require "minitar"
require "find" unless defined?(Find)
require "zlib" unless defined?(Zlib)

module Berkshelf
  # A class for archiving and compressing directory containing one or more cookbooks.
  #
  # Example:
  #   Archiving a path containing the cookbooks:
  #     * "/path/to/cookbooks/my_face"
  #     * "/path/to/cookbooks/nginx"
  #
  #   irb> source   = "/path/to/cookbooks"
  #   irb> packager = Berkshelf::Packager.new("some/path/cookbooks.tar.gz")
  #   irb> packager.run(source) #=> "some/path/cookbooks.tar.gz"
  class Packager
    class << self
      def validate_destination(path)
        path.to_s
      end
    end

    # @return [String]
    attr_reader :out_file

    # @param [#to_s] out_file
    #   path to write the archive to
    def initialize(out_file)
      @out_file           = out_file.to_s
      @out_dir, @filename = File.split(@out_file)
    end

    # Archive the contents of given path
    #
    # @param [#to_s] source
    #   the filepath to archive the contents of
    #
    # @raise [PackageError]
    #   if an error is encountered while writing the out_file
    #
    # @return [String]
    #   path to the generated archive
    def run(source)
      begin
        dest = Zlib::GzipWriter.open(out_file)
        tar = RelativeTarWriter.new(dest, source)
        Find.find(source) do |entry|
          next if source == entry

          Minitar.pack_file(entry, tar)
        end
      ensure
        tar.close
        dest.close
      end

      out_file
    rescue SystemCallError => ex
      raise PackageError, ex
    end

    # Validate that running the packager would be successful. Returns nil if would be
    # successful and raises an error if would not.
    #
    # @raise [PackageError]
    #   if running the packager would absolutely not result in a success
    #
    # @return [nil]
    def validate!
      raise PackageError, "Path is not a directory: #{out_dir}" unless File.directory?(out_dir)
      raise PackageError, "Directory is not writable: #{out_dir}" unless File.writable?(out_dir)
    end

    private

    # @return [String]
    attr_reader :out_dir

    # @return [String]
    attr_reader :filename

    # A private decorator for Minitar::Writer that
    # turns absolute paths into relative ones.
    class RelativeTarWriter < SimpleDelegator # :nodoc:
      def initialize(io, base_path)
        @base_path = Pathname.new(base_path)
        super(Minitar::Writer.new(io))
      end

      %w{add_file add_file_simple mkdir}.each do |method|
        class_eval <<~RUBY
          def #{method}(name, *opts, &block)
            super(relative_path(name), *opts, &block)
          end
        RUBY
      end

      private

      attr_reader :base_path

      def relative_path(path)
        Pathname.new(path).relative_path_from(base_path).to_s
      end
    end
  end
end