module Risc

  # MethodCompiler (old name) is used to generate risc instructions for methods
  # and to instantiate the methods correctly. Most of the init is typed layer stuff,
  # but there is some logic too.

  class MethodCompiler

    def initialize( method )
      @regs = []
      if method == :main
        @type = Parfait.object_space.get_type()
        @method = @type.get_method( :main )
        @method = @type.create_method( :main ,{}) unless @method
      else
        @method = method
        @type = method.for_type
      end
      @current = @method.risc_instructions
    end
    attr_reader :type , :method

    # create the method, do some checks and set it as the current method to be added to
    # class_name and method_name are pretty clear, args are given as a ruby array
    def self.create_method( class_name , method_name , args , frame )
      raise "create_method #{class_name}.#{class_name.class}" unless class_name.is_a? Symbol
      clazz = Parfait.object_space.get_class_by_name! class_name
      create_method_for( clazz.instance_type , method_name , args , frame)
    end

    # create a method for the given type ( Parfait type object)
    # method_name is a Symbol
    # args a hash that will be converted to a type
    # the created method is set as the current and the given type too
    # return the compiler (for chaining)
    def self.create_method_for( type , method_name , args , frame)
      raise "create_method #{type.inspect} is not a Type" unless type.is_a? Parfait::Type
      raise "Args must be Type #{args}" unless args.is_a?(Parfait::Type)
      raise "create_method #{method_name}.#{method_name.class}" unless method_name.is_a? Symbol
      method = type.create_method( method_name , args , frame)
      self.new(method)
    end

    def add_known(name)
      case name
      when :receiver
        ret = use_reg @type
        add_slot_to_reg(" load self" , :message , :receiver , ret )
        return ret
      when :space
        space = Parfait.object_space
        reg = use_reg :Space , space
        add_load_constant( "load space", space , reg )
        return reg
      when :message
        reg = use_reg :Message
        add_transfer( "load message", Risc.message_reg , reg )
        return reg
      else
        raise "Unknow expression #{name}"
      end
    end

    # set the insertion point (where code is added with add_code)
    def set_current c
      @current = c
    end

    # convert the given mom instruction to_risc and then add it (see add_code)
    # continue down the instruction chain unti depleted
    # (adding moves the insertion point so the whole mom chain is added as a risc chain)
    def add_mom( instruction )
      while( instruction )
        raise "whats this a #{instruction}" unless instruction.is_a?(Mom::Instruction)
        #puts "adding mom #{instruction.to_s}:#{instruction.next.to_s}"
        risc = instruction.to_risc( self )
        add_code(risc)
        #puts "adding risc #{risc.to_s}:#{risc.next.to_s}"
        instruction = instruction.next
      end
    end
    # add a risc instruction after the current (insertion point)
    # the added instruction will become the new insertion point
    def add_code( instruction )
      raise "Not an instruction:#{instruction.to_s}" unless  instruction.is_a?(Risc::Instruction)
      raise instruction.to_s if( instruction.class.name.split("::").first == "Arm")
      new_current = instruction.last #after insertion this point is lost
      @current.insert(instruction) #insert after current
      @current = new_current
      self
    end

    # for computationally building code (ie writing assembler) these short cuts
    # help to instantiate risc instructions and add them immediately
    [:label, :reg_to_slot , :slot_to_reg , :load_constant, :load_data,
      :function_return , :function_call, :op ,
      :transfer , :reg_to_slot , :byte_to_reg , :reg_to_byte].each do |method|
      define_method("add_#{method}".to_sym) do |*args|
        add_code Risc.send( method , *args )
      end
    end

    # require a (temporary) register. code must give this back with release_reg
    def use_reg( type , value = nil )
      raise "Not type #{type.inspect}" unless type.is_a?(Symbol) or type.is_a?(Parfait::Type)
      if @regs.empty?
        reg = Risc.tmp_reg(type , value)
      else
        reg = @regs.last.next_reg_use(type , value)
      end
      @regs << reg
      return reg
    end

    def copy( reg , source )
      copied = use_reg reg.type
      add_code Register.transfer( source , reg , copied )
      copied
    end

    # releasing a register (accuired by use_reg) makes it available for use again
    # thus avoiding possibly using too many registers
    def release_reg( reg )
      last = @regs.pop
      raise "released register in wrong order, expect #{last} but was #{reg}" if reg != last
    end

    # reset the registers to be used. Start at r4 for next usage.
    # Every statement starts with this, meaning each statement may use all registers, but none
    # get saved. Statements have affect on objects.
    def reset_regs
      @regs.clear
    end

    # move a machine int from register "from" to a Parfait::Integer in register "to"
    # have to grab an integer from space and stick it in the "to" register first.
    def add_new_int( source , from, to )
      source += "add_new_int "
      space = use_reg(:Space)
      int = use_reg(:Integer)
      space_i = Risc.resolve_to_index(:Space, :next_integer)
      add_load_constant( source + "space" , Parfait.object_space , space  )
      add_slot_to_reg( source + "next_i1" , space , space_i , to)
      add_slot_to_reg( source + "next_i2" , to , Risc.resolve_to_index(:Integer, :next_integer) , int)
      add_reg_to_slot( source + "store link" , int , space , space_i  )
      add_reg_to_slot( source + "store value" , from , to , Parfait::Integer.integer_index)
    end
    def add_constant(const)
      Risc.machine.add_constant(const)
    end

    # load receiver and the first argument (int)
    # return both registers
    def self_and_int_arg( source )
      me = add_known( :receiver )
      int_arg = load_int_arg_at(source , 1 )
      return me , int_arg
    end

    # Load the first argument, assumed to be integer
    def load_int_arg_at( source , at)
      int_arg = use_reg :Integer
      add_slot_to_reg(source , :message , :arguments , int_arg )
      add_slot_to_reg(source , int_arg , at + 1, int_arg ) #1 for type
      return int_arg
    end

    # assumed Integer in given register is replaced by the fixnum that it is holding
    def reduce_int( source , register )
      add_slot_to_reg( source + "int -> fix" , register , Parfait::Integer.integer_index , register)
    end
  end
end