update

lib/shared/models/transaction.dart

@@ -0,0 +1,59 @@
+import 'package:flutter/foundation.dart';
+
+enum TransactionType { income, expense }
+
+@immutable
+class Transaction {
+  final String id;
+  final double amount;
+  final String category;
+  final TransactionType type;
+  final DateTime date;
+  final String? note;
+
+  const Transaction({
+    required this.id,
+    required this.amount,
+    required this.category,
+    required this.type,
+    required this.date,
+    this.note,
+  });
+
+  factory Transaction.fromJson(Map<String, dynamic> json) => Transaction(
+        id: json['id'] as String,
+        amount: (json['amount'] as num).toDouble(),
+        category: json['category'] as String,
+        type: TransactionType.values.firstWhere(
+          (e) => e.name == json['type'],
+        ),
+        date: DateTime.parse(json['date'] as String),
+        note: json['note'] as String?,
+      );
+
+  Map<String, dynamic> toJson() => {
+        'id': id,
+        'amount': amount,
+        'category': category,
+        'type': type.name,
+        'date': date.toIso8601String(),
+        'note': note,
+      };
+
+  Transaction copyWith({
+    String? id,
+    double? amount,
+    String? category,
+    TransactionType? type,
+    DateTime? date,
+    String? note,
+  }) =>
+      Transaction(
+        id: id ?? this.id,
+        amount: amount ?? this.amount,
+        category: category ?? this.category,
+        type: type ?? this.type,
+        date: date ?? this.date,
+        note: note ?? this.note,
+      );
+}

lib/shared/services/storage_service.dart

@@ -0,0 +1,36 @@
+import 'dart:convert';
+import 'package:shared_preferences/shared_preferences.dart';
+import '../models/transaction.dart';
+
+class StorageService {
+  static const _key = 'transactions';
+
+  final SharedPreferences _prefs;
+
+  StorageService(this._prefs);
+
+  List<Transaction> loadTransactions() {
+    final raw = _prefs.getString(_key);
+    if (raw == null) return [];
+    final list = jsonDecode(raw) as List<dynamic>;
+    return list
+        .map((e) => Transaction.fromJson(e as Map<String, dynamic>))
+        .toList();
+  }
+
+  Future<void> saveTransactions(List<Transaction> transactions) async {
+    final encoded = jsonEncode(transactions.map((t) => t.toJson()).toList());
+    await _prefs.setString(_key, encoded);
+  }
+
+  Future<void> addTransaction(Transaction transaction) async {
+    final list = loadTransactions();
+    list.add(transaction);
+    await saveTransactions(list);
+  }
+
+  Future<void> deleteTransaction(String id) async {
+    final list = loadTransactions()..removeWhere((t) => t.id == id);
+    await saveTransactions(list);
+  }
+}