refactor(mobile): add Isar DB & Store class (#1574)

* refactor(mobile): add Isar DB & Store class

new Store: globally accessible key-value store like Hive (but based on Isar)

replace first few places of Hive usage with the new Store

* reduce max. DB size to prevent errors on older iOS devices

---------

Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/lib/shared/models/store.dart

@@ -0,0 +1,96 @@
+import 'package:isar/isar.dart';
+import 'dart:convert';
+
+part 'store.g.dart';
+
+/// Key-value store for individual items enumerated in StoreKey.
+/// Supports String, int and JSON-serializable Objects
+/// Can be used concurrently from multiple isolates
+class Store {
+  static late final Isar _db;
+  static final List<dynamic> _cache = List.filled(StoreKey.values.length, null);
+
+  /// Initializes the store (call exactly once per app start)
+  static void init(Isar db) {
+    _db = db;
+    _populateCache();
+    _db.storeValues.where().build().watch().listen(_onChangeListener);
+  }
+
+  /// clears all values from this store (cache and DB), only for testing!
+  static Future<void> clear() {
+    _cache.fillRange(0, _cache.length, null);
+    return _db.writeTxn(() => _db.storeValues.clear());
+  }
+
+  /// Returns the stored value for the given key, or the default value if null
+  static T? get<T>(StoreKey key, [T? defaultValue]) =>
+      _cache[key._id] ?? defaultValue;
+
+  /// Stores the value synchronously in the cache and asynchronously in the DB
+  static Future<void> put<T>(StoreKey key, T value) {
+    _cache[key._id] = value;
+    return _db.writeTxn(() => _db.storeValues.put(StoreValue._of(value, key)));
+  }
+
+  /// Removes the value synchronously from the cache and asynchronously from the DB
+  static Future<void> delete(StoreKey key) {
+    _cache[key._id] = null;
+    return _db.writeTxn(() => _db.storeValues.delete(key._id));
+  }
+
+  /// Fills the cache with the values from the DB
+  static _populateCache() {
+    for (StoreKey key in StoreKey.values) {
+      final StoreValue? value = _db.storeValues.getSync(key._id);
+      if (value != null) {
+        _cache[key._id] = value._extract(key);
+      }
+    }
+  }
+
+  /// updates the state if a value is updated in any isolate
+  static void _onChangeListener(List<StoreValue>? data) {
+    if (data != null) {
+      for (StoreValue value in data) {
+        _cache[value.id] = value._extract(StoreKey.values[value.id]);
+      }
+    }
+  }
+}
+
+/// Internal class for `Store`, do not use elsewhere.
+@Collection(inheritance: false)
+class StoreValue {
+  StoreValue(this.id, {this.intValue, this.strValue});
+  Id id;
+  int? intValue;
+  String? strValue;
+
+  T? _extract<T>(StoreKey key) => key._isInt
+      ? intValue
+      : (key._fromJson != null
+          ? key._fromJson!(json.decode(strValue!))
+          : strValue);
+  static StoreValue _of(dynamic value, StoreKey key) => StoreValue(
+        key._id,
+        intValue: key._isInt ? value : null,
+        strValue: key._isInt
+            ? null
+            : (key._fromJson == null ? value : json.encode(value.toJson())),
+      );
+}
+
+/// Key for each possible value in the `Store`.
+/// Defines the data type (int, String, JSON) for each value
+enum StoreKey {
+  userRemoteId(0),
+  assetETag(1),
+  ;
+
+  // ignore: unused_element
+  const StoreKey(this._id, [this._isInt = false, this._fromJson]);
+  final int _id;
+  final bool _isInt;
+  final Function(dynamic)? _fromJson;
+}