Delegate bulk operations to a TopicsBulkAction object.

app/controllers/topics_controller.rb

@@ -1,6 +1,7 @@
 require_dependency 'topic_view'
 require_dependency 'promotion'
 require_dependency 'url_helper'
+require_dependency 'topics_bulk_action'
 
 class TopicsController < ApplicationController
   include UrlHelper
@@ -269,7 +270,11 @@ class TopicsController < ApplicationController
 
   def bulk
     topic_ids = params.require(:topic_ids).map {|t| t.to_i}
-    render_json_dump topic_ids: topic_ids
+    operation = params.require(:operation).symbolize_keys
+    raise ActionController::ParameterMissing.new(:operation_type) if operation[:type].blank?
+    operator = TopicsBulkAction.new(current_user, topic_ids, operation)
+    changed_topic_ids = operator.perform!
+    render_json_dump topic_ids: changed_topic_ids
   end
 
   private