cake_wallet/lib/core/validator.dart

import 'package:flutter/foundation.dart';

abstract class Validator<T> {
  Validator({required this.errorMessage});

  final String errorMessage;

  bool isValid(T? value);

  String? call(T? value) =>  !isValid(value) ? errorMessage : null;
}

class TextValidator extends Validator<String> {
  TextValidator(
      {this.minLength,
      this.maxLength,
      this.pattern,
      String errorMessage = '',
      this.length,
      this.isAutovalidate = false})
      : super(errorMessage: errorMessage);

  final int? minLength;
  final int? maxLength;
  final List<int>? length;
  final bool isAutovalidate;
  String? pattern;

  @override
  bool isValid(String? value) {
    if (value == null || value.isEmpty) {
      return isAutovalidate ? true : false;
    }

    return value.length > (minLength ?? 0) &&
        (length?.contains(value.length) ?? true) &&
        ((maxLength ?? 0) > 0 ? (value.length <= maxLength!) : true) &&
        (pattern != null ? match(value) : true);
  }

  bool match(String value) => pattern != null ? RegExp(pattern!).hasMatch(value) : false;
}