/** Standard Iranian national-code (کد ملی) checksum validator. */
export function isValidIranNationalCode(code: string): boolean {
  const value = String(code || "");
  if (!/^\d{10}$/.test(value)) return false;
  if (/^(\d)\1{9}$/.test(value)) return false;

  const digits = value.split("").map(Number);
  const sum = digits
    .slice(0, 9)
    .reduce((acc, digit, index) => acc + digit * (10 - index), 0);
  const remainder = sum % 11;
  const checkDigit = remainder < 2 ? remainder : 11 - remainder;

  return checkDigit === digits[9];
}