Refactored json storage

lib/repositories/metadata/models/metadata.dart

@@ -0,0 +1,39 @@
+import 'package:tunas/repositories/metadata/models/budget.dart';
+import 'package:tunas/repositories/metadata/models/category.dart';
+import 'package:tunas/repositories/json/models/json.dart';
+import 'package:tunas/repositories/metadata/models/account.dart';
+
+class Metadata implements Json {
+  List<Budget> budgets;
+  List<Category> categories;
+  List<Account> accounts;
+
+  Metadata({
+    this.budgets = const [],
+    this.categories = const [],
+    this.accounts = const [],
+  });
+
+  @override
+  Map<String, dynamic> toJson() => {
+    'budgets': budgets.map((budget) => budget.toJson()).toList(),
+    'categories': categories.map((category) => category.toJson()).toList(),
+    'accounts': accounts.map((account) => account.toJson()).toList(),
+  };
+  
+  @override
+  String getJsonFileName() {
+    return 'metadata.json';
+  }
+}
+
+class MetadataFactory implements JsonFactory<Metadata> {
+  @override
+  Metadata fromJson(Map<String, dynamic> json) {
+    return Metadata(
+      budgets: List<Budget>.from(json['budgets']?.map((budget) => Budget.fromJson(budget))),
+      categories: List<Category>.from(json['categories']?.map((category) => Category.fromJson(category))),
+      accounts: List<Account>.from(json['accounts']?.map((account) => Account.fromJson(account))),
+    );
+  }
+}