module TTFunk
  module Reader
    private

      def io
        @file.contents
      end

      def read(bytes, format)
        io.read(bytes).unpack(format)
      end

      def read_signed(count)
        read(count*2, "n*").map { |i| to_signed(i) }
      end

      def to_signed(n)
        (n>=0x8000) ? -((n ^ 0xFFFF) + 1) : n
      end

      def parse_from(position)
        saved, io.pos = io.pos, position
        result = yield position
        io.pos = saved
        return result
      end

      # For debugging purposes
      def hexdump(string)
        bytes = string.unpack("C*")
        bytes.each_with_index do |c, i|
          print "%02X" % c
          if (i+1) % 16 == 0
            puts
          elsif (i+1) % 8 == 0
            print "  "
          else
            print " "
          end
        end
        puts unless bytes.length % 16 == 0
      end
  end
end