Repository with local provider

main.dart

/*
  https://gist.github.com/PlugFox/a013510572bb2115d6ac2e434cb8d197
  https://dartpad.dartlang.org/a013510572bb2115d6ac2e434cb8d197
*/

import 'dart:html'; // for _LocalProviderStorage

abstract class Repository {
  static final RepositoryProvider _repository = RepositoryProvider();

  static String get token => _repository.localProvider.token;
  static set token(dynamic value) => _repository.localProvider.token = value;

  static Map<String,String> get userInfo => _repository.localProvider.userInfo;
  static set userInfo(Map<String,String> value) => _repository.localProvider.userInfo = value;

  // Это класс возможно использовать только для миксинов, а также дергать его методы напрямую
  factory Repository._() => null;

  // Эмуляция задержки
  static Future<void> emulateDelay({int milliseconds = 500}) async => await Future.delayed(Duration(milliseconds: milliseconds));
}

// Репозиторий
class RepositoryProvider {
  final LocalProvider localProvider = LocalProvider();
  
  // СИНГЛТОН +
  static final RepositoryProvider _repository = RepositoryProvider._internal();
  factory RepositoryProvider() => _repository;
  RepositoryProvider._internal() {
    print('Создаем синглтон RepositoryProvider');
  }
  // СИНГЛТОН -
}

class LocalProvider {
  LocalProvider();
  final _LocalProviderStorage _store = _LocalProviderStorage();

  String get token => this._store['token'];
  set token(dynamic value) => this._store['token'] = value;

  Map<String,String> get userInfo =>
      <String, String>{}
      ..['token'] = this._store['token']
      ..['name'] = this._store['name']
      ..['email'] = this._store['email']
      ..['avatar'] = this._store['avatar'];
  set userInfo(Map<String,String> value) =>
      value.forEach((String key, String value) => this._store[key] = value);
}

class _LocalProviderStorage {
  Storage get _lcl => window.localStorage;
  final Map<String,String> _mem = <String,String>{};
  String _get(String key) => key?.isEmpty ?? true ? '' : this._mem[key] ?? (this._lcl[key] ?? '');
  void _set(String key, dynamic value) {
    if (key?.isEmpty ?? true) return;
    value = this._map(value);
    this._lcl[key] = value;
    this._mem[key] = value;
  }
  String _map(dynamic value) => value is String ? value : value?.toString() ?? '';
  _LocalProviderStorage();
  String operator [](String key) => _get(key);
  void operator []=(String key, dynamic value) => _set(key, value);
}

void main() {
  Repository.token = '<sample>';
  print(Repository.token);
}