タグ・グループを Wiki から分離 (#425) (#429)

Reviewed-on: #429
Co-authored-by: miteruzo <miteruzo@naver.com>

backend/app/controllers/tag_groups_controller.rb

@@ -0,0 +1,39 @@
+class TagGroupsController < ApplicationController
+  def index
+    groups = TagGroup.includes(:created_by_user, :updated_by_user).order(:id)
+    render json: TagGroupRepr.many(groups.to_a)
+  end
+
+  def show
+    group = TagGroup.includes(:created_by_user, :updated_by_user).find_by(id: params[:id])
+    return head :not_found unless group
+
+    render json: TagGroupRepr.one(group)
+  end
+
+  def create
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    group = TagGroupOperation.create!(**write_attributes, actor: current_user)
+    render json: TagGroupRepr.one(group), status: :created
+  end
+
+  def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    group = TagGroup.find_by(id: params[:id])
+    return head :not_found unless group
+
+    TagGroupOperation.update!(group:, **write_attributes, actor: current_user)
+    render json: TagGroupRepr.one(group.reload)
+  end
+
+  private
+
+  def write_attributes
+    { name: params[:name], description: params[:description],
+      members: params[:members], placements: params[:placements] }
+  end
+end

backend/app/controllers/wiki_pages_controller.rb

@@ -3,23 +3,27 @@ class WikiPagesController < ApplicationController
 
   def index
     # 互換性のための化石リソース
-    # TODO: ヘルプおよびタグ・グループ追加後に，
-    # TODO: タグ説明とヘルプ、タグ・グループから取得する作りに変更する．
-    #
+
     title = params[:title].to_s.strip
-    descriptions = TagDescription.where(language_code: 'ja')
+    descriptions =
+        TagDescription.where(language_code: 'ja')
         .includes(tag: :tag_names)
     pages = unmigrated_wiki_pages.includes(tag_name: :tag)
 
+    tag_groups = TagGroup.all
     if title.present?
       pattern = "%#{ ApplicationRecord.sanitize_sql_like(title) }%"
-      descriptions = descriptions.joins(tag: :tag_names)
+      descriptions =
+          descriptions.joins(tag: :tag_names)
           .where(tag_names: { language_code: 'ja', primary_flg: true })
           .where('tag_names.name LIKE ?', pattern).limit(20)
+      tag_groups = tag_groups.where(
+          'CONCAT(?, name) LIKE ?', TagGroupRepr::PREFIX, pattern).limit(20)
       pages = pages.where('tag_names.name LIKE ?', pattern).limit(20)
     end
 
     json = descriptions.map { |description| WikiPageRepr.tag_description(description) }
+    json.concat(tag_groups.map { WikiPageRepr.tag_group(_1) })
     json.concat(WikiPageRepr.base(pages))
     json = json.first(20) if title.present?
     render json:
@@ -30,6 +34,9 @@ class WikiPagesController < ApplicationController
 
     return render_wiki_page_by_tag_description tag_description if tag_description
 
+    tag_group = TagGroup.find_by(id: params[:id])
+    return render_tag_group tag_group if tag_group
+
     page = WikiPage.joins(:tag_name)
                    .includes(tag_name: :tag)
                    .find_by(id: params[:id])
@@ -40,25 +47,39 @@ class WikiPagesController < ApplicationController
   def show_by_title
     title = params[:title].to_s.strip
 
+    if title.start_with?(TagGroupRepr::PREFIX)
+      name = title.delete_prefix(TagGroupRepr::PREFIX)
+      tag_group = TagGroup.find_by(name:)
+      return render_tag_group tag_group if tag_group
+      return head :not_found
+    end
+
     tag_description = tag_description_by_title(title)
 
     return render_wiki_page_by_tag_description tag_description if tag_description
 
-    page = WikiPage.joins(:tag_name)
-                   .includes(tag_name: :tag)
-                   .find_by(tag_name: { name: title })
+    page =
+        WikiPage
+        .joins(:tag_name)
+        .includes(tag_name: :tag)
+        .find_by(tag_name: { name: title })
 
     render_wiki_page_or_404 page
   end
 
   def exists
     return head :no_content if TagDescription.exists?(id: params[:id])
+    return head :no_content if TagGroup.exists?(id: params[:id])
 
     head WikiPage.exists?(id: params[:id]) ? :no_content : :not_found
   end
 
   def exists_by_title
     title = params[:title].to_s.strip
+    if title.start_with?(TagGroupRepr::PREFIX)
+      exists = TagGroup.exists?(name: title.delete_prefix(TagGroupRepr::PREFIX))
+      return head exists ? :no_content : :not_found
+    end
     return head :no_content if tag_description_by_title(title)
 
     exists = WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
@@ -79,29 +100,33 @@ class WikiPagesController < ApplicationController
       to_rev = to ? versions.find(to) : versions.find_by!(version_no: description.version_no)
       resource = WikiPageRepr.tag_description(description)
     else
-      page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
-      from_rev = from && page.wiki_revisions.find(from)
-      to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
-      if ((from_rev && !from_rev.content?) || !to_rev&.content?)
-        return render_unprocessable_entity('差分を表示できない版です．')
+      tag_group = TagGroup.find_by(id:)
+      if tag_group
+        from_rev = from && group_version(tag_group, from)
+        to_rev = to ? group_version(tag_group, to) : current_group_version(tag_group)
+        return head :not_found if (from && !from_rev) || !to_rev
+
+        from_body = from_rev && render_group_version(from_rev)
+        to_body = render_group_version(to_rev)
+        resource = { 'id' => tag_group.id,
+                     'title' => "#{ TagGroupRepr::PREFIX }#{ tag_group.name }",
+                     'deprecated_at' => nil }
+      else
+        page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
+        from_rev = from && page.wiki_revisions.find(from)
+        to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
+        if ((from_rev && !from_rev.content?) || !to_rev&.content?)
+          return render_unprocessable_entity('差分を表示できない版です．')
+        end
+        from_body = from_rev&.body
+        to_body = to_rev.body
+        resource = WikiPageRepr.base(page)
       end
-      resource = WikiPageRepr.base(page)
     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 ?!
-        [{ type: 'removed', content: change.old_element },
-         { type: 'added', content: change.new_element }]
-      when ?+
-        { type: 'added', content: change.new_element }
-      when ?-
-        { type: 'removed', content: change.old_element }
-      end
-    }.flatten.compact
+    from_body ||= from_rev&.body
+    to_body ||= to_rev.body
+    diff_json = wiki_diff(from_body, to_body)
 
     render json: { wiki_page_id:      resource.fetch('id'),
                    title:             resource.fetch('title'),
@@ -109,6 +134,8 @@ class WikiPagesController < ApplicationController
                    older_revision_id: from_rev&.id,
                    newer_revision_id: to_rev.id,
                    diff:              diff_json }
+  rescue TagGroupMarkdownRenderer::UnsupportedStructure => error
+    render_unprocessable_entity(error.message)
   end
 
   def create
@@ -122,6 +149,17 @@ class WikiPagesController < ApplicationController
     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?
 
+    if title.start_with?(TagGroupRepr::PREFIX)
+      name = title.delete_prefix(TagGroupRepr::PREFIX)
+      parsed = TagGroupMarkdownParser.parse(body:, group: nil)
+      group = TagGroupOperation.create!(name:, **parsed, actor: current_user,
+                                         require_compatibility: true)
+      version = current_group_version(group)
+      return render_group_representation(TagGroupRepr.one(group), version,
+                                         body: parsed.fetch(:compatibility_body),
+                                         status: :created)
+    end
+
     page = if title.include?(':')
       ApplicationRecord.transaction do
         tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
@@ -146,6 +184,8 @@ class WikiPagesController < ApplicationController
     render_validation_error e.record
   rescue ActiveRecord::RecordNotUnique
     render_record_not_unique
+  rescue TagGroupMarkdownParser::InvalidDocument => error
+    render_unprocessable_entity(error.message)
   end
 
   def update
@@ -158,7 +198,26 @@ class WikiPagesController < ApplicationController
     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?
 
-    page = WikiPage.find(params[:id])
+    group = TagGroup.find_by(id: params[:id])
+    if title.start_with?(TagGroupRepr::PREFIX)
+      return head :not_found unless group
+
+      name = title.delete_prefix(TagGroupRepr::PREFIX)
+      parsed = TagGroupMarkdownParser.parse(body:, group:)
+      TagGroupOperation.update!(group:, name:, **parsed, actor: current_user,
+                                require_compatibility: true)
+      return head :ok
+    end
+
+    page = WikiPage.find_by(id: params[:id])
+    if legacy_group_page?(page)
+      return render_unprocessable_entity field: :title
+    end
+    if group && !legacy_update_identified?(page, title, group)
+      return render_unprocessable_entity field: :title
+    end
+    return head :not_found unless page
+
     base_revision_id = params[:base_revision_id].presence
 
     ApplicationRecord.transaction do
@@ -175,11 +234,17 @@ class WikiPagesController < ApplicationController
       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:)
+      description = TagDescription.find_by(id: page.id)
+      description_page = description && (
+          tag&.id == description.tag_id ||
+          (tag.nil? && !old_title.include?(':')))
+      if description && !description_page
+        Wiki::Commit.legacy_content!(page:, body:, created_user: current_user,
+                                     message:, base_revision_id:)
+      else
+        Wiki::Commit.content!(page:, body:, created_user: current_user,
+                              message:, base_revision_id:)
+      end
 
       if tag && title != old_title
         tag.reload
@@ -188,6 +253,12 @@ class WikiPagesController < ApplicationController
     end
 
     head :ok
+  rescue ActiveRecord::RecordInvalid => e
+    render_validation_error e.record
+  rescue ActiveRecord::RecordNotUnique
+    render_record_not_unique
+  rescue TagGroupMarkdownParser::InvalidDocument => error
+    render_unprocessable_entity(error.message)
   end
 
   def changes
@@ -197,6 +268,11 @@ class WikiPagesController < ApplicationController
       return render json: description_changes(TagDescription.where(id: description.id))
     end
 
+    tag_group = id && TagGroup.find_by(id:)
+    if tag_group
+      return render json: tag_group_changes(TagGroupVersion.where(tag_group_id: tag_group.id))
+    end
+
     pages = id ? WikiPage.where(id:) : unmigrated_wiki_pages
     revisions = WikiRevision.joins(wiki_page: :tag_name)
         .where(wiki_page_id: pages.select(:id))
@@ -215,14 +291,122 @@ class WikiPagesController < ApplicationController
         timestamp: rev.created_at }
     }
     unless id
+      json.concat(tag_group_changes(TagGroupVersion.all))
       json.concat(description_changes(TagDescription.where(language_code: 'ja')))
-      json.sort_by! { |row| -row[:revision_id] }
+      json = json.each_with_index.sort_by do |row, index|
+        [-row.fetch(:timestamp).to_f, index]
+      end.map(&:first)
     end
     render json: json.first(200)
   end
 
   private
 
+  def legacy_group_page? page
+    return false unless page
+    return true if page.title.start_with?(TagGroupRepr::PREFIX)
+
+    prefix = ApplicationRecord.sanitize_sql_like(TagGroupRepr::PREFIX)
+    page.wiki_versions.where('title LIKE ?', "#{ prefix }%").exists?
+  end
+
+  def legacy_update_identified? page, title, group
+    return false unless page
+    return true if page.title == title
+    return false if title == group.name
+
+    namespace = page.title.split(':', 2)
+    return true if namespace.size == 2 && title.start_with?("#{ namespace.first }:")
+
+    base = params[:base_revision_id].presence
+    base && page.wiki_revisions.exists?(id: base)
+  end
+
+  def render_tag_group group
+    version = if params[:version].present?
+      group_version(group, params[:version])
+    else
+      current_group_version(group)
+    end
+    return head :not_found unless version
+
+    representation = if params[:version].present?
+      TagGroupRepr.historical(version)
+    else
+      TagGroupRepr.one(group)
+    end
+    render_group_representation(representation, version)
+  end
+
+  def render_group_version version
+    representation = TagGroupRepr.historical(version)
+    TagGroupMarkdownRenderer.render(representation)
+  end
+
+  def render_group_representation representation, version, body: nil, status: :ok
+    body ||= TagGroupMarkdownRenderer.render(representation)
+    versions = TagGroupVersion.where(tag_group_id: version.tag_group_id)
+    pred = versions.find_by(version_no: version.version_no - 1)&.id
+    succ = versions.find_by(version_no: version.version_no + 1)&.id
+    updated_at = version.created_at
+    render json: {
+        'id' => version.tag_group_id,
+        'title' => "#{ TagGroupRepr::PREFIX }#{ representation.fetch('name') }",
+        'deprecated_at' => nil,
+        'body' => body,
+        'revision_id' => version.id,
+        'pred' => pred,
+        'succ' => succ,
+        'updated_at' => updated_at }, status:
+  rescue TagGroupMarkdownRenderer::UnsupportedStructure => error
+    render_unprocessable_entity(error.message)
+  end
+
+  def current_group_version group
+    TagGroupVersion.find_by(tag_group_id: group.id, version_no: group.version_no)
+  end
+
+  def group_version group, version_id
+    TagGroupVersion.find_by(tag_group_id: group.id, id: version_id)
+  end
+
+  def wiki_diff from_body, to_body
+    diffs = Diff::LCS.sdiff(from_body.to_s.lines, to_body.to_s.lines)
+    diffs.map { |change|
+      case change.action
+      when ?=
+        { type: 'context', content: change.old_element }
+      when ?!
+        [{ type: 'removed', content: change.old_element },
+         { type: 'added', content: change.new_element }]
+      when ?+
+        { type: 'added', content: change.new_element }
+      when ?-
+        { type: 'removed', content: change.old_element }
+      end
+    }.flatten.compact
+  end
+
+  def tag_group_changes versions
+    rows = versions.includes(:created_by_user).order(id: :desc).limit(200).to_a
+    groups = TagGroup.where(id: rows.map(&:tag_group_id).uniq).index_by(&:id)
+    predecessors = TagGroupVersion.where(tag_group_id: groups.keys,
+                                         version_no: rows.map { _1.version_no - 1 })
+        .pluck(:tag_group_id, :version_no, :id)
+        .to_h { |group_id, number, version_id| [[group_id, number], version_id] }
+    rows.map do |version|
+      group = groups.fetch(version.tag_group_id)
+      user = version.created_by_user
+      { revision_id: version.id,
+        pred: predecessors[[group.id, version.version_no - 1]],
+        succ: nil,
+        wiki_page: { id: group.id, title: "#{ TagGroupRepr::PREFIX }#{ version.name }",
+                     deprecated_at: nil },
+        user: user && { id: user.id, name: user.name },
+        kind: 'content', message: nil, timestamp: version.created_at }
+    end
+  end
+
   def render_wiki_page_or_404 page
     return head :not_found unless page
 
@@ -271,7 +455,10 @@ class WikiPagesController < ApplicationController
 
   def unmigrated_wiki_pages
     descriptions = TagDescription.where(language_code: 'ja')
-    WikiPage.joins(:tag_name).where.not(id: descriptions.select(:id))
+
+    WikiPage
+        .joins(:tag_name)
+        .where.not('tag_names.name LIKE ?', "#{ TagGroupRepr::PREFIX }%")
         .where('tag_names.tag_id IS NULL OR tag_names.tag_id NOT IN (?)',
                descriptions.select(:tag_id))
   end

backend/app/models/tag_group.rb

@@ -0,0 +1,16 @@
+class TagGroup < ApplicationRecord
+  belongs_to :created_by_user, class_name: 'User', optional: true
+  belongs_to :updated_by_user, class_name: 'User', optional: true
+
+  has_many :tag_group_tags, dependent: :delete_all
+  has_many :tags, through: :tag_group_tags
+  has_many :tag_group_groups, dependent: :delete_all
+  has_many :child_tag_groups, through: :tag_group_groups
+  has_many :placements, -> { order(:position) },
+           class_name: 'TagGroupPlacement', dependent: :delete_all
+  has_many :versions, -> { order(:version_no) },
+           class_name: 'TagGroupVersion', dependent: :delete_all
+
+  validates :name, presence: true, uniqueness: true, length: { maximum: 255 }
+  validates :version_no, numericality: { only_integer: true, greater_than: 0 }
+end

backend/app/models/tag_group_group.rb

@@ -0,0 +1,7 @@
+class TagGroupGroup < ApplicationRecord
+  self.primary_key = [:tag_group_id, :child_tag_group_id]
+
+  belongs_to :tag_group
+  belongs_to :child_tag_group, class_name: 'TagGroup'
+  belongs_to :created_by_user, class_name: 'User', optional: true
+end

backend/app/models/tag_group_placement.rb

@@ -0,0 +1,9 @@
+class TagGroupPlacement < ApplicationRecord
+  self.primary_key = [:tag_group_id, :position]
+
+  belongs_to :tag_group
+  belongs_to :tag, optional: true
+  belongs_to :child_tag_group, class_name: 'TagGroup', optional: true
+  belongs_to :created_by_user, class_name: 'User', optional: true
+  belongs_to :updated_by_user, class_name: 'User', optional: true
+end

backend/app/models/tag_group_tag.rb

@@ -0,0 +1,7 @@
+class TagGroupTag < ApplicationRecord
+  self.primary_key = [:tag_group_id, :tag_id]
+
+  belongs_to :tag_group
+  belongs_to :tag
+  belongs_to :created_by_user, class_name: 'User', optional: true
+end

backend/app/models/tag_group_version.rb

@@ -0,0 +1,7 @@
+class TagGroupVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag_group
+
+  scope :ordered, -> { order(:version_no) }
+end

backend/app/representations/tag_group_repr.rb

@@ -0,0 +1,194 @@
+module TagGroupRepr
+  PREFIX = 'タググループ:'
+
+  module_function
+
+  def many groups
+    ids = groups.map(&:id)
+    return [] if ids.empty?
+
+    tag_members = TagGroupTag.where(tag_group_id: ids)
+        .group_by(&:tag_group_id)
+    group_members = TagGroupGroup.where(tag_group_id: ids)
+        .group_by(&:tag_group_id)
+    placements = TagGroupPlacement.where(tag_group_id: ids).order(:position)
+        .group_by(&:tag_group_id)
+
+    target_ids = tag_members.values.flatten.map(&:tag_id) +
+        group_members.values.flatten.map(&:child_tag_group_id) +
+        placements.values.flatten.filter_map(&:tag_id)
+    child_ids = group_members.values.flatten.map(&:child_tag_group_id) +
+        placements.values.flatten.filter_map(&:child_tag_group_id)
+    tags = Tag.select(:id, :category).where(id: target_ids.uniq).index_by(&:id)
+    names = TagName.where(tag_id: target_ids.uniq, language_code: 'ja', primary_flg: true)
+        .pluck(:tag_id, :name).to_h
+    child_groups = TagGroup.where(id: child_ids.uniq).index_by(&:id)
+
+    groups.map do |group|
+      group_json(group,
+                 tag_members.fetch(group.id, []),
+                 group_members.fetch(group.id, []),
+                 placements.fetch(group.id, []), tags, names, child_groups)
+    end
+  end
+
+  def one group
+    many([group]).first
+  end
+
+  def tag_group wiki_page
+    { 'id' => wiki_page.id,
+      'title' => "#{ PREFIX }#{ wiki_page.name }",
+      'deprecated_at' => nil,
+      'created_at' => wiki_page.created_at,
+      'updated_at' => wiki_page.updated_at }
+  end
+
+  def current_version group
+    TagGroupVersion.find_by(tag_group_id: group.id, version_no: group.version_no)
+  end
+
+  def historical version
+    members = Array(version.members)
+    placements = Array(version.placements)
+    tag_references = members.filter_map { |member| member['tag_id'] } +
+        collect_ids(placements, 'tag_id')
+    group_references = members.filter_map { |member| member['tag_group_id'] } +
+        collect_ids(placements, 'tag_group_id')
+    tag_versions = historical_tag_versions(tag_references)
+    group_versions = historical_group_versions(group_references)
+    tag_version_numbers = members.filter_map do |member|
+      next unless member['tag_id']
+
+      [member.fetch('tag_id'), member.fetch('version_no')]
+    end.to_h
+    group_version_numbers = members.filter_map do |member|
+      next unless member['tag_group_id']
+
+      [member.fetch('tag_group_id'), member.fetch('version_no')]
+    end.to_h
+    historical_members = members.map do |member|
+      historical_member(member, tag_versions, group_versions)
+    end
+    historical_placements = placements.map do |node|
+      historical_placement(node, tag_versions, group_versions,
+                           tag_version_numbers, group_version_numbers)
+    end
+    { 'id' => version.tag_group_id,
+      'name' => version.name,
+      'description' => version.description,
+      'version_no' => version.version_no,
+      'members' => historical_members,
+      'placements' => historical_placements,
+      'created_at' => version.created_at,
+      'updated_at' => version.created_at,
+      'created_by_user' => user_json(version.created_by_user),
+      'updated_by_user' => user_json(version.created_by_user) }
+  end
+
+  def group_json group, tag_members, group_members, rows, tags, names, child_groups
+    tree = placement_tree(rows, tags, names, child_groups)
+    members = tag_members.sort_by(&:tag_id).map do |member|
+      { 'tag' => tag_json(tags.fetch(member.tag_id), names.fetch(member.tag_id)) }
+    end
+    members.concat(group_members.sort_by(&:child_tag_group_id).map do |member|
+      { 'tag_group' => group_json_reference(child_groups.fetch(member.child_tag_group_id)) }
+    end)
+    { 'id' => group.id,
+      'name' => group.name,
+      'description' => group.description,
+      'version_no' => group.version_no,
+      'members' => members,
+      'placements' => tree,
+      'created_at' => group.created_at,
+      'updated_at' => group.updated_at,
+      'created_by_user' => user_json(group.created_by_user),
+      'updated_by_user' => user_json(group.updated_by_user) }
+  end
+
+  def user_json user
+    UserRepr.base(user) if user
+  end
+
+  def placement_tree rows, tags, names, child_groups
+    by_parent = rows.group_by(&:parent_position)
+    build = lambda do |parent|
+      by_parent.fetch(parent, []).sort_by(&:position).map do |row|
+        node = if row.tag_id
+          { 'tag' => tag_json(tags.fetch(row.tag_id), names.fetch(row.tag_id)) }
+        elsif row.child_tag_group_id
+          { 'tag_group' => group_json_reference(child_groups.fetch(row.child_tag_group_id)) }
+        else
+          { 'section_name' => row.section_name, 'description' => row.description }
+        end
+        node.merge('children' => build.call(row.position))
+      end
+    end
+    build.call(nil)
+  end
+
+  def tag_json tag, name
+    { 'id' => tag.id, 'name' => name, 'category' => tag.category }
+  end
+
+  def group_json_reference group
+    { 'id' => group.id, 'name' => group.name }
+  end
+
+  def collect_ids nodes, key
+    nodes.flat_map do |node|
+      [node[key], *collect_ids(Array(node['children']), key)].compact
+    end
+  end
+
+  def historical_tag_versions ids
+    TagVersion.where(tag_id: ids.uniq).to_a.index_by do |version|
+      [version.tag_id, version.version_no]
+    end
+  end
+
+  def historical_group_versions ids
+    TagGroupVersion.where(tag_group_id: ids.uniq).to_a.index_by do |version|
+      [version.tag_group_id, version.version_no]
+    end
+  end
+
+  def historical_member member, tag_versions, group_versions
+    if member['tag_id']
+      id = member.fetch('tag_id')
+      version = tag_versions.fetch([id, member.fetch('version_no')])
+      { 'tag' => { 'id' => id, 'name' => japanese_version_name(version),
+                   'category' => version.category } }
+    else
+      id = member.fetch('tag_group_id')
+      version = group_versions.fetch([id, member.fetch('version_no')])
+      { 'tag_group' => { 'id' => id, 'name' => version.name } }
+    end
+  end
+
+  def historical_placement(node, tag_versions, group_versions,
+                           tag_version_numbers, group_version_numbers)
+    result = if node['tag_id']
+      id = node.fetch('tag_id')
+      version_no = tag_version_numbers.fetch(id)
+      version = tag_versions.fetch([id, version_no])
+      { 'tag' => { 'id' => id, 'name' => japanese_version_name(version),
+                   'category' => version.category } }
+    elsif node['tag_group_id']
+      id = node.fetch('tag_group_id')
+      version_no = group_version_numbers.fetch(id)
+      version = group_versions.fetch([id, version_no])
+      { 'tag_group' => { 'id' => id, 'name' => version.name } }
+    else
+      { 'section_name' => node.fetch('section_name'), 'description' => node['description'] }
+    end
+    result.merge('children' => Array(node['children']).map do |child|
+      historical_placement(child, tag_versions, group_versions,
+                           tag_version_numbers, group_version_numbers)
+    end)
+  end
+
+  def japanese_version_name version
+    version.names.fetch('ja').fetch('name')
+  end
+end

backend/app/representations/wiki_page_repr.rb

@@ -25,6 +25,10 @@ module WikiPageRepr
       'deprecated_at' => tag.deprecated_at }
   end
 
+  def tag_group tag_group
+    TagGroupRepr.tag_group(tag_group)
+  end
+
   def many wiki_pages
     wiki_pages.map { |p| base(p) }
   end

backend/app/services/tag_group_markdown_parser.rb

@@ -0,0 +1,177 @@
+require 'kramdown'
+
+class TagGroupMarkdownParser
+  PREFIX = TagGroupRepr::PREFIX
+
+  class InvalidDocument < StandardError
+    ;
+  end
+
+  def self.parse(body:, group: nil)
+    new(body:, group:).parse
+  end
+
+  def initialize(body:, group:)
+    @body = body.to_s.gsub(/\r\n?/, "\n")
+    @group = group
+  end
+
+  def parse
+    parse_body = @body.gsub(/([^\n])\n([\x23]{1,6}[ \t]+\S)/, "\\1\n\n\\2")
+    root = Kramdown::Document.new(parse_body, input: 'GFM', auto_ids: false).root
+    placements = []
+    description_parts = []
+    headings = []
+
+    root.children.each do |node|
+      case node.type
+      when :blank
+        next
+      when :header
+        level = node.options.fetch(:level)
+        name = inline_text(node).strip
+        invalid!('Section 名は必須です．') if name.blank?
+
+        headings.pop while headings.any? && headings.last.fetch(:level) >= level
+        parent = headings.last&.fetch(:node)
+        section = { 'section_name' => name, 'description' => nil,
+                    'children' => [] }
+        (parent ? parent.fetch('children') : placements) << section
+        headings << { level:, node: section }
+      when :p
+        text = inline_markdown(node).strip
+        next if text.empty?
+
+        if headings.any?
+          section = headings.last.fetch(:node)
+          section['description'] = [section['description'], text].compact.join("\n\n")
+        else
+          description_parts << text
+        end
+      when :ul
+        invalid!('未対応のリスト項目があります．') if node.attr.any?
+        target = headings.any? ? headings.last.fetch(:node).fetch('children') : placements
+        target.concat(node.children.map { parse_list_item(_1) })
+      else
+        invalid!("未対応の Markdown 構文 #{ node.type.inspect } です．")
+      end
+    end
+
+    description = description_parts.presence&.join("\n\n")
+    { description:, placements:, members: build_members(placements),
+      compatibility_body: @body.sub(/\n+\z/, '') }
+  rescue Kramdown::Error => error
+    invalid!("Markdown を解析できません：#{ error.message }")
+  end
+
+  private
+
+  def parse_list_item(item)
+    invalid!('リスト項目ではありません．') unless item.type == :li
+    invalid!('未対応のリスト項目があります．') if item.attr.any?
+
+    nested, own = item.children.partition { |child| child.type == :ul }
+    invalid!('順序付きリストは使用できません．') if own.any? { _1.type == :ol }
+    own.reject! { _1.type == :blank }
+    invalid!('未対応のリスト項目があります．') unless own.all? do |child|
+      [:p, :text].include?(child.type)
+    end
+    invalid!('リスト項目は一つの段落で指定してください．') if own.size != 1
+
+    label = own.map { inline_text(_1) }.join(' ').strip
+    invalid!('空のリスト項目は使用できません．') if label.blank?
+
+    node = if label.start_with?(PREFIX)
+      group_name = label.delete_prefix(PREFIX).strip
+      child_group = TagGroup.find_by(name: group_name)
+      invalid!("Tag Group #{ group_name.inspect } を解決できません．") unless child_group
+      invalid!('自分自身を含めることはできません．') if child_group.id == @group&.id
+      { 'tag_group_id' => child_group.id }
+    elsif label.end_with?(':', '：')
+      section_name = label.sub(/[:：]\z/, '').strip
+      invalid!('Section 名は必須です．') if section_name.blank?
+      { 'section_name' => section_name, 'description' => nil }
+    else
+      { 'tag_id' => resolve_tag(label) }
+    end
+
+    node['children'] = nested.flat_map do |list|
+      invalid!('未対応の入れ子リストです．') unless list.type == :ul
+      list.children.map { parse_list_item(_1) }
+    end
+    node
+  end
+
+  def resolve_tag(name)
+    names = TagName.where(language_code: 'ja', name:).to_a
+    tag_ids = names.filter_map(&:tag_id).uniq
+    invalid!("Tag #{ name.inspect } を解決できません．") if tag_ids.empty?
+    invalid!("Tag 名 #{ name.inspect } が曖昧です．") if tag_ids.many?
+
+    tag_ids.first
+  end
+
+  def build_members(nodes)
+    references = []
+    visit = lambda do |items|
+      items.each do |node|
+        references << node.slice('tag_id', 'tag_group_id') if
+            node.key?('tag_id') || node.key?('tag_group_id')
+        visit.call(node.fetch('children'))
+      end
+    end
+    visit.call(nodes)
+    references.uniq
+  end
+
+  def inline_text(node)
+    if node.attr.any?
+      invalid!("未対応のインライン構文 #{ node.type.inspect } です．")
+    end
+
+    case node.type
+    when :text
+      node.value.to_s
+    when :p, :header
+      node.children.map { inline_text(_1) }.join
+    else
+      invalid!("未対応のインライン構文 #{ node.type.inspect } です．")
+    end
+  end
+
+  def inline_markdown(node)
+    case node.type
+    when :text
+      node.value.to_s
+    when :codespan
+      text = node.value.to_s
+      longest = text.scan(/`+/).map(&:length).max || 0
+      delimiter = '`' * (longest + 1)
+      padded = text.start_with?('`', ' ') || text.end_with?('`', ' ')
+      content = padded ? " #{ text } " : text
+      "#{ delimiter }#{ content }#{ delimiter }"
+    when :softbreak
+      "\n"
+    when :br
+      "  \n"
+    when :p
+      node.children.map { inline_markdown(_1) }.join
+    when :a
+      href = node.attr.fetch('href')
+      label = node.children.map { inline_markdown(_1) }.join
+      title = node.attr['title']&.gsub('"', '\\"')
+      suffix = title ? " \"#{ title }\"" : ''
+      "[#{ label }](#{ href }#{ suffix })"
+    when :em
+      "*#{ node.children.map { inline_markdown(_1) }.join }*"
+    when :strong
+      "**#{ node.children.map { inline_markdown(_1) }.join }**"
+    else
+      invalid!("未対応の説明文構文 #{ node.type.inspect } です．")
+    end
+  end
+
+  def invalid! message
+    raise InvalidDocument, message
+  end
+end

backend/app/services/tag_group_markdown_renderer.rb

@@ -0,0 +1,118 @@
+class TagGroupMarkdownRenderer
+  class UnsupportedStructure < StandardError
+    ;
+  end
+
+  def self.render group
+    new(group).render
+  end
+
+  def initialize group
+    @group = group
+  end
+
+  def render
+    placements = @group.fetch('placements')
+    validate_membership!(placements)
+    blocks = []
+    if @group['description'].present?
+      blocks << clean_text(@group['description'])
+    end
+
+    sections = placements.select { _1.key?('section_name') }
+    if sections.any? && sections.size != placements.size
+      raise UnsupportedStructure,
+          '最上位の見出し Section と Placement の混在は Markdown にできません．'
+    end
+
+    if placements.all? { _1.key?('section_name') }
+      blocks.concat(placements.map { render_heading(_1, 2) })
+    else
+      blocks << render_list(placements, 0)
+    end
+
+    blocks.compact.reject(&:empty?).join("\n").sub(/\n+\z/, '')
+  end
+
+  private
+
+  def validate_membership! placements
+    placed = placement_members(placements).uniq.sort
+    members = @group.fetch('members').map { |member|
+      if member['tag']
+        ['tag', member.fetch('tag').fetch('id')]
+      else
+        ['tag_group', member.fetch('tag_group').fetch('id')]
+      end
+    }.uniq.sort
+    missing = members - placed
+    if missing.any?
+      raise UnsupportedStructure, '掲載位置のない membership は Markdown にできません．'
+    end
+  end
+
+  def placement_members nodes
+    nodes.flat_map do |node|
+      own = if node['tag']
+        [['tag', node.fetch('tag').fetch('id')]]
+      elsif node['tag_group']
+        [['tag_group', node.fetch('tag_group').fetch('id')]]
+      else
+        []
+      end
+      own + placement_members(node.fetch('children'))
+    end
+  end
+
+  def render_heading section, level
+    header = "#{ '#' * level } #{ clean_text(section.fetch('section_name')) }"
+    blocks = [header]
+    blocks << clean_text(section['description']) if section['description'].present?
+    children = section.fetch('children')
+    section_indexes = children.each_index.select { |index| children[index].key?('section_name') }
+    if section_indexes.any?
+      first_section = section_indexes.first
+      if children[first_section..].any? { !_1.key?('section_name') }
+        raise UnsupportedStructure,
+            '見出し Section と兄弟 Placement の交互配置は Markdown にできません．'
+      end
+      list_nodes = children[0...first_section]
+      blocks << render_list(list_nodes, 0) if list_nodes.any?
+      blocks.concat(children[first_section..].map { render_heading(_1, level + 1) })
+    elsif children.any?
+      blocks << render_list(children, 0)
+    end
+    blocks.join("\n")
+  end
+
+  def render_list nodes, depth
+    nodes.map do |node|
+      indent = '  ' * depth
+      if node.key?('section_name')
+        raise UnsupportedStructure,
+            'リスト内 Section の説明文は Markdown にできません．' if node['description'].present?
+
+        children = node.fetch('children')
+        head = "#{ indent }- #{ clean_text(node.fetch('section_name')) }:"
+        tail = render_list(children, depth + 1) if children.any?
+        [head, tail].compact.join("\n")
+      else
+        label = if node['tag']
+          node.fetch('tag').fetch('name')
+        else
+          "#{ TagGroupRepr::PREFIX }#{ node.fetch('tag_group').fetch('name') }"
+        end
+        raise UnsupportedStructure, '名称のない Placement は Markdown にできません．' if label.blank?
+
+        head = "#{ indent }- #{ clean_text(label) }"
+        children = node.fetch('children')
+        tail = render_list(children, depth + 1) if children.any?
+        [head, tail].compact.join("\n")
+      end
+    end.join("\n")
+  end
+
+  def clean_text value
+    value.to_s.gsub(/\r\n?/, "\n").lines.map(&:rstrip).join("\n").strip
+  end
+end

backend/app/services/tag_group_operation.rb

@@ -0,0 +1,410 @@
+class TagGroupOperation
+  MAX_PLACEMENT_DEPTH = 5
+  PREFIX = TagGroupRepr::PREFIX
+
+  def self.create!(name:, description:, members:, placements:, actor:,
+                   require_compatibility: false, compatibility_body: nil)
+    group, sync_issue = ApplicationRecord.transaction do
+      group = TagGroup.new(version_no: 1, created_by_user: actor,
+                           updated_by_user: actor)
+      attributes = prepare!(group:, name:, description:, members:, placements:)
+      group.assign_attributes(name: attributes.fetch(:name),
+                              description: attributes.fetch(:description))
+      group.save!
+      persist_structure!(group:, attributes:, actor:)
+      persist_version!(group:, attributes:, actor:, event_type: 'create')
+      issue = sync_compatibility!(group:, actor:, old_name: nil,
+                                  require_compatibility:, compatibility_body:)
+      [group, issue]
+    end
+    report_sync_issue(group, actor, sync_issue)
+    group
+  end
+
+  def self.update!(group:, name:, description:, members:, placements:, actor:,
+                   require_compatibility: false, compatibility_body: nil)
+    group, sync_issue = ApplicationRecord.transaction do
+      group.lock!
+      old_name = group.name
+      attributes = prepare!(group:, name:, description:, members:, placements:)
+      next [group, nil] if unchanged?(group, attributes)
+
+      group.update!(name: attributes.fetch(:name),
+                    description: attributes.fetch(:description),
+                    version_no: group.version_no + 1,
+                    updated_by_user: actor)
+      persist_structure!(group:, attributes:, actor:)
+      persist_version!(group:, attributes:, actor:, event_type: 'update')
+      issue = sync_compatibility!(group:, actor:, old_name:,
+                                  require_compatibility:, compatibility_body:)
+      [group, issue]
+    end
+    report_sync_issue(group, actor, sync_issue)
+    group
+  end
+
+  def self.prepare!(group:, name:, description:, members:, placements:)
+    record = group
+    normalized_name = name.to_s.strip
+    invalid!(record, :name, 'グループ名は必須です．') if normalized_name.blank?
+    if normalized_name.length > 255
+      invalid!(record, :name, 'グループ名は 255 文字以内で入力してください．')
+    end
+    invalid!(record, :description, '説明文は文字列で入力してください．') unless
+        description.nil? || description.is_a?(String)
+
+    record.name = normalized_name
+    record.description = description
+    unless record.valid?
+      raise ActiveRecord::RecordInvalid, record
+    end
+
+    member_rows = normalize_members(record, members)
+    placement_tree = normalize_placements(record, placements)
+    validate_references!(record, member_rows, placement_tree)
+    validate_containment!(record, member_rows)
+    { name: normalized_name, description:, members: member_rows,
+      placements: placement_tree }
+  end
+  private_class_method :prepare!
+
+  def self.unchanged?(group, attributes)
+    unless (group.name_in_database == attributes.fetch(:name) &&
+            group.description_in_database == attributes.fetch(:description))
+      return false
+    end
+
+    members = TagGroupTag.where(tag_group_id: group.id).pluck(:tag_id)
+        .map { { 'tag_id' => _1 } }
+    members.concat(TagGroupGroup.where(tag_group_id: group.id)
+        .pluck(:child_tag_group_id).map { { 'tag_group_id' => _1 } })
+    requested_members = attributes.fetch(:members).map do |member|
+      member.except('version_no')
+    end
+    return false unless members.to_set == requested_members.to_set
+
+    rows = TagGroupPlacement.where(tag_group_id: group.id).order(:position)
+        .group_by(&:parent_position)
+    build = lambda do |parent_position|
+      rows.fetch(parent_position, []).map do |row|
+        node = if row.tag_id
+          { 'tag_id' => row.tag_id }
+        elsif row.child_tag_group_id
+          { 'tag_group_id' => row.child_tag_group_id }
+        else
+          { 'section_name' => row.section_name, 'description' => row.description }
+        end
+        node.merge('children' => build.call(row.position))
+      end
+    end
+    build.call(nil) == comparable_placements(attributes.fetch(:placements))
+  end
+  private_class_method :unchanged?
+
+  def self.comparable_placements(nodes)
+    nodes.map do |node|
+      result = node.dup
+      result['description'] = node['description'] if node.key?('section_name')
+      result['children'] = comparable_placements(node.fetch('children'))
+      result
+    end
+  end
+  private_class_method :comparable_placements
+
+  def self.normalize_members(record, members)
+    invalid!(record, :members, 'members は配列で指定してください．') unless members.is_a?(Array)
+
+    result = members.map do |member|
+      member = stringify_keys(member)
+      unless member.is_a?(Hash) && member.keys.one? &&
+             (member.key?('tag_id') || member.key?('tag_group_id'))
+        invalid!(record, :members, '各 member は tag_id または tag_group_id を一つ指定してください．')
+      end
+      key = member.keys.first
+      id = integer_id(record, member.fetch(key), :members)
+      { key => id }
+    end
+    invalid!(record, :members, 'membership に重複があります．') unless result.uniq == result
+    result
+  end
+  private_class_method :normalize_members
+
+  def self.normalize_placements(record, placements)
+    invalid!(record, :placements, 'placements は配列で指定してください．') unless
+        placements.is_a?(Array)
+
+    normalize_placement_nodes(record, placements, 1)
+  end
+  private_class_method :normalize_placements
+
+  def self.normalize_placement_nodes(record, nodes, depth)
+    if depth > MAX_PLACEMENT_DEPTH && nodes.any?
+      invalid!(record, :placements, '配置の深さは 5 階層までです．')
+    end
+
+    nodes.map do |raw_node|
+      node = stringify_keys(raw_node)
+      unless node.is_a?(Hash) && node.key?('children')
+        invalid!(record, :placements, '各 Placement に children 配列が必要です．')
+      end
+      children = node.delete('children')
+      unless children.is_a?(Array)
+        invalid!(record, :placements, 'children は配列で指定してください．')
+      end
+
+      kinds = ['tag_id', 'tag_group_id', 'section_name'].select { node.key?(_1) }
+      invalid!(record, :placements, 'Placement の種類を一つ指定してください．') unless
+          kinds.one?
+      kind = kinds.first
+      allowed = [kind, 'description']
+      invalid!(record, :placements, '不明な Placement 項目があります．') unless
+          (node.keys - allowed).empty?
+
+      case kind
+      when 'tag_id', 'tag_group_id'
+        node[kind] = integer_id(record, node.fetch(kind), :placements)
+        if node['description'].present?
+          invalid!(record, :placements, 'Tag / Tag Group Placement に説明文は指定できません．')
+        end
+        node.delete('description')
+      when 'section_name'
+        section_name = node.fetch(kind)
+        unless section_name.is_a?(String) && section_name.strip.present? &&
+               section_name.length <= 255
+          invalid!(record, :placements, 'Section 名は 1〜255 文字で入力してください．')
+        end
+        node[kind] = section_name.strip
+        unless node['description'].nil? || node['description'].is_a?(String)
+          invalid!(record, :placements, 'Section の説明文は文字列で入力してください．')
+        end
+      end
+
+      node['children'] = normalize_placement_nodes(record, children, depth + 1)
+      node
+    end
+  end
+  private_class_method :normalize_placement_nodes
+
+  def self.validate_references!(record, members, placements)
+    membership = members.to_set
+    placed = placement_references(placements).uniq
+    missing = placed - membership.to_a
+    invalid!(record, :placements, 'Placement の対象は membership に含めてください．') if
+        missing.any?
+
+    tag_ids = members.filter_map { _1['tag_id'] }
+    group_ids = members.filter_map { _1['tag_group_id'] }
+    tags = Tag.where(id: tag_ids).index_by(&:id)
+    groups = TagGroup.where(id: group_ids).index_by(&:id)
+    invalid!(record, :members, '存在しない Tag が含まれています．') if
+        tags.size != tag_ids.uniq.size
+    invalid!(record, :members, '存在しない Tag Group が含まれています．') if
+        groups.size != group_ids.uniq.size
+
+    tag_versions = TagVersion.where(tag_id: tag_ids).pluck(:tag_id, :version_no).to_set
+    group_versions = TagGroupVersion.where(tag_group_id: group_ids)
+        .pluck(:tag_group_id, :version_no).to_set
+    tag_names = TagName.where(tag_id: tag_ids, language_code: 'ja', primary_flg: true)
+        .pluck(:tag_id).uniq
+
+    members.each do |member|
+      if member.key?('tag_id')
+        id = member.fetch('tag_id')
+        invalid!(record, :members, "Tag ##{ id } に日本語の正規名がありません．") unless
+            tag_names.include?(id)
+        version_no = tags.fetch(id).version_no
+        unless tag_versions.include?([id, version_no])
+          invalid!(record, :members, "Tag ##{ id } の Version がありません．")
+        end
+        member['version_no'] = version_no
+      else
+        id = member.fetch('tag_group_id')
+        version_no = groups.fetch(id).version_no
+        unless group_versions.include?([id, version_no])
+          invalid!(record, :members, "Tag Group ##{ id } の Version がありません．")
+        end
+        member['version_no'] = version_no
+      end
+    end
+  end
+  private_class_method :validate_references!
+
+  def self.validate_containment!(record, members)
+    target_id = record.id
+    return unless target_id
+
+    children = members.filter_map { _1['tag_group_id'] }
+    edges = TagGroupGroup.pluck(:tag_group_id, :child_tag_group_id)
+        .group_by(&:first).transform_values { _1.map(&:last) }
+    edges[target_id] = children
+    visiting = Set.new
+    visited = Set.new
+    visit = lambda do |group_id|
+      invalid!(record, :members, 'Tag Group の循環包含はできません．') if
+          group_id == target_id && visiting.include?(group_id)
+      return if visited.include?(group_id)
+
+      visiting.add(group_id)
+      edges.fetch(group_id, []).each do |child_id|
+        invalid!(record, :members, 'Tag Group の循環包含はできません．') if
+            child_id == target_id
+        visit.call(child_id)
+      end
+      visiting.delete(group_id)
+      visited.add(group_id)
+    end
+    children.each { visit.call(_1) }
+  end
+  private_class_method :validate_containment!
+
+  def self.persist_structure!(group:, attributes:, actor:)
+    tag_members = TagGroupTag.where(tag_group_id: group.id).index_by(&:tag_id)
+    group_members = TagGroupGroup.where(tag_group_id: group.id).index_by(&:child_tag_group_id)
+    attributes.fetch(:members).each do |member|
+      if member.key?('tag_id')
+        next if tag_members.delete(member.fetch('tag_id'))
+
+        TagGroupTag.create!(tag_group_id: group.id, tag_id: member.fetch('tag_id'),
+                            created_by_user: actor)
+      else
+        next if group_members.delete(member.fetch('tag_group_id'))
+
+        TagGroupGroup.create!(tag_group_id: group.id,
+                              child_tag_group_id: member.fetch('tag_group_id'),
+                              created_by_user: actor)
+      end
+    end
+    existing = TagGroupPlacement.where(tag_group_id: group.id).index_by(&:position)
+    persist_placements!(group:, nodes: attributes.fetch(:placements), actor:, existing:)
+    existing.values.sort_by(&:position).reverse_each(&:delete)
+    tag_members.each_value(&:delete)
+    group_members.each_value(&:delete)
+  end
+  private_class_method :persist_structure!
+
+  def self.persist_placements!(group:, nodes:, actor:, existing:, parent_position: nil,
+                               next_position: [0])
+    nodes.each do |node|
+      next_position[0] += 1
+      position = next_position[0]
+      row = existing.delete(position) || TagGroupPlacement.new(
+          tag_group_id: group.id, position:, created_by_user: actor)
+      row.assign_attributes(
+          parent_position:,
+          section_name: node['section_name'], description: node['description'],
+          tag_id: node['tag_id'], child_tag_group_id: node['tag_group_id'])
+      if row.new_record? || row.changed?
+        row.updated_by_user = actor
+        row.save!
+      end
+      persist_placements!(group:, nodes: node.fetch('children'), actor:, existing:,
+                          parent_position: position, next_position:)
+    end
+  end
+  private_class_method :persist_placements!
+
+  def self.persist_version!(group:, attributes:, actor:, event_type:)
+    TagGroupVersion.create!(tag_group: group, version_no: group.version_no,
+                            event_type:, name: group.name,
+                            description: group.description,
+                            members: attributes.fetch(:members),
+                            placements: attributes.fetch(:placements),
+                            created_by_user: actor)
+  end
+  private_class_method :persist_version!
+
+  def self.sync_compatibility!(group:, actor:, old_name:,
+                               require_compatibility:, compatibility_body:)
+    representation = TagGroupRepr.one(group)
+    body = begin
+      TagGroupMarkdownRenderer.render(representation)
+    rescue TagGroupMarkdownRenderer::UnsupportedStructure => error
+      if compatibility_body.present?
+        compatibility_body
+      elsif require_compatibility
+        invalid!(group, :base, error.message)
+      else
+        return error.message
+      end
+    end
+    invalid!(group, :base, '本文は必須です．') if body.blank?
+
+    title = "#{ PREFIX }#{ group.name }"
+    old_title = old_name && "#{ PREFIX }#{ old_name }"
+    page = if old_title
+      WikiPage.joins(:tag_name).find_by(tag_names: { name: old_title })
+    else
+      nil
+    end
+    page ||= WikiPage.joins(:tag_name).find_by(tag_names: { name: title })
+
+    if page
+      tag_name = page.tag_name
+      tag_name.update!(name: title) if tag_name.name != title
+      Wiki::Commit.legacy_content!(page:, body:, created_user: actor, message: nil,
+                                   base_revision_id: nil)
+    else
+      tag_name = TagName.find_or_initialize_by(language_code: 'ja', name: title)
+      tag_name.script_code = 'Jpan'
+      tag_name.primary_flg = true
+      tag_name.auto_generated = false
+      tag_name.save!
+      Wiki::Commit.create_legacy_content!(tag_name:, body:, created_by_user: actor)
+    end
+    nil
+  end
+  private_class_method :sync_compatibility!
+
+  def self.report_sync_issue(group, actor, reason)
+    return unless reason
+
+    payload = { status: 'unsupported_structure', tag_group_id: group.id,
+                version_no: group.version_no, user_id: actor&.id, reason: }
+    Rails.logger.warn("tag_group_wiki_sync_skipped #{ payload.to_json }")
+  end
+  private_class_method :report_sync_issue
+
+  def self.placement_references(nodes)
+    nodes.flat_map do |node|
+      own = if node.key?('tag_id')
+        [{ 'tag_id' => node.fetch('tag_id') }]
+      elsif node.key?('tag_group_id')
+        [{ 'tag_group_id' => node.fetch('tag_group_id') }]
+      else
+        []
+      end
+      own + placement_references(node.fetch('children'))
+    end
+  end
+  private_class_method :placement_references
+
+  def self.stringify_keys(value)
+    case value
+    when ActionController::Parameters
+      value.to_unsafe_h.deep_stringify_keys
+    when Hash
+      value.deep_stringify_keys
+    else
+      value
+    end
+  end
+  private_class_method :stringify_keys
+
+  def self.integer_id(record, value, attribute)
+    integer = if value.is_a?(Integer)
+      value
+    elsif value.is_a?(String) && value.match?(/\A[0-9]+\z/)
+      value.to_i
+    end
+    invalid!(record, attribute, 'ID は正の整数で指定してください．') unless integer
+    invalid!(record, attribute, 'ID は正の整数で指定してください．') unless integer.positive?
+    integer
+  end
+  private_class_method :integer_id
+
+  def self.invalid!(record, attribute, message)
+    record.errors.add(attribute, message)
+    raise ActiveRecord::RecordInvalid, record
+  end
+  private_class_method :invalid!
+end