ean-epc/epc/utils/utils.js

EPC Tag Data Standard encoding and decoding library, written in javascript

/*
 * EPC Tag Data Standard
 * 2021 Sergio S. - https://github.com/sergiss/epc-tds
 */

const HEX_TABLE = [
  '0',
  '1',
  '2',
  '3',
  '4',
  '5',
  '6',
  '7',
  '8',
  '9',
  'A',
  'B',
  'C',
  'D',
  'E',
  'F',
];

const DEC_TABLE = [
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, -1, 10, 11, 12,
  13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1,
];

const NUMBER_TABLE = [
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1, // 00 - 09
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1, // 10 - 19
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1, // 20 - 29
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1, // 30 - 39
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  0,
  1, // 40 - 49
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  -1,
  -1, // 50 - 59
];

function computeCheckDigit(barcode) {
  // https://www.gs1.org/services/how-calculate-check-digit-manually

  // CHECK DIGIT
  // GTIN-8                                          n01 n02 n03 n04 n05 n06 n07 | n08
  // GTIN-12                         n01 n02 n03 n04 n05 n06 n07 n08 n09 n10 n11 | n12
  // GTIN-13                     n01 n02 n03 n04 n05 n06 n07 n08 n09 n10 n11 n12 | n13
  // GTIN-14                 n01 n02 n03 n04 n05 n06 n07 n08 n09 n10 n11 n12 n13 | n14
  // GSIN        n01 n02 n03 n04 n05 n06 n07 n08 n09 n10 n11 n12 n13 n14 n15 n16 | n17
  // SSCC    n01 n02 n03 n04 n05 n06 n07 n08 n09 n10 n11 n12 n13 n14 n15 n16 n17 | n18
  // ----------------------------------------------------------------------------------------
  // Mult     x3  x1  x3  x1  x3  x1  x3  x1  x3  x1  x3  x1  x3  x1  x3  x1  x3

  let odd,
    even = 0;
  let i = barcode.length - 1;

  if (i & 0b1) {
    // even check
    odd = 0;
  } else {
    odd = NUMBER_TABLE[barcode.charCodeAt(0)];
  }
  // Multiply value of each position by x3, x1 and add results together to create sum
  for (; i > 0; i -= 2) {
    odd += NUMBER_TABLE[barcode.charCodeAt(i)];
    even += NUMBER_TABLE[barcode.charCodeAt(i - 1)];
  }
  // Subtract the sum from nearest equal or higher multiple of ten
  let result = (even + odd * 3) % 10;
  if (result !== 0) {
    result = 10 - result;
  }
  return result;
}

function getMaxValue(bits) {
  return Math.pow(2, bits) - 1;
}

function hexToByte(hex, offset) {
  return (DEC_TABLE[hex.charCodeAt(offset)] << 4) | DEC_TABLE[hex.charCodeAt(offset + 1)];
}

function randomEan(n) {
  let result = '';
  for (let i = 1; i < n; ++i) {
    result += Math.floor(Math.random() * 10);
  }
  return result + computeCheckDigit(result);
}

function randomHex(len) {
  let result = '';
  for (let i = 0; i < len; ++i) {
    result += HEX_TABLE[Math.floor(Math.random() * HEX_TABLE.length)];
  }
  return result;
}

export default {
  getMaxValue,
  randomEan,
  randomHex,
  hexToByte,
  computeCheckDigit,
};