module Risc
  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.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
          compiler.add_mom( Mom::ReturnSequence.new)
          return compiler
        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.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
          compiler.add_mom( Mom::ReturnSequence.new)
          return compiler
        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 ,{})
          builder = compiler.builder(compiler.source)
          builder.prepare_int_return # makes integer_tmp variable as return
          emit_syscall( builder , :exit )
          return compiler
        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 = MethodCompiler.compiler_for_class(:Object,:__init__ ,
                            Parfait::NamedList.type_for({}) , Parfait::NamedList.type_for({}))
          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

        # the exit function
        # mainly calls exit_sequence
        def exit( context )
          compiler = compiler_for(:Object,:exit ,{})
          builder = compiler.builder(compiler.source)
          builder.prepare_int_return # makes integer_tmp variable as return
          exit_sequence(builder)
          return compiler
        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 exit_sequence(builder)
          save_message( builder )
          builder.build do
            message << message[:return_value]
            message.reduce_int
            add_code Syscall.new("emit_syscall(exit)", :exit )
          end
        end

        # emit the syscall with given name
        # there is a Syscall instruction, but the message has to be saved and restored
        def emit_syscall( builder , name )
          save_message( builder )
          builder.add_code 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

        # save the current message, as the syscall destroys all context
        #
        # This relies on linux to save and restore all registers
        #
        def save_message(builder)
          r8 = 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 restore_message(builder)
          r8 = 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
      extend ClassMethods
    end
  end
end