You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: post_event_decorator.rb
    path of file: ./repos/e621ng/app/decorators
    
    the code of the file until where you have to start completion: # frozen_string_literal: 
    
  def format_description
    vals = object.extra_data

    case object.action
    when "deleted", "flag_created"
      "#{vals['reason']}"
    when "favorites_moved"
      "Target: post ##{vals['parent_id']}"
    when "favorites_received"
      "From: post ##{vals['child_id']}"
    when "replacement_promoted"
      "From: post ##{vals['source_post_id']}"
    end