/**
 * 十六进制工具函数
 */

/**
 * ArrayBuffer 转十六进制字符串
 * @param {ArrayBuffer} buffer - ArrayBuffer 数据
 * @returns {string} 十六进制字符串（大写）
 */
function arrayBufferToHex(buffer) {
  const hexArr = Array.prototype.map.call(
    new Uint8Array(buffer),
    function (byte) {
      return ('0' + byte.toString(16)).slice(-2);
    }
  );
  return hexArr.join('').toUpperCase();
}

/**
 * 十六进制字符串转 ArrayBuffer
 * @param {string} hex - 十六进制字符串
 * @returns {ArrayBuffer} ArrayBuffer 数据
 */
function hexToArrayBuffer(hex) {
  // 去除空格和换行
  hex = hex.replace(/\s+/g, '');

  // 确保长度为偶数
  if (hex.length % 2 !== 0) {
    hex = '0' + hex;
  }

  const length = hex.length / 2;
  const buffer = new ArrayBuffer(length);
  const dataView = new DataView(buffer);

  for (let i = 0; i < length; i++) {
    const byte = parseInt(hex.substr(i * 2, 2), 16);
    dataView.setUint8(i, byte);
  }

  return buffer;
}

/**
 * 十六进制字符串转字节数组
 * @param {string} hex - 十六进制字符串
 * @returns {Array<number>} 字节数组
 */
function hexToBytes(hex) {
  hex = hex.replace(/\s+/g, '');
  const bytes = [];
  for (let i = 0; i < hex.length; i += 2) {
    bytes.push(parseInt(hex.substr(i, 2), 16));
  }
  return bytes;
}

/**
 * 字节数组转十六进制字符串
 * @param {Array<number>} bytes - 字节数组
 * @returns {string} 十六进制字符串
 */
function bytesToHex(bytes) {
  return bytes
    .map(b => ('0' + b.toString(16)).slice(-2))
    .join('')
    .toUpperCase();
}

/**
 * CRC16 校验（Modbus RTU）
 * @param {string} hex - 十六进制字符串（不含 CRC）
 * @returns {string} CRC16 校验码（4位十六进制）
 */
function crc16(hex) {
  const bytes = hexToBytes(hex);
  let crc = 0xFFFF;

  for (let i = 0; i < bytes.length; i++) {
    crc ^= bytes[i];
    for (let j = 0; j < 8; j++) {
      if (crc & 0x0001) {
        crc = (crc >> 1) ^ 0xA001;
      } else {
        crc = crc >> 1;
      }
    }
  }

  // 返回低位在前，高位在后
  const low = (crc & 0xFF).toString(16).padStart(2, '0');
  const high = ((crc >> 8) & 0xFF).toString(16).padStart(2, '0');
  return (low + high).toUpperCase();
}

/**
 * 验证 CRC16 校验码
 * @param {string} hex - 完整的十六进制字符串（含 CRC）
 * @returns {boolean} 校验是否通过
 */
function verifyCrc16(hex) {
  if (hex.length < 4) return false;

  const data = hex.slice(0, -4);
  const crc = hex.slice(-4);

  return crc16(data) === crc;
}

module.exports = {
  arrayBufferToHex,
  hexToArrayBuffer,
  hexToBytes,
  bytesToHex,
  crc16,
  verifyCrc16,
};