#21 完了

backend/app/controllers/tags_controller.rb

@@ -2,14 +2,36 @@ class TagsController < ApplicationController
   before_action :set_tags, only: %i[ show update destroy ]
 
   def index
-    if params[:post].present?
-      @tags = Tag.joins(:posts).where(posts: { id: params[:post] })
-    else
-      @tags = Tag.all
-    end
+    @tags =
+      if params[:post].present?
+        Tag.joins(:posts).where(posts: { id: params[:post] })
+      else
+        Tag.all
+      end
     render json: @tags
   end
 
+  def autocomplete
+    q = params[:q].to_s.strip
+    return render json: [] if q.blank?
+
+    tags = (Tag
+            .left_joins(:posts)
+            .select('tags.id, tags.name, tags.category, COUNT(posts.id) AS post_count')
+            .where('(tags.category = ? AND tags.name LIKE ?)
+                    OR tags.name LIKE ?',
+                   'nico', "nico:#{ q }%", "#{ q }%")
+            .group('tags.id')
+            .order('post_count DESC, tags.name ASC')
+            .limit(20))
+    render json: tags.map do |tag|
+      { id:       tag.id,
+        name:     tag.name,
+        category: tag.category,
+        count:    tag.post_count }
+    end
+  end
+
   def show
     render json: @tag
   end
@@ -24,13 +46,14 @@ class TagsController < ApplicationController
   end
 
   private
-    # Use callbacks to share common setup or constraints between actions.
-    def set_tag
-      @tag = Tag.find(params.expect(:id))
-    end
 
-    # Only allow a list of trusted parameters through.
-    def tag_params
-      params.expect(tag: [ :title, :body ])
-    end
+  # Use callbacks to share common setup or constraints between actions.
+  def set_tag
+    @tag = Tag.find(params.expect(:id))
+  end
+
+  # Only allow a list of trusted parameters through.
+  def tag_params
+    params.expect(tag: [ :title, :body ])
+  end
 end