-import React from 'react'
-
 import { CATEGORIES, USER_ROLES, ViewFlagBehavior } from '@/consts'
 
+import type { ReactNode } from 'react'
+
 export type Category = typeof CATEGORIES[number]
 
 export type Menu = MenuItem[]
@@ -29,19 +29,26 @@ export type Post = {
     originalCreatedFrom:    string | null
     originalCreatedBefore:  string | null }
 
-export type SubMenuItem = {
-    component:  React.ReactNode
-    visible:    boolean
-    } | {
-    name:     string
-    to:       string
-    visible?: boolean }
+export type PostTagChange = {
+    post:       Post
+    tag:        Tag
+    user?:      User
+    changeType: 'add' | 'remove'
+    timestamp:  string }
+
+export type SubMenuItem =
+    | { component:  ReactNode
+	visible:    boolean }
+    | { name:     string
+	to:       string
+	visible?: boolean }
 
 export type Tag = {
     id:         number
     name:       string
     category:   Category
-    postCount:  number }
+    postCount:  number
+    children?:  Tag[] }
 
 export type User = {
     id:               number