Made GradeAverage persistent

lib/storage/base/settingsProvider.dart

@@ -0,0 +1,54 @@
+import 'dart:convert';
+import 'dart:developer';
+import 'package:flutter/material.dart';
+import 'package:marianum_mobile/storage/gradeAverages/gradeAveragesSettings.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'settings.dart';
+
+class SettingsProvider extends ChangeNotifier {
+  static const String _fieldName = "settings";
+
+  late SharedPreferences _storage;
+  late Settings _settings = _defaults();
+
+  Settings val({bool write = false}) {
+    if(write) {
+      notifyListeners();
+      Future.delayed(const Duration(milliseconds: 300)).then((_) => update());
+    }
+    return _settings;
+  }
+
+  SettingsProvider() {
+    init();
+  }
+
+  void init() async {
+    _storage = await SharedPreferences.getInstance();
+
+    if(_storage.containsKey(_fieldName)) {
+      log("Settings from disk: ${_storage.getString(_fieldName)}");
+      _settings = Settings.fromJson(jsonDecode(_storage.getString(_fieldName)!));
+    } else {
+      _settings = _defaults();
+    }
+
+    notifyListeners();
+  }
+
+  void update() async {
+    await _storage.setString(_fieldName, jsonEncode(_settings.toJson()));
+  }
+
+  Settings _defaults() {
+    return Settings(
+      appTheme: ThemeMode.system,
+      devToolsEnabled: false,
+      gradeAveragesSettings: GradeAveragesSettings(
+        useGradeSystem: true,
+        inputs: []
+      ),
+    );
+  }
+}