#281 テストまだ通ってないので要確認

backend/app/models/tag.rb

@@ -160,9 +160,15 @@ class Tag < ApplicationRecord
         end
 
         tag_name = st.tag_name
+        nico_flg = st.nico?
         st.destroy!
         tag_name.reload
-        tag_name.update!(canonical: target_tag.tag_name)
+
+        if nico_flg
+          tag_name.destroy!
+        else
+          tag_name.update!(canonical: target_tag.tag_name)
+        end
       end
 
       # 投稿件数を再集計

backend/app/models/tag_name.rb

@@ -1,4 +1,6 @@
 class TagName < ApplicationRecord
+  before_validation :sanitise_name
+
   has_one :tag
   has_one :wiki_page
 
@@ -22,6 +24,10 @@ class TagName < ApplicationRecord
 
   private
 
+  def sanitise_name
+    self.name = TagNameSanitisationRule.sanitise(name)
+  end
+
   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．'

backend/app/models/tag_name_sanitisation_rule.rb

@@ -0,0 +1,55 @@
+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
+
+            if existing_tn.tag
+              Tag.merge_tags!(existing_tn.tag, tn.tag) if tn.tag
+            elsif tn.tag
+              tn.tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
+            end
+            tn.destroy!
+
+            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