feat: Encoder and Decoder can return a Future

Author: hoc081098

lib/src/interface/storage.dart

@@ -1,10 +1,12 @@
-/// Convert [T] to type that can be persisted in [Storage].
-/// This used in [Storage.write].
-typedef Encoder<T> = Object? Function(T);
+import 'dart:async';
+
+/// Convert [T] to a value of type that can be persisted in [Storage].
+/// This is used in [Storage.write].
+typedef Encoder<T> = FutureOr<Object?> Function(T t);
 
 /// Convert storage persisted type to [T].
-/// This used in [Storage.read].
-typedef Decoder<T> = T Function(Object?);
+/// This is used in [Storage.read].
+typedef Decoder<T> = FutureOr<T> Function(Object? o);
 
 /// A persistent store for simple data. Data is persisted to disk asynchronously.
 abstract class Storage<Key extends Object, Options> {

test/fake_storage.dart

@@ -66,6 +66,8 @@ class FakeStorage implements StringKeyStorage {
 
   Future<void> _setValue(String key, Object? value) {
     return _wrapCanThrows(() {
+      assert(value is! Future<dynamic>, 'Actual type is ${value.runtimeType}');
+
       if (value is List<String>?) {
         _map[key] = value?.toList();
       } else {
@@ -96,7 +98,8 @@ class FakeStorage implements StringKeyStorage {
   Future<void> write<T extends Object>(
           String key, T? value, Encoder<T?> encoder, [void _]) =>
       Future<void>.delayed(const Duration(milliseconds: 10))
-          .then((_) => _setValue(key, encoder(value)));
+          .then((_) => encoder(value))
+          .then((encoded) => _setValue(key, encoded));
 
   @override
   Future<Map<String, Object?>> reload() {

test/utils/user.dart

@@ -48,12 +48,15 @@ extension RxStoreageExtensionsForUser on RxStorage<String, void> {
   Stream<User?> observeUser() => observe<User>('User', jsonStringToUser);
 }
 
-User? jsonStringToUser(Object? s) {
+Future<User?> jsonStringToUser(Object? s) async {
+  await Future<void>.delayed(const Duration(milliseconds: 10));
+
   if (s == null) {
     return null;
   }
   final map = jsonDecode(s as String) as Map<String, Object?>;
   return User.fromJson(map);
 }
 
-String? userToJsonString(User? u) => u == null ? null : jsonEncode(u);
+Future<String?> userToJsonString(User? u) async =>
+    u == null ? null : jsonEncode(u);