module Arm
  # ADDRESSING MODE 4

  class StackInstruction < Instruction
    include Arm::Constants

    def initialize(first , attributes)
      super(attributes)
      @first = first
      @attributes[:update_status] = 0 if @attributes[:update_status] == nil
      @attributes[:condition_code] = :al if @attributes[:condition_code] == nil
      @attributes[:opcode] = attributes[:opcode]
      @operand = 0

      @attributes[:update_status]= 0
      @rn = :r0 # register zero = zero bit pattern
      # downward growing, decrement before memory access
      # official ARM style stack as used by gas
    end

    def assemble(io)
      # don't overwrite instance variables, to make assembly repeatable
      operand = @operand

      if (@first.is_a?(Array))
        operand = 0
        @first.each do |r|
          raise "nil register in push, index #{r}- #{inspect}" if r.nil?
          operand = operand | (1 << reg_code(r))
        end
      else
        raise "invalid operand argument #{inspect}"
      end
      write_base = 1
      if (opcode == :push)
        pre_post_index = 1
        up_down = 0
        is_pop = 0
      else  #pop
        pre_post_index = 0
        up_down = 1
        is_pop = 1
      end
      instuction_class = 0b10 # OPC_STACK
      cond = @attributes[:condition_code].is_a?(Symbol) ?  COND_CODES[@attributes[:condition_code]]   : @attributes[:condition_code]
      @rn = :sp # sp register
      #assemble of old
      val = operand
      val = val | (reg_code(@rn) <<             16)
      val = val | (is_pop <<              16+4) #20
      val = val | (write_base <<          16+4+ 1)
      val = val | (@attributes[:update_status] <<  16+4+ 1+1)
      val = val | (up_down <<             16+4+ 1+1+1)
      val = val | (pre_post_index <<      16+4+ 1+1+1+1)#24
      val = val | (instuction_class <<    16+4+ 1+1+1+1 +2)
      val = val | (cond <<                16+4+ 1+1+1+1 +2+2)
      io.write_uint32 val
    end

    def is_push?
      opcode == :push
    end
    def is_pop?
      !is_push?
    end
    def uses
      is_push? ? regs : []
    end
    def assigns
      is_pop? ? regs : []
    end
    def regs
      @first
    end
    def to_s
      "#{opcode} [#{@first.collect {|f| f.to_asm}.join(',') }] #{super}"
    end
  end

end