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

require_relative "../vendor/pub_grub"
require_relative "../../../vendor/pub_grub/lib/pub_grub/rubygems"

require_relative "package"
require_relative "../platform"

module Gel::PubGrub
  class Source < Gel::Vendor::PubGrub::BasicPackageSource
    attr_reader :root

    def initialize(gemfile, catalog_set, active_platforms, preference_strategy)
      @gemfile = gemfile
      @catalog_set = catalog_set
      @active_platforms = active_platforms
      @preference_strategy = preference_strategy

      # pub_grub-0.5
    
    def dependencies_for(package, version)
      deps = {}

      if package.is_a?(Package::Pseudo)
        case package.role
        when :root
          deps = { Package::Pseudo.new(:arguments) => [], Package::Pseudo.new(:gemfile) => [] }

        when :gemfile
          @gemfile.gems.each do |name, constraints, _|
            platforms = active_platforms_map[name]
            platforms = [nil] if platforms.empty?

            platforms.each do |platform|
              (deps[Package.new(name, platform)] ||= []).concat(constraints.flatten)
            end
          end

          deps.values.each(&:uniq!)

        when :arguments
          if @preference_strategy
            @preference_strategy.constraints.each do |name, constraints|
              @active_platforms.each do |platform|
                (deps[Package.new(name, platform)] ||= []).concat(constraints.flatten)
              end
            end
          end