module Mom
  module Builtin
    class Object
      module ClassMethods
        include CompileHelper

        # self[index] basically. Index is the first arg
        # return is stored in return_value
        def get_internal_word( context )
          compiler = compiler_for(:Object , :get_internal_word ,{at: :Integer})
          compiler.add_code GetInternalWord.new("get_internal_word")
          return compiler
        end
        class GetInternalWord < ::Mom::Instruction
          def to_risc(compiler)
            compiler.builder(compiler.source).build do
              object! << message[:receiver]
              integer! << message[:arguments]
              integer << integer[Parfait::NamedList.type_length + 0] #"at" is at index 0
              integer.reduce_int
              object << object[integer]
              message[:return_value] << object
            end
          end
        end

        # self[index] = val basically. Index is the first arg , value the second
        # return the value passed in
        def set_internal_word( context )
          compiler = compiler_for(:Object , :set_internal_word , {at: :Integer, value: :Object} )
          compiler.add_code SetInternalWord.new("set_internal_word")
          return compiler
        end

        class SetInternalWord < ::Mom::Instruction
          def to_risc(compiler)
            compiler.builder(compiler.source).build do
              object! << message[:receiver]
              integer! << message[:arguments]
              object_reg! << integer[Parfait::NamedList.type_length + 1] #"value" is at index 1
              integer << integer[Parfait::NamedList.type_length + 0] #"at" is at index 0
              integer.reduce_int
              object[integer] << object_reg
              message[:return_value] << object_reg
            end
            return compiler
          end
        end

        # every object needs a method missing.
        # Even if it's just this one, sys_exit (later raise)
        def _method_missing( context )
          compiler = compiler_for(:Object,:method_missing ,{})
          compiler.add_code MethodMissing.new("missing")
          return compiler
        end

        class MethodMissing < ::Mom::Instruction
          def to_risc(compiler)
            builder = compiler.builder(compiler.source)
            builder.prepare_int_return # makes integer_tmp variable as return
            Builtin.emit_syscall( builder , :exit )
            return compiler
          end
        end

        # this is the really really first place the machine starts (apart from the jump here)
        # it isn't really a function, ie it is jumped to (not called), exits and may not return
        # so it is responsible for initial setup:
        # - load fist message, set up Space as receiver
        # - call main, ie set up message for that etc
        # - exit (exit_sequence) which passes a machine int out to c
        def __init__( context )
          compiler = Mom::MethodCompiler.compiler_for_class(:Object,:__init__ ,
                            Parfait::NamedList.type_for({}) , Parfait::NamedList.type_for({}))
                            compiler.add_code MethodMissing.new("missing")
          return compiler
        end

        class Init < ::Mom::Instruction
          def to_risc(compiler)
            builder = compiler.builder(compiler.source)
            builder.build do
              factory! << Parfait.object_space.get_factory_for(:Message)
              message << factory[:next_object]
              next_message! << message[:next_message]
              factory[:next_object] << next_message
            end

            Mom::MessageSetup.new(Parfait.object_space.get_main).build_with( builder )

            builder.build do
              message << message[:next_message]
              space? << Parfait.object_space
              message[:receiver] << space
            end

            exit_label = Risc.label(compiler.source , "#{compiler.receiver_type.object_class.name}.#{compiler.source.name}" )
            ret_tmp = compiler.use_reg(:Label).set_builder(builder)
            builder.build do
              ret_tmp << exit_label
              message[:return_address] << ret_tmp
              add_code Risc.function_call( "__init__ issue call" ,  Parfait.object_space.get_main)
              add_code exit_label
            end
            compiler.reset_regs
            exit_sequence(builder)
            return compiler
          end
        end

        # the exit function
        # mainly calls exit_sequence
        def exit( context )
          compiler = compiler_for(:Object,:exit ,{})
          compiler.add_code Exit.new("exit")
          return compiler
        end

        class Exit < ::Mom::Instruction
          def to_risc(compiler)
            builder = compiler.builder(compiler.source)
            builder.prepare_int_return # makes integer_tmp variable as return
            Builtin.exit_sequence(builder)
            return compiler
          end
        end
      end
      extend ClassMethods
    end

    # emit the syscall with given name
    # there is a Syscall instruction, but the message has to be saved and restored
    def self.emit_syscall( builder , name )
      save_message( builder )
      builder.add_code Risc::Syscall.new("emit_syscall(#{name})", name )
      restore_message(builder)
      return unless (@clazz and @method)
      builder.add_code Risc.label( "#{@clazz.name}.#{@message.name}" , "return_syscall" )
    end

    # a sort of inline version of exit method.
    # Used by exit and __init__ (so it doesn't have to call it)
    # Assumes int return value and extracts the fixnum for process exit code
    def self.exit_sequence(builder)
      save_message( builder )
      builder.build do
        message << message[:return_value]
        message.reduce_int
        add_code Risc::Syscall.new("emit_syscall(exit)", :exit )
      end
    end

    # save the current message, as the syscall destroys all context
    #
    # This relies on linux to save and restore all registers
    #
    def self.save_message(builder)
      r8 = Risc::RegisterValue.new( :r8 , :Message).set_builder(builder)
      builder.build {r8 << message}
    end

    # restore the message that we save in r8
    # before th restore, the syscall return, a fixnum, is saved
    # The caller of this method is assumed to caal prepare_int_return
    # so that the return value already has an integer instance
    # This instance is filled with os return value
    def self.restore_message(builder)
      r8 = Risc::RegisterValue.new( :r8 , :Message)
      builder.build do
        integer_reg! << message
        message << r8
        integer_2! << message[:return_value]
        integer_2[Parfait::Integer.integer_index] << integer_reg
      end
    end
  end
end