let crc16 = require('./crc16.js')

const SOH = 0x01 /* start of 128-byte data packet */
const STX = 0x02  /* start of 1024-byte data packet */
const EOT = 0x04  /* end of transmission */
const ACK = 0x06 /* acknowledge */
const NAK = 0x15 /* negative acknowledge */
const CA = 0x18 /* two of these in succession aborts transfer */
const CRC16 = 0x43  /* 'C' == 0x43, request 16-bit CRC */
const NEGATIVE_BYTE = 0xFF

const ABORT1 = 0x41  /* 'A' == 0x41, abort by user */
const ABORT2 = 0x61  /* 'a' == 0x61, abort by user */

const NAK_TIMEOUT = 10000
const DOWNLOAD_TIMEOUT = 1000 /* One second retry delay */
const MAX_ERRORS = 10

const NORMAL_LEN = 128;
const LONG_LEN = 1024;
const DATA_INDEX = 3;

function getNormalPacket(id, contentBuf) {
  let buf = new Uint8Array(NORMAL_LEN + 3 + 2); //NORMAL_LEN
  let i = 0;
  buf[i++] = SOH;

  buf[i++] = id;
  buf[i++] = 0xFF - id;

  if (contentBuf.length > NORMAL_LEN) {
    throw new Error("Over normal packet size limit");
  }

  for (let j = 0; j < contentBuf.length; j++) {
    buf[i++] = contentBuf[j];
  }

  while (i < NORMAL_LEN + 3) {
    buf[i++] = 0x1A;
  }
  let bufcrc = buf.slice(3, 3 + NORMAL_LEN)
  let crc = crc16(bufcrc, NORMAL_LEN);

  buf[i++] = (crc >> 8) & 0xFF;
  buf[i++] = crc & 0xFF;

  // console.log("packet forming End i = ", i);

  return buf;
}

function getLongPacket (id, contentBuf) {
  let buf = new Uint8Array(LONG_LEN + 3 + 2);
  let i = 0;
  buf[i++] = STX;

  buf[i++] = id;
  buf[i++] = 0xFF - id;

  if (contentBuf.length > LONG_LEN) {
    throw new Error("Over long packet size limit");
  }

  for (let j = 0; j < contentBuf.length; j++) {
    buf[i++] = contentBuf[j];
  }

  while (i < LONG_LEN + 3) {
    buf[i++] = 0x1A;
  }
  let bufcrc = buf.slice(3, LONG_LEN + 3)
  let crc = crc16(bufcrc, LONG_LEN);

  buf[i++] = (crc >> 8) & 0xFF;
  buf[i++] = crc & 0xFF;

  // console.log("packet forming End i = ", i);

  return buf;
}
function getZeroContent (fileSymbol, fileLen) {

  let buf = new Uint8Array(128);

  // let fileLenBuf = Uint8Array.from(fileLen + '')
  // let symbolBuf = Uint8Array.from(fileSymbol)
  let fileLenStr = fileLen.toString()
  let i = 0, j = 0;
  for (j = 0; j < fileSymbol.length; j++) {
    buf[i++] = fileSymbol.charCodeAt(j)
  }
  buf[i++] = 0;
  for (j = 0; j < fileLenStr.length; j++) {
    buf[i++] = fileLenStr.charCodeAt(j)
  }
  // buf[i++] = 32;

  return buf;
}

let packet = {
  getZeroContent: getZeroContent,
  getNormalPacket: getNormalPacket,
  getLongPacket: getLongPacket
};

module.exports = packet;