#41 ウィニング・ラン修正

Reviewed-on: #365
Co-authored-by: miteruzo <miteruzo@naver.com>
Co-committed-by: miteruzo <miteruzo@naver.com>

.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 +1,234 @@
+# 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 test
+npm run test:run
+npm run preview
+```
+
+`npm run build` runs `tsc -b && vite build`, then `postbuild` runs
+`node scripts/generate-sitemap.js`.
+
+`npm run test` runs Vitest in watch mode. Use `npm run test:run` for a non-watch frontend test run.
+
+## 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: never put a line break immediately before `)`.
+- Ruby: do not use `%w` or `%i`.
+- Ruby hashes are not blocks; keep `}` on the same line as the final pair.
+- Ruby hashes keep the first pair on the same line as `{` unless line length
+  requires a break.
+- Ruby blocks use separate `{ ... }` rules from hashes, with 2-space body
+  indentation.
+- For arrays, never put whitespace or a line break immediately before `]`.
+- Keep the first element on the same line as `[` by default.
+- If an array would exceed the line limit, break after `[` and indent
+  elements by 4 spaces.
+- TypeScript and Python: use GNU-style spacing before parentheses where
+  syntactically valid.
+- Never write Ruby, TypeScript, or TSX lines longer than 99 characters.
+- Aim to keep Ruby, TypeScript, and TSX lines within 79 characters where practical.
+- TypeScript and TSX use 4-space logical indentation.
+- In TypeScript and TSX only, replace every leading run of 8 spaces with a tab.
+- Tabs are only for leading indentation, never for spaces after non-space text.
+- Do not add production dependencies without explicit approval.
+- Do not create, modify, or run tests unless the user explicitly asks for
+  test work. When the user asks for tests, keep working and rerun them until
+  they pass or the remaining failure is clearly blocked.
+
+## 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` only when the user explicitly asks for tests.
+- 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.
+- Be sensitive to N+1 queries; avoid introducing them and proactively fix
+  existing N+1 issues in the code path being edited.
+- 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.
+
+### Frontend TSX style
+
+- Preserve the local TSX formatting style.
+- Do not normalize TSX to common Prettier-style React formatting unless
+  explicitly asked.
+- Prefer `const` arrow functions for TypeScript/TSX component and helper declarations.
+- Put two blank lines before and after top-level `const` function
+  declarations, unless imports, exports, or file boundaries make that awkward.
+- In TSX, indent with 4-space logical indentation.
+- A leading tab is exactly equivalent to 8 leading spaces.
+- Keep a tag's closing marker on the same line as the final prop when the tag
+  spans multiple lines.
+- Do not put `/>` or `>` on its own line unless the existing surrounding code
+  does so.
+- Keep JSX closing parentheses in the existing compact style, for example
+  `</div>)` rather than moving `)` onto a separate line.
+- Do not add braces around `if`, `else`, or `for` bodies when the body is a
+  single physical line.
+- Always add braces around `if`, `else`, or `for` bodies when the body spans
+  two or more physical lines, even if it is one statement.
+
+Preferred:
+
+```tsx
+const PostFormTagsArea: FC<Props> = ({ tags, setTags, errors, ...rest }) => {
+  return (
+      <TextArea
+	  {...rest}
+	  ref={ref}
+	  value={tags}
+	  invalid={errors && errors.length > 0}
+	  onChange={ev => setTags (ev.target.value)}/>)
+}
+```
+
+Avoid:
+
+```tsx
+function PostFormTagsArea ({ tags, setTags }: Props) {
+  return (
+    <TextArea
+      value={tags}
+      onChange={ev => setTags (ev.target.value)}
+    />
+  )
+}
+```
+
+## 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 only non-test verification commands that
+  apply, such as `npm run build` and `npm run lint`. Run `npm run test:run`
+  only when the user explicitly asks for tests.
+- If backend code changes, do not run RSpec unless the user explicitly asks
+  for tests.
+- 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 non-test 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 +1,219 @@
+# 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.
+
+Do not create, modify, or run tests unless the user explicitly asks for test
+work. When the user asks for tests, keep working and rerun them until they
+pass or the remaining failure is clearly blocked.
+
+## 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.
+- Never put a line break immediately before `)` in Ruby.
+- Do not use `%w` or `%i` in new Ruby code.
+- Never write a Ruby line longer than 99 characters.
+- Aim to keep Ruby lines within 79 characters where practical.
+- For small Ruby method definitions that take keyword arguments, match the
+  local no-parentheses style when nearby code uses it.
+- Treat Ruby hash `{ ... }` style and Ruby block `{ ... }` style as separate
+  rules.
+- Do not format Ruby hashes like Ruby blocks.
+- For Ruby hashes, keep the closing `}` on the same line as the final pair.
+- Keep the first pair on the same line as `{` by default.
+- If the hash would exceed the line limit, break after `{` and indent pairs
+  by 4 spaces.
+- Put one logical pair per line when the expression would otherwise become
+  dense.
+- For Ruby arrays, never put whitespace or a line break immediately before `]`.
+- Keep the first element on the same line as `[` by default.
+- If an array would exceed the line limit, break after `[` and indent
+  elements by 4 spaces.
+- For Ruby blocks, use 2-space indentation for the block body.
+- 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 only when
+  the user explicitly asks for tests.
+
+## 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 only when the user
+  explicitly asks for tests, 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. Cover conflicts in request specs only when the user
+  explicitly asks for tests.
+
+## 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.
+- For diagnostic or internal helper JSON, prefer a deliberately light response
+  shape over full representation classes when callers only need identifiers,
+  labels, URLs, or weights.
+
+## Active Record performance
+
+- When a controller action serializes nested associations, preload the
+  associations it will touch instead of allowing N+1 queries.
+- Be sensitive to N+1 queries in all backend work.
+- Avoid introducing N+1 queries, and proactively fix existing N+1 issues when
+  you find them in the code path you are editing.
+- When an association may already be preloaded, prefer loaded-association
+  checks that reuse the preloaded data without losing the efficient database
+  path.
+
+## 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"
@@ -63,3 +63,11 @@ gem 'diff-lcs'
 gem 'dotenv-rails'
 
 gem 'whenever', require: false
+
+gem 'discard'
+
+gem "rspec-rails", "~> 8.0", :groups => [:development, :test]
+
+gem 'aws-sdk-s3', require: false
+
+gem 'rails-i18n', '~> 8.0.0'

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)
@@ -90,6 +109,8 @@ GEM
     crass (1.0.6)
     date (3.4.1)
     diff-lcs (1.6.2)
+    discard (1.4.0)
+      activerecord (>= 4.2, < 9.0)
     dotenv (3.1.8)
     dotenv-rails (3.1.8)
       dotenv (= 3.1.8)
@@ -97,6 +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)
@@ -150,6 +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
@@ -279,6 +306,9 @@ GEM
     rails-html-sanitizer (1.6.2)
       loofah (~> 2.21)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
+    rails-i18n (8.0.2)
+      i18n (>= 0.7, < 2)
+      railties (>= 8.0.0, < 9)
     railties (8.0.2)
       actionpack (= 8.0.2)
       activesupport (= 8.0.2)
@@ -296,6 +326,23 @@ 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)
@@ -417,10 +464,13 @@ 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
@@ -430,6 +480,8 @@ DEPENDENCIES
   puma (>= 5.0)
   rack-cors
   rails (~> 8.0.2)
+  rails-i18n (~> 8.0.0)
+  rspec-rails (~> 8.0)
   rubocop-rails-omakase
   sprockets-rails
   sqlite3 (>= 2.1)

backend/app/controllers/application_controller.rb

@@ -1,14 +1,88 @@
 class ApplicationController < ActionController::API
-  before_action :authenticate_user
+  rescue_from ActiveRecord::RecordInvalid, with: :render_record_invalid
+  rescue_from ActiveRecord::RecordNotUnique, with: :render_record_not_unique
 
-  def current_user
-    @current_user
-  end
+  before_action :reject_banned_ip_address!
+  before_action :authenticate_user
+  before_action :reject_banned_user!
+
+  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 render_bad_request message = 'リクエストが不正です．'
+    render json: { type: 'bad_request',
+                   message:,
+                   errors: { },
+                   base_errors: [message] },
+           status: :bad_request
+  end
+
+  def render_unprocessable_entity message = '入力を確認してください．', field: nil
+    render_validation_error(fields: field ? { field => [message] } : { },
+                            base: field ? [] : [message])
+  end
+
+  def render_record_invalid error
+    render_validation_error error.record
+  end
+
+  def render_record_not_unique _error = nil
+    render_validation_error base: ['すでに存在してゐます．']
+  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
+
+  def render_validation_error record = nil, fields: { }, base: [], status: :unprocessable_entity
+    errors = { }
+
+    if record
+      record.errors.each do |error|
+        errors[error.attribute] ||= []
+        errors[error.attribute] << error.message
+      end
+    end
+
+    fields.each do |attr, messages|
+      errors[attr.to_sym] ||= []
+      errors[attr.to_sym].concat(Array(messages))
+    end
+
+    base_errors = Array(base) + Array(errors.delete(:base))
+
+    render json: { type: 'validation_error',
+                   message: '入力内容を確認してください．',
+                   errors:,
+                   base_errors: },
+           status:
+  end
 end

backend/app/controllers/deerjikists_controller.rb

@@ -0,0 +1,51 @@
+class DeerjikistsController < ApplicationController
+  def show
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    return render_bad_request('platform は必須です．') if platform.blank?
+    return render_bad_request('code は必須です．') if 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 render_bad_request('platform は必須です．') if platform.blank?
+    return render_bad_request('code は必須です．') if code.blank?
+    return render_bad_request('tag_id が不正です．') if 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 render_bad_request('platform は必須です．') if platform.blank?
+    return render_bad_request('code は必須です．') if code.blank?
+
+    Deerjikist.find([platform, code]).destroy!
+
+    head :no_content
+  end
+end

backend/app/controllers/gekanator_games_controller.rb

@@ -0,0 +1,140 @@
+class GekanatorGamesController < ApplicationController
+  def create
+    return head :not_found unless current_user&.admin?
+
+    guessed_post_id = params.require(:guessed_post_id)
+    correct_post_id = params[:correct_post_id].presence
+    answers = params.require(:answers).as_json
+
+    game = GekanatorGame.new(
+        user: current_user,
+        guessed_post_id:,
+        correct_post_id:,
+        won: correct_post_id.present? && guessed_post_id.to_i == correct_post_id.to_i,
+        question_count: answers.length,
+        answers:)
+
+    if game.save
+      render json: { id: game.id }, status: :created
+    else
+      render json: { errors: game.errors.full_messages }, status: :unprocessable_entity
+    end
+  end
+
+  def extra_questions
+    return head :not_found unless current_user&.admin?
+
+    game = GekanatorGame.find_by(id: params[:id])
+    return head :not_found unless game
+
+    questions =
+        GekanatorQuestion
+        .accepted
+        .includes(:gekanator_question_examples)
+        .where(kind: 'post_similarity', source: 'user_suggested')
+        .to_a
+
+    selected = weighted_sample_questions(
+        questions,
+        post_id: game.correct_post_id,
+        limit: 2)
+
+    render json: {
+      questions: selected.map { |question| extra_question_json(question) }
+    }
+  end
+
+  def extra_question_answers
+    return head :not_found unless current_user&.admin?
+
+    game = GekanatorGame.find_by(id: params[:id])
+    return head :not_found unless game
+
+    answer_params = params.require(:answers)
+    if !answer_params.is_a?(Array)
+      return render_validation_error fields: { answers: ['配列で指定してください．'] }
+    end
+
+    answers = answer_params.map { |answer|
+      {
+        question_id: answer.require(:question_id).to_i,
+        answer: answer.require(:answer)
+      }
+    }
+    questions = GekanatorQuestion.where(id: answers.map { _1[:question_id] })
+    question_by_id = questions.index_by(&:id)
+    if questions.length != answers.length
+      return render_validation_error fields: { answers: ['質問が見つかりません．'] }
+    end
+    if questions.any? { |question| question.status != 'accepted' || question.kind != 'post_similarity' }
+      return render_validation_error fields: { answers: ['質問が不正です．'] }
+    end
+
+    ActiveRecord::Base.transaction do
+      answers.each do |item|
+        question = question_by_id[item[:question_id]]
+        example =
+            GekanatorQuestionExample.find_or_initialize_by(
+                gekanator_question: question,
+                post: game.correct_post,
+                user: current_user)
+        example.record_answer!(
+            answer: item[:answer],
+            source: 'post_game_extra',
+            gekanator_game: game)
+        example.save!
+      end
+    end
+
+    render json: { count: answers.length }, status: :created
+  end
+
+  private
+
+  def extra_question_json question
+    {
+      id: question.id,
+      text: question.text,
+      source: question.source,
+      priority_weight: question.priority_weight
+    }
+  end
+
+  def weighted_sample_questions questions, post_id:, limit:
+    remaining = questions.uniq(&:id)
+    selected = []
+
+    while selected.length < limit && remaining.any?
+      weighted =
+          remaining.map { |question|
+            [question, selection_weight_for(question, post_id: post_id)]
+          }
+      total_weight = weighted.sum { |_question, weight| weight }
+      break if total_weight <= 0
+
+      target = rand * total_weight
+      cumulative = 0.0
+      chosen =
+          weighted.find do |_question, weight|
+            cumulative += weight
+            cumulative >= target
+          end&.first || weighted.first.first
+
+      selected << chosen
+      remaining.reject! { |question| question.id == chosen.id }
+    end
+
+    selected
+  end
+
+  def selection_weight_for question, post_id:
+    sample_count =
+        question.gekanator_question_examples.sum { |example|
+          next 0 unless example.post_id == post_id
+
+          example.sample_count.presence || 1
+        }
+
+    question.priority_weight.to_f / (1.0 + sample_count * 0.15)
+  end
+end

backend/app/controllers/gekanator_posts_controller.rb

@@ -0,0 +1,46 @@
+class GekanatorPostsController < ApplicationController
+  def index
+    return head :not_found unless current_user&.admin?
+
+    posts =
+        Post
+        .preload(tags: :tag_name)
+        .with_attached_thumbnail
+        .order(Arel.sql(
+            'COALESCE(posts.original_created_before - INTERVAL 1 MINUTE, ' \
+            'posts.original_created_from, posts.created_at) DESC, posts.id DESC'))
+
+    render json: { posts: posts.map { |post| post_json(post) } }
+  end
+
+  private
+
+  def post_json post
+    {
+      id: post.id,
+      url: post.url,
+      title: post.title,
+      thumbnail: thumbnail_url(post),
+      thumbnail_base: post.thumbnail_base,
+      original_created_from: post.original_created_from,
+      original_created_before: post.original_created_before,
+      tags: post.tags.map { |tag| tag_json(tag) }
+    }
+  end
+
+  def tag_json tag
+    {
+      id: tag.id,
+      name: tag.name,
+      category: tag.category
+    }
+  end
+
+  def thumbnail_url post
+    return nil unless post.thumbnail.attached?
+
+    rails_storage_proxy_url(post.thumbnail, only_path: false)
+  rescue
+    nil
+  end
+end

backend/app/controllers/gekanator_question_suggestions_controller.rb

@@ -0,0 +1,53 @@
+class GekanatorQuestionSuggestionsController < ApplicationController
+  def create
+    return head :not_found unless current_user&.admin?
+
+    game = GekanatorGame.find_by(id: params.require(:gekanator_game_id))
+    return head :not_found unless game
+
+    suggestion = GekanatorQuestionSuggestion.new(
+        gekanator_game: game,
+        user: current_user,
+        question_text: params.require(:question_text),
+        answer: params.require(:answer))
+
+    if suggestion.valid?
+      ActiveRecord::Base.transaction do
+        suggestion.save!
+        Gekanator::QuestionSuggestionPromoter.call(
+            suggestion: suggestion,
+            user: current_user)
+      end
+
+      render json: {
+        id: suggestion.id,
+        count: game.question_suggestions.count
+      }, status: :created
+    else
+      render_validation_error suggestion
+    end
+  end
+
+  def ai_convert
+    return head :not_found unless current_user&.admin?
+
+    suggestion = GekanatorQuestionSuggestion.find_by(id: params[:id])
+    return head :not_found unless suggestion
+    if Gekanator::AiRunBudget.exceeded_after_next_run?
+      suggestion.gekanator_ai_runs.create!(
+          model: 'budget_guard',
+          status: 'blocked_budget',
+          input_tokens: 0,
+          output_tokens: 0,
+          estimated_cost_jpy: 0)
+      return head :payment_required
+    end
+
+    Gekanator::QuestionSuggestionAiConverter.call(
+        suggestion: suggestion,
+        user: current_user)
+    head :no_content
+  rescue NotImplementedError
+    head :not_implemented
+  end
+end

backend/app/controllers/gekanator_questions_controller.rb

@@ -0,0 +1,100 @@
+class GekanatorQuestionsController < ApplicationController
+  def index
+    return head :not_found unless current_user&.admin?
+
+    questions =
+        GekanatorQuestion
+        .accepted
+        .includes(:gekanator_question_examples)
+        .order(priority_weight: :desc, id: :asc)
+
+    render json: {
+      questions: questions.map { |question| question_json(question) }
+    }
+  end
+
+  private
+
+  def question_json question
+    condition = condition_json(question.condition).deep_symbolize_keys
+    json = {
+      id: question_id_for(question, condition),
+      text: question_text_for(question, condition),
+      kind: question.kind,
+      condition: condition,
+      source: question.source,
+      priority_weight: question.priority_weight
+    }
+    if question.kind == 'post_similarity'
+      json[:example_answers] = example_answers_json(question)
+    end
+    json
+  end
+
+  def question_id_for question, condition
+    case condition[:type]
+    when 'tag'
+      "tag:#{ condition[:key] }"
+    when 'source'
+      "source:#{ condition[:host] }"
+    when 'original-year'
+      "original-year:#{ condition[:year] }"
+    when 'original-month'
+      "original-month:#{ condition[:month] }"
+    when 'original-month-day'
+      "original-month-day:#{ condition[:monthDay] || condition[:month_day] }"
+    when 'title-length-at-least'
+      "title:length-at-least:#{ condition[:length] }"
+    when 'title-length-greater-than'
+      "title:length-at-least:#{ condition[:length].to_i + 1 }"
+    when 'title-has-ascii'
+      'title:ascii'
+    when 'post-similarity'
+      "post-similarity:#{ question.id }"
+    else
+      "catalog:#{ question.id }"
+    end
+  end
+
+  def condition_json condition
+    json = condition.deep_dup.as_json
+
+    if json['type'] == 'original-month-day' && json['monthDay'].blank?
+      json['monthDay'] = json.delete('month_day')
+    end
+
+    if json['type'] == 'title-length-greater-than'
+      json['type'] = 'title-length-at-least'
+      json['length'] = json['length'].to_i + 1
+    end
+
+    json
+  end
+
+  def question_text_for question, condition
+    return question.text unless question.kind == 'title'
+
+    case condition[:type]
+    when 'title-length-at-least'
+      "タイトルは #{ condition[:length] } 文字以上?"
+    else
+      question.text
+    end
+  end
+
+  def example_answers_json question
+    question
+        .gekanator_question_examples
+        .group_by(&:post_id)
+        .transform_values { |examples| aggregate_answer(examples) }
+  end
+
+  def aggregate_answer examples
+    examples
+        .group_by(&:answer)
+        .map { |answer, grouped| [answer, grouped.sum(&:weight), grouped.max_by(&:updated_at)&.updated_at] }
+        .sort_by { |(_answer, weight, updated_at)| [-weight, -(updated_at&.to_f || 0)] }
+        .first
+        &.first
+  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 +1,109 @@
+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 render_unprocessable_entity('タグは必須です．', field: :tag) if tag_name_raw.blank?
+    if file.blank? && url.blank?
+      return render_validation_error fields: { file: ['ファイルまたは URL は必須です．'],
+                                               url: ['ファイルまたは URL は必須です．'] }
+    end
+
+    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_validation_error material
+    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 render_unprocessable_entity('タグは必須です．', field: :tag) if tag_name_raw.blank?
+    if file.blank? && url.blank?
+      return render_validation_error fields: { file: ['ファイルまたは URL は必須です．'],
+                                               url: ['ファイルまたは URL は必須です．'] }
+    end
+
+    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_validation_error material
+    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

@@ -1,41 +1,114 @@
 class NicoTagsController < ApplicationController
   def index
-    limit = (params[:limit] || 20).to_i
-    cursor = params[:cursor].presence
+    name = params[:name].presence
+    linked_tag = params[:linked_tag].presence
+    link_status = params[:link_status].presence
+    order = params[:order].to_s.split(':', 2).map(&:strip)
+    order[0] = 'updated_at' unless order[0].in?(['name', 'created_at', 'updated_at'])
+    unless order[1].in?(['asc', 'desc'])
+      order[1] = order[0] == 'name' ? 'asc' : 'desc'
+    end
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
 
-    q = Tag.nico_tags.includes(:linked_tags).order(updated_at: :desc)
-    q = q.where('tags.updated_at < ?', Time.iso8601(cursor)) if cursor
+    page = 1 if page < 1
+    limit = 1 if limit < 1
 
-    tags = q.limit(limit + 1)
+    post_tag_max_sql =
+        PostTag
+        .select('tag_id, MAX(created_at) AS max_created_at')
+        .group('tag_id')
+        .to_sql
 
-    next_cursor = nil
-    if tags.size > limit
-      next_cursor = tags.last.updated_at.iso8601(6)
-      tags = tags.first(limit)
+    q = Tag.nico_tags
+           .joins(:tag_name)
+           .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
+                  'ON post_tag_max.tag_id = tags.id')
+           .includes(:tag_name, tag_name: :wiki_page, linked_tags: { tag_name: :wiki_page })
+    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
+    if linked_tag
+      linked_tag_ids =
+        Tag
+        .joins(:tag_name)
+        .where('tag_names.name LIKE ?', "%#{ linked_tag }%")
+        .pluck(:id)
+      linked_nico_tag_ids = NicoTagRelation.where(tag_id: linked_tag_ids).pluck(:nico_tag_id)
+      q = q.where(id: linked_nico_tag_ids)
+    end
+    if link_status.in?(['linked', 'unlinked'])
+      exists_sql =
+          'EXISTS (SELECT 1 FROM nico_tag_relations ' \
+          'WHERE nico_tag_relations.nico_tag_id = tags.id)'
+      q = link_status == 'linked' ? q.where(exists_sql) : q.where("NOT #{ exists_sql }")
     end
 
+    count = q.count
+    sort_sql =
+        case order[0]
+        when 'name'
+          'tag_names.name'
+        when 'updated_at'
+          'post_tag_max.max_created_at'
+        else
+          "tags.#{ order[0] }"
+        end
+    tags = q.reselect('tags.*',
+                      Arel.sql('post_tag_max.max_created_at AS recent_post_tag_created_at'))
+            .order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
+            .limit(limit)
+            .offset((page - 1) * limit)
+            .to_a
+
     render json: { tags: tags.map { |tag|
-      tag.as_json(include: :linked_tags)
-    }, next_cursor: }
+      TagRepr.base(tag).merge(
+          recent_post_tag_created_at: tag.recent_post_tag_created_at,
+          linked_tags: tag.linked_tags.map { |lt| TagRepr.base(lt) })
+    }, count: }
   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 render_bad_request('ニコニコ・タグを指定してください．') 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 = nil
 
-    tag.linked_tags = linked_tags
-    tag.updated_at = Time.now
-    tag.save!
+    ApplicationRecord.transaction do
+      linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
+                                                          with_no_deerjikist: false)
+      if linked_tags.any? { |t| t.nico? }
+        raise Tag::NicoTagNormalisationError
+      end
 
-    render json: tag.linked_tags, status: :ok
+      TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
+
+      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
+  rescue Tag::NicoTagNormalisationError
+    render_validation_error fields: { tags: ['ニコニコ・タグ同士は連携できません．'] }
+  rescue ActiveRecord::RecordInvalid => e
+    render_nico_tag_form_record_invalid e.record
+  end
+
+  private
+
+  def render_nico_tag_form_record_invalid record
+    if record.is_a?(TagName) || record.is_a?(Tag)
+      render_validation_error fields: { tags: record.errors.full_messages.map { |message|
+        "タグ名 “#{ record.name }”: #{ message }"
+      } }
+    else
+      render_validation_error record
+    end
   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

@@ -1,29 +1,90 @@
-require 'open-uri'
-require 'nokogiri'
-
-
 class PostsController < ApplicationController
-  # GET /posts
+  Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
+
   def index
-    limit = params[:limit].presence&.to_i
-    cursor = params[:cursor].presence
+    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
 
-    created_at = ('COALESCE(posts.original_created_before - INTERVAL 1 SECOND,' +
-                  'posts.original_created_from,' +
-                  'posts.created_at)')
-    q = filtered_posts.order(Arel.sql("#{ created_at } DESC"))
-    q = q.where("#{ created_at } < ?", Time.iso8601(cursor)) if cursor
-
-    posts = limit ? q.limit(limit + 1) : q
-
-    next_cursor = nil
-    if limit && posts.size > limit
-      next_cursor = posts.last.created_at.iso8601(6)
-      posts = posts.first(limit)
+    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
+
+    page = 1 if page < 1
+    limit = 1 if limit < 1
+
+    offset = (page - 1) * limit
+
+    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
+        .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(:uploaded_user, :parents, :children,
+                 tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+        .with_attached_thumbnail
+
+    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)
@@ -31,58 +92,83 @@ class PostsController < ApplicationController
               nil
             end
       end
-    }, 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(:uploaded_user, :parents, :children,
+                                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                         .with_attached_thumbnail
+                         .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(:uploaded_user, :parents, :children,
+                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+        .with_attached_thumbnail
+        .find_by(id: params[:id])
     return head :not_found unless post
 
-    viewed = current_user&.viewed?(post) || false
+    parent_posts = post.parents.with_attached_thumbnail.order(:id).to_a
+    child_posts = post.children.with_attached_thumbnail.order(:id).to_a
+    sibling_posts = sibling_posts_by_parent(parent_posts.map(&:id))
+    related = post.related(limit: 20).to_a
 
-    render json: (post
-                  .as_json(include: { tags: { only: [:id, :name, :category, :post_count] } })
-                  .merge(related: post.related(limit: 20), viewed:))
+    render json: PostRepr.detail(post, current_user,
+                                 parent_posts:,
+                                 child_posts:,
+                                 sibling_posts:,
+                                 related:)
+                         .merge(tags: build_tag_tree_for(post.tags))
   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.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)
+
+      sync_parent_posts!(post, parent_post_ids)
+
       post.resized_thumbnail!
-      post.tags = Tag.normalise_tags(tag_names)
-      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
+
+      PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
     end
+
+    post.reload
+    render json: PostRepr.base(post), status: :created
+  rescue Tag::NicoTagNormalisationError
+    render_validation_error fields: { tags: 'ニコニコ・タグは直接指定できません．' }
+  rescue ArgumentError => e
+    render_validation_error fields: { parent_post_ids: [e.message] }
+  rescue ActiveRecord::RecordInvalid => e
+    render_post_form_record_invalid e.record
   end
 
   def viewed
@@ -99,47 +185,500 @@ 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 render_bad_request('force と merge は同時に指定できません．') if force && merge
+
+    base_version_no = parse_base_version_no
+    return render_bad_request('base_version_no は必須です．') 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)
-    tags = post.tags.where(category: 'nico').to_a + Tag.normalise_tags(tag_names)
-    if post.update(title:, tags:, original_created_from:, original_created_before:)
-      render json: post.as_json(include: { tags: { only: [:id, :name, :category, :post_count] } }),
-             status: :ok
-    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
+
+    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
+    render_validation_error fields: { tags: ['ニコニコ・タグは直接指定できません．'] }
+  rescue ArgumentError => e
+    render_validation_error fields: { parent_post_ids: [e.message] }
+  rescue ActiveRecord::RecordInvalid => e
+    render_post_form_record_invalid e.record
   end
 
-  # DELETE /posts/1
-  def destroy
+  def changes
+    id = params[:id].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
+
+    pts = PostTag.with_discarded
+    pts = pts.where(post_id: id) if id.present?
+    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:,
+          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:,
+            tag:,
+            user: pt.deleted_user && { id: pt.deleted_user.id, name: pt.deleted_user.name },
+            change_type: 'remove',
+            timestamp: pt.discarded_at)
+      end
+    end
+    events.sort_by!(&:timestamp)
+    events.reverse!
+
+    render json: { changes: (events.slice(offset, limit) || []).as_json, count: events.size }
   end
 
   private
 
   def filtered_posts
-    tag_names = params[:tags]&.split(' ')
+    tag_names = params[:tags].to_s.split
     match_type = params[:match]
-    tag_names.present? ? filter_posts_by_tags(tag_names, match_type) : Post.all
+    if tag_names.present?
+      filter_posts_by_tags(tag_names, match_type)
+    else
+      Post.all
+    end
   end
 
   def filter_posts_by_tags tag_names, match_type
-    posts = Post.joins(:tags)
+    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?
+    end
+
+    desired_ids = desired_tags.map(&:id).to_set
+    current_ids = post.tags.pluck(:id).to_set
+
+    to_add = desired_ids - current_ids
+    to_remove = current_ids - desired_ids
+
+    Tag.where(id: to_add).find_each do |tag|
+      begin
+        PostTag.create!(post:, tag:, created_user: current_user)
+      rescue ActiveRecord::RecordNotUnique
+        ;
+      end
+    end
+
+    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+      pt.discard_by!(current_user)
+    end
+  end
+
+  def build_tag_tree_for tags
+    tags = tags.to_a
+    tag_ids = tags.map(&:id)
+
+    implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
+
+    children_ids_by_parent = Hash.new { |h, k| h[k] = [] }
+    implications.each do |imp|
+      children_ids_by_parent[imp.parent_tag_id] << imp.tag_id
+    end
+
+    child_ids = children_ids_by_parent.values.flatten.uniq
+
+    root_ids = tag_ids - child_ids
+
+    tags_by_id = tags.index_by(&:id)
+
+    memo = { }
+
+    build_node = -> tag_id, path do
+      tag = tags_by_id[tag_id]
+      return nil unless tag
+
+      if path.include?(tag_id)
+        return TagRepr.inline(tag).merge(children: [])
+      end
+
+      if memo.key?(tag_id)
+        return memo[tag_id]
+      end
+
+      new_path = path + [tag_id]
+      child_ids = children_ids_by_parent[tag_id] || []
+
+      children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
+
+      memo[tag_id] = TagRepr.inline(tag).merge(children:)
+    end
+
+    root_ids.filter_map { |id| build_node.call(id, []) }
+  end
+
+  def sibling_posts_by_parent parent_post_ids
+    return { } if parent_post_ids.blank?
+
+    implications =
+        PostImplication
+        .where(parent_post_id: parent_post_ids)
+        .includes(post: { thumbnail_attachment: :blob })
+        .order(:parent_post_id, :post_id)
+
+    implications.group_by(&:parent_post_id).transform_values { |items|
+      items.map(&:post)
+    }
+  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 :parent_post_ids, '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 :parent_post_ids,
+                      "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
+
+  def render_post_form_record_invalid record
+    if record.is_a?(TagName) || record.is_a?(Tag)
+      render_validation_error fields: { tags: record.errors.full_messages.map { |message|
+        "タグ名 “#{ record.name }”: #{ message }"
+      } }
+    else
+      render_validation_error record
+    end
   end
 end

backend/app/controllers/preview_controller.rb

@@ -4,7 +4,7 @@ class PreviewController < ApplicationController
     return head :unauthorized unless current_user
 
     url = params[:url]
-    return head :bad_request unless url.present?
+    return render_bad_request('URL は必須です．') unless url.present?
 
     unless url.start_with?(/http(s)?:\/\//)
       url = 'http://' + url
@@ -16,7 +16,7 @@ class PreviewController < ApplicationController
 
     render json: { title: title }
   rescue => e
-    render json: { error: e.message }, status: :bad_request
+    render_bad_request(e.message)
   end
 
   def thumbnail
@@ -25,7 +25,7 @@ class PreviewController < ApplicationController
     return head :unauthorized unless current_user
 
     url = params[:url]
-    return head :bad_request if url.blank?
+    return render_bad_request('URL は必須です．') if url.blank?
 
     unless url.start_with?(/http(s)?:\/\//)
       url = 'http://' + url
@@ -40,7 +40,11 @@ class PreviewController < ApplicationController
       File.delete(path) rescue nil
       send_file image.path, type: 'image/png', disposition: 'inline'
     else
-      render json: { error: 'Failed to generate thumbnail' }, status: :internal_server_error
+      render json: { type: 'internal_server_error',
+                     message: 'サムネールを生成できませんでした．',
+                     errors: { },
+                     base_errors: ['サムネールを生成できませんでした．'] },
+             status: :internal_server_error
     end
   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 +1,47 @@
+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 render_bad_request('parent_id は必須です．') if parent_id.blank?
+    return render_bad_request('child_id は必須です．') if child_id.blank?
+
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    return render_bad_request('ニコニコ・タグの階層は変更できません．') 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 render_bad_request('parent_id は必須です．') if parent_id.blank?
+    return render_bad_request('child_id は必須です．') if child_id.blank?
+
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    return render_bad_request('ニコニコ・タグの階層は変更できません．') 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 +1,460 @@
+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 render_bad_request('name は必須です．') 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 render_bad_request('name は必須です．') 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.with_index do |item, i|
+        platform = item[:platform]
+        code = normalise_deerjikist_code(platform, item[:code])
+        deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
+        deerjikist.tag = tag
+        render_deerjikist_form_record_invalid(deerjikist, i) unless deerjikist.save
+        raise ActiveRecord::Rollback if performed?
+      end
+    end
+
+    return if performed?
+
+    render json: DeerjikistRepr.many(tag.reload.deerjikists)
+  end
+
+  def materials_by_name
+    name = params[:name].to_s.strip
+    return render_bad_request('name は必須です．') 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 render_unprocessable_entity('名前は必須です．', field: :name) if name.blank?
+    return render_unprocessable_entity('カテゴリは必須です．', field: :category) if category.blank?
+
+    if name != tag.name &&
+        tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
+      return render_unprocessable_entity('システム・タグの名称は変更できません．', field: :name)
+    end
+
+    if tag.nico? || category == 'nico'
+      return render_unprocessable_entity('ニコタグは変更できません．', field: :category)
+    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_unprocessable_entity('ニコタグは変更できません．', field: :category)
+    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
+
+  def render_deerjikist_form_record_invalid deerjikist, index
+    fields = { }
+
+    deerjikist.errors.each do |error|
+      field =
+          case error.attribute
+          when :platform, :code
+            "deerjikists.#{ index }.#{ error.attribute }"
+          else
+            :deerjikists
+          end
+
+      fields[field] ||= []
+      fields[field] << error.full_message
+    end
+
+    render_validation_error fields:
   end
 end

backend/app/controllers/theatre_comments_controller.rb

@@ -0,0 +1,54 @@
+class TheatreCommentsController < ApplicationController
+  def index
+    limit = params[:limit].to_i
+    limit = 20 if limit <= 0
+
+    no_gt = params[:no_gt].to_i
+    no_gt = 0 if no_gt < 0
+
+    comments = TheatreComment
+               .where(theatre_id: params[:theatre_id])
+               .where('no > ?', no_gt)
+               .order(no: :desc)
+               .limit(limit)
+
+    render json: comments.map {
+      _1.as_json(include: { user: { only: [:id, :name] } })
+          .merge(content: _1.discarded? ? nil : _1.content, deleted: _1.discarded?)
+    }
+  end
+
+  def create
+    return head :unauthorized unless current_user
+
+    content = params[:content]
+    return render_unprocessable_entity('本文は必須です．', field: :content) 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
+
+  def destroy
+    return head :unauthorized unless current_user
+
+    theatre_id = params[:theatre_id].to_i
+    no = params[:id].to_i
+
+    comment = TheatreComment.find_by(theatre_id:, no:)
+    return head :not_found unless comment
+    return head :forbidden unless comment.user == current_user
+
+    comment.discard!
+
+    head :no_content
+  end
+end

backend/app/controllers/theatre_programmes_controller.rb

@@ -0,0 +1,22 @@
+class TheatreProgrammesController < ApplicationController
+  def index
+    limit = params[:limit].to_i
+    limit = 100 if limit <= 0
+
+    position_gt = params[:position_gt].to_i
+    position_gt = 0 if position_gt < 0
+
+    programmes = TheatreProgramme
+                 .where(theatre_id: params[:theatre_id])
+                 .where('position > ?', position_gt)
+                 .includes(:post)
+                 .order(position: :desc).limit(100)
+                 .limit(limit)
+
+    render json: programmes.map { |programme|
+      programme.as_json.merge(post: { id: programme.post.id,
+                                      title: programme.post.title,
+                                      url: programme.post.url })
+    }
+  end
+end

backend/app/controllers/theatre_skip_events_controller.rb

@@ -0,0 +1,22 @@
+class TheatreSkipEventsController < ApplicationController
+  def index
+    limit = params[:limit].to_i
+    limit = 50 if limit <= 0
+
+    events =
+        TheatreSkipEvent
+        .where(theatre_id: params[:theatre_id])
+        .includes(:post, tags: :tag_name)
+        .order(created_at: :desc)
+        .limit(limit)
+
+    render json: events.map { |event|
+      { id: event.id,
+        theatre_id: event.theatre_id,
+        post: { id: event.post.id, title: event.post.title, url: event.post.url },
+        tags: event.tags.map { |tag| { id: tag.id, name: tag.name } },
+        programme_position: event.programme_position,
+        created_at: event.created_at }
+    }
+  end
+end

backend/app/controllers/theatres_controller.rb

@@ -0,0 +1,159 @@
+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: theatre_info_json(theatre, host_flg:, post_id:, post_started_at:)
+  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
+
+    ApplicationRecord.transaction do
+      theatre.lock!
+      TheatrePostAdvancer.call(theatre:)
+    end
+
+    head :no_content
+  end
+
+  def skip_vote
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+    requested_post_id = params[:post_id].to_i
+    return head :unprocessable_entity if requested_post_id <= 0
+
+    skipped = false
+    conflicted = false
+
+    ApplicationRecord.transaction do
+      theatre.lock!
+      if theatre.current_post
+        TheatreWatchingUser.find_or_initialize_by(theatre:, user: current_user).tap {
+          _1.expires_at = 30.seconds.from_now
+        }.save!
+
+        if theatre.current_post_id != requested_post_id
+          conflicted = true
+          next
+        end
+
+        TheatreSkipVote.find_or_create_by!(theatre:, post_id: requested_post_id, user: current_user)
+
+        vote_status = skip_vote_status(theatre)
+        if vote_status[:votes_count] >= vote_status[:required_count]
+          TheatreSkipFinalizer.call(theatre:, user: current_user)
+          TheatrePostAdvancer.call(theatre:)
+          skipped = true
+        end
+      end
+    end
+
+    theatre.reload
+    return render json: theatre_info_json(theatre, skipped: false), status: :conflict if conflicted
+
+    render json: theatre_info_json(theatre, skipped:)
+  end
+
+  def unskip_vote
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+    requested_post_id = params[:post_id].to_i
+    return head :unprocessable_entity if requested_post_id <= 0
+
+    conflicted = false
+
+    theatre.with_lock do
+      if theatre.current_post
+        if theatre.current_post_id != requested_post_id
+          conflicted = true
+        else
+          TheatreSkipVote.where(theatre:, post_id: requested_post_id, user: current_user).delete_all
+        end
+      end
+    end
+
+    theatre.reload
+    return render json: theatre_info_json(theatre, skipped: false), status: :conflict if conflicted
+
+    render json: theatre_info_json(theatre, skipped: false)
+  end
+
+  def post_selection_weights
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    render json: TheatrePostSelector.new(theatre:).weight_json
+  end
+
+  private
+
+  def theatre_info_json(theatre, host_flg: nil, post_id: nil, post_started_at: nil, skipped: nil)
+    host_flg = theatre.host_user_id == current_user&.id if host_flg.nil?
+    post_id = theatre.current_post_id if post_id.nil?
+    post_started_at = theatre.current_post_started_at if post_started_at.nil?
+
+    json = { host_flg:,
+             post_id:,
+             post_started_at:,
+             post_elapsed_ms: post_started_at ? ((Time.current - post_started_at) * 1000).floor : nil,
+             watching_users: theatre.watching_users.as_json(only: [:id, :name]),
+             skip_vote: skip_vote_status(theatre) }
+    json[:skipped] = skipped unless skipped.nil?
+    json
+  end
+
+  def skip_vote_status(theatre)
+    watching_user_ids = theatre.watching_users.ids
+    watching_users_count = watching_user_ids.size
+    required_count = (watching_users_count / 2) + 1
+    post = theatre.current_post
+    votes =
+        if post
+          TheatreSkipVote.where(theatre:, post:, user_id: watching_user_ids)
+        else
+          TheatreSkipVote.none
+        end
+
+    { votes_count: post ? votes.count : 0,
+      required_count:,
+      watching_users_count:,
+      voted: post && current_user ? votes.exists?(user_id: current_user.id) : false }
+  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

@@ -1,20 +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
     user = User.find_by(inheritance_code: params[:code])
-    render json: if user
-                   { valid: true, user: user.slice(:id, :name, :inheritance_code, :role) }
-                 else
-                   { valid: false }
-                 end
+    return render json: { valid: false } unless user
+    return head :forbidden if user.banned?
+
+    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!
@@ -33,12 +42,21 @@ class UsersController < ApplicationController
     return head :unauthorized if user&.id != params[:id].to_i
 
     name = params[:name]
-    return head :bad_request if name.blank?
+    return render_unprocessable_entity('名前は必須です．', field: :name) 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
+      render_validation_error user
     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

@@ -1,35 +1,70 @@
 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?(id: params[:id])
+      head :no_content
+    else
+      head :not_found
+    end
+  end
+
+  def exists_by_title
+    title = params[:title].to_s.strip
+    if WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
+      head :no_content
+    else
+      head :not_found
+    end
   end
 
   def diff
     id = params[:id]
-    from = params[:from]
+    return render_bad_request('id は必須です．') 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 render_unprocessable_entity('差分を表示できない版です．')
+    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 ?+
@@ -39,97 +74,137 @@ 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 render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
+    return render_unprocessable_entity('本文は必須です．', field: :body) if 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 => e
+    render_validation_error e.record
+  rescue ActiveRecord::RecordNotUnique
+    render_record_not_unique
   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?
+    return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
+    return render_unprocessable_entity('本文は必須です．', field: :body) if 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/gekanator_ai_run.rb

@@ -0,0 +1,21 @@
+class GekanatorAiRun < ApplicationRecord
+  STATUSES = ['pending', 'running', 'succeeded', 'failed', 'blocked_budget'].freeze
+
+  belongs_to :gekanator_question_suggestion
+
+  validates :model, presence: true, length: { maximum: 255 }
+  validates :status, presence: true, inclusion: { in: STATUSES }
+  validates :input_tokens,
+            presence: true,
+            numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :output_tokens,
+            presence: true,
+            numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :estimated_cost_jpy,
+            presence: true,
+            numericality: { greater_than_or_equal_to: 0 }
+
+  scope :this_month, lambda {
+    where(created_at: Time.current.beginning_of_month..Time.current.end_of_month)
+  }
+end

backend/app/models/gekanator_game.rb

@@ -0,0 +1,15 @@
+class GekanatorGame < ApplicationRecord
+  belongs_to :user
+  belongs_to :guessed_post, class_name: 'Post'
+  belongs_to :correct_post, class_name: 'Post'
+  has_many :question_suggestions,
+           class_name: 'GekanatorQuestionSuggestion',
+           dependent: :delete_all
+  has_many :question_examples,
+           class_name: 'GekanatorQuestionExample',
+           dependent: :delete_all
+
+  validates :answers, presence: true
+  validates :question_count, numericality: { greater_than_or_equal_to: 0 }
+  validates :won, inclusion: { in: [true, false] }
+end

backend/app/models/gekanator_question.rb

@@ -0,0 +1,23 @@
+class GekanatorQuestion < ApplicationRecord
+  KINDS = ['tag', 'source', 'title', 'original_date', 'post_similarity'].freeze
+  SOURCES = ['user_suggested', 'ai_generated', 'admin_curated'].freeze
+  STATUSES = ['pending', 'accepted', 'rejected', 'disabled'].freeze
+
+  belongs_to :gekanator_question_suggestion, optional: true
+  belongs_to :created_by, class_name: 'User', optional: true
+  has_many :gekanator_question_examples, dependent: :delete_all
+
+  validates :kind, presence: true, inclusion: { in: KINDS }
+  validates :source, presence: true, inclusion: { in: SOURCES }
+  validates :status, presence: true, inclusion: { in: STATUSES }
+  validates :text, presence: true, length: { maximum: 1000 }
+  validates :condition, presence: true
+  validates :priority_weight,
+            presence: true,
+            numericality: {
+              greater_than: 0,
+              less_than_or_equal_to: 3
+            }
+
+  scope :accepted, -> { where(status: 'accepted') }
+end

backend/app/models/gekanator_question_example.rb

@@ -0,0 +1,97 @@
+class GekanatorQuestionExample < ApplicationRecord
+  ANSWERS = GekanatorQuestionSuggestion::ANSWERS
+  NON_UNKNOWN_ANSWERS = ANSWERS - ['unknown']
+  SOURCES = ['initial_suggestion', 'post_game_extra'].freeze
+
+  belongs_to :gekanator_question
+  belongs_to :post
+  belongs_to :user
+  belongs_to :gekanator_game, optional: true
+
+  validates :answer, presence: true, inclusion: { in: ANSWERS }
+  validates :answer_counts, presence: true
+  validates :sample_count,
+            presence: true,
+            numericality: {
+              only_integer: true,
+              greater_than: 0
+            }
+  validates :source, presence: true, inclusion: { in: SOURCES }
+  validates :weight,
+            presence: true,
+            numericality: {
+              greater_than: 0
+            }
+
+  before_validation :normalize_learning_state
+
+  def record_answer!(answer:, source:, gekanator_game: nil)
+    answer = answer.to_s
+    raise ArgumentError, 'invalid answer' unless ANSWERS.include?(answer)
+
+    counts = normalized_answer_counts
+    counts[answer] += 1
+
+    self.answer_counts = counts
+    self.sample_count = counts.values.sum
+    self.gekanator_game = gekanator_game if gekanator_game.present?
+    self.source = source if new_record?
+
+    apply_aggregated_answer!(preferred_answer: answer)
+    self
+  end
+
+  private
+
+  def normalize_learning_state
+    counts = normalized_answer_counts
+
+    if counts.values.sum.zero? && answer.present?
+      counts[answer] = 1
+    end
+
+    self.answer_counts = counts
+    self.sample_count = counts.values.sum
+
+    apply_aggregated_answer!
+  end
+
+  def apply_aggregated_answer!(preferred_answer: nil)
+    counts = normalized_answer_counts
+    known_counts = counts.slice(*NON_UNKNOWN_ANSWERS)
+    known_total = known_counts.values.sum
+
+    if known_total.zero?
+      self.answer = 'unknown'
+      self.weight = 0.1
+      return
+    else
+      max_count = known_counts.values.max
+      candidates = known_counts.select { |_answer, count| count == max_count }.keys
+      self.answer =
+          if preferred_answer.present? && candidates.include?(preferred_answer)
+            preferred_answer
+          elsif answer.present? && candidates.include?(answer)
+            answer
+          else
+            candidates.first
+          end
+    end
+
+    consensus = max_count.to_f / known_total
+    self.weight = Math.sqrt(known_total) * consensus
+  end
+
+  def normalized_answer_counts
+    base = ANSWERS.index_with(0)
+
+    answer_counts.to_h.each do |key, value|
+      answer_key = key.to_s
+      next unless ANSWERS.include?(answer_key)
+
+      base[answer_key] = value.to_i
+    end
+
+    base
+  end
+end

backend/app/models/gekanator_question_suggestion.rb

@@ -0,0 +1,25 @@
+class GekanatorQuestionSuggestion < ApplicationRecord
+  MAX_QUESTIONS_PER_GAME = 3
+  ANSWERS = ['yes', 'no', 'partial', 'probably_no', 'unknown'].freeze
+
+  belongs_to :gekanator_game
+  belongs_to :user
+  has_many :gekanator_questions, dependent: :nullify
+  has_many :gekanator_ai_runs, dependent: :destroy
+
+  validates :question_text, presence: true, length: { maximum: 1000 }
+  validates :answer, presence: true, inclusion: { in: ANSWERS }
+  validates :processed, inclusion: { in: [true, false] }
+  validate :question_suggestion_limit_per_game, on: :create
+
+  private
+
+  def question_suggestion_limit_per_game
+    return if gekanator_game_id.blank?
+
+    count = GekanatorQuestionSuggestion.where(gekanator_game_id:).count
+    if count >= MAX_QUESTIONS_PER_GAME
+      errors.add(:base, '質問追加数を超えてゐます．')
+    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_relation.rb

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

backend/app/models/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

@@ -1,44 +1,85 @@
-require 'mini_magick'
-
-
 class Post < ApplicationRecord
-  belongs_to :parent, class_name: 'Post', optional: true, foreign_key: 'parent_id'
+  require 'mini_magick'
+
   belongs_to :uploaded_user, class_name: 'User', optional: true
-  has_many :post_tags, dependent: :destroy
-  has_many :tags, through: :post_tags
-  has_many :user_post_views, dependent: :destroy
-  has_many :post_similarities_as_post,
-           class_name: 'PostSimilarity',
-           foreign_key: :post_id
-  has_many :post_similarities_as_target_post,
-           class_name: 'PostSimilarity',
-           foreign_key: :target_post_id
+
+  has_many :post_tags, dependent: :destroy, inverse_of: :post
+  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
+  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
+  has_many :tags, through: :active_post_tags
+
+  has_many :user_post_views, dependent: :delete_all
+  has_many :post_similarities, dependent: :delete_all
+  has_many :post_versions
+  has_many :gekanator_guessed_games,
+           class_name: 'GekanatorGame',
+           foreign_key: :guessed_post_id,
+           dependent: :delete_all,
+           inverse_of: :guessed_post
+  has_many :gekanator_correct_games,
+           class_name: 'GekanatorGame',
+           foreign_key: :correct_post_id,
+           dependent: :delete_all,
+           inverse_of: :correct_post
+  has_many :gekanator_question_examples, dependent: :delete_all
+
+  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!
@@ -64,7 +105,36 @@ class Post < ApplicationRecord
     return if !(f) || !(b)
 
     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．'
+      errors.add :original_created_at, '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

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

backend/app/models/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

@@ -1,72 +1,231 @@
+require 'set'
+
+
 class Tag < ApplicationRecord
-  has_many :post_tags, dependent: :destroy
-  has_many :posts, through: :post_tags
-  has_many :tag_aliases, dependent: :destroy
+  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 :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
   has_many :linked_tags, through: :nico_tag_relations, source: :tag
 
-  has_many :reversed_nico_tag_relations, class_name: 'NicoTagRelation',
-                                         foreign_key: :tag_id,
-                                         dependent: :destroy
+  has_many :reversed_nico_tag_relations,
+           class_name: 'NicoTagRelation', foreign_key: :tag_id, dependent: :destroy
   has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
-  enum :category, { deerjikist:  'deerjikist',
-                    meme:        'meme',
-                    character:   'character',
-                    general:     'general',
-                    material:    'material',
-                    nico:        'nico',
-                    meta:        'meta' }
+  has_many :tag_implications, foreign_key: :parent_tag_id, dependent: :destroy
+  has_many :children, through: :tag_implications, source: :tag
+
+  has_many :reversed_tag_implications,
+           class_name: 'TagImplication', foreign_key: :tag_id, dependent: :destroy
+  has_many :parents, through: :reversed_tag_implications, source: :parent_tag
+
+  has_many :tag_similarities, dependent: :delete_all
+  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_initialize_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_initialize_by(name: 'bot操作') do |tag|
-      tag.category = 'meta'
-    end
-  end
+  def has_wiki = wiki_page.present?
+
+  def material_id = materials.first&.id
+
+  def has_deerjikists = deerjikists.loaded? ? deerjikists.any? : deerjikists.exists?
+
+  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 < 20 && tags.none?(Tag.tagme)
-    tags.uniq
+
+    tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
+    tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
+    tags.uniq(&:id)
+  end
+
+  def self.expand_parent_tags tags
+    return [] if tags.blank?
+
+    seen = Set.new
+    result = []
+    stack = tags.compact.dup
+
+    until stack.empty?
+      tag = stack.pop
+      next unless tag
+
+      tag.parents.each do |parent|
+        next if seen.include?(parent.id)
+
+        seen << parent.id
+        result << parent
+        stack << parent
+      end
+    end
+
+    (result + tags).uniq { |t| t.id }
+  end
+
+  def self.find_or_create_by_tag_name! name, category:
+    tn = TagName.find_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_implication.rb

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

backend/app/models/tag_name.rb

@@ -0,0 +1,51 @@
+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 +1,17 @@
+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
+
+  has_many :programmes, class_name: 'TheatreProgramme'
+  has_many :skip_votes, class_name: 'TheatreSkipVote', dependent: :delete_all
+  has_many :skip_events, class_name: 'TheatreSkipEvent', dependent: :delete_all
+
+  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_programme.rb

@@ -0,0 +1,6 @@
+class TheatreProgramme < ApplicationRecord
+  self.primary_key = :theatre_id, :position
+
+  belongs_to :theatre
+  belongs_to :post
+end

backend/app/models/theatre_skip_event.rb

@@ -0,0 +1,10 @@
+class TheatreSkipEvent < ApplicationRecord
+  belongs_to :theatre
+  belongs_to :post
+  belongs_to :skipped_by_user, class_name: 'User'
+
+  has_many :voters, class_name: 'TheatreSkipEventVoter', dependent: :delete_all
+  has_many :event_tags, class_name: 'TheatreSkipEventTag', dependent: :delete_all
+  has_many :users, through: :voters
+  has_many :tags, through: :event_tags
+end

backend/app/models/theatre_skip_event_tag.rb

@@ -0,0 +1,6 @@
+class TheatreSkipEventTag < ApplicationRecord
+  self.primary_key = :theatre_skip_event_id, :tag_id
+
+  belongs_to :theatre_skip_event
+  belongs_to :tag
+end

backend/app/models/theatre_skip_event_voter.rb

@@ -0,0 +1,6 @@
+class TheatreSkipEventVoter < ApplicationRecord
+  self.primary_key = :theatre_skip_event_id, :user_id
+
+  belongs_to :theatre_skip_event
+  belongs_to :user
+end

backend/app/models/theatre_skip_vote.rb

@@ -0,0 +1,7 @@
+class TheatreSkipVote < ApplicationRecord
+  self.primary_key = :theatre_id, :post_id, :user_id
+
+  belongs_to :theatre
+  belongs_to :post
+  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

@@ -1,30 +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 :ip_addresses
   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 +1,66 @@
+# frozen_string_literal: true
+
+
+module PostRepr
+  BASE_FIELDS = [
+      :id,
+      :version_no,
+      :url,
+      :title,
+      :thumbnail_base,
+      :original_created_from,
+      :original_created_before,
+      :created_at,
+      :updated_at
+  ].freeze
+
+  module_function
+
+  def base post, current_user = nil
+    json = common(post)
+    json['tags'] = tag_json(post.tags)
+    json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
+    json['viewed'] = current_user ? current_user.viewed?(post) : false
+    json
+  end
+
+  def detail post, current_user = nil, parent_posts: [], child_posts: [],
+             sibling_posts: { }, related: []
+    base(post, current_user).merge(
+        'parent_posts' => cards(parent_posts),
+        'child_posts' => cards(child_posts),
+        'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
+          cards(posts)
+        },
+        'related' => cards(related))
+  end
+
+  def card post
+    common(post).merge('parent_posts' => [], 'child_posts' => [])
+  end
+
+  def cards posts
+    posts.map { |post| card(post) }
+  end
+
+  def many posts, current_user = nil
+    posts.map { |p| base(p, current_user) }
+  end
+
+  def common post
+    BASE_FIELDS.to_h { |field| [field.to_s, post.public_send(field)] }
+               .merge('thumbnail' => thumbnail_url(post))
+  end
+
+  def tag_json tags
+    tags.map { |tag| TagRepr.inline(tag) }
+  end
+
+  def thumbnail_url post
+    return nil unless post.thumbnail.attached?
+
+    Rails.application.routes.url_helpers.rails_blob_url(post.thumbnail, only_path: false)
+  rescue
+    nil
+  end
+end

backend/app/representations/tag_repr.rb

@@ -0,0 +1,20 @@
+# 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 inline tag
+    tag.as_json(BASE).merge(aliases: [], parents: [])
+  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/gekanator/ai_run_budget.rb

@@ -0,0 +1,22 @@
+module Gekanator
+  class AiRunBudget
+    MONTHLY_LIMIT_JPY = BigDecimal('450').freeze
+    MAX_RUN_ESTIMATED_COST_JPY = BigDecimal('5').freeze
+
+    def self.remaining_monthly_budget_jpy
+      MONTHLY_LIMIT_JPY - monthly_cost_jpy
+    end
+
+    def self.monthly_cost_jpy
+      GekanatorAiRun.this_month.sum(:estimated_cost_jpy)
+    end
+
+    def self.exceeded?
+      monthly_cost_jpy >= MONTHLY_LIMIT_JPY
+    end
+
+    def self.exceeded_after_next_run?
+      monthly_cost_jpy + MAX_RUN_ESTIMATED_COST_JPY >= MONTHLY_LIMIT_JPY
+    end
+  end
+end

backend/app/services/gekanator/question_suggestion_ai_converter.rb

@@ -0,0 +1,18 @@
+module Gekanator
+  class QuestionSuggestionAiConverter
+    def self.call(...) = new(...).call
+
+    def initialize suggestion:, user:
+      @suggestion = suggestion
+      @user = user
+    end
+
+    def call
+      raise NotImplementedError, 'AI question conversion is not implemented yet.'
+    end
+
+    private
+
+    attr_reader :suggestion, :user
+  end
+end

backend/app/services/gekanator/question_suggestion_promoter.rb

@@ -0,0 +1,52 @@
+module Gekanator
+  class QuestionSuggestionPromoter
+    def self.call(...) = new(...).call
+
+    def initialize suggestion:, user:
+      @suggestion = suggestion
+      @user = user
+    end
+
+    def call
+      suggestion.with_lock do
+        return promoted_question if suggestion.processed?
+        return suggestion if suggestion.answer == 'unknown'
+
+        question = GekanatorQuestion.create!(
+            text: suggestion.question_text,
+            kind: 'post_similarity',
+            source: 'user_suggested',
+            status: 'accepted',
+            priority_weight: 1.2,
+            condition: {
+              type: 'post-similarity',
+              postId: suggestion.gekanator_game.correct_post_id,
+              answer: suggestion.answer,
+              threshold: 0.65
+            },
+            gekanator_question_suggestion: suggestion,
+            created_by: user)
+        example =
+            GekanatorQuestionExample.new(
+                gekanator_question: question,
+                post: suggestion.gekanator_game.correct_post,
+                user: user)
+        example.record_answer!(
+            answer: suggestion.answer,
+            source: 'initial_suggestion',
+            gekanator_game: suggestion.gekanator_game)
+        example.save!
+        suggestion.update!(processed: true)
+        question
+      end
+    end
+
+    private
+
+    attr_reader :suggestion, :user
+
+    def promoted_question
+      suggestion.gekanator_questions.order(id: :desc).first
+    end
+  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/theatre_post_advancer.rb

@@ -0,0 +1,29 @@
+class TheatrePostAdvancer
+  def self.call(theatre:)
+    new(theatre:).call
+  end
+
+  def initialize(theatre:)
+    @theatre = theatre
+  end
+
+  def call
+    previous_post = theatre.current_post
+    post = TheatrePostSelector.new(theatre:).select
+
+    TheatreSkipVote.where(theatre:, post: previous_post).delete_all if previous_post
+
+    theatre.update!(current_post: post, current_post_started_at: post ? Time.current : nil)
+
+    if post
+      position = (theatre.programmes.maximum(:position) || 0) + 1
+      theatre.programmes.create!(position:, post:)
+    end
+
+    post
+  end
+
+  private
+
+  attr_reader :theatre
+end

backend/app/services/theatre_post_selector.rb

@@ -0,0 +1,119 @@
+class TheatrePostSelector
+  Candidate = Struct.new(:post, :weight, :penalty, :tags, keyword_init: true)
+  ELIGIBLE_POST_URL_CONDITION =
+      ["url LIKE '%nicovideo.jp%'",
+       "url LIKE '%youtube.com/watch%'",
+       "url LIKE '%youtu.be/%'"]
+      .join(' OR ')
+
+  def initialize theatre:
+    @theatre = theatre
+  end
+
+  def select
+    candidates = weighted_candidates
+    return nil if candidates.empty?
+
+    total = candidates.sum(&:weight)
+    target = rand * total
+
+    candidates.each do |candidate|
+      target -= candidate.weight
+      return candidate.post if target <= 0
+    end
+
+    candidates.last.post
+  end
+
+  def weight_json limit: 20
+    candidates = weighted_candidates
+    sorted = candidates.sort_by { |candidate| [candidate.weight, candidate.post.id] }
+
+    { tag_penalties: tag_penalty_json,
+      lightest_posts: post_weight_json(sorted.first(limit)),
+      heaviest_posts: post_weight_json(sorted.reverse.first(limit)) }
+  end
+
+  private
+
+  attr_reader :theatre
+
+  def weighted_candidates
+    @weighted_candidates ||= begin
+      penalties = tag_penalties
+      posts = eligible_posts.includes(tags: :tag_name).to_a
+
+      posts.map do |post|
+        post_tags = post.tags.to_a
+        penalty = post_tags.sum { |tag| penalties[tag.id].to_i }
+
+        Candidate.new(
+            post:,
+            penalty:,
+            tags: post_tags,
+            weight: 1.0 / (1.0 + penalty))
+      end
+    end
+  end
+
+  def eligible_posts
+    posts = Post.where(ELIGIBLE_POST_URL_CONDITION)
+    posts = posts.where.not(id: theatre.current_post_id) if theatre.current_post_id
+    posts
+  end
+
+  def active_user_ids
+    @active_user_ids ||= theatre.watching_users.ids
+  end
+
+  def tag_penalties
+    @tag_penalties ||=
+      if active_user_ids.empty?
+        {}
+      else
+        TheatreSkipEventVoter
+          .joins(theatre_skip_event: :event_tags)
+          .where(user_id: active_user_ids)
+          .group('theatre_skip_event_tags.tag_id')
+          .count
+      end
+  end
+
+  def tag_penalty_json
+    return [] if tag_penalties.empty?
+
+    tags = Tag.where(id: tag_penalties.keys).includes(:tag_name).index_by(&:id)
+
+    tag_penalties
+      .map { |tag_id, penalty|
+        tag = tags[tag_id]
+        next unless tag
+
+        { tag: light_tag_json(tag),
+          penalty: }
+      }
+      .compact
+      .sort_by { |row| [-row[:penalty], row[:tag][:name].to_s] }
+  end
+
+  def post_weight_json candidates
+    candidates.map { |candidate|
+      { post: light_post_json(candidate.post),
+        weight: candidate.weight,
+        penalty: candidate.penalty,
+        tags: candidate.tags.map { |tag| light_tag_json(tag) } }
+    }
+  end
+
+  def light_post_json post
+    { id: post.id,
+      title: post.title,
+      url: post.url }
+  end
+
+  def light_tag_json tag
+    { id: tag.id,
+      name: tag.name,
+      category: tag.category }
+  end
+end

backend/app/services/theatre_skip_finalizer.rb

@@ -0,0 +1,40 @@
+class TheatreSkipFinalizer
+  def self.call(theatre:, user:)
+    new(theatre:, user:).call
+  end
+
+  def initialize(theatre:, user:)
+    @theatre = theatre
+    @user = user
+  end
+
+  def call
+    return unless theatre.current_post
+
+    post = theatre.current_post
+    voters = TheatreSkipVote.where(theatre:, post:).includes(:user).map(&:user)
+    return if voters.empty?
+
+    event = TheatreSkipEvent.create!(
+        theatre:,
+        post:,
+        skipped_by_user: user,
+        programme_position: theatre.programmes.maximum(:position))
+
+    voters.uniq(&:id).each do |voter|
+      TheatreSkipEventVoter.create!(theatre_skip_event: event, user: voter)
+    end
+
+    post.tags.find_each do |tag|
+      TheatreSkipEventTag.create!(theatre_skip_event: event, tag:)
+    end
+
+    TheatreSkipVote.where(theatre:, post:).delete_all
+
+    event
+  end
+
+  private
+
+  attr_reader :theatre, :user
+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