formatEditUpdate method

Implementation

@override
TextEditingValue formatEditUpdate(
  TextEditingValue oldValue,
  TextEditingValue newValue,
) {
  final text = newValue.text;

  /// Allow deleting
  if (text.length < oldValue.text.length) {
    return newValue;
  }

  /// Remove any non-digit characters except /
  String cleaned = text.replaceAll(RegExp(r'[^\d/]'), '');

  /// Don't allow consecutive slashes
  cleaned = cleaned.replaceAll(RegExp(r'/+'), '/');

  /// Split by / to check each part
  List<String> parts = cleaned.split('/');

  /// Validate and limit each part
  String formatted = '';

  if (parts.isNotEmpty) {
    /// Day - max 2 digits, max value 31
    String day = parts[0];
    if (day.length > 2) {
      day = day.substring(0, 2);
    }
    if (day.isNotEmpty && int.tryParse(day) != null) {
      int dayNum = int.parse(day);
      if (dayNum > 31) {
        day = '31';
      }
    }
    formatted = day;

    /// Auto-add slash after 2 digits for day
    if (day.length == 2 && text.endsWith(day) && !text.contains('/')) {
      formatted += '/';
    }
  }

  if (parts.length > 1) {
    /// Month - max 2 digits, max value 12 (for Gregorian calendar)
    String month = parts[1];
    if (month.length > 2) {
      month = month.substring(0, 2);
    }
    if (month.isNotEmpty && int.tryParse(month) != null) {
      int monthNum = int.parse(month);
      if (monthNum > 12) {
        month = '12';
      }
    }
    formatted += '/$month';

    /// Auto-add slash after 2 digits for month
    if (month.length == 2 && text.endsWith(month) && parts.length == 2) {
      formatted += '/';
    }
  }

  if (parts.length > 2) {
    /// Year - max 4 digits
    String year = parts[2];
    if (year.length > 4) {
      year = year.substring(0, 4);
    }
    formatted += '/$year';
  }

  /// Don't allow more than 3 parts (dd/mm/yyyy)
  if (parts.length > 3) {
    formatted = oldValue.text;
  }

  /// Limit total length (dd/mm/yyyy = 10 characters)
  if (formatted.length > 10) {
    formatted = formatted.substring(0, 10);
  }

  return TextEditingValue(
    text: formatted,
    selection: TextSelection.collapsed(offset: formatted.length),
  );
}