Server side implementation for bulk editing categories

lib/topics_bulk_action.rb

@@ -6,9 +6,34 @@ class TopicsBulkAction
     @operation = operation
   end
 
-  def perform!
-    []
+  def self.operations
+    %w(change_category)
   end
 
+  def perform!
+    raise Discourse::InvalidParameters.new(:operation) unless TopicsBulkAction.operations.include?(@operation[:type])
+    send(@operation[:type])
+  end
+
+  private
+
+    def change_category
+      changed_ids = []
+      topics.each do |t|
+        if guardian.can_edit?(t)
+          changed_ids << t.id if t.change_category(@operation[:category_name])
+        end
+      end
+      changed_ids
+    end
+
+    def guardian
+      @guardian ||= Guardian.new(@user)
+    end
+
+    def topics
+      @topics ||= Topic.where(id: @topic_ids)
+    end
+
 end