module Vool

  class YieldStatement < Statement
    attr_reader :arguments

    def initialize(name , receiver , arguments)
      @arguments = arguments
      @receiver = receiver
      @name = name
      @arguments ||= []
    end

    def to_s
      "#{receiver}.#{name}(#{arguments.join(', ')})"
    end

    def each(&block)
      block.call(self)
      block.call(@receiver)
      @arguments.each do |arg|
        block.call(arg)
      end
    end

    # When used as right hand side, this tells what data to move to get the result into
    # a varaible. It is (off course) the return value of the message
    def slot_definition(compiler)
      Mom::SlotDefinition.new(:message ,[ :return_value])
    end

    # A Send breaks down to 2 steps:
    # - Setting up the next message, with receiver, arguments, and (importantly) return address
    # - a SimpleCall,
    def to_mom( compiler )
      @parfait_block = @block.to_mom(compiler) if @block
      @receiver = SelfExpression.new(compiler.receiver_type) if @receiver.is_a?(SelfExpression)
      yield_call(compiler)
    end

    # this breaks into two parts:
    # - check the calling method and break to a (not implemented) dynamic version
    # - call the block, that is the last argument of the method
    def yield_call(compiler)
      method_check(compiler) << yield_arg_block(compiler)
    end

    # check that the calling method is the method that the block was created in.
    # In that case variable resolution is reasy and we can prceed to yield
    # Note: the else case is not implemented (ie passing lambdas around)
    #      this needs run-time variable resolution, which is just not done.
    #      we brace ourselves with the check, and exit (later raise) if . . .
    def method_check(compiler)
      ok_label = Mom::Label.new("method_ok_#{self.object_id}")
      compile_method = Mom::SlotDefinition.new( compiler.get_method , [])
      runtime_method = Mom::SlotDefinition.new( :message , [ :method] )
      check = Mom::NotSameCheck.new(compile_method , runtime_method, ok_label)
      # TODO? Maybe create mom instructions for this
      #builder = compiler.code_builder("yield")
      #Risc::Builtin::Object.exit_sequence(builder)
      #check << builder.built
      check << ok_label
    end

    # to call the block (that we know now to be the last arg),
    # we do a message setup, arg transfer and the a arg_yield (which is similar to dynamic_call)
    def yield_arg_block(compiler)
      arg_index = compiler.get_method.arguments_type.get_length - 1
      setup  = Mom::MessageSetup.new( arg_index )
      mom_receive = @receiver.slot_definition(compiler)
      arg_target = [:message , :next_message , :arguments]
      args = []
      @arguments.each_with_index do |arg , index| # +1 because of type
        args << Mom::SlotLoad.new( arg_target + [index + 1] , arg.slot_definition(compiler))
      end
      setup << Mom::ArgumentTransfer.new( mom_receive , args )
      setup << Mom::BlockYield.new( arg_index )
    end

    def to_s(depth = 0)
      sen = "#{receiver}.#{name}(#{@arguments.collect{|a| a.to_s}.join(', ')})"
      at_depth(depth , sen)
    end

  end
end