update

lib/shared/services/storage_service.dart

@@ -3,14 +3,15 @@ import 'package:shared_preferences/shared_preferences.dart';
 import '../models/transaction.dart';
 
 class StorageService {
-  static const _key = 'transactions';
+  static const _transactionsKey = 'transactions';
+  static const _budgetKey = 'monthly_budget';
 
   final SharedPreferences _prefs;
 
   StorageService(this._prefs);
 
   List<Transaction> loadTransactions() {
-    final raw = _prefs.getString(_key);
+    final raw = _prefs.getString(_transactionsKey);
     if (raw == null) return [];
     final list = jsonDecode(raw) as List<dynamic>;
     return list
@@ -20,7 +21,7 @@ class StorageService {
 
   Future<void> saveTransactions(List<Transaction> transactions) async {
     final encoded = jsonEncode(transactions.map((t) => t.toJson()).toList());
-    await _prefs.setString(_key, encoded);
+    await _prefs.setString(_transactionsKey, encoded);
   }
 
   Future<void> addTransaction(Transaction transaction) async {
@@ -29,8 +30,29 @@ class StorageService {
     await saveTransactions(list);
   }
 
+  Future<void> updateTransaction(Transaction transaction) async {
+    final list = loadTransactions();
+    final index = list.indexWhere((t) => t.id == transaction.id);
+    if (index != -1) {
+      list[index] = transaction;
+      await saveTransactions(list);
+    }
+  }
+
   Future<void> deleteTransaction(String id) async {
     final list = loadTransactions()..removeWhere((t) => t.id == id);
     await saveTransactions(list);
   }
+
+  double? loadBudget() {
+    return _prefs.getDouble(_budgetKey);
+  }
+
+  Future<void> saveBudget(double? budget) async {
+    if (budget == null) {
+      await _prefs.remove(_budgetKey);
+    } else {
+      await _prefs.setDouble(_budgetKey, budget);
+    }
+  }
 }