more refactor

lib/tools/shared_preferences.dart

@@ -0,0 +1,80 @@
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:shared_preferences/shared_preferences.dart';
+
+abstract mixin class SharedPreferencesBacked<T> {
+  SharedPreferences get _sharedPreferences;
+  String keyName();
+  T valueFromJson(Object? obj);
+  Object? valueToJson(T val);
+
+  /// Load things from storage
+  Future<T> load() async {
+    final valueJsonStr = _sharedPreferences.getString(keyName());
+    final Object? valueJsonObj =
+        valueJsonStr != null ? jsonDecode(valueJsonStr) : null;
+    return valueFromJson(valueJsonObj);
+  }
+
+  /// Store things to storage
+  Future<T> store(T obj) async {
+    final valueJsonObj = valueToJson(obj);
+    if (valueJsonObj == null) {
+      await _sharedPreferences.remove(keyName());
+    } else {
+      await _sharedPreferences.setString(keyName(), jsonEncode(valueJsonObj));
+    }
+    return obj;
+  }
+}
+
+class SharedPreferencesValue<T> extends SharedPreferencesBacked<T> {
+  SharedPreferencesValue({
+    required SharedPreferences sharedPreferences,
+    required String keyName,
+    required T Function(Object? obj) valueFromJson,
+    required Object? Function(T obj) valueToJson,
+  })  : _sharedPreferencesInstance = sharedPreferences,
+        _valueFromJson = valueFromJson,
+        _valueToJson = valueToJson,
+        _keyName = keyName,
+        _streamController = StreamController<T>.broadcast();
+
+  @override
+  SharedPreferences get _sharedPreferences => _sharedPreferencesInstance;
+
+  T? get value => _value;
+  T get requireValue => _value!;
+  Stream<T> get stream => _streamController.stream;
+
+  Future<T> get() async {
+    final val = _value;
+    if (val != null) {
+      return val;
+    }
+    final loadedValue = await load();
+    return _value = loadedValue;
+  }
+
+  Future<void> set(T newVal) async {
+    _value = await store(newVal);
+    _streamController.add(newVal);
+  }
+
+  T? _value;
+  final SharedPreferences _sharedPreferencesInstance;
+  final String _keyName;
+  final T Function(Object? obj) _valueFromJson;
+  final Object? Function(T obj) _valueToJson;
+  final StreamController<T> _streamController;
+
+  //////////////////////////////////////////////////////////////
+  /// SharedPreferencesBacked
+  @override
+  String keyName() => _keyName;
+  @override
+  T valueFromJson(Object? obj) => _valueFromJson(obj);
+  @override
+  Object? valueToJson(T val) => _valueToJson(val);
+}