validateDate static method

String? validateDate(String value)

Implementation

static String? validateDate(String value) {
  if (value.isEmpty) {
    return "Required";
  }

  int year;
  int month;
  // The value contains a forward slash if the month and year has been
  // entered.
  if (value.contains(new RegExp(r'(\/)'))) {
    var split = value.split(new RegExp(r'(\/)'));
    // The value before the slash is the month while the value to right of
    // it is the year.
    month = int.parse(split[0]);
    year = int.parse(split[1]);
  } else {
    // Only the month was entered
    month = int.parse(value.substring(0, (value.length)));
    year = -1; // Lets use an invalid year intentionally
  }

  if ((month < 1) || (month > 12)) {
    // A valid month is between 1 (January) and 12 (December)
    return 'Expiry month is invalid';
  }

  var fourDigitsYear = convertYearTo4Digits(year);
  if ((fourDigitsYear < 1) || (fourDigitsYear > 2099)) {
    // We are assuming a valid year should be between 1 and 2099.
    // Note that, it's valid doesn't mean that it has not expired.
    return 'Expiry year is invalid';
  }

  if (!hasDateExpired(month, year)) {
    return "Card has expired";
  }
  return null;
}