/**
 * Calculates CRC16 according to the UHF Reader Manual.
 * Polynomial: 0x8408
 * Preset: 0xFFFF
 */
export const calculateCRC16 = (data: Uint8Array): number => {
  const PRESET_VALUE = 0xFFFF;
  const POLYNOMIAL = 0x8408;

  let uiCrcValue = PRESET_VALUE;

  for (let i = 0; i < data.length; i++) {
    uiCrcValue = uiCrcValue ^ data[i];
    for (let j = 0; j < 8; j++) {
      if ((uiCrcValue & 0x0001) !== 0) {
        uiCrcValue = (uiCrcValue >> 1) ^ POLYNOMIAL;
      } else {
        uiCrcValue = (uiCrcValue >> 1);
      }
    }
  }

  return uiCrcValue;
};

/**
 * Splits a 16-bit CRC into LSB and MSB bytes
 */
export const getCRCBytes = (crc: number): [number, number] => {
  const lsb = crc & 0xFF;
  const msb = (crc >> 8) & 0xFF;
  return [lsb, msb];
};

/**
 * Converts a hex string (e.g., "A1 B2") to Uint8Array
 */
export const hexStringToBytes = (hex: string): Uint8Array | null => {
  const cleanHex = hex.replace(/[\s-]/g, '');
  if (cleanHex.length % 2 !== 0 || !/^[0-9A-Fa-f]+$/.test(cleanHex)) {
    return null;
  }
  const bytes = new Uint8Array(cleanHex.length / 2);
  for (let i = 0; i < cleanHex.length; i += 2) {
    bytes[i / 2] = parseInt(cleanHex.substring(i, i + 2), 16);
  }
  return bytes;
};

/**
 * Converts bytes to Hex String
 */
export const bytesToHexString = (bytes: Uint8Array | number[]): string => {
  return Array.from(bytes)
    .map(b => b.toString(16).padStart(2, '0').toUpperCase())
    .join(' ');
};

/**
 * Converts a hex string (with spaces) to ASCII string
 */
export const hexToAscii = (hex: string): string => {
  if (!hex) return "";
  const cleanHex = hex.replace(/[\s-]/g, '');
  let str = "";
  for (let i = 0; i < cleanHex.length; i += 2) {
    const charCode = parseInt(cleanHex.substring(i, i + 2), 16);
    // Replace non-printable characters with dots
    if (charCode >= 32 && charCode <= 126) {
      str += String.fromCharCode(charCode);
    } else {
      str += ".";
    }
  }
  return str;
};

/**
 * Converts an ASCII string to Hex string
 */
export const asciiToHex = (ascii: string): string => {
  let hex = "";
  for (let i = 0; i < ascii.length; i++) {
    const code = ascii.charCodeAt(i);
    hex += code.toString(16).padStart(2, "0").toUpperCase();
  }
  return hex;
};