module Berkshelf
  # @author Jamie Winsor <jamie@vialstudios.com>
  class Downloader
    extend Forwardable

    attr_reader :cookbook_store
    attr_reader :queue

    def_delegators :@cookbook_store, :storage_path

    def initialize(cookbook_store)
      @cookbook_store = cookbook_store
      @queue = []
    end

    # Add a CookbookSource to the downloader's queue
    #
    # @param [Berkshelf::CookbookSource] source
    # 
    # @return [Array<Berkshelf::CookbookSource>]
    #   the queue - an array of Berkshelf::CookbookSources
    def enqueue(source)
      unless validate_source(source)
        raise ArgumentError, "Invalid CookbookSource: can only enqueue valid instances of CookbookSource."
      end

      @queue << source
    end

    # Remove a CookbookSource from the downloader's queue
    #
    # @param [Berkshelf::CookbookSource] source
    #
    # @return [Berkshelf::CookbookSource]
    #   the CookbookSource removed from the queue
    def dequeue(source)
      @queue.delete(source)
    end

    # Download each CookbookSource in the queue. Upon successful download
    # of a CookbookSource it is removed from the queue. If a CookbookSource
    # fails to download it remains in the queue.
    #
    # @return [TXResultSet]
    def download_all
      results = TXResultSet.new

      queue.each do |source|
        results.add_result download(source)
      end

      results.success.each { |result| dequeue(result.source) }
      
      results
    end

    # Downloads the given CookbookSource
    #
    # @param [CookbookSource] source
    #   the source to download
    #
    # @return [TXResult]
    def download(source)
      status, message = source.download(storage_path)
      TXResult.new(status, message, source)
    end

    # Downloads the given CookbookSource. Raises a DownloadFailure error
    # if the download was not successful.
    #
    # @param [CookbookSource] source
    #   the source to download
    #
    # @return [TXResult]
    def download!(source)
      result = download(source)
      raise DownloadFailure, result.message if result.failed?
      
      result
    end

    def downloaded?(source)
      source.downloaded? || cookbook_store.downloaded?(source.name, source.local_version)
    end

    private

      def validate_source(source)
        source.is_a?(Berkshelf::CookbookSource)
      end
  end
end