Merge remote-tracking branch 'origin/main' into feature/346

#346

Merge remote-tracking branch 'origin/main' into feature/346

#346

#346

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: #348

.gitea/ISSUE_TEMPLATE.md

@@ -0,0 +1,35 @@
+## 背景
+
+なぜ必要か。
+
+## 対象範囲
+
+- backend:
+- frontend:
+- docs:
+- migration:
+
+## やること
+
+- [ ] 
+
+## 受け入れ条件
+
+- [ ] 
+
+## 実行すべき確認
+
+- [ ] `cd backend && bundle exec rspec`
+- [ ] `cd frontend && npm run build`
+- [ ] `cd frontend && npm run lint`
+
+## 禁止事項
+
+- unrelated refactor はしない
+- 既存 API response shape を壊さない
+- 認証・認可・BAN を弱めない
+
+## Codex への指示
+
+この issue を読んで実装してください。
+不明点があれば、実装前に調査結果と選択肢を提示してください。

AGENTS.md

@@ -0,0 +1,143 @@
+# AGENTS.md
+
+## Project overview
+
+BTRC Hub / タグ広場 is a split Rails API and React frontend repository.
+
+- Backend: Rails API under `backend/`.
+- Frontend: React + TypeScript + Vite under `frontend/`.
+- Docs: lightweight command notes under `docs/`.
+- There is no README or Makefile at the repository root as of this inspection.
+
+## Stack
+
+- Backend: Ruby `3.2.2` from `backend/.ruby-version`, Rails `~> 8.0.2`.
+- Backend dependencies include `mysql2`, `sqlite3`, `rspec-rails`, `factory_bot_rails`, `rack-cors`, `jwt`, `discard`, `gollum`, `whenever`, `aws-sdk-s3`, `brakeman`, and `rubocop-rails-omakase`.
+- Frontend: React `^19.1.0`, TypeScript `~5.8.3`, Vite `^6.3.5`.
+- Frontend data/UI dependencies include Axios, TanStack Query, Tailwind CSS, Framer Motion, Radix UI components, lucide-react, MDX/Markdown tooling, and Zustand.
+
+## Main directories
+
+- `backend/app/controllers`: Rails API controllers.
+- `backend/app/models`: Active Record models.
+- `backend/app/representations`: API response representation classes.
+- `backend/app/services`: domain services such as version recording, wiki commit, YouTube sync, and similarity calculation.
+- `backend/config/routes.rb`: API routes.
+- `backend/db/migrate`: migrations.
+- `backend/db/schema.rb`: current schema snapshot.
+- `backend/lib/tasks`: custom Rake tasks.
+- `backend/spec`: RSpec tests.
+- `backend/test`: Rails minitest files that still exist in the tree.
+- `frontend/src/App.tsx`: frontend route definitions and initial user setup.
+- `frontend/src/pages`: page-level React components.
+- `frontend/src/components`: shared and feature components.
+- `frontend/src/lib`: API client helpers, query keys, prefetchers, and domain helpers.
+- `frontend/src/stores`: Zustand stores.
+- `docs/commands.md`: command notes.
+
+## Commands
+
+Only list commands that are backed by files inspected in this repository.
+
+### Backend
+
+The following binstubs exist under `backend/bin`:
+
+```sh
+cd backend
+bin/setup
+bin/dev
+bin/rails
+bin/rake
+bin/rubocop
+bin/brakeman
+bin/kamal
+bin/thrust
+```
+
+Common Rails/Rake usage through existing binstubs:
+
+```sh
+cd backend
+bin/rails db:prepare
+bin/rails db:migrate
+bin/rails routes
+bin/rails server
+bin/rake
+bin/rubocop
+bin/brakeman
+```
+
+RSpec is present in `Gemfile` and `.rspec` exists:
+
+```sh
+cd backend
+bundle exec rspec
+```
+
+### Frontend
+
+The following npm scripts exist in `frontend/package.json`:
+
+```sh
+cd frontend
+npm run dev
+npm run build
+npm run lint
+npm run preview
+```
+
+`npm run build` runs `tsc -b && vite build`, then `postbuild` runs `node scripts/generate-sitemap.js`.
+
+Do not write or report `npm test` as a repository command unless a `test` script is added to `frontend/package.json`.
+
+## Coding style
+
+- Prefer precise, minimal changes.
+- Do not flatter or over-explain.
+- Explain risks directly.
+- Prefer single quotes for strings unless interpolation or escaping makes double quotes better.
+- Ruby: never put a space before method-call parentheses.
+- Ruby: do not use `%w` or `%i`.
+- TypeScript and Python: use GNU-style spacing before parentheses where syntactically valid.
+- Do not add production dependencies without explicit approval.
+
+## Backend rules
+
+- Inspect existing routes, controllers, models, services, and specs before editing backend behavior.
+- For API behavior changes, add or update request specs under `backend/spec/requests`.
+- Prefer RSpec for new backend tests; existing minitest files under `backend/test` do not make minitest the default for new coverage.
+- Do not weaken authentication, BAN user checks, or IP BAN checks.
+- Preserve the `X-Transfer-Code` user identification flow unless the task explicitly changes authentication.
+- Be careful with version tables, `version_no`, optimistic concurrency, wiki revisions, and restore/diff behavior.
+- Be careful with tag names, tag normalization, implications, similarities, and discard behavior.
+- Keep migration files and `backend/db/schema.rb` consistent when changing schema.
+
+## Frontend rules
+
+- Use `frontend/src/lib/api.ts` for API calls so headers and camelCase conversion stay consistent.
+- Add or reuse TanStack Query keys through `frontend/src/lib/queryKeys.ts`; avoid ad hoc query key arrays.
+- Encode URL path-segment values with `encodeURIComponent`.
+- React hooks must be called unconditionally.
+- Keep page-level code under `frontend/src/pages` and shared UI/feature code under `frontend/src/components` unless existing patterns point elsewhere.
+- Match existing Tailwind, component, and import alias conventions.
+
+## Codex workflow
+
+- First inspect existing patterns; do not invent new architecture when a local convention exists.
+- Keep changes scoped to the requested issue.
+- Do not scan or summarize dependency/generated/runtime directories such as `node_modules`, `dist`, `tmp`, `log`, and `storage` unless explicitly needed.
+- Before touching wiki, tag, versioning, BAN, IP BAN, or authentication behavior, inspect the related request specs and service objects.
+- If frontend code changes, run the existing frontend verification commands that apply: `npm run build` and `npm run lint`.
+- If backend code changes, run the relevant RSpec command; for broad backend changes, run `bundle exec rspec`.
+- If a verification command cannot be run or fails, report the exact command and failure.
+
+## Completion criteria
+
+A task is complete only when:
+
+- implementation is complete,
+- relevant verification commands pass, or failures are clearly explained,
+- unrelated files are not changed,
+- migrations and schema are consistent when schema changes are made,
+- user-facing behavior is documented when needed.

backend/.rspec

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

backend/AGENTS.md

@@ -0,0 +1,147 @@
+# backend/AGENTS.md
+
+## Scope
+
+These rules apply to work under `backend/`.
+
+This is a Rails API app using Active Record, RSpec, request specs, service objects, representation classes, and version tables for post/tag/wiki history.
+
+## Commands
+
+Use commands backed by files and dependencies in this directory:
+
+```sh
+bin/setup
+bin/dev
+bin/rails
+bin/rake
+bin/rubocop
+bin/brakeman
+bundle exec rspec
+```
+
+Common checks:
+
+```sh
+bundle exec rspec
+bin/rubocop
+bin/brakeman
+```
+
+Common Rails commands:
+
+```sh
+bin/rails db:prepare
+bin/rails db:migrate
+bin/rails routes
+bin/rails server
+```
+
+After backend behavior changes, run the relevant RSpec files. For broad backend changes, run:
+
+```sh
+bundle exec rspec
+```
+
+If a command cannot be run or fails, report the exact command and failure.
+
+## Rails structure
+
+- `app/controllers`: API controllers.
+- `app/models`: Active Record models and concerns.
+- `app/representations`: JSON response shaping.
+- `app/services`: domain services such as version recorders, wiki commit, YouTube sync, and similarity calculation.
+- `config/routes.rb`: public API routes.
+- `db/migrate`: migrations.
+- `db/schema.rb`: schema snapshot.
+- `lib/tasks`: custom Rake tasks.
+- `spec`: RSpec tests.
+
+Before changing behavior, inspect the matching route, controller, model, service, representation, and spec.
+
+## Ruby style
+
+- Prefer precise, minimal changes.
+- Use single quotes unless interpolation or escaping makes double quotes better.
+- Do not put a space before Ruby method-call parentheses.
+- Do not use `%w` or `%i` in new Ruby code.
+- Keep comments short and useful; avoid narrating obvious code.
+- Do not add production dependencies without approval.
+
+## Authentication and authorization
+
+- Authentication is handled through the `X-Transfer-Code` header in `ApplicationController#authenticate_user`.
+- `current_user` is set by looking up `User.inheritance_code`.
+- Do not bypass or weaken the `X-Transfer-Code` flow unless the task explicitly changes authentication.
+- Unauthenticated write actions should return `:unauthorized` consistently with existing controllers.
+- Role checks use `User` enum roles: `guest`, `member`, and `admin`.
+- Use `current_user.gte_member?` for member-or-admin write permissions where existing controllers do so.
+- Use `current_user.admin?` only for admin-only paths, such as tag child relationship changes.
+- Do not replace role checks with looser presence checks.
+
+## BAN and IP BAN
+
+- `ApplicationController` runs these before actions in order:
+  - `reject_banned_ip_address!`
+  - `authenticate_user`
+  - `reject_banned_user!`
+- User and IP bans use `banned_at`, not a boolean `banned` column.
+- `User#banned?` and `IpAddress#banned?` check `banned_at.present?`.
+- Do not weaken BAN or IP BAN behavior.
+- If changing request authentication or controller before actions, add or update request specs covering banned users and banned IP addresses.
+
+## RSpec
+
+- Prefer RSpec for new backend tests.
+- Put API behavior coverage under `spec/requests`.
+- Put model behavior under `spec/models`.
+- Put service behavior under `spec/services`.
+- Put Rake task coverage under `spec/tasks`.
+- `spec/rails_helper.rb` loads `spec/support/**/*.rb`.
+- Request specs include `AuthHelper` and `JsonHelper`.
+- `AuthHelper#sign_in_as(user)` stubs `ApplicationController#current_user`; use it when matching existing request spec style.
+- Add or update request specs for API behavior changes, especially status codes, permissions, response shape, and version conflict behavior.
+
+## Migrations
+
+- Keep migrations and `db/schema.rb` consistent.
+- Use reversible migrations where practical; otherwise define explicit `up` and `down`.
+- For data backfills inside migrations, follow the existing pattern of defining migration-local `ActiveRecord::Base` classes with `self.table_name`.
+- Preserve existing indexes, foreign keys, check constraints, and null constraints.
+- Be careful with MySQL-specific options already present in migrations, such as `after:`.
+- Do not edit old migrations just to change current behavior unless explicitly requested; add a new migration.
+
+## Version tables
+
+- Versioned records include posts, tags, nico tags, and wiki pages.
+- Current records have `version_no`; version tables have positive `version_no` with unique indexes scoped to the parent record.
+- Version event types are `create`, `update`, `discard`, and `restore`.
+- Version rows are readonly through the `VersionRecord` concern.
+- Use the existing recorder services instead of manually inserting version rows in application code:
+  - `PostVersionRecorder`
+  - `TagVersionRecorder`
+  - `NicoTagVersionRecorder`
+  - `WikiVersionRecorder`
+  - `TagVersioning`
+- `VersionRecorder` locks the current record, validates sequence consistency, skips unchanged update snapshots, creates the next version row, and updates the record `version_no`.
+- Do not update versioned records without considering whether a version snapshot must be created.
+- For optimistic concurrency paths, preserve `base_version_no`, `force`, and `merge` semantics and cover conflicts in request specs.
+
+## Domain cautions
+
+- Posts have tag snapshots, parent post implications, original-created ranges, viewed state, and version conflict behavior.
+- Tags have canonical names, aliases through `TagName`, categories, parent implications, discard behavior, and version snapshots.
+- Nico tags have separate relation/version behavior; do not treat them like normal editable tags without checking existing code.
+- Wiki pages involve page content, revisions/history, version rows, title/tag-name behavior, and diff/restore paths.
+- Materials, theatres, and comments have user and permission checks; inspect the controller before changing them.
+
+## API responses
+
+- Use representation classes under `app/representations` when existing endpoints do.
+- Keep response keys consistent with existing JSON contracts; frontend code expects camelCase conversion client-side, while Rails params and JSON keys are generally snake_case.
+- Preserve existing HTTP status conventions: `:unauthorized` for no user, `:forbidden` for insufficient role or banned user, `:not_found` for missing records, and `:unprocessable_entity` for validation failures.
+
+## Files to avoid in routine work
+
+- Do not inspect or edit `tmp/`, `log/`, `storage/`, `vendor/`, or dependency directories unless explicitly needed.
+- Do not modify generated schema or migration output without the corresponding migration when schema changes are made.

backend/Gemfile

@@ -46,10 +46,10 @@ 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
 
-
-
 gem "mysql2", "~> 0.5.6"
 
 gem "image_processing", "~> 1.14"
@@ -65,3 +65,7 @@ gem 'dotenv-rails'
 gem 'whenever', require: false
 
 gem 'discard'
+
+gem "rspec-rails", "~> 8.0", :groups => [:development, :test]
+
+gem 'aws-sdk-s3', require: false

backend/Gemfile.lock

@@ -73,6 +73,25 @@ GEM
       tzinfo (~> 2.0, >= 2.0.5)
       uri (>= 0.13.1)
     ast (2.4.3)
+    aws-eventstream (1.4.0)
+    aws-partitions (1.1231.0)
+    aws-sdk-core (3.244.0)
+      aws-eventstream (~> 1, >= 1.3.0)
+      aws-partitions (~> 1, >= 1.992.0)
+      aws-sigv4 (~> 1.9)
+      base64
+      bigdecimal
+      jmespath (~> 1, >= 1.6.1)
+      logger
+    aws-sdk-kms (1.123.0)
+      aws-sdk-core (~> 3, >= 3.244.0)
+      aws-sigv4 (~> 1.5)
+    aws-sdk-s3 (1.217.0)
+      aws-sdk-core (~> 3, >= 3.244.0)
+      aws-sdk-kms (~> 1)
+      aws-sigv4 (~> 1.5)
+    aws-sigv4 (1.12.1)
+      aws-eventstream (~> 1, >= 1.0.2)
     base64 (0.2.0)
     bcrypt_pbkdf (1.1.1)
     bcrypt_pbkdf (1.1.1-arm64-darwin)
@@ -99,6 +118,11 @@ 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)
@@ -152,6 +176,7 @@ GEM
       pp (>= 0.6.0)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
+    jmespath (1.6.2)
     json (2.12.0)
     jwt (2.10.1)
       base64
@@ -298,6 +323,23 @@ 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)
@@ -419,11 +461,13 @@ PLATFORMS
   x86_64-linux-musl
 
 DEPENDENCIES
+  aws-sdk-s3
   bootsnap
   brakeman
   diff-lcs
   discard
   dotenv-rails
+  factory_bot_rails
   gollum
   image_processing (~> 1.14)
   jwt
@@ -433,6 +477,7 @@ 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

@@ -1,14 +1,40 @@
 class ApplicationController < ActionController::API
+  before_action :reject_banned_ip_address!
   before_action :authenticate_user
+  before_action :reject_banned_user!
 
-  def current_user
-    @current_user
-  end
+  def current_user = @current_user
 
   private
 
   def authenticate_user
     code = request.headers['X-Transfer-Code'] || request.headers['HTTP_X_TRANSFER_CODE']
+    return if code.blank?
+
     @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
+
+  def reject_banned_ip_address!
+    ip_address = IpAddress.find_by(ip_address: IPAddr.new(request.remote_ip).hton)
+    return unless ip_address&.banned?
+
+    head :forbidden
+  end
+
+  def reject_banned_user!
+    return unless current_user&.banned?
+
+    head :forbidden
+  end
 end

backend/app/controllers/deerjikists_controller.rb

@@ -0,0 +1,47 @@
+class DeerjikistsController < ApplicationController
+  def show
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    return head :bad_request if platform.blank? || code.blank?
+
+    deerjikist = Deerjikist
+                 .joins(:tag)
+                 .includes(tag: :tag_name)
+                 .find_by(platform:, code:)
+    if deerjikist
+      render json: DeerjikistRepr.base(deerjikist)
+    else
+      head :not_found
+    end
+  end
+
+  def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    tag_id = params[:tag_id].to_i
+    return head :bad_request if platform.blank? || code.blank? || tag_id <= 0
+
+    deerjikist = Deerjikist.find_or_initialize_by(platform:, code:).tap do |d|
+      d.tag_id = tag_id
+      d.save!
+    end
+
+    render json: DeerjikistRepr.base(deerjikist)
+  end
+
+  def destroy
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    return head :bad_request if platform.blank? || code.blank?
+
+    Deerjikist.find([platform, code]).destroy!
+
+    head :no_content
+  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/materials_controller.rb

@@ -0,0 +1,101 @@
+class MaterialsController < ApplicationController
+  def index
+    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
+
+    tag_id = params[:tag_id].presence
+    parent_id = params[:parent_id].presence
+
+    q = Material.includes(:tag, :created_by_user).with_attached_file
+    q = q.where(tag_id:) if tag_id
+    q = q.where(parent_id:) if parent_id
+
+    count = q.count
+    materials = q.order(created_at: :desc, id: :desc).limit(limit).offset(offset)
+
+    render json: { materials: MaterialRepr.many(materials, host: request.base_url), count: count }
+  end
+
+  def show
+    material =
+        Material
+        .includes(:tag)
+        .with_attached_file
+        .find_by(id: params[:id])
+    return head :not_found unless material
+
+    wiki_page_body = material.tag.tag_name.wiki_page&.current_revision&.body
+
+    render json: MaterialRepr.base(material, host: request.base_url).merge(wiki_page_body:)
+  end
+
+  def create
+    return head :unauthorized unless current_user
+
+    tag_name_raw = params[:tag].to_s.strip
+    file = params[:file]
+    url = params[:url].to_s.strip.presence
+    return head :bad_request if tag_name_raw.blank? || (file.blank? && url.blank?)
+
+    tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
+    tag = tag_name.tag
+    tag = Tag.create!(tag_name:, category: :material) unless tag
+
+    material = Material.new(tag:, url:,
+                            created_by_user: current_user,
+                            updated_by_user: current_user)
+    material.file.attach(file)
+
+    if material.save
+      render json: MaterialRepr.base(material, host: request.base_url), status: :created
+    else
+      render json: { errors: material.errors.full_messages }, status: :unprocessable_entity
+    end
+  end
+
+  def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    material = Material.with_attached_file.find_by(id: params[:id])
+    return head :not_found unless material
+
+    tag_name_raw = params[:tag].to_s.strip
+    file = params[:file]
+    url = params[:url].to_s.strip.presence
+    return head :bad_request if tag_name_raw.blank? || (file.blank? && url.blank?)
+
+    tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
+    tag = tag_name.tag
+    tag = Tag.create!(tag_name:, category: :material) unless tag
+
+    material.update!(tag:, url:, updated_by_user: current_user)
+    if file
+      material.file.attach(file)
+    else
+      material.file.purge
+    end
+
+    if material.save
+      render json: MaterialRepr.base(material, host: request.base_url)
+    else
+      render json: { errors: material.errors.full_messages }, status: :unprocessable_entity
+    end
+  end
+
+  def destroy
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    material = Material.find_by(id: params[:id])
+    return head :not_found unless material
+
+    material.discard
+    head :no_content
+  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

@@ -3,10 +3,12 @@ class NicoTagsController < ApplicationController
     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, tag_name: :wiki_page, linked_tags: { tag_name: :wiki_page })
+           .order(updated_at: :desc)
     q = q.where('tags.updated_at < ?', Time.iso8601(cursor)) if cursor
 
-    tags = q.limit(limit + 1)
+    tags = q.limit(limit + 1).to_a
 
     next_cursor = nil
     if tags.size > limit
@@ -15,27 +17,35 @@ class NicoTagsController < ApplicationController
     end
 
     render json: { tags: tags.map { |tag|
-      tag.as_json(include: :linked_tags)
+      TagRepr.base(tag).merge(linked_tags: tag.linked_tags.map { |lt|
+        TagRepr.base(lt)
+      })
     }, next_cursor: }
   end
 
   def update
     return head :unauthorized unless current_user
-    return head :forbidden unless current_user.member?
+    return head :forbidden unless current_user.gte_member?
 
     id = params[:id].to_i
 
     tag = Tag.find(id)
-    return head :bad_request if tag.category != 'nico'
+    return head :bad_request unless tag.nico?
 
-    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?
+    linked_tag_names = params[:tags].to_s.split
+    linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
+                                                        with_no_deerjikist: false)
+    return head :bad_request if linked_tags.any? { |t| t.nico? }
 
-    tag.linked_tags = linked_tags
-    tag.updated_at = Time.now
-    tag.save!
+    ApplicationRecord.transaction do
+      TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
 
-    render json: tag.linked_tags, status: :ok
+      tag.linked_tags = linked_tags
+      tag.save!
+
+      NicoTagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+    end
+
+    render json: tag.linked_tags.map { |t| TagRepr.base(t) }, 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/post_versions_controller.rb

@@ -0,0 +1,119 @@
+class PostVersionsController < ApplicationController
+  def index
+    post_id = params[:post].presence
+    tag_id = params[:tag].presence
+    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
+
+    tag_name =
+        if tag_id
+          TagName.joins(:tag).find_by(tag: { id: tag_id })
+        end
+    return render json: { versions: [], count: 0 } if tag_id && tag_name.blank?
+
+    q = PostVersion.joins(<<~SQL.squish)
+          LEFT JOIN
+            post_versions prev
+            ON
+              prev.post_id = post_versions.post_id
+              AND prev.version_no = post_versions.version_no - 1
+        SQL
+        .select('post_versions.*', 'prev.title AS prev_title', 'prev.url AS prev_url',
+                'prev.thumbnail_base AS prev_thumbnail_base', 'prev.tags AS prev_tags',
+                'prev.original_created_from AS prev_original_created_from',
+                'prev.original_created_before AS prev_original_created_before')
+    q = q.where('post_versions.post_id = ?', post_id) if post_id
+    if tag_name
+      escaped = ActiveRecord::Base.sanitize_sql_like(tag_name.name)
+      q = q.where(("CONCAT(' ', post_versions.tags, ' ') LIKE :kw " +
+                   "OR CONCAT(' ', prev.tags, ' ') LIKE :kw"),
+                  kw: "% #{ escaped } %")
+    end
+
+    count = q.except(:select, :order, :limit, :offset).count
+
+    versions = q.order(Arel.sql('post_versions.created_at DESC, post_versions.id DESC'))
+                .limit(limit)
+                .offset(offset)
+
+    render json: { versions: serialise_versions(versions), count: }
+  end
+
+  private
+
+  def serialise_versions rows
+    user_ids = rows.map(&:created_by_user_id).compact.uniq
+    users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
+
+    rows.map do |row|
+      cur_tags = split_tags(row.tags)
+      prev_tags = split_tags(row.attributes['prev_tags'])
+
+      {
+        post_id: row.post_id,
+        version_no: row.version_no,
+        event_type: row.event_type,
+        title: {
+          current: row.title,
+          prev: row.attributes['prev_title']
+        },
+        url: {
+          current: row.url,
+          prev: row.attributes['prev_url']
+        },
+        thumbnail: {
+          current: nil,
+          prev: nil
+        },
+        thumbnail_base: {
+          current: row.thumbnail_base,
+          prev: row.attributes['prev_thumbnail_base']
+        },
+        tags: build_version_tags(cur_tags, prev_tags),
+        original_created_from: {
+          current: row.original_created_from&.iso8601,
+          prev: row.attributes['prev_original_created_from']&.iso8601
+        },
+        original_created_before: {
+          current: row.original_created_before&.iso8601,
+          prev: row.attributes['prev_original_created_before']&.iso8601
+        },
+        created_at: row.created_at.iso8601,
+        created_by_user:
+          if row.created_by_user_id
+            {
+              id: row.created_by_user_id,
+              name: users_by_id[row.created_by_user_id]
+            }
+          end
+      }
+    end
+  end
+
+  def build_version_tags(cur_tags, prev_tags)
+    (cur_tags | prev_tags).map do |name|
+      type =
+        if cur_tags.include?(name) && prev_tags.include?(name)
+          'context'
+        elsif cur_tags.include?(name)
+          'added'
+        else
+          'removed'
+        end
+
+      {
+        name:,
+        type:
+      }
+    end
+  end
+
+  def split_tags(tags)
+    tags.to_s.split(/\s+/).reject(&:blank?)
+  end
+end

backend/app/controllers/posts_controller.rb

@@ -1,42 +1,89 @@
 class PostsController < ApplicationController
   Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
 
-  # GET /posts
   def index
+    url = params[:url].presence
+    title = params[:title].presence
+    original_created_from = params[:original_created_from].presence
+    original_created_to = params[:original_created_to].presence
+    created_between = params[:created_from].presence, params[:created_to].presence
+    updated_between = params[:updated_from].presence, params[:updated_to].presence
+
+    order = params[:order].to_s.split(':', 2).map(&:strip)
+    unless order[0].in?(['title', 'url', 'original_created_at', 'created_at', 'updated_at'])
+      order[0] = 'original_created_at'
+    end
+    unless order[1].in?(['asc', 'desc'])
+      order[1] =
+          if order[0].in?(['title', 'url'])
+            'asc'
+          else
+            'desc'
+          end
+    end
+
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
-    cursor = params[:cursor].presence
 
     page = 1 if page < 1
     limit = 1 if limit < 1
 
     offset = (page - 1) * limit
 
-    sort_sql =
-        'COALESCE(posts.original_created_before - INTERVAL 1 SECOND,' +
-        'posts.original_created_from,' +
-        'posts.created_at)'
+    pt_max_sql =
+        PostTag
+        .select('post_id, MAX(updated_at) AS max_updated_at')
+        .group('post_id')
+        .to_sql
+
+    updated_at_all_sql =
+        'GREATEST(posts.updated_at,' +
+        'COALESCE(pt_max.max_updated_at, posts.updated_at))'
+
     q =
         filtered_posts
-        .preload(:tags)
+        .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
+        .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
+        .preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
         .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 cursor && posts.length > limit
-      next_cursor = posts.last.read_attribute('sort_ts').iso8601(6)
-      posts = posts.first(limit)
+    q = q.where('posts.url LIKE ?', "%#{ url }%") if url
+    q = q.where('posts.title LIKE ?', "%#{ title }%") if title
+    if original_created_from
+      q = q.where('posts.original_created_before > ?', original_created_from)
+    end
+    if original_created_to
+      q = q.where('posts.original_created_from <= ?', original_created_to)
+    end
+    q = q.where('posts.created_at >= ?', created_between[0]) if created_between[0]
+    q = q.where('posts.created_at <= ?', created_between[1]) if created_between[1]
+    if updated_between[0]
+      q = q.where("#{ updated_at_all_sql } >= ?", updated_between[0])
+    end
+    if updated_between[1]
+      q = q.where("#{ updated_at_all_sql } <= ?", updated_between[1])
     end
 
+    sort_sql =
+        case order[0]
+        when 'original_created_at'
+          'COALESCE(posts.original_created_before - INTERVAL 1 MINUTE,' +
+          'posts.original_created_from,' +
+          'posts.created_at) '
+        when 'updated_at'
+          updated_at_all_sql
+        else
+          "posts.#{ order[0] }"
+        end
+    posts = q.order(Arel.sql("#{ sort_sql } #{ order[1] }, posts.id #{ order[1] }"))
+             .limit(limit)
+             .offset(offset)
+             .to_a
+
+    q = q.except(:select, :order)
+
     render json: { posts: posts.map { |post|
-      post.as_json(include: { tags: { only: [:id, :name, :category, :post_count] } }).tap do |json|
+      PostRepr.base(post).merge(updated_at: post.updated_at_all).tap do |json|
         json['thumbnail'] =
             if post.thumbnail.attached?
               rails_storage_proxy_url(post.thumbnail, only_path: false)
@@ -44,63 +91,68 @@ class PostsController < ApplicationController
               nil
             end
       end
-    }, count: filtered_posts.count(:id), next_cursor: }
+    }, count: q.group_values.present? ? q.count.size : q.count }
   end
 
   def random
-    post = filtered_posts.order('RAND()').first
+    post = filtered_posts.preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                         .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] } })
-                  .merge(viewed:))
+    render json: PostRepr.base(post, current_user)
   end
 
-  # GET /posts/1
   def show
-    post = Post.includes(:tags).find(params[:id])
+    post = Post.includes(tags: [:deerjikists, :materials, { tag_name: :wiki_page }]).find_by(id: params[:id])
     return head :not_found unless post
 
-    viewed = current_user&.viewed?(post) || false
-
-    json = post.as_json
-    json['tags'] = build_tag_tree_for(post.tags)
-    json['related'] = post.related(limit: 20)
-    json['viewed'] = viewed
-
-    render json:
+    render json: PostRepr.base(post, current_user)
+                         .merge(tags: build_tag_tree_for(post.tags),
+                                related: PostRepr.many(post.related(limit: 20)))
   end
 
-  # POST /posts
   def create
     return head :unauthorized unless current_user
-    return head :forbidden unless current_user.member?
+    return head :forbidden unless current_user.gte_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(' ')
+    tag_names = params[:tags].to_s.split
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
+    parent_post_ids = parse_parent_post_ids
 
-    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!
-      tags = Tag.normalise_tags(tag_names)
+    post.thumbnail.attach(thumbnail) if thumbnail.present?
+
+    ApplicationRecord.transaction do
+      post.save!
+
+      tags = Tag.normalise_tags!(tag_names)
+      TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
+
       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
-      render json: { errors: post.errors.full_messages }, status: :unprocessable_entity
+
+      sync_parent_posts!(post, parent_post_ids)
+
+      post.resized_thumbnail!
+
+      PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
     end
+
+    post.reload
+    render json: PostRepr.base(post), status: :created
+  rescue Tag::NicoTagNormalisationError
+    head :bad_request
+  rescue ArgumentError => e
+    render json: { errors: [e.message] }, status: :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
   end
 
   def viewed
@@ -117,36 +169,85 @@ 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?
+    return head :forbidden unless current_user.gte_member?
 
-    title = params[:title]
-    tag_names = params[:tags].to_s.split(' ')
+    force = bool?(:force)
+    merge = bool?(:merge)
+    return head :bad_request if force && merge
+
+    base_version_no = parse_base_version_no
+    return head :bad_request if !(force) && !(base_version_no)
+
+    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]
+    parent_post_ids = parse_parent_post_ids
 
-    post = Post.find(params[:id].to_i)
-    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
+    post = nil
+    conflict_json = nil
+
+    ApplicationRecord.transaction do
+      post = Post.lock.find(params[:id].to_i)
+
+      base_version = nil
+      base_snapshot = nil
+      current_snapshot = nil
+      unless force
+        base_version = post.post_versions.find_by!(version_no: base_version_no)
+
+        base_snapshot = post_snapshot_from_version(base_version)
+        current_snapshot = post_snapshot_from_record(post)
+      end
+      incoming_snapshot = post_incoming_snapshot(title:,
+                                                 original_created_from:,
+                                                 original_created_before:,
+                                                 tag_names:,
+                                                 parent_post_ids:)
+
+      snapshot_to_apply =
+          if force || post.version_no == base_version_no || current_snapshot == base_snapshot
+            incoming_snapshot
+          else
+            changes = post_snapshot_changes(base_snapshot, current_snapshot, incoming_snapshot)
+            conflicts = changes.select { |change| change[:conflict] }
+
+            if merge && conflicts.empty?
+              merge_post_snapshots(base_snapshot, current_snapshot, incoming_snapshot)
+            else
+              conflict_json = post_conflict_json(post:,
+                                                 base_version_no:,
+                                                 base_snapshot:,
+                                                 current_snapshot:,
+                                                 incoming_snapshot:,
+                                                 changes:,
+                                                 conflicts:)
+              raise ActiveRecord::Rollback
+            end
+          end
+
+      apply_post_snapshot!(post, snapshot_to_apply)
     end
-  end
 
-  # DELETE /posts/1
-  def destroy
+    return render json: conflict_json, status: :conflict if conflict_json
+
+    post.reload
+    json = PostRepr.base(post, current_user)
+    json['tags'] = build_tag_tree_for(post.tags)
+    render json:, status: :ok
+  rescue Tag::NicoTagNormalisationError
+    head :bad_request
+  rescue ArgumentError => e
+    render json: { errors: [e.message] }, status: :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
   end
 
   def changes
-    id = params[:id]
+    id = params[:id].presence
+    tag_id = params[:tag].presence
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -157,36 +258,41 @@ class PostsController < ApplicationController
 
     pts = PostTag.with_discarded
     pts = pts.where(post_id: id) if id.present?
-    pts = pts.includes(:post, :tag, :created_user, :deleted_user)
+    pts = pts.where(tag_id:) if tag_id.present?
+    pts = pts.includes(:post, :created_user, :deleted_user,
+                       tag: [:deerjikists, :materials, { tag_name: :wiki_page }])
 
     events = []
     pts.each do |pt|
+      tag = TagRepr.base(pt.tag)
+      post = pt.post
+
       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)
+          post:,
+          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)
+            post:,
+            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 }
+    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]
     if tag_names.present?
       filter_posts_by_tags(tag_names, match_type)
@@ -196,17 +302,41 @@ class PostsController < ApplicationController
   end
 
   def filter_posts_by_tags tag_names, match_type
-    posts = Post.joins(:tags)
+    literals = tag_names.map do |raw_name|
+      { name: TagName.canonicalise(raw_name.sub(/\Anot:/i, '')).first,
+        negative: raw_name.downcase.start_with?('not:') }
+    end
+
+    return Post.all if literals.empty?
+
     if match_type == 'any'
-      posts = posts.where(tags: { name: tag_names }).distinct
+      literals.reduce(Post.none) do |posts, literal|
+        posts.or(tag_literal_relation(literal[:name], negative: literal[:negative]))
+      end
     else
-      tag_names.each do |tag|
-        posts = posts.where(id: Post.joins(:tags).where(tags: { name: tag }))
+      literals.reduce(Post.all) do |posts, literal|
+        ids = tagged_post_ids_for(literal[:name])
+        if literal[:negative]
+          posts.where.not(id: ids)
+        else
+          posts.where(id: ids)
+        end
       end
     end
-    posts.distinct
   end
 
+  def tag_literal_relation name, negative:
+    ids = tagged_post_ids_for(name)
+    if negative
+      Post.where.not(id: ids)
+    else
+      Post.where(id: ids)
+    end
+  end
+
+  def tagged_post_ids_for(name) =
+      Post.joins(tags: :tag_name).where(tag_names: { name: }).select(:id)
+
   def sync_post_tags! post, desired_tags
     desired_tags.each do |t|
       t.save! if t.new_record?
@@ -255,7 +385,7 @@ class PostsController < ApplicationController
       return nil unless tag
 
       if path.include?(tag_id)
-        return tag.as_json(only: [:id, :name, :category, :post_count]).merge(children: [])
+        return TagRepr.base(tag).merge(children: [])
       end
 
       if memo.key?(tag_id)
@@ -267,9 +397,247 @@ class PostsController < ApplicationController
 
       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:)
+      memo[tag_id] = TagRepr.base(tag).merge(children:)
     end
 
     root_ids.filter_map { |id| build_node.call(id, []) }
   end
+
+  def parse_parent_post_ids
+    raise ArgumentError, 'parent_post_ids は必須です．' unless params.key?(:parent_post_ids)
+
+    params[:parent_post_ids].to_s.split.map { |token|
+      id = Integer(token, exception: false)
+      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if id.nil? || id <= 0
+
+      id
+    }.uniq
+  end
+
+  def sync_parent_posts! post, parent_post_ids
+    if parent_post_ids.include?(post.id)
+      post.errors.add(:base, '自分自身を親投稿にはできません．')
+      raise ActiveRecord::RecordInvalid, post
+    end
+
+    existing_ids = Post.where(id: parent_post_ids).pluck(:id)
+    missing_ids = parent_post_ids - existing_ids
+
+    if missing_ids.present?
+      post.errors.add(:base, "存在しない親投稿 ID があります: #{ missing_ids.join(' ') }")
+      raise ActiveRecord::RecordInvalid, post
+    end
+
+    current_ids = post.parent_posts.pluck(:id)
+
+    ids_to_add = parent_post_ids - current_ids
+    ids_to_remove = current_ids - parent_post_ids
+
+    PostImplication.where(post_id: post.id, parent_post_id: ids_to_remove).delete_all
+
+    ids_to_add.each do |parent_post_id|
+      PostImplication.create_or_find_by!(post_id: post.id, parent_post_id:)
+    end
+  end
+
+  def parse_base_version_no
+    version_no = Integer(params[:base_version_no], exception: false)
+    if version_no&.positive?
+      version_no
+    else
+      nil
+    end
+  end
+
+  def post_snapshot_from_version version
+    { title: version.title,
+      original_created_from: snapshot_time(version.original_created_from),
+      original_created_before: snapshot_time(version.original_created_before),
+      tag_names: editable_tag_names_from_version(version),
+      parent_post_ids: snapshot_parent_post_ids_from_version(version) }
+  end
+
+  def editable_tag_names_from_version version
+    version.tags.to_s.split.reject { |name| name.downcase.start_with?('nico:') }.sort
+  end
+
+  def post_snapshot_from_record post
+    { title: post.title,
+      original_created_from: snapshot_time(post.original_created_from),
+      original_created_before: snapshot_time(post.original_created_before),
+      tag_names: editable_tag_names_from_post(post),
+      parent_post_ids: post.parent_posts.order(:id).pluck(:id) }
+  end
+
+  def editable_tag_names_from_post post
+    post.tags.not_nico.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  end
+
+  def post_incoming_snapshot title:, original_created_from:, original_created_before:,
+                             tag_names:, parent_post_ids:
+    { title:,
+      original_created_from: snapshot_time(original_created_from),
+      original_created_before: snapshot_time(original_created_before),
+      tag_names: incoming_tag_names_for_snapshot(tag_names),
+      parent_post_ids: parent_post_ids.sort }
+  end
+
+  def snapshot_parent_post_ids_from_version version
+    if version.respond_to?(:parent_post_ids)
+      version.parent_post_ids.to_s.split.map { |id| id.to_i }.sort
+    elsif version.respond_to?(:parent_id) && version.parent_id
+      [version.parent_id]
+    else
+      []
+    end
+  end
+
+  def snapshot_time value
+    return nil if value.blank?
+
+    value = Time.zone.parse(value.to_s) if value in String
+    value&.in_time_zone&.iso8601(6)
+  rescue ArgumentError, TypeError
+    value.to_s
+  end
+
+  def incoming_tag_names_for_snapshot raw_tag_names
+    tags = Tag.normalise_tags!(raw_tag_names, with_tagme: false)
+
+    Tag.expand_parent_tags(tags).map(&:name).uniq.sort
+  end
+
+  def post_conflict_json post:, base_version_no:, base_snapshot:,
+                         current_snapshot:, incoming_snapshot:, changes:, conflicts:
+    { error: 'conflict',
+      message: '競合が発生しました．',
+      post_id: post.id,
+      base_version_no:,
+      current_version_no: post.version_no,
+      base: base_snapshot,
+      current: current_snapshot,
+      mine: incoming_snapshot,
+      changes:,
+      conflicts:,
+      mergeable: conflicts.empty? }
+  end
+
+  def post_snapshot_changes base_snapshot, current_snapshot, incoming_snapshot
+    [scalar_snapshot_change(:title, 'タイトル',
+                            base_snapshot, current_snapshot, incoming_snapshot),
+     scalar_snapshot_change(:original_created_from, 'オリジナルの作成日時（以降）',
+                            base_snapshot, current_snapshot, incoming_snapshot),
+     scalar_snapshot_change(:original_created_before, 'オリジナルの作成日時（より前）',
+                            base_snapshot, current_snapshot, incoming_snapshot),
+     set_snapshot_change(:tag_names, 'タグ',
+                         base_snapshot, current_snapshot, incoming_snapshot),
+     set_snapshot_change(:parent_post_ids, '親投稿',
+                         base_snapshot, current_snapshot, incoming_snapshot)].compact
+  end
+
+  def scalar_snapshot_change field, label, base_snapshot, current_snapshot, incoming_snapshot
+    base = base_snapshot[field]
+    current = current_snapshot[field]
+    mine = incoming_snapshot[field]
+
+    return nil if current == base && mine == base
+
+    { field:, label:, base:, current:, mine:,
+      changed_by_current: current != base,
+      changed_by_me: mine != base,
+      conflict: scalar_snapshot_conflict?(base, current, mine) }
+  end
+
+  def scalar_snapshot_conflict? base, current, mine
+    current != base && mine != base && current != mine
+  end
+
+  def set_snapshot_change field, label, base_snapshot, current_snapshot, incoming_snapshot
+    base = base_snapshot[field].to_a
+    current = current_snapshot[field].to_a
+    mine = incoming_snapshot[field].to_a
+
+    added_by_current = current - base
+    removed_by_current = base - current
+    added_by_me = mine - base
+    removed_by_me = base - mine
+
+    if (added_by_current.empty? &&
+        removed_by_current.empty? &&
+        added_by_me.empty? &&
+        removed_by_me.empty?)
+      return nil
+    end
+
+    { field:, label:, base:, current:, mine:, added_by_current:, removed_by_current:,
+      added_by_me:, removed_by_me:,
+      changed_by_current: added_by_current.present? || removed_by_current.present?,
+      changed_by_me: added_by_me.present? || removed_by_me.present?,
+      conflict: set_snapshot_conflict?(added_by_current:,
+                                       removed_by_current:,
+                                       added_by_me:,
+                                       removed_by_me:) }
+  end
+
+  def set_snapshot_conflict? added_by_current:, removed_by_current:,
+                             added_by_me:, removed_by_me:
+    (added_by_current & removed_by_me).present? || (removed_by_current & added_by_me).present?
+  end
+
+  def apply_post_snapshot! post, snapshot
+    PostVersionRecorder.ensure_snapshot!(post, created_by_user: current_user)
+
+    post.update!(title: snapshot[:title],
+                 original_created_from: snapshot[:original_created_from],
+                 original_created_before: snapshot[:original_created_before])
+
+    editable_tags = Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false)
+    TagVersioning.record_tag_snapshots!(editable_tags, created_by_user: current_user)
+
+    readonly_tags = post.tags.nico.to_a
+
+    tags = readonly_tags + editable_tags
+    tags = Tag.expand_parent_tags(tags)
+
+    sync_post_tags!(post, tags)
+    sync_parent_posts!(post, snapshot[:parent_post_ids])
+
+    PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
+  end
+
+  def merge_post_snapshots base_snapshot, current_snapshot, incoming_snapshot
+    [:title, :original_created_from, :original_created_before].map {
+      [_1, merge_scalar_snapshot_value(base_snapshot[_1],
+                                       current_snapshot[_1],
+                                       incoming_snapshot[_1])]
+    }.to_h.merge([:tag_names, :parent_post_ids].map {
+      [_1, merge_set_snapshot_value(base_snapshot[_1],
+                                    current_snapshot[_1],
+                                    incoming_snapshot[_1])]
+    }.to_h)
+  end
+
+  def merge_scalar_snapshot_value base, current, mine
+    return mine if current == base
+    return current if mine == base || current == mine
+
+    raise ArgumentError, '競合してゐる項目はマージできません．'
+  end
+
+  def merge_set_snapshot_value base, current, mine
+    base = base.to_a
+    current = current.to_a
+    mine = mine.to_a
+
+    added_by_current = current - base
+    removed_by_current = base - current
+    added_by_me = mine - base
+    removed_by_me = base - mine
+
+    merged = base + added_by_current + added_by_me
+    merged -= removed_by_current
+    merged -= removed_by_me
+
+    merged.uniq.sort
+  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 +1,45 @@
+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?
+
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    return head :bad_request if parent.nico? || child.nico?
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
+
+      TagImplication.find_or_create_by!(parent_tag: parent, tag: child)
+      TagVersionRecorder.record!(tag: child, event_type: :update, created_by_user: current_user)
+    end
+
+    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?
+
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    return head :bad_request if parent.nico? || child.nico?
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
+
+      TagImplication.find_by(parent_tag: parent, tag: child)&.destroy!
+      TagVersionRecorder.record!(tag: child, event_type: :update, created_by_user: current_user)
+    end
+
+    head :no_content
+  end
+end

backend/app/controllers/tag_versions_controller.rb

@@ -0,0 +1,92 @@
+class TagVersionsController < ApplicationController
+  def index
+    tag_id = params[:id].presence
+    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
+
+    q = TagVersion.joins(<<~SQL.squish)
+          LEFT JOIN
+            tag_versions prev
+            ON
+              prev.tag_id = tag_versions.tag_id
+              AND prev.version_no = tag_versions.version_no - 1
+        SQL
+      .select('tag_versions.*', 'prev.name AS prev_name', 'prev.category AS prev_category',
+              'prev.aliases AS prev_aliases', 'prev.parent_tag_ids AS prev_parent_tag_ids')
+    q = q.where('tag_versions.tag_id = ?', tag_id) if tag_id
+
+    count = q.except(:select, :order, :limit, :offset).count
+
+    versions = q.order(Arel.sql('tag_versions.created_at DESC, tag_versions.id DESC'))
+                .limit(limit)
+                .offset(offset)
+
+    render json: { versions: serialise_versions(versions), count: }
+  end
+
+  private
+
+  def serialise_versions rows
+    user_ids = rows.map(&:created_by_user_id).compact.uniq
+    users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
+
+    rows.map do |row|
+      cur_aliases = split_values(row.aliases)
+      prev_aliases = split_values(row.attributes['prev_aliases'])
+
+      cur_parent_tag_ids = split_parent_tag_ids(row.parent_tag_ids)
+      prev_parent_tag_ids = split_parent_tag_ids(row.attributes['prev_parent_tag_ids'])
+
+      all_parent_tag_ids = (cur_parent_tag_ids | prev_parent_tag_ids)
+
+      tags_by_id =
+          Tag
+          .includes(:tag_name, :materials, { tag_name: :wiki_page })
+          .where(id: all_parent_tag_ids)
+          .index_by(&:id)
+
+      parent_tags =
+          build_version_values(cur_parent_tag_ids, prev_parent_tag_ids, key: :tag_id)
+          .map do |h|
+            { tag: TagRepr.base(tags_by_id[h[:tag_id]]),
+              type: h[:type] }
+          end
+
+      { tag_id: row.tag_id,
+        version_no: row.version_no,
+        event_type: row.event_type,
+        name: { current: row.name, prev: row.attributes['prev_name'] },
+        category: { current: row.category, prev: row.attributes['prev_category'] },
+        aliases: build_version_values(cur_aliases, prev_aliases, key: :name),
+        parent_tags:,
+        created_at: row.created_at.iso8601,
+        created_by_user: row.created_by_user_id &&
+                         { id: row.created_by_user_id,
+                           name: users_by_id[row.created_by_user_id] } }
+    end
+  end
+
+  def build_version_values cur_values, prev_values, key:
+    (cur_values | prev_values).map do |value|
+      type =
+          if cur_values.include?(value) && prev_values.include?(value)
+            'context'
+          elsif cur_values.include?(value)
+            'added'
+          else
+            'removed'
+          end
+
+      { key => value, type: }
+    end
+  end
+
+  def split_values(values) = values.to_s.split(/\s+/).reject(&:blank?)
+
+  def split_parent_tag_ids(values) = split_values(values).map(&:to_i)
+end

backend/app/controllers/tags_controller.rb

@@ -1,46 +1,440 @@
+require 'net/http'
+require 'uri'
+
+
 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
+
+    name = params[:name].presence
+    category = params[:category].presence
+    post_count_between = (params[:post_count_gte].presence || -1).to_i,
+                         (params[:post_count_lte].presence || -1).to_i
+    post_count_between[0] = nil if post_count_between[0] < 0
+    post_count_between[1] = nil if post_count_between[1] < 0
+    created_between = params[:created_from].presence, params[:created_to].presence
+    updated_between = params[:updated_from].presence, params[:updated_to].presence
+
+    order = params[:order].to_s.split(':', 2).map(&:strip)
+    unless order[0].in?(['name', 'category', 'post_count', 'created_at', 'updated_at'])
+      order[0] = 'post_count'
+    end
+    unless order[1].in?(['asc', 'desc'])
+      order[1] = order[0].in?(['name', 'category']) ? 'asc' : 'desc'
+    end
+
+    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
+
+    q =
+        if post_id.present?
+          Tag.joins(:posts, :tag_name)
+        else
+          Tag.joins(:tag_name)
+        end
+        .includes(:tag_name, :materials, tag_name: :wiki_page)
+    q = q.where(posts: { id: post_id }) if post_id.present?
+
+    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
+    q = q.where(category:) if category
+    q = q.where('tags.post_count >= ?', post_count_between[0]) if post_count_between[0]
+    q = q.where('tags.post_count <= ?', post_count_between[1]) if post_count_between[1]
+    q = q.where('tags.created_at >= ?', created_between[0]) if created_between[0]
+    q = q.where('tags.created_at <= ?', created_between[1]) if created_between[1]
+    q = q.where('tags.updated_at >= ?', updated_between[0]) if updated_between[0]
+    q = q.where('tags.updated_at <= ?', updated_between[1]) if updated_between[1]
+
+    sort_sql =
+        case order[0]
+        when 'name'
+          'tag_names.name'
+        when 'category'
+          'CASE tags.category ' +
+          "WHEN 'deerjikist' THEN 0 " +
+          "WHEN 'meme' THEN 1 " +
+          "WHEN 'character' THEN 2 " +
+          "WHEN 'general' THEN 3 " +
+          "WHEN 'material' THEN 4 " +
+          "WHEN 'meta' THEN 5 " +
+          "WHEN 'nico' THEN 6 END"
+        else
+          "tags.#{ order[0] }"
+        end
+    tags = q.order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
+            .limit(limit)
+            .offset(offset)
+            .to_a
+
+    render json: { tags: TagRepr.many(tags), count: q.size }
+  end
+
+  def with_depth
+    parent_tag_id = params[:parent].to_i
+    parent_tag_id = nil if parent_tag_id <= 0
+
+    tag_ids =
+        if parent_tag_id
+          TagImplication.where(parent_tag_id:).select(:tag_id)
+        else
+          Tag.where.not(id: TagImplication.select(:tag_id)).select(:id)
+        end
+
+    tags =
+        Tag
+        .joins(:tag_name)
+        .includes(:tag_name, :materials, tag_name: :wiki_page)
+        .where(category: [:meme, :character, :material])
+        .where(id: tag_ids)
+        .order('tag_names.name')
+        .distinct
+        .to_a
+
+    has_children_tag_ids =
+        if tags.empty?
+          []
+        else
+          TagImplication
+              .joins(:tag)
+              .where(parent_tag_id: tags.map(&:id),
+                     tags: { category: [:meme, :character, :material] })
+              .distinct
+              .pluck(:parent_tag_id)
+        end
+
+    render json: tags.map { |tag|
+      TagRepr.base(tag).merge(has_children: has_children_tag_ids.include?(tag.id), children: [])
+    }
   end
 
   def autocomplete
-    q = params[:q].to_s.strip
-    return render json: [] if q.blank?
+    q = params[:q].to_s.strip.sub(/\Anot:/i, '')
 
-    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, :materials, tag_name: :wiki_page)
+    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|
+      TagRepr.base(tag).merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
+    }
   end
 
   def show
-    tag = Tag.find(params[:id])
-    render json: tag
-  end
-
-  def show_by_name
-    tag = Tag.find_by(name: params[:name])
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, :materials, tag_name: :wiki_page)
+             .find_by(id: params[:id])
     if tag
-      render json: tag
+      render json: TagRepr.base(tag)
     else
       head :not_found
     end
   end
 
-  def create
+  def show_by_name
+    name = params[:name].to_s.strip
+    return head :bad_request if name.blank?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, :materials, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
+    if tag
+      render json: TagRepr.base(tag)
+    else
+      head :not_found
+    end
+  end
+
+  def deerjikists
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
+    return head :not_found unless tag
+
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+  end
+
+  def deerjikists_by_name
+    name = params[:name].to_s.strip
+    return head :bad_request if name.blank?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
+    return head :not_found unless tag
+
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+  end
+
+  def update_deerjikists
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
+    return head :not_found unless tag
+
+    ApplicationRecord.transaction do
+      tag.deerjikists = []
+      params[:_json].each do
+        platform = _1[:platform]
+        code = normalise_deerjikist_code(platform, _1[:code])
+        deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
+        deerjikist.tag = tag
+        deerjikist.save!
+      end
+    end
+
+    render json: DeerjikistRepr.many(tag.reload.deerjikists)
+  end
+
+  def materials_by_name
+    name = params[:name].to_s.strip
+    return head :bad_request if name.blank?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, :materials, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
+    return head :not_found unless tag
+
+    render json: build_tag_children(tag)
+  end
+
+  def update_all
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    tag = Tag.find_by(id: params[:id])
+    return head :not_found unless tag
+
+    name = params[:name].to_s.strip
+    category = params[:category].to_s.strip
+    return head :unprocessable_entity if name.blank? || category.blank?
+
+    if name != tag.name &&
+        tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
+      return render json: { error: 'システム・タグの名称は変更できません．' },
+                    status: :unprocessable_entity
+    end
+
+    if tag.nico? || category == 'nico'
+      return render json: { error: 'ニコタグは変更できません．' },
+                    status: :unprocessable_entity
+    end
+
+    alias_names = params[:aliases].to_s.split.uniq
+    parent_names = params[:parent_tags].to_s.split.uniq
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+
+      old_name = tag.name
+      name_changed = name != old_name
+      wiki_page = tag.tag_name.wiki_page if name_changed
+
+      tag.update!(category:)
+      tag.tag_name.update!(name:)
+
+      alias_names << old_name if name_changed
+      alias_names.delete(name)
+
+      update_aliases!(tag, alias_names)
+      update_parent_tags!(tag, parent_names)
+
+      tag.reload
+
+      record_tag_version!(
+          tag,
+          event_type: :update,
+          created_by_user: current_user,
+          name_changed:,
+          wiki_page:)
+    end
+
+    render json: TagRepr.base(tag.reload)
   end
 
   def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    name = params[:name].presence
+    category = params[:category].presence
+
+    tag = Tag.find(params[:id])
+
+    if tag.nico? || (category.present? && category == 'nico')
+      return render json: { error: 'ニコタグは変更できません．' },
+                    status: :unprocessable_entity
+    end
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+
+      old_name = tag.name
+      name_changed = name.present? && name != old_name
+      wiki_page = tag.tag_name.wiki_page if name_changed
+
+      tag.tag_name.update!(name:) if name.present?
+      tag.update!(category:) if category.present?
+
+      tag.reload
+
+      record_tag_version!(
+          tag,
+          event_type: :update,
+          created_by_user: current_user,
+          name_changed:,
+          wiki_page:)
+    end
+
+    render json: TagRepr.base(tag.reload)
   end
 
-  def destroy
+  private
+
+  def build_tag_children tag
+    material = tag.materials.first
+    file = nil
+    content_type = nil
+    if material&.file&.attached?
+      file = rails_storage_proxy_url(material.file, only_path: false)
+      content_type = material.file.blob.content_type
+    end
+
+    TagRepr.base(tag).merge(
+        children: tag.children.sort_by { _1.name }.map { build_tag_children(_1) },
+        material: material.as_json&.merge(file:, content_type:))
+  end
+
+  def record_tag_version! tag, event_type:, created_by_user:, name_changed: false, wiki_page: nil
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+      return
+    end
+
+    TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+
+    return unless name_changed
+
+    wiki_page ||= tag.tag_name.wiki_page
+    return unless wiki_page&.wiki_versions&.exists?
+
+    WikiVersionRecorder.record!(
+        page: wiki_page,
+        event_type: :update,
+        created_by_user:)
+  end
+
+  def update_aliases! tag, alias_names
+    alias_names = alias_names.uniq
+
+    affected_tags = [tag]
+
+    current_aliases = tag.tag_name.aliases.to_a
+
+    current_aliases.each do |alias_tag_name|
+      next if alias_names.include?(alias_tag_name.name)
+
+      affected_tags << alias_tag_name.canonical&.tag
+    end
+
+    alias_names.each do |alias_name|
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      affected_tags << alias_tag_name.canonical&.tag
+    end
+
+    affected_tags.compact.uniq.each do |affected_tag|
+      TagVersioning.ensure_snapshot!(affected_tag, created_by_user: current_user)
+    end
+
+    current_aliases.each do |alias_tag_name|
+      next if alias_names.include?(alias_tag_name.name)
+
+      alias_tag_name.update!(canonical: nil)
+    end
+
+    alias_names.each do |alias_name|
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      alias_tag_name.update!(canonical: tag.tag_name)
+    end
+
+    affected_tags.compact.uniq.each do |affected_tag|
+      record_tag_version!(affected_tag, event_type: :update, created_by_user: current_user)
+    end
+  end
+
+  def update_parent_tags! tag, parent_names
+    parent_tags = Tag.normalise_tags!(parent_names, with_tagme: false,
+                                                    with_no_deerjikist: false,
+                                                    deny_nico: true)
+
+    old_parent_tags = tag.parents.to_a
+
+    TagVersioning.record_tag_snapshots!((old_parent_tags + parent_tags).uniq,
+                                        created_by_user: current_user)
+
+    tag.reversed_tag_implications.destroy_all
+
+    parent_tags.each do |parent_tag|
+      next if parent_tag == tag
+
+      TagImplication.create!(tag:, parent_tag:)
+    end
+  end
+
+  def normalise_deerjikist_code platform, code
+    return code if platform != 'youtube' || code[0] != '@'
+
+    url = "https://www.youtube.com/#{ code }"
+
+    html = Net::HTTP.get(URI(url))
+
+    canonical = html[
+        /<link rel="canonical" href="https:\/\/www\.youtube\.com\/channel\/(UC[a-zA-Z0-9_-]{22})"/,
+        1]
+    return canonical if canonical
+
+    html[/"channelId":"(UC[a-zA-Z0-9_-]{22})"/, 1] || html[/\bUC[a-zA-Z0-9_-]{22}\b/]
+  rescue
+    nil
   end
 end

backend/app/controllers/theatre_comments_controller.rb

@@ -0,0 +1,32 @@
+class TheatreCommentsController < ApplicationController
+  def index
+    no_gt = params[:no_gt].to_i
+    no_gt = 0 if no_gt.negative?
+
+    comments = TheatreComment
+               .where(theatre_id: params[:theatre_id])
+               .where('no > ?', no_gt)
+               .order(no: :desc)
+
+    render json: comments.as_json(include: { user: { only: [:id, :name] } })
+  end
+
+  def create
+    return head :unauthorized unless current_user
+
+    content = params[:content]
+    return head :unprocessable_entity if content.blank?
+
+    theatre = Theatre.find_by(id: params[:theatre_id])
+    return head :not_found unless theatre
+
+    comment = nil
+    theatre.with_lock do
+      no = theatre.next_comment_no
+      comment = TheatreComment.create!(theatre:, no:, user: current_user, content:)
+      theatre.update!(next_comment_no: no + 1)
+    end
+
+    render json: comment, status: :created
+  end
+end

backend/app/controllers/theatres_controller.rb

@@ -0,0 +1,54 @@
+class TheatresController < ApplicationController
+  def show
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    render json: TheatreRepr.base(theatre)
+  end
+
+  def watching
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    host_flg = false
+    post_id = nil
+    post_started_at = nil
+
+    theatre.with_lock do
+      TheatreWatchingUser.find_or_initialize_by(theatre:, user: current_user).tap {
+        _1.expires_at = 30.seconds.from_now
+      }.save!
+
+      if (!(theatre.host_user_id?) ||
+          !(theatre.watching_users.exists?(id: theatre.host_user_id)))
+        theatre.update!(host_user_id: current_user.id)
+      end
+
+      host_flg = theatre.host_user_id == current_user.id
+      post_id = theatre.current_post_id
+      post_started_at = theatre.current_post_started_at
+    end
+
+    render json: {
+        host_flg:, post_id:, post_started_at:,
+        watching_users: theatre.watching_users.as_json(only: [:id, :name]) }
+  end
+
+  def next_post
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+    return head :forbidden if theatre.host_user != current_user
+
+    post = Post.where("url LIKE '%nicovideo.jp%'")
+           .or(Post.where("url LIKE '%youtube.com%'"))
+           .order('RAND()')
+           .first
+    theatre.update!(current_post: post, current_post_started_at: Time.current)
+
+    head :no_content
+  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

@@ -1,23 +1,29 @@
 class UsersController < ApplicationController
   def create
-    user = User.create!(inheritance_code: SecureRandom.uuid, role: 'guest')
+    user = nil
+    User.transaction do
+      user = User.create!(inheritance_code: SecureRandom.uuid, role: :guest)
+      attach_ip_address!(user)
+    end
+
     render json: { code: user.inheritance_code,
-                   user: user.slice(:id, :name, :inheritance_code, :role) }
+                   user: user.slice(:id, :name, :inheritance_code, :role) },
+           status: :created
   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])
     return render json: { valid: false } unless user
+    return head :forbidden if user.banned?
 
-    UserIp.find_or_create_by!(user:, ip_address:)
+    attach_ip_address!(user)
 
     render json: { valid: true, user: user.slice(:id, :name, :inheritance_code, :role) }
   end
 
   def renew
+    return head :unauthorized unless current_user
+
     user = current_user
     user.inheritance_code = SecureRandom.uuid
     user.save!
@@ -39,9 +45,18 @@ class UsersController < ApplicationController
     return head :bad_request if name.blank?
 
     if user.update(name:)
-      render json: user.slice(:id, :name, :inheritance_code, :role), status: :created
+      render json: user.slice(:id, :name, :inheritance_code, :role), status: :ok
     else
       render json: user.errors, status: :unprocessable_entity
     end
   end
+
+  private
+
+  def attach_ip_address! user
+    ip_bin = IPAddr.new(request.remote_ip).hton
+    ip_address = IpAddress.create_or_find_by!(ip_address: ip_bin)
+
+    UserIp.create_or_find_by!(user:, ip_address:)
+  end
 end

backend/app/controllers/wiki_pages_controller.rb

@@ -1,20 +1,34 @@
 class WikiPagesController < ApplicationController
-  def index
-    wiki_pages = WikiPage.all
+  rescue_from Wiki::Commit::Conflict, with: :render_wiki_conflict
 
-    render json: wiki_pages
+  def index
+    title = params[:title].to_s.strip
+    if title.blank?
+      return render json: WikiPageRepr.base(WikiPage.joins(:tag_name).includes(:tag_name))
+    end
+
+    q = WikiPage.joins(:tag_name).includes(:tag_name)
+        .where('tag_names.name LIKE ?', "%#{ WikiPage.sanitize_sql_like(title) }%")
+    render json: WikiPageRepr.base(q.limit(20))
   end
 
   def show
-    render_wiki_page_or_404 WikiPage.find(params[:id])
+    page = WikiPage.joins(:tag_name)
+                   .includes(:tag_name)
+                   .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_name: { name: title })
+    render_wiki_page_or_404 page
   end
 
   def exists
-    if WikiPage.exists?(params[:id])
+    if WikiPage.exists?(id: params[:id])
       head :no_content
     else
       head :not_found
@@ -22,7 +36,8 @@ class WikiPagesController < ApplicationController
   end
 
   def exists_by_title
-    if WikiPage.exists?(title: params[:title])
+    title = params[:title].to_s.strip
+    if WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
       head :no_content
     else
       head :not_found
@@ -31,21 +46,25 @@ class WikiPagesController < ApplicationController
 
   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.joins(:tag_name).includes(:tag_name).find(id)
 
-    diffs = Diff::LCS.sdiff(wiki_page_from.body, wiki_page_to.body)
+    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(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 ?+
@@ -55,97 +74,133 @@ 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.gte_member?
 
-    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
-    else
-      render json: { errors: wiki_page.errors.full_messages }, status: :unprocessable_entity
-    end
+    title = params[:title].to_s.strip
+    body = params[:body].to_s
+    message = params[:message].presence
+
+    return head :unprocessable_entity if title.blank? || body.blank?
+
+    tag_name = TagName.find_undiscard_or_create_by!(name: title)
+
+    page =
+        Wiki::Commit.create_content!(
+            tag_name:,
+            body:,
+            created_by_user: current_user,
+            message:)
+
+    render json: WikiPageRepr.base(page), status: :created
+  rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotUnique
+    head :unprocessable_entity
   end
 
   def update
     return head :unauthorized unless current_user
-    return head :forbidden unless current_user.member?
+    return head :forbidden unless current_user.gte_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 = params[:base_revision_id].presence
+
+    ApplicationRecord.transaction do
+      page.lock!
+
+      old_title = page.title
+
+      tag = Tag.find_by(tag_name_id: page.tag_name_id)
+
+      if tag && title != old_title
+        TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+      end
+
+      page.tag_name.update!(name: title) if title != old_title
+
+      message = params[:message].presence
+      Wiki::Commit.content!(page:,
+                            body:,
+                            created_user: current_user,
+                            message:,
+                            base_revision_id:)
+
+      if tag && title != old_title
+        tag.reload
+        TagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+      end
+    end
 
     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
+    id = params[:id].presence
+    q = WikiRevision.joins(wiki_page: :tag_name)
+                    .includes(:created_user, wiki_page: :tag_name)
+                    .order(id: :desc)
+    q = q.where(wiki_page_id: id) if id
 
-    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 }
+    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:         rev.created_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)
+    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
+
+    render json: WikiPageRepr.base(page).merge(body:, revision_id:, pred:, succ:, updated_at:)
   end
 
-  def render_wiki_page_or_404 wiki_page
-    return head :not_found unless wiki_page
+  def find_revision page
+    if params[:version].present?
+      page.wiki_revisions.find_by(id: params[:version])
+    else
+      page.current_revision
+    end
+  end
 
-    wiki_page.sha = params[:version].presence
-
-    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/deerjikist.rb

@@ -0,0 +1,21 @@
+class Deerjikist < ApplicationRecord
+  self.primary_key = :platform, :code
+
+  belongs_to :tag
+
+  validates :platform, presence: true
+  validates :code, presence: true
+  validates :tag_id, presence: true
+
+  validate :tag_must_be_deerjikist
+
+  enum :platform, nico: 'nico', youtube: 'youtube'
+
+  private
+
+  def tag_must_be_deerjikist
+    if tag && !(tag.deerjikist?)
+      errors.add :tag, 'タグはニジラー・カテゴリである必要があります．'
+    end
+  end
+end

backend/app/models/ip_address.rb

@@ -1,6 +1,10 @@
 class IpAddress < ApplicationRecord
   validates :ip_address, presence: true, length: { maximum: 16 }
-  validates :banned, inclusion: { in: [true, false] }
 
-  has_many :users
+  has_many :user_ips, dependent: :destroy
+  has_many :users, through: :user_ips
+
+  def banned? = banned_at.present?
+  def ban! = banned? || update!(banned_at: Time.current)
+  def unban! = update!(banned_at: nil)
 end

backend/app/models/material.rb

@@ -0,0 +1,39 @@
+class Material < ApplicationRecord
+  include MyDiscard
+
+  default_scope -> { kept }
+
+  belongs_to :parent, class_name: 'Material', optional: true
+  has_many :children, class_name: 'Material', foreign_key: :parent_id, dependent: :nullify
+
+  belongs_to :tag, optional: true
+  belongs_to :created_by_user, class_name: 'User', optional: true
+  belongs_to :updated_by_user, class_name: 'User', optional: true
+
+  has_one_attached :file, dependent: :purge
+
+  validates :tag_id, presence: true, uniqueness: true
+
+  validate :file_must_be_attached
+  validate :tag_must_be_material_category
+
+  def content_type
+    return nil unless file&.attached?
+
+    file.blob.content_type
+  end
+
+  private
+
+  def file_must_be_attached
+    return if url.present? || file.attached?
+
+    errors.add(:url, 'URL かファイルのどちらかは必須です．')
+  end
+
+  def tag_must_be_material_category
+    return if tag.blank? || tag.character? || tag.material?
+
+    errors.add(:tag, '素材カテゴリのタグを指定してください．')
+  end
+end

backend/app/models/my_discard.rb

@@ -0,0 +1,24 @@
+module MyDiscard
+  extend ActiveSupport::Concern
+
+  included do
+    include Discard::Model
+
+    default_scope -> { kept }
+  end
+
+  class_methods do
+    def find_undiscard_or_create_by! attrs, &block
+      record = with_discarded.find_by(attrs)
+
+      if record&.discarded?
+        record.undiscard!
+        record.update_columns(created_at: record.reload.updated_at)
+      end
+
+      record or create!(attrs, &block)
+    rescue ActiveRecord::RecordNotUnique
+      retry
+    end
+  end
+end

backend/app/models/nico_tag_version.rb

@@ -0,0 +1,7 @@
+class NicoTagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  validates :name, presence: true
+end

backend/app/models/post.rb

@@ -1,46 +1,74 @@
 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, 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',
-           foreign_key: :post_id
-  has_many :post_similarities_as_target_post,
-           class_name: 'PostSimilarity',
-           foreign_key: :target_post_id
+
+  has_many :user_post_views, dependent: :delete_all
+  has_many :post_similarities, dependent: :delete_all
+  has_many :post_versions
+
+  has_many :parent_post_implications,
+           class_name: 'PostImplication',
+           foreign_key: :post_id,
+           dependent: :destroy,
+           inverse_of: :post
+  has_many :parents, through: :parent_post_implications, source: :parent_post
+
+  has_many :child_post_implications,
+           class_name: 'PostImplication',
+           foreign_key: :parent_post_id,
+           dependent: :destroy,
+           inverse_of: :parent_post
+  has_many :children, through: :child_post_implications, source: :post
+
   has_one_attached :thumbnail
 
+  attribute :version_no, :integer, default: 1
+
+  before_validation :normalise_url
+
+  validates :url, presence: true, uniqueness: true
+
   validate :validate_original_created_range
+  validate :url_must_be_http_url
+
+  def parent_posts = parents
+
+  def child_posts = children
+
+  def sibling_posts
+    parent_post_ids = parent_posts.order(:id).pluck(:id)
+
+    parent_post_ids.to_h { [_1, PostImplication.where(parent_post: _1).map(&:post)] }
+  end
 
   def as_json options = { }
-    super(options).merge({ thumbnail: thumbnail.attached? ?
-                                      Rails.application.routes.url_helpers.rails_blob_url(
-                                          thumbnail, only_path: false) :
-                                      nil })
+    super(options).merge(thumbnail: thumbnail.attached? ?
+                                    Rails.application.routes.url_helpers.rails_blob_url(
+                                        thumbnail, only_path: false) :
+                                    nil)
   rescue
     super(options).merge(thumbnail: nil)
   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] }
+  def snapshot_tag_names = tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
 
-    sorted = ids_with_cos.sort_by { |_, cos| -cos }
+  def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
 
-    ids = sorted.map(&:first)
-    ids = ids.first(limit) if limit
+  def related limit: nil
+    ids = post_similarities.order(cos: :desc)
+    ids = ids.limit(limit) if limit
+    ids = ids.pluck(:target_post_id)
+    return Post.none if ids.empty?
 
-    Post.where(id: ids).index_by(&:id).values_at(*ids)
+    Post.where(id: ids)
+        .with_attached_thumbnail
+        .order(Arel.sql("FIELD(posts.id, #{ ids.join(',') })"))
   end
 
   def resized_thumbnail!
@@ -69,4 +97,33 @@ 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_implication.rb

@@ -0,0 +1,19 @@
+class PostImplication < ApplicationRecord
+  self.primary_key = :post_id, :parent_post_id
+
+  belongs_to :post, inverse_of: :parent_post_implications
+  belongs_to :parent_post, class_name: 'Post', inverse_of: :child_post_implications
+
+  validates :post_id, presence: true, uniqueness: { scope: :parent_post_id }
+  validates :parent_post_id, presence: true
+
+  validate :parent_post_mustnt_be_itself
+
+  private
+
+  def parent_post_mustnt_be_itself
+    if parent_post_id == post_id
+      errors.add :parent_post_id, '親投稿に同じ投稿を設定することはできません．'
+    end
+  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

@@ -1,6 +1,10 @@
 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

backend/app/models/post_version.rb

@@ -0,0 +1,22 @@
+class PostVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :post
+  belongs_to :parent, class_name: 'Post', optional: true
+
+  validates :url, presence: true
+
+  validate :validate_original_created_range
+
+  private
+
+  def validate_original_created_range
+    f = original_created_from
+    b = original_created_before
+    return if f.blank? || b.blank?
+
+    if f >= b
+      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
+end

backend/app/models/tag.rb

@@ -1,81 +1,113 @@
+require 'set'
+
+
 class Tag < ApplicationRecord
-  has_many :post_tags, dependent: :delete_all, inverse_of: :tag
+  include MyDiscard
+
+  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 :tag_aliases, dependent: :destroy
 
   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
 
   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 :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',
-                    general:     'general',
-                    material:    'material',
-                    nico:        'nico',
-                    meta:        'meta' }
+  has_many :tag_similarities, dependent: :delete_all
+  has_many :tag_similarities_as_target,
+           class_name: 'TagSimilarity', foreign_key: :target_tag_id, dependent: :delete_all
+
+  has_many :deerjikists, dependent: :delete_all
+  has_many :materials
+
+  has_many :tag_versions
+  has_many :nico_tag_versions
+
+  belongs_to :tag_name
+  delegate :wiki_page, to: :tag_name
+
+  attribute :version_no, :integer, default: 1
+
+  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
+  validate :category_must_be_deerjikist_with_deerjikists
 
-  scope :nico_tags, -> { where(category: :nico) }
+  scope :nico_tags, -> { nico }
 
   CATEGORY_PREFIXES = {
-      'gen:'  => 'general',
-      'djk:'  => 'deerjikist',
-      'meme:' => 'meme',
-      'chr:'  => 'character',
-      'mtr:'  => 'material',
-      'meta:' => 'meta' }.freeze
+      'general:'    => :general,
+      'gen:'        => :general,
+      'deerjikist:' => :deerjikist,
+      'djk:'        => :deerjikist,
+      'meme:'       => :meme,
+      'character:'  => :character,
+      'chr:'        => :character,
+      'material:'   => :material,
+      'mtr:'        => :material,
+      'meta:'       => :meta }.freeze
 
-  def self.tagme
-    @tagme ||= Tag.find_or_create_by!(name: 'タグ希望') do |tag|
-      tag.category = 'meta'
-    end
+  def name= val
+    (self.tag_name ||= build_tag_name).name = val
   end
 
-  def self.bot
-    @bot ||= Tag.find_or_create_by!(name: 'bot操作') do |tag|
-      tag.category = 'meta'
-    end
-  end
+  def has_wiki = wiki_page.present?
 
-  def self.no_deerjikist
-    @no_deerjikist ||= Tag.find_or_initialize_by(name: 'ニジラー情報不詳') do |tag|
-      tag.category = 'meta'
-    end
-  end
+  def material_id = materials.first&.id
+
+  def has_deerjikists = deerjikists.present?
+
+  def self.tagme = find_or_create_by_tag_name!('タグ希望', category: :meta)
+  def self.bot = find_or_create_by_tag_name!('bot操作', category: :meta)
+  def self.no_deerjikist = find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
+  def self.video = find_or_create_by_tag_name!('動画', category: :meta)
+  def self.niconico = find_or_create_by_tag_name!('ニコニコ', category: :meta)
+  def self.youtube = find_or_create_by_tag_name!('YouTube', category: :meta)
+
+  def self.normalise_tags! tag_names, with_tagme: true,
+                                      with_no_deerjikist: true,
+                                      deny_nico: true
+    if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
+      raise NicoTagNormalisationError
+    end
 
-  def self.normalise_tags tag_names, with_tagme: true
     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|
-        if cat && tag.category != cat
-          tag.category = cat
-          tag.save!
-        end
+      pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
+      name = TagName.canonicalise(name.sub(/\A#{ pf }/i, '')).first
+      find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
+        tag.update!(category: cat) if cat && tag.category != cat
       end
     end
+
     tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
-    tags << Tag.no_deerjikist if tags.all? { |t| t.category != 'deerjikist' }
-    tags.uniq
+    tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
+    tags.uniq(&:id)
   end
 
   def self.expand_parent_tags tags
@@ -101,12 +133,99 @@ class Tag < ApplicationRecord
     (result + tags).uniq { |t| t.id }
   end
 
+  def self.find_or_create_by_tag_name! name, category:
+    tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
+    tn = tn.canonical if tn.canonical_id?
+
+    Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) do |t|
+      t.category = category
+    end
+  rescue ActiveRecord::RecordNotUnique
+    retry
+  end
+
+  def self.merge_tags! target_tag, source_tags, created_by_user: nil
+    target_tag => Tag
+
+    affected_post_ids = Set.new
+
+    Tag.transaction do
+      TagVersioning.ensure_snapshot!(target_tag, created_by_user:)
+
+      Array(source_tags).compact.uniq.each do |source_tag|
+        source_tag => Tag
+
+        next if source_tag == target_tag
+
+        TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
+
+        source_tag.post_tags.kept.find_each do |source_pt|
+          post_id = source_pt.post_id
+          affected_post_ids << post_id
+          source_pt.discard_by!(created_by_user)
+          unless PostTag.kept.exists?(post_id:, tag: target_tag)
+            PostTag.create!(post_id:, tag: target_tag)
+          end
+        end
+
+        source_tag_name = source_tag.tag_name
+
+        if source_tag_name.wiki_page.present?
+          raise ActiveRecord::RecordInvalid.new(source_tag_name)
+        end
+
+        TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
+        source_tag.discard!
+
+        if source_tag.nico?
+          source_tag_name.discard!
+        else
+          source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
+                                         updated_at: Time.current)
+        end
+
+        TagVersioning.record!(target_tag, event_type: :update, created_by_user:)
+      end
+
+      Post.where(id: affected_post_ids.to_a).find_each do |post|
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user:)
+        PostVersionRecorder.record!(post:, event_type: :update, created_by_user:)
+      end
+
+      # 投稿件数を再集計
+      target_tag.update_columns(post_count: PostTag.kept.where(tag: target_tag).count)
+    end
+
+    target_tag.reload
+  end
+
+  def snapshot_aliases = tag_name.aliases.kept.order(:name).pluck(:name)
+
+  def snapshot_parent_tag_ids = parents.order(:id).pluck(:id)
+
+  def snapshot_linked_tag_names
+    linked_tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  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 ((nico? && !(n.downcase.start_with?('nico:'))) || 
+        (!(nico?) && n.downcase.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
+
+  def category_must_be_deerjikist_with_deerjikists
+    if !(deerjikist?) && deerjikists.exists?
+      errors.add :category, 'ニジラーと紐づいてゐるタグはニジラー・カテゴリである必要があります．'
+    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_name.rb

@@ -0,0 +1,51 @@
+class TagName < ApplicationRecord
+  include MyDiscard
+
+  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
+  validate :name_must_be_sanitised
+
+  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
+
+  def name_must_be_sanitised
+    if name? && name != TagNameSanitisationRule.sanitise(name)
+      errors.add :name, '名前に使用できない文字が含まれてゐます．'
+    end
+  end
+end

backend/app/models/tag_name_sanitisation_rule.rb

@@ -0,0 +1,58 @@
+class TagNameSanitisationRule < ApplicationRecord
+  include Discard::Model
+
+  self.primary_key = :priority
+
+  default_scope -> { kept }
+
+  validates :source_pattern, presence: true, uniqueness: true
+
+  validate :source_pattern_must_be_regexp
+
+  class << self
+    def sanitise(name) =
+        rules.reduce(name.dup) { |name, (pattern, replacement)| name.gsub(pattern, replacement) }
+
+    def apply!
+      TagName.find_each do |tn|
+        name = sanitise(tn.name)
+        next if name == tn.name
+
+        TagName.transaction do
+          existing_tn = TagName.find_by(name:)
+          if existing_tn
+            existing_tn = existing_tn.canonical || existing_tn
+            next if existing_tn.id == tn.id
+
+            existing_tag = Tag.find_by(tag_name_id: existing_tn.id)
+            source_tag = Tag.find_by(tag_name_id: tn.id)
+
+            if existing_tag
+              Tag.merge_tags!(existing_tag, source_tag) if tn.tag
+            elsif source_tag
+              source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
+            end
+            tn.discard!
+
+            next
+          end
+
+          # TagName 側の自動サニタイズを回避
+          tn.update_columns(name:, updated_at: Time.current)
+        end
+      end
+    end
+
+    private
+
+    def rules = kept.order(:priority).map { |r| [Regexp.new(r.source_pattern), r.replacement] }
+  end
+
+  private
+
+  def source_pattern_must_be_regexp
+    Regexp.new(source_pattern)
+  rescue RegexpError
+    errors.add :source_pattern, '変な正規表現だね〜（笑）'
+  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/tag_version.rb

@@ -0,0 +1,15 @@
+class TagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  enum :category, { deerjikist: 'deerjikist',
+                    meme: 'meme',
+                    character: 'character',
+                    general: 'general',
+                    material: 'material',
+                    meta: 'meta' }, validate: true
+
+  validates :name, presence: true
+  validates :category, presence: true
+end

backend/app/models/theatre.rb

@@ -0,0 +1,13 @@
+class Theatre < ApplicationRecord
+  include MyDiscard
+
+  has_many :comments, class_name: 'TheatreComment'
+  has_many :theatre_watching_users, dependent: :delete_all
+  has_many :active_theatre_watching_users, -> { active },
+           class_name: 'TheatreWatchingUser', inverse_of: :theatre
+  has_many :watching_users, through: :active_theatre_watching_users, source: :user
+
+  belongs_to :host_user, class_name: 'User', optional: true
+  belongs_to :current_post, class_name: 'Post', optional: true
+  belongs_to :created_by_user, class_name: 'User'
+end

backend/app/models/theatre_comment.rb

@@ -0,0 +1,8 @@
+class TheatreComment < ApplicationRecord
+  include Discard::Model
+
+  self.primary_key = :theatre_id, :no
+
+  belongs_to :theatre
+  belongs_to :user
+end

backend/app/models/theatre_watching_user.rb

@@ -0,0 +1,13 @@
+class TheatreWatchingUser < ApplicationRecord
+  self.primary_key = :theatre_id, :user_id
+
+  belongs_to :theatre
+  belongs_to :user
+
+  scope :active, -> { where('expires_at >= ?', Time.current) }
+  scope :expired, -> { where('expires_at < ?', Time.current) }
+
+  def active? = expires_at >= Time.current
+
+  def refresh! = update!(expires_at: 30.seconds.from_now)
+end

backend/app/models/user.rb

@@ -1,29 +1,27 @@
 class User < ApplicationRecord
-  enum :role, { guest: 'guest', member: 'member', admin: 'admin' }
+  enum :role, guest: 'guest', member: 'member', admin: 'admin'
 
   validates :name, length: { maximum: 255 }
   validates :inheritance_code, presence: true, length: { maximum: 64 }
   validates :role, presence: true, inclusion: { in: roles.keys }
-  validates :banned, inclusion: { in: [true, false] }
 
-  has_many :posts
+  has_many :created_posts,
+           class_name: 'Post', foreign_key: :uploaded_user_id, dependent: :nullify
   has_many :settings
   has_many :user_ips, dependent: :destroy
   has_many :ip_addresses, through: :user_ips
   has_many :user_post_views, dependent: :destroy
   has_many :viewed_posts, through: :user_post_views, source: :post
-  has_many :created_wiki_pages, class_name: 'WikiPage', foreign_key: 'created_user_id', dependent: :nullify
-  has_many :updated_wiki_pages, class_name: 'WikiPage', foreign_key: 'updated_user_id', dependent: :nullify
+  has_many :created_wiki_pages,
+           class_name: 'WikiPage', foreign_key: :created_user_id, dependent: :nullify
+  has_many :updated_wiki_pages,
+           class_name: 'WikiPage', foreign_key: :updated_user_id, dependent: :nullify
 
-  def viewed? post
-    user_post_views.exists? post_id: post.id
-  end
+  def viewed?(post) = user_post_views.exists?(post_id: post.id)
 
-  def member?
-    ['member', 'admin'].include?(role)
-  end
+  def gte_member? = member? || admin?
 
-  def admin?
-    role == 'admin'
-  end
+  def banned? = banned_at.present?
+  def ban! = banned? || update!(banned_at: Time.current)
+  def unban! = update!(banned_at: nil)
 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/version_record.rb

@@ -0,0 +1,19 @@
+module VersionRecord
+  extend ActiveSupport::Concern
+
+  def readonly? = persisted?
+
+  included do
+    belongs_to :created_by_user, class_name: 'User', optional: true
+
+    enum :event_type, { create: 'create',
+                        update: 'update',
+                        discard: 'discard',
+                        restore: 'restore' }, prefix: true, validate: true
+
+    validates :version_no, presence: true, numericality: { only_integer: true, greater_than: 0 }
+    validates :event_type, presence: true
+
+    scope :chronological, -> { order(:version_no, :id) }
+  end
+end

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 +1,54 @@
-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'
+  include MyDiscard
 
-  validates :title, presence: true, length: { maximum: 255 }, uniqueness: true
+  has_many :wiki_revisions, dependent: :destroy
+  belongs_to :created_user, class_name: 'User'
+  belongs_to :updated_user, class_name: 'User'
 
-  def as_json options = { }
-    self.sha = nil
-    super options
+  has_many :redirected_from_revisions,
+           class_name: 'WikiRevision',
+           foreign_key: :redirect_page_id,
+           dependent: :nullify
+
+  has_many :wiki_versions
+
+  attribute :version_no, :integer, default: 1
+
+  belongs_to :tag_name
+  validates :tag_name, presence: true
+  validates :body, presence: true
+
+  def title = tag_name.name
+
+  def title= val
+    (self.tag_name ||= build_tag_name).name = val
   end
 
-  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
+  def current_revision = wiki_revisions.order(id: :desc).first
+
+  def resolve_redirect limit: 10
+    page = self
+    visited = Set.new
+
+    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)
+
+      page = rev.redirect_page
     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
+
+    page
   end
 
-  def sha
-    @sha
-  end
-
-  def pred
-    @pred
-  end
-
-  def succ
-    @succ
-  end
-
-  def updated_at
-    @updated_at
-  end
-
-  def body
-    sha = nil unless @page
-    @page&.raw_data&.force_encoding('UTF-8')
-  end
-
-  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)
-    end
-  end
-
-  private
-
-  WIKI_PATH = Rails.root.join('wiki').to_s
-
-  def wiki
-    @wiki ||= Gollum::Wiki.new(WIKI_PATH)
-  end
+  def pred_revision_id(revision_id) =
+      wiki_revisions.where('id < ?', revision_id).order(id: :desc).limit(1).pick(:id)
+  def succ_revision_id(revision_id) =
+      wiki_revisions.where('id > ?', revision_id).order(id: :asc).limit(1).pick(:id)
 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/models/wiki_version.rb

@@ -0,0 +1,8 @@
+class WikiVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :wiki_page
+
+  validates :title, presence: true
+  validates :body, presence: true
+end

backend/app/representations/deerjikist_repr.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+
+module DeerjikistRepr
+  BASE = { only: [:platform, :code], include: { tag: TagRepr::BASE } }.freeze
+
+  module_function
+
+  def base deerjikist
+    deerjikist.as_json(BASE)
+  end
+
+  def many deerjikists
+    deerjikists.map { |d| base(d) }
+  end
+end

backend/app/representations/material_repr.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+
+module MaterialRepr
+  BASE = { only: [:id, :url, :created_at, :updated_at],
+           methods: [:content_type],
+           include: { tag: TagRepr::BASE,
+                      created_by_user: UserRepr::BASE,
+                      updated_by_user: UserRepr::BASE } }.freeze
+
+  module_function
+
+  def base material, host:
+    material.as_json(BASE).merge(
+        file: if material.file.attached?
+                Rails.application.routes.url_helpers.rails_storage_proxy_url(
+                    material.file, host:)
+              end)
+  end
+
+  def many materials, host:
+    materials.map { |m| base(m, host:) }
+  end
+end

backend/app/representations/post_repr.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+
+module PostRepr
+  BASE = { include: { tags: TagRepr::BASE, uploaded_user: UserRepr::BASE },
+           methods: [:parent_posts, :child_posts, :sibling_posts] }.freeze
+
+  module_function
+
+  def base post, current_user = nil
+    json = post.as_json(BASE)
+    return json.merge(viewed: false) unless current_user
+
+    viewed = current_user.viewed?(post)
+    json.merge(viewed:)
+  end
+
+  def many posts, current_user = nil
+    posts.map { |p| base(p, current_user) }
+  end
+end

backend/app/representations/tag_repr.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+
+module TagRepr
+  BASE = { only: [:id, :category, :post_count, :created_at, :updated_at],
+           methods: [:name, :has_wiki, :material_id, :has_deerjikists] }.freeze
+
+  module_function
+
+  def base tag
+    tag.as_json(BASE).merge(aliases: tag.snapshot_aliases,
+                            parents: tag.parents.map { _1.as_json(BASE) })
+  end
+
+  def many(tags) = tags.map { |t| base(t) }
+end

backend/app/representations/theatre_repr.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+
+module TheatreRepr
+  BASE = { only: [:id, :name, :opens_at, :closes_at, :created_at, :updated_at],
+           include: { created_by_user: { only: [:id, :name] } } }.freeze
+
+  module_function
+
+  def base theatre
+    theatre.as_json(BASE)
+  end
+
+  def many theatre
+    theatre.map { |t| base(t) }
+  end
+end

backend/app/representations/user_repr.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+
+module UserRepr
+  BASE = { only: [:id, :name] }.freeze
+
+  module_function
+
+  def base user
+    user.as_json(BASE)
+  end
+
+  def many users
+    users.map { |u| base(u) }
+  end
+end

backend/app/representations/wiki_page_repr.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+
+module WikiPageRepr
+  BASE = { methods: [:title] }.freeze
+
+  module_function
+
+  def base wiki_page
+    wiki_page.as_json(BASE)
+  end
+
+  def many wiki_pages
+    wiki_pages.map { |p| base(p) }
+  end
+end

backend/app/services/nico_tag_version_recorder.rb

@@ -0,0 +1,19 @@
+class NicoTagVersionRecorder < VersionRecorder
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
+  end
+
+  def initialize tag:, event_type:, created_by_user:
+    super(record: tag, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = NicoTagVersion
+  def version_association = :nico_tag_versions
+  def record_key = :tag
+
+  def snapshot_attributes
+    { name: @record.name, linked_tags: @record.snapshot_linked_tag_names.join(' ') }
+  end
+end

backend/app/services/post_version_recorder.rb

@@ -0,0 +1,31 @@
+class PostVersionRecorder < VersionRecorder
+  def self.record! post:, event_type:, created_by_user:
+    new(post:, event_type:, created_by_user:).record!
+  end
+
+  def initialize post:, event_type:, created_by_user:
+    super(record: post, event_type:, created_by_user:)
+  end
+
+  def self.ensure_snapshot! post, created_by_user:
+    return if post.post_versions.exists?
+
+    record!(post:, event_type: :create, created_by_user:)
+  end
+
+  private
+
+  def version_class = PostVersion
+  def version_association = :post_versions
+  def record_key = :post
+
+  def snapshot_attributes
+    { title: @record.title,
+      url: @record.url,
+      thumbnail_base: @record.thumbnail_base,
+      tags: @record.snapshot_tag_names.join(' '),
+      parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
+      original_created_from: @record.original_created_from,
+      original_created_before: @record.original_created_before }
+  end
+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/tag_version_recorder.rb

@@ -0,0 +1,22 @@
+class TagVersionRecorder < VersionRecorder
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
+  end
+
+  def initialize tag:, event_type:, created_by_user:
+    super(record: tag, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = TagVersion
+  def version_association = :tag_versions
+  def record_key = :tag
+
+  def snapshot_attributes
+    { name: @record.name,
+      category: @record.category,
+      aliases: @record.snapshot_aliases.join(' '),
+      parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
+  end
+end

backend/app/services/tag_versioning.rb

@@ -0,0 +1,38 @@
+class TagVersioning
+  def self.record! tag, event_type:, created_by_user:
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    else
+      TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    end
+  end
+
+  def self.ensure_snapshot! tag, created_by_user:
+    if tag.nico?
+      return if tag.nico_tag_versions.exists?
+
+      NicoTagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    else
+      return if tag.tag_versions.exists?
+
+      TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    end
+  end
+
+  def self.record_tag_snapshot! tag, created_by_user:
+    event_type =
+        if tag.nico?
+          tag.nico_tag_versions.exists? ? :update : :create
+        else
+          tag.tag_versions.exists? ? :update : :create
+        end
+
+    record!(tag, event_type:, created_by_user:)
+  end
+
+  def self.record_tag_snapshots! tags, created_by_user:
+    tags.each do |tag|
+      record_tag_snapshot!(tag, created_by_user:)
+    end
+  end
+end

backend/app/services/version_recorder.rb

@@ -0,0 +1,87 @@
+class VersionRecorder
+  EVENT_TYPES = ['create', 'update', 'discard', 'restore'].freeze
+
+  def initialize record:, event_type:, created_by_user:
+    @record = record
+    @event_type = event_type.to_s
+    @created_by_user = created_by_user
+
+    validate_event_type!
+  end
+
+  def record!
+    raise "#{ record_class.name } must be persisted" unless @record.persisted?
+
+    ApplicationRecord.transaction do
+      @record = record_class.unscoped.lock.find(@record.id)
+      latest = latest_version
+
+      validate_version_sequence!(latest)
+
+      attrs = snapshot_attributes
+
+      if @event_type == 'update' && latest && same_snapshot?(latest, attrs)
+        return latest
+      end
+
+      version = version_class.create!(
+          base_attributes(latest).merge(record_key => @record).merge(attrs))
+
+      update_record_version_no!(version.version_no)
+
+      version
+    end
+  end
+
+  private
+
+  def latest_version = versions.order(version_no: :desc).first
+
+  def versions = @record.public_send(version_association)
+
+  def base_attributes latest
+    { version_no: (latest&.version_no || 0) + 1,
+      event_type: @event_type,
+      created_at: Time.current,
+      created_by_user: @created_by_user }
+  end
+
+  def update_record_version_no! version_no
+    @record.update_columns(version_no:)
+    @record.version_no = version_no
+  end
+
+  def validate_version_sequence! latest
+    if !(latest) && @event_type != 'create'
+      raise "#{ version_class.name } first event must be create"
+    end
+
+    if @event_type == 'create' && latest
+      raise "#{ version_class.name } create event already exists"
+    end
+
+    return unless latest
+
+    if @record.version_no != latest.version_no
+      raise ("#{ record_class.name }##{ @record.id } version_no is #{ @record.version_no }, " +
+             "but latest #{ version_class.name } version_no is #{ latest.version_no }")
+    end
+  end
+
+  def same_snapshot? version, attrs
+    attrs.all? { |k, v| version.public_send(k) == v }
+  end
+
+  def validate_event_type!
+    return if EVENT_TYPES.include?(@event_type)
+
+    raise ArgumentError, "Invalid event_type: #{ @event_type }"
+  end
+
+  def version_class = raise NotImplementedError
+  def version_association = raise NotImplementedError
+  def record_key = raise NotImplementedError
+  def snapshot_attributes = raise NotImplementedError
+
+  def record_class = @record.class
+end

backend/app/services/wiki/commit.rb

@@ -0,0 +1,141 @@
+require 'digest'
+
+
+module Wiki
+  class Commit
+    class Conflict < StandardError
+      ;
+    end
+
+    def self.create_content! tag_name:, body:, created_by_user:, message: nil
+      normalised = normalise_body(body)
+
+      page = WikiPage.new(tag_name:,
+                          body: normalised,
+                          created_user: created_by_user,
+                          updated_user: created_by_user)
+
+      if normalised.blank?
+        page.errors.add(:body, :blank)
+        raise ActiveRecord::RecordInvalid, page
+      end
+
+      ActiveRecord::Base.transaction do
+        page.save!
+
+        new(page:, created_user: created_by_user).content!(
+            body: normalised,
+            message:,
+            base_revision_id: nil)
+
+        page
+      end
+    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 = self.class.normalise_body(body)
+      if normalised.blank?
+        @page.errors.add(:body, :blank)
+        raise ActiveRecord::RecordInvalid, @page
+      end
+
+      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
+
+        @page.update!(body: normalised)
+
+        WikiVersionRecorder.record!(
+            page: @page,
+            event_type: @page.wiki_versions.exists? ? :update : :create,
+            reason: message,
+            created_by_user: @created_user)
+
+        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) if rows.any?
+
+        rev
+      end
+    end
+
+    def redirect!(redirect_page:, message:, base_revision_id:) = raise '廃止しました．'
+
+    def self.normalise_body body
+      s = body.to_s
+      s.gsub!(/\r\n?/, "\n")
+      s.encode('UTF-8', invalid: :replace, undef: :replace, replace: '🖕')
+      s.gsub(/\n+$/, '')
+    end
+
+    private
+
+    def split_lines(body) = body.split("\n")
+
+    def upsert_lines! lines, line_shas
+      now = Time.current
+
+      id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+
+      missing_by_sha = { }
+
+      line_shas.each_with_index do |sha, i|
+        next if id_by_sha.key?(sha)
+        next if missing_by_sha.key?(sha)
+
+        missing_by_sha[sha] = {
+            sha256:     sha,
+            body:       lines[i],
+            created_at: now,
+            updated_at: now }
+      end
+
+      if missing_by_sha.any?
+        WikiLine.upsert_all(missing_by_sha.values)
+        id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
+      end
+
+      id_by_sha
+    end
+  end
+end

backend/app/services/wiki_version_recorder.rb

@@ -0,0 +1,21 @@
+class WikiVersionRecorder < VersionRecorder
+  def self.record! page:, event_type:, reason: nil, created_by_user:
+    new(page:, event_type:, reason:, created_by_user:).record!
+  end
+
+  def initialize page:, event_type:, reason: nil, created_by_user:
+    @reason = reason
+    super(record: page, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = WikiVersion
+  def version_association = :wiki_versions
+  def record_key = :wiki_page
+
+  def snapshot_attributes = {
+      title: @record.title,
+      body: @record.body,
+      reason: @reason }
+end

backend/app/services/youtube/api_client.rb

@@ -0,0 +1,73 @@
+require 'json'
+require 'net/http'
+require 'uri'
+
+
+module Youtube
+  class ApiClient
+    ENDPOINT = 'https://www.googleapis.com/youtube/v3'
+
+    def initialize api_key: ENV.fetch('YOUTUBE_API_KEY')
+      @api_key = api_key
+    end
+
+    def search_videos q:, published_after: nil, published_before: nil, page_token: nil
+      get_json('/search', {
+          part:           'snippet',
+          type:           'video',
+          q:,
+          order:          'date',
+          maxResults:     50,
+          regionCode:     'JP',
+          relevanceLanguage: 'ja',
+          publishedAfter: published_after&.iso8601,
+          publishedBefore: published_before&.iso8601,
+          pageToken:      page_token }.compact)
+    end
+
+    def videos ids
+      return { 'items' => [] } if ids.empty?
+
+      get_json('/videos', part: 'snippet,status,contentDetails', id: ids.join(','))
+    end
+
+    def playlist_items playlist_id:, page_token: nil
+      get_json('/playlistItems', {
+          part:       'snippet,contentDetails,status',
+          playlistId: playlist_id,
+          maxResults: 50,
+          pageToken:  page_token }.compact)
+    end
+
+    def channel id: nil, handle: nil
+      raise ArgumentError, 'id or handle is required' if id.present? == handle.present?
+
+      params = { part: 'snippet,contentDetails' }
+      params[:id] = id if id.present?
+      params[:forHandle] = handle if handle.present?
+
+      get_json('/channels', params)
+    end
+
+    private
+
+    def get_json path, params
+      uri = URI(ENDPOINT + path)
+      uri.query = URI.encode_www_form(params.merge(key: @api_key))
+
+      response = Net::HTTP.start(uri.host,
+                                 uri.port,
+                                 use_ssl: true,
+                                 open_timeout: 10,
+                                 read_timeout: 30) do |http|
+        http.get(uri)
+      end
+
+      unless response.is_a?(Net::HTTPSuccess)
+        raise "YouTube API error: #{ response.code } #{ response.body }"
+      end
+
+      JSON.parse(response.body)
+    end
+  end
+end

backend/app/services/youtube/sync.rb

@@ -0,0 +1,168 @@
+require 'open-uri'
+require 'set'
+require 'time'
+
+
+module Youtube
+  class Sync
+    def initialize client: ApiClient.new
+      @client = client
+    end
+
+    def sync!
+      video_ids = discover_video_ids
+      return if video_ids.empty?
+
+      video_ids.each_slice(50) do |ids|
+        @client.videos(ids).fetch('items', []).each do |item|
+          sync_video!(VideoItem.new(item))
+        end
+      end
+    end
+
+    private
+
+    def discover_video_ids
+      ids = Set.new
+
+      query_terms.each do |q|
+        response = @client.search_videos(q:, published_after: sync_since)
+
+        response.fetch('items', []).each do |item|
+          video_id = item.dig('id', 'videoId')
+          ids << video_id if video_id.present?
+        end
+      end
+
+      playlist_ids.each do |playlist_id|
+        each_playlist_item(playlist_id) do |item|
+          video_id = item.dig('contentDetails', 'videoId')
+          video_id ||= item.dig('snippet', 'resourceId', 'videoId')
+
+          ids << video_id if video_id.present?
+        end
+      end
+
+      ids.to_a
+    end
+
+    def sync_video! video
+      post = Post.where('url REGEXP ?', youtube_url_regexp(video.id)).first
+
+      original_created_from = video.published_at.change(sec: 0)
+      original_created_before = original_created_from + 1.minute
+
+      post_created = false
+      post_changed = false
+
+      if post
+        post.assign_attributes(title: video.title,
+                               original_created_from:,
+                               original_created_before:,
+                               thumbnail_base: video.thumbnail_url)
+
+        post_changed = post.changed?
+        post.save! if post_changed
+
+        attach_thumbnail_if_needed!(post, video.thumbnail_url)
+      else
+        post_created = true
+        post = Post.create!(
+            title: video.title,
+            url: video.url,
+            thumbnail_base: video.thumbnail_url,
+            uploaded_user_id: nil,
+            original_created_from:,
+            original_created_before:)
+
+        attach_thumbnail_if_needed!(post, video.thumbnail_url)
+
+        sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.youtube.id, Tag.video.id])
+      end
+
+      kept_tag_ids = post.tags.pluck(:id).to_set
+      desired_tag_ids = kept_tag_ids.to_a
+
+      deerjikist = Deerjikist.find_by(platform: :youtube, code: video.channel_id)
+      if deerjikist
+        desired_tag_ids.delete(Tag.no_deerjikist.id)
+        desired_tag_ids << deerjikist.tag_id
+      elsif post.tags.where(category: :deerjikist).none?
+        desired_tag_ids << Tag.no_deerjikist.id
+      end
+
+      desired_tag_ids.uniq!
+
+      sync_post_tags!(post, desired_tag_ids, current_tag_ids: kept_tag_ids)
+
+      if post_created
+        PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
+      elsif post_changed || kept_tag_ids != desired_tag_ids.to_set
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user: nil)
+        PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
+      end
+    end
+
+    def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
+      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      desired_tag_ids = desired_tag_ids.compact.to_set
+
+      to_add = desired_tag_ids - current_tag_ids
+      to_remove = current_tag_ids - desired_tag_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
+
+    def attach_thumbnail_if_needed! post, thumbnail_url
+      return if post.thumbnail.attached?
+      return if thumbnail_url.blank?
+
+      post.thumbnail.attach(
+          io:           URI.open(thumbnail_url),
+          filename:     File.basename(URI.parse(thumbnail_url).path),
+          content_type: 'image/jpeg')
+
+      post.resized_thumbnail!
+    end
+
+    def youtube_url_regexp id
+      escaped = Regexp.escape(id)
+      "(youtube\\.com/watch\\?v=#{ escaped }|youtu\\.be/#{ escaped })([^A-Za-z0-9_-]|$)"
+    end
+
+    def query_terms = ['ぼざろクリーチャーシリーズ', '伊地知ニジカ', '伊地知虹鹿']
+
+    def playlist_ids
+      ['PLrOch4zHkI5vu29b-f9umUQQ4tQkuWLPX',
+       'PLrOch4zHkI5vOK0RaytQq6PbucxQkkL0K',
+       'PLrOch4zHkI5tdwm9vSegiDQJOM-hgpcOC']
+    end
+
+    def sync_since = 14.days.ago
+
+    def each_playlist_item playlist_id
+      page_token = nil
+
+      loop do
+        response = @client.playlist_items(playlist_id:, page_token:)
+
+        response.fetch('items', []).each do |item|
+          yield item
+        end
+
+        page_token = response['nextPageToken']
+        break if page_token.blank?
+      end
+    end
+  end
+end

backend/app/services/youtube/video_item.rb

@@ -0,0 +1,32 @@
+require 'time'
+
+
+module Youtube
+  class VideoItem
+    attr_reader :id, :title, :channel_id, :published_at, :thumbnail_url, :raw_tags
+
+    def initialize item
+      snippet = item.fetch('snippet')
+
+      @id = item.fetch('id')
+      @title = snippet['title']
+      @channel_id = snippet['channelId']
+      @published_at = Time.iso8601(snippet['publishedAt'])
+      @thumbnail_url = pick_thumbnail(snippet['thumbnails'] || { })
+      @raw_tags = snippet['tags'] || []
+    end
+
+    def url = "https://www.youtube.com/watch?v=#{ @id }"
+
+    private
+
+    def pick_thumbnail thumbnails
+      ['maxres', 'standard', 'high', 'medium', 'default'].each do |key|
+        url = thumbnails.dig(key, 'url')
+        return url if url.present?
+      end
+
+      nil
+    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/environments/production.rb

@@ -18,8 +18,7 @@ Rails.application.configure do
   # Enable serving of images, stylesheets, and JavaScripts from an asset server.
   # config.asset_host = "http://assets.example.com"
 
-  # Store uploaded files on the local file system (see config/storage.yml for options).
-  config.active_storage.service = :local
+  config.active_storage.service = :r2
 
   # Assume all access to the app is happening through a SSL-terminating reverse proxy.
   config.assume_ssl = true

backend/config/environments/test.rb

@@ -50,4 +50,6 @@ Rails.application.configure do
 
   # Raise error when a before_action's only/except options reference missing actions.
   config.action_controller.raise_on_missing_callback_actions = true
+
+  Rails.application.routes.default_url_options[:host] = 'www.example.com'
 end

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

@@ -1,10 +1,30 @@
 Rails.application.routes.draw do
   resources :nico_tags, path: 'tags/nico', only: [:index, :update]
 
-  resources :tags do
+  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] do
     collection do
       get :autocomplete
-      get 'name/:name', action: :show_by_name
+      get :'with-depth', action: :with_depth
+      get :versions, to: 'tag_versions#index'
+
+      scope :name do
+        get ':name/deerjikists', action: :deerjikists_by_name
+        get ':name/materials', action: :materials_by_name
+        get ':name', action: :show_by_name
+      end
+    end
+
+    member do
+      put '', action: :update_all
+      patch '', action: :update
+
+      get :deerjikists
+      put :deerjikists, action: :update_deerjikists
     end
   end
 
@@ -30,10 +50,11 @@ Rails.application.routes.draw do
     end
   end
 
-  resources :posts do
+  resources :posts, only: [:index, :show, :create, :update] do
     collection do
       get :random
       get :changes
+      get :versions, to: 'post_versions#index'
     end
 
     member do
@@ -50,11 +71,24 @@ Rails.application.routes.draw do
     end
   end
 
-  resources :ip_addresses
-  resources :nico_tag_relations
-  resources :post_tags
-  resources :settings
-  resources :tag_aliases
-  resources :user_ips
-  resources :user_post_views
+  resources :deerjikists, only: [] do
+    collection do
+      scope ':platform/:code' do
+        get '', action: :show
+        put '', action: :update
+        delete '', action: :destroy
+      end
+    end
+  end
+
+  resources :theatres, only: [:show] do
+    member do
+      put :watching
+      patch :next_post
+    end
+
+    resources :comments, controller: :theatre_comments, only: [:index, :create]
+  end
+
+  resources :materials, only: [:index, :show, :create, :update, :destroy]
 end

backend/config/schedule.rb

@@ -1,12 +1,27 @@
 env :PATH, '/root/.rbenv/shims:/root/.rbenv/bin:/usr/local/bin:/usr/bin:/bin'
 
+set :path, '/var/www/btrc-hub/backend'
+set :environment, 'production'
 set :output, standard: '/var/log/btrc_hub_nico_sync.log',
              error:    '/var/log/btrc_hub_nico_sync_err.log'
 
-every 1.day, at: '3:00 pm' do
+job_type :rake,
+         'cd :path && set -a && . /etc/btrc-hub/backend.env && set +a && ' \
+         ':environment_variable=:environment bundle exec rake :task --silent :output'
+
+every 1.day, at: '11:00 am' do
   rake 'nico:sync', environment: 'production'
 end
 
 every 1.day, at: '0:00 am' do
   rake 'post_similarity:calc', environment: 'production'
+  rake 'tag_similarity:calc', environment: 'production'
+end
+
+every 1.day, at: '7:50 am' do
+  rake 'nico:export', environment: 'production'
+end
+
+every :hour do
+  rake 'post:sync', environment: 'production'
 end

backend/config/storage.yml

@@ -6,29 +6,11 @@ local:
   service: Disk
   root: <%= Rails.root.join("storage") %>
 
-# Use bin/rails credentials:edit to set the AWS secrets (as aws:access_key_id|secret_access_key)
-# amazon:
-#   service: S3
-#   access_key_id: <%= Rails.application.credentials.dig(:aws, :access_key_id) %>
-#   secret_access_key: <%= Rails.application.credentials.dig(:aws, :secret_access_key) %>
-#   region: us-east-1
-#   bucket: your_own_bucket-<%= Rails.env %>
-
-# Remember not to checkin your GCS keyfile to a repository
-# google:
-#   service: GCS
-#   project: your_project
-#   credentials: <%= Rails.root.join("path/to/gcs.keyfile") %>
-#   bucket: your_own_bucket-<%= Rails.env %>
-
-# Use bin/rails credentials:edit to set the Azure Storage secret (as azure_storage:storage_access_key)
-# microsoft:
-#   service: AzureStorage
-#   storage_account_name: your_account_name
-#   storage_access_key: <%= Rails.application.credentials.dig(:azure_storage, :storage_access_key) %>
-#   container: your_container_name-<%= Rails.env %>
-
-# mirror:
-#   service: Mirror
-#   primary: local
-#   mirrors: [ amazon, google, microsoft ]
+r2:
+  service: S3
+  endpoint: <%= ENV['R2_ENDPOINT'] %>
+  access_key_id: <%= ENV['R2_ACCESS_KEY_ID'] %>
+  secret_access_key: <%= ENV['R2_SECRET_ACCESS_KEY'] %>
+  bucket: <%= ENV['R2_BUCKET'] %>
+  region: auto
+  request_checksum_calculation: when_required

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 +1,5 @@
+class AddUniqueIndexToIpAddresses < ActiveRecord::Migration[8.0]
+  def change
+    add_index :ip_addresses, :ip_address, unique: true, name: 'index_ip_addresses_on_ip_address'
+  end
+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/migrate/20260303122700_create_deerjikists.rb

@@ -0,0 +1,10 @@
+class CreateDeerjikists < ActiveRecord::Migration[8.0]
+  def change
+    create_table :deerjikists, primary_key: [:platform, :code] do |t|
+      t.string :platform, null: false, limit: 16
+      t.string :code, null: false
+      t.references :tag, null: false
+      t.timestamps
+    end
+  end
+end

backend/db/migrate/20260309123200_create_tag_name_sanitisation_rules.rb

@@ -0,0 +1,31 @@
+class CreateTagNameSanitisationRules < ActiveRecord::Migration[8.0]
+  def up
+    create_table :tag_name_sanitisation_rules, id: :integer, primary_key: :priority do |t|
+      t.string :source_pattern, null: false
+      t.string :replacement, null: false
+      t.timestamps
+      t.datetime :discarded_at
+      t.index :source_pattern, unique: true
+      t.index :discarded_at
+    end
+
+    now = ActiveRecord::Base.connection.quote(Time.current)
+    execute <<~SQL
+      INSERT INTO
+        tag_name_sanitisation_rules(priority, source_pattern, replacement, created_at, updated_at)
+      VALUES
+        (10, '\\\\*',           '_',         #{ now }, #{ now })
+      , (20, '\\\\?',           '_',         #{ now }, #{ now })
+      , (25, '\\\\/',           '_',         #{ now }, #{ now })
+      , (30, '_+',              '_',         #{ now }, #{ now })
+      , (40, '_$',              '',          #{ now }, #{ now })
+      , (45, '^([^:]+\\\\:)?_', '\\\\1',     #{ now }, #{ now })
+      , (50, '^([^:]+\\\\:)?$', '\\\\1null', #{ now }, #{ now })
+      ;
+    SQL
+  end
+
+  def down
+    drop_table :tag_name_sanitisation_rules
+  end
+end