module Gem
  # Gem::StubSpecification reads the stub: line from the gemspec
  # This prevents us having to eval the entire gemspec in order to
  # find out certain information.
  class StubSpecification < BasicSpecification
    # :nodoc:
    PREFIX = "# stub: "

    OPEN_MODE = # :nodoc:
      if Object.const_defined? :Encoding then
        'r:UTF-8:-'
      else
        'r'
      end

    # :nodoc:
    class StubLine
      attr_reader :parts

      def initialize(data)
        @parts = data[PREFIX.length..-1].split(" ")
      end

      def name
        @parts[0]
      end

      def version
        Gem::Version.new @parts[1]
      end

      def platform
        Gem::Platform.new @parts[2]
      end

      def require_paths
        @parts[3..-1].join(" ").split("\0")
      end
    end

    def initialize(filename)
      self.filename = filename
      @data         = nil
      @spec         = nil
    end

    ##
    # Name of the gem

    def name
      @name ||= data.name
    end

    ##
    # Version of the gem

    def version
      @version ||= data.version
    end

    ##
    # Platform of the gem

    def platform
      @platform ||= data.platform
    end

    ##
    # Require paths of the gem

    def require_paths
      @require_paths ||= data.require_paths
    end

    ##
    # The full Gem::Specification for this gem, loaded from evalling its gemspec

    def to_spec
      @spec ||= Gem::Specification.load(filename)
    end

    ##
    # True when this gem has been activated

    def activated?
      loaded = Gem.loaded_specs[name]
      loaded && loaded.version == version
    end

    ##
    # Is this StubSpecification valid? i.e. have we found a stub line, OR does
    # the filename contain a valid gemspec?

    def valid?
      data
    end

    private

    ##
    # If the gemspec contains a stubline, returns a StubLine instance. Otherwise
    # returns the full Gem::Specification.

    def data
      unless @data
        open filename, OPEN_MODE do |file|
          begin
            file.readline # discard encoding line
            stubline = file.readline.chomp
            @data = StubLine.new(stubline) if stubline.start_with?(PREFIX)
          rescue EOFError
          end
        end
      end

      @data ||= to_spec
    end
  end
end