isBankCard static method

Implementation

static bool isBankCard(String? cardNumber) {
  if (cardNumber?.isEmpty ?? true) return false;

  final digits =
      cardNumber!.replaceAll(' ', '').split('').map(int.tryParse).toList();
  if (digits.any((d) => d == null) ||
      digits.length < 13 ||
      digits.length > 19) {
    return false;
  }

  int sum = 0;
  bool alternate = false;

  for (int i = digits.length - 1; i >= 0; i--) {
    int digit = digits[i]!;

    if (alternate) {
      digit *= 2;
      if (digit > 9) {
        digit = (digit % 10) + 1;
      }
    }

    sum += digit;
    alternate = !alternate;
  }

  return sum % 10 == 0;
}