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: gem_updater.rb
    path of file: ./repos/gem_updater/lib
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require 'erb'
require 'gem_updater/changelog_parser'
require 'gem_updater/gemfile'
require 'gem_updater/ruby_gems_fetcher'

# Base lib.
module GemUpdater
  # Updater's main responsability is to fill changes
  # happened before and after update of `Gemfile`, and then format them.
  class Updater
    RUBYGEMS_SOURCE_NAME = 'rubygems repository https://rubygems.org/'

    attr_accessor :gemfile

    def 
    
    def fill_changelogs
      [].tap do |threads|
        gemfile.changes.each do |gem_changes, details|
          threads << Thread.new { retrieve_changelog(gem_changes, details) }
        end
      end.each(&:join)
    end

    # Get the changelog URL.
    def retrieve_changelog(gem_name, details)
      return unless details[:source].name == RUBYGEMS_SOURCE_NAME

      changelog_uri = RubyGemsFetcher.new(gem_name).changelog_uri

      return unless changelog_uri

      changelog = ChangelogParser
                  .new(uri: changelog_uri, version: details.dig(:versions, :new)).changelog
      gemfile.changes[gem_name][:changelog] = changelog&.to_s
    end

    # Get the template for gem's diff.
    # It can use a custom template.
    #
    # @return [ERB] the template
    def template
      File.read("#{Dir.home}/.gem_updater_template.erb")
    rescue Errno::ENOENT
      File.read(File.expand_path('../lib/gem_updater_template.erb', __dir__))
    end
  end