module Stomper
  module Frames
    # Encapsulates a client side frame for the Stomp Protocol.
    #
    # See the {Stomp Protocol Specification}[http://stomp.codehaus.org/Protocol]
    # for more details.
    class ClientFrame
      attr_reader :headers, :body, :command

      # Creates a new ClientFrame instance with the specified +command+,
      # +headers+ and +body+.
      # If +headers+ includes a key of :generate_content_length, the
      # associated value will determine if a 'content-length' header is automatically
      # generated for this particular frame instance.  This key can be
      # specified in the +headers+ parameter of any of the subclasses of ClientFrame,
      # and it will be interpretted in the same fashion.
      def initialize(command, headers={}, body=nil)
        @command = command
        @generate_content_length = headers.delete(:generate_content_length)
        @headers = Headers.new(headers)
        @body = body
      end

      # If +bool+ false or nil, this frame instance will not attempt to
      # automatically generate a content-length header.  This is useful when
      # dealing with ActiveMQ as a stomp message broker, which will treat incoming
      # messages lacking a content-length header as +TextMessage+s and
      # +BytesMessage+s if the header is present.  For more information see:
      # {Apache ActiveMQ - Stomp}[http://activemq.apache.org/stomp.html]
      def generate_content_length=(bool)
        @generate_content_length=bool
      end

      # If generate_content_length= has been called on this instance, then the
      # value supplied there is returned here.  Otherwise, we defer to the
      # class method of the same name.
      def generate_content_length?
        @generate_content_length.nil? ? self.class.generate_content_length? : @generate_content_length
      end

      # Converts the frame instance into a valid string representation of the
      # desired command according to the specifications of the
      # {Stomp Protocol}[http://stomp.codehaus.org/Protocol]
      #
      # This is where the content-length header is generated if the frame
      # has a body of non-zero length and generate_content_length? is true.
      def to_stomp
        @headers["content-length"] = str_size(@body) if @body && !@body.empty? && generate_content_length?
        "#{@command}\n#{@headers.to_stomp}\n#{@body}\0"
      end

      class << self
        # Sets a class level setting for determining if a content-length header
        # should automatically be generated.
        def generate_content_length=(bool)
          @generate_content_length = bool
        end

        # Returns the value passed to the class level generate_content_length=
        # method, or true if no value has been set (thus, defaults to true.)
        #
        # The precedence for resolving whether or not a content-length header
        # is generated by the to_stomp method is: check the instance setting,
        # if it has not been set, defer to the class setting, if it hasn't
        # been set, default to true.
        def generate_content_length?
          if @generate_content_length.nil?
            @generate_content_length = true
          end
          @generate_content_length
        end
      end

      private
      def str_size(str)
        if str.respond_to?(:bytesize)
          def str_size(strng); strng.bytesize; end
          str.bytesize
        else
          def str_size(strng); strng.size; end
          str.size
        end
      end
    end
  end
end