n65/lib/n65/directives/dw.rb

# frozen_string_literal: true

require_relative '../instruction_base'

module N65
  # This directive instruction can include a binary file
  class DW < InstructionBase
    # Try to parse a dw directive
    def self.parse(line)
      # Maybe it is a straight up bit of hex
      match_data = line.match(/^\.dw\s+\$([0-9A-F]{1,4})$/)
      unless match_data.nil?
        word = match_data[1].to_i(16)
        return DW.new(word)
      end

      # Or maybe it points to a symbol
      match_data = line.match(/^\.dw\s+([A-Za-z_][A-Za-z0-9_.]+)/)
      unless match_data.nil?
        symbol = match_data[1]
        return DW.new(symbol)
      end
      nil
    end

    #  Initialize with filename
    def initialize(value)
      @value = value
    end

    # Execute on the assembler, now in this case value may
    # be a symbol that needs to be resolved, if so we return
    # a lambda which can be executed later, with the promise
    # that that symbol will have then be defined
    # This is a little complicated, I admit.
    def exec(assembler)
      promise = assembler.with_saved_state do |saved_assembler|
        value = saved_assembler.symbol_table.resolve_symbol(@value)
        bytes = [value & 0xFFFF].pack('S').bytes
        saved_assembler.write_memory(bytes)
      end

      # Try to execute it now, or setup the promise to return
      case @value
      when Integer
        bytes = [@value & 0xFFFF].pack('S').bytes
        assembler.write_memory(bytes)
      when String
        begin
          promise.call
        rescue SymbolTable::UndefinedSymbol
          # Must still advance PC before returning promise, so we'll write
          # a place holder value of 0xDEAD
          assembler.write_memory([0xDE, 0xAD])
          promise
        end
      else
        raise('Uknown argument in .dw directive')
      end
    end

    # Display
    def to_s
      case @value
      when String
        ".dw #{@value}"
      when Integer
        '.dw $%4.X' % @value
      end
    end
  end
end