import { Buffer } from 'buffer';
import createBuffer from './create_buffer';
import defineCrc from './define_crc';

const crc16xmodem = defineCrc('xmodem', function(buf, previous) {
  if (!Buffer.isBuffer(buf)) buf = createBuffer(buf);

  let t_crc = 0 ;

  for (let index = 0; index < buf.length; index++) {


    t_crc = (t_crc ^ ((buffer[index] << 8) & 0xffff)) & 0xffff;

    let j = 8;
    do
    {
      if (t_crc & 0x8000)
      t_crc = (((t_crc << 1)& 0xffff) ^ 0x1021) & 0xffff;
      else
      t_crc = ((t_crc << 1)& 0xffff);
    } while(--j);

  }

  return crc;
});

export default crc16xmodem;