#77

backend/app/models/tag.rb

@@ -26,6 +26,14 @@ class Tag < ApplicationRecord
 
   scope :nico_tags, -> { where(category: :nico) }
 
+  CATEGORY_PREFIXES = {
+      'gen:'  => 'general',
+      'djk:'  => 'deerjikist',
+      'meme:' => 'meme',
+      'chr:'  => 'character',
+      'mtr:'  => 'material',
+      'meta:' => 'meta' }.freeze
+
   def self.tagme
     @tagme ||= Tag.find_or_initialize_by(name: 'タグ希望') do |tag|
       tag.category = 'meta'
@@ -38,11 +46,26 @@ class Tag < ApplicationRecord
     end
   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
+      end
+    end
+    tags << Tag.tagme if with_tagme && tags.size < 20 && tags.none?(Tag.tagme)
+    tags.uniq
+  end
+
   private
 
   def nico_tag_name_must_start_with_nico
-    if ((category == 'nico' && name&.[](0, 5) != 'nico:') || 
-        (category != 'nico' && name&.[](0, 5) == 'nico:'))
+    if ((category == 'nico' && !(name.start_with?('nico:'))) || 
+        (category != 'nico' && name.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