#428

backend/app/controllers/posts_controller.rb

@@ -400,8 +400,76 @@ class PostsController < ApplicationController
     render_post_form_record_invalid e.record
   end
 
+  def tag_filters
+    source = resolve_locale!
+    code = params[:target_locale]
+    return head :not_found unless code.is_a?(String) && Locale.codes.value?(code)
+
+    target = Locale.find_by(code:, deprecated_at: nil)
+    return head :not_found unless target
+
+    literals = params[:tags].to_s.split
+    references = tag_filter_references(literals)
+    names = literals.each_with_index.map do |literal, index|
+      reference = references&.[](index)
+      (reference && reference['negative'] == false) ? literal : literal.sub(/\Anot:/i, '')
+    end
+    internal = references ? {} : TagName.where(
+        language_code: source.language_code, name: names).pluck(:name, :tag_id).to_h
+    canonical = references ? {} : TagName.where(
+        language_code: source.language_code, primary_flg: true,
+        tag_id: internal.values).pluck(:tag_id, :name).to_h
+    external_names = names.map { canonical[internal[_1]] || _1 }
+    external = references ? {} : ExternalTag.where(
+        "CONCAT(platform, ':', name) IN (?)", external_names).pluck(
+        Arel.sql("CONCAT(platform, ':', name)"), :id).to_h
+    ids = references ? references.filter_map { _1['tag_id'] } : internal.values
+    translated = TagName.where(language_code: target.language_code,
+                               primary_flg: true, tag_id: ids).pluck(:tag_id, :name).to_h
+
+    filters = literals.each_with_index.map do |literal, index|
+      name = names[index]
+      reference = if references
+                    references[index].except('name')
+                  else
+                    matches = {}
+                    matches['tag_id'] = internal[name] if internal[name]
+                    external_id = external[external_names[index]]
+                    matches['external_tag_id'] = external_id if external_id
+                    matches.empty? ? { 'missing' => true } : matches
+                  end
+      name = translated[reference['tag_id']] || name
+      negative = reference.fetch('negative', literal.downcase.start_with?('not:'))
+      prefix = negative ? literal[/\Anot:/i] || 'not:' : ''
+      reference.merge('name' => "#{ prefix }#{ name }", 'negative' => negative)
+    end
+    render json: { references: filters }
+  end
+
   private
 
+  def tag_filter_references literals
+    raw = params[:tag_refs]
+    return nil if raw.blank?
+
+    references = JSON.parse(raw)
+    valid = references.is_a?(Array) && references.all? do |reference|
+      next false unless reference.is_a?(Hash) && reference['name'].is_a?(String)
+
+      ids = [reference['tag_id'], reference['external_tag_id']].compact
+      ((ids.any? || reference['missing'] == true) &&
+          ids.all? { _1.is_a?(Integer) && _1.positive? } &&
+          (!reference.key?('missing') || (reference['missing'] == true && ids.empty?)) &&
+          (!reference.key?('negative') || [true, false].include?(reference['negative'])))
+    end
+    raise ActionController::BadRequest unless valid
+    return nil unless references.map { _1['name'] } == literals
+
+    references
+  rescue JSON::ParserError, TypeError
+    raise ActionController::BadRequest
+  end
+
   def filtered_posts locale
     tag_names = params[:tags].to_s.split
     match_type = params[:match]
@@ -413,20 +481,29 @@ class PostsController < ApplicationController
   end
 
   def filter_posts_by_tags locale, tag_names, match_type
-    literals = tag_names.map do |raw_name|
-      { name: TagName.canonicalise(locale, raw_name.sub(/\Anot:/i, '')).first,
-        negative: raw_name.downcase.start_with?('not:') }
+    references = tag_filter_references(tag_names)
+    literals = tag_names.each_with_index.map do |raw_name, index|
+      name = raw_name.sub(/\Anot:/i, '')
+      name = TagName.canonicalise(locale, name).first unless references
+      reference = references&.[](index)
+      negative = if reference&.key?('negative')
+                   reference['negative']
+                 else
+                   raw_name.downcase.start_with?('not:')
+                 end
+      { name:, negative:, reference: }
     end
 
     return Post.all if literals.empty?
 
     if match_type == 'any'
       literals.reduce(Post.none) do |posts, literal|
-        posts.or(tag_literal_relation(locale, literal[:name], negative: literal[:negative]))
+        posts.or(tag_literal_relation(locale, literal[:name], negative: literal[:negative],
+                                      reference: literal[:reference]))
       end
     else
       literals.reduce(Post.all) do |posts, literal|
-        ids = tagged_post_ids_for(locale, literal[:name])
+        ids = tagged_post_ids_for(locale, literal[:name], reference: literal[:reference])
         if literal[:negative]
           posts.where.not(id: ids)
         else
@@ -436,8 +513,8 @@ class PostsController < ApplicationController
     end
   end
 
-  def tag_literal_relation locale, name, negative:
-    ids = tagged_post_ids_for(locale, name)
+  def tag_literal_relation locale, name, negative:, reference: nil
+    ids = tagged_post_ids_for(locale, name, reference:)
     if negative
       Post.where.not(id: ids)
     else
@@ -445,7 +522,20 @@ class PostsController < ApplicationController
     end
   end
 
-  def tagged_post_ids_for locale, name
+  def tagged_post_ids_for locale, name, reference: nil
+    if reference
+      matches = Post.none
+      if reference['tag_id']
+        matches = matches.or(Post.where(id: PostTag.where(
+            tag_id: reference['tag_id']).select(:post_id)))
+      end
+      if reference['external_tag_id']
+        matches = matches.or(Post.where(id: PostExternalTag.where(
+            external_tag_id: reference['external_tag_id']).select(:post_id)))
+      end
+      return matches.select(:id)
+    end
+
     posts_by_internal_tags =
         Post
         .joins(tags: :tag_names)