/**
 * Whether a GTIN is a real barcode number: 8, 12, 13 or 14 digits whose
 * last is the check digit of the others (GS1 mod 10).
 *
 * @param {string} value - What was typed.
 * @returns {boolean} True for a valid GTIN.
 */
export const isValidGtin = (value: string): boolean => {
  const digits = value.replace(/[\s-]/g, '');
  if (!/^(\d{8}|\d{12}|\d{13}|\d{14})$/.test(digits)) {
    return false;
  }
  const body = digits.slice(0, -1).split('').reverse();
  const sum = body.reduce(
    (total, digit, index) => total + Number(digit) * (index % 2 === 0 ? 3 : 1),
    0
  );
  return (10 - (sum % 10)) % 10 === Number(digits[digits.length - 1]);
};