Format input date

main.dart

/*
 * Format input date
 * https://gist.github.com/PlugFox/9364d6a88d0baf1284e4cdc0581957e7
 * https://dartpad.dev/9364d6a88d0baf1284e4cdc0581957e7
 * Matiunin Mikhail <plugfox@gmail.com>, 27 January 2023
 */

void main() => [
      '',
      '.',
      '..',
      '1.2',
      '.3.',
      '4.5.6',
      '0.3.4000',
      '32.14.1995',
      '12.11.2003',
    ].map(formatDate).forEach(print);

String formatDate(
  String input, {
  int minYear = 1970,
  int maxYear = 3000,
}) {
  final l = <int>[
    ...input.split('.')
            .map<int?>(int.tryParse)
            .map<int>((i) => i ?? 1),
    ...const <int>[1,1],
  ];
  final y = l[2].clamp(minYear, maxYear),
        m = l[1].clamp(1, 12),
        d = l[0].clamp(1, DateTime(y, m + 1, 0).day);
  String pad(int v, int w) => v.toString().padLeft(w, '0');
  return '${pad(d, 2)}'
         '.'
         '${pad(m, 2)}'
         '.'
         '${pad(y, 4)}';
}