Add backup and restore functionality for rental data in settings

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/state/rent_controller.dart

@@ -5,7 +5,6 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:http/http.dart' as http;
 import 'package:intl/intl.dart';
-import 'package:path_provider/path_provider.dart';
 import 'package:rental_income_tracker/models/app_settings.dart';
 import 'package:rental_income_tracker/models/monthly_rent_record.dart';
 import 'package:rental_income_tracker/services/notification_service.dart';
@@ -417,7 +416,7 @@ class RentController extends ChangeNotifier {
     }
   }
 
-  Future<String> exportJson() async {
+  String _buildBackupJson() {
     final records = _records.values.toList()
       ..sort((a, b) {
         final byYear = a.year.compareTo(b.year);
@@ -433,14 +432,72 @@ class RentController extends ChangeNotifier {
       'records': records.map((e) => e.toJson()).toList(),
     };
 
-    final jsonString = const JsonEncoder.withIndent('  ').convert(payload);
-    final dir = await getApplicationDocumentsDirectory();
+    return const JsonEncoder.withIndent('  ').convert(payload);
+  }
+
+  Future<String> exportBackupToDirectory(String directoryPath) async {
+    final jsonString = _buildBackupJson();
     final timestamp = DateFormat('yyyyMMdd_HHmmss').format(DateTime.now());
-    final file = File('${dir.path}/rent_tracker_export_$timestamp.json');
+    final normalizedDirectory = directoryPath.endsWith(Platform.pathSeparator)
+        ? directoryPath.substring(0, directoryPath.length - 1)
+        : directoryPath;
+    final file = File(
+      '$normalizedDirectory${Platform.pathSeparator}rent_tracker_backup_$timestamp.json',
+    );
     await file.writeAsString(jsonString);
     return file.path;
   }
 
+  Future<void> _restoreFromPayload(Map<String, dynamic> payload) async {
+    final settingsJson = payload['settings'] as Map<String, dynamic>?;
+    final recordsJson = payload['records'] as List<dynamic>?;
+    if (settingsJson == null || recordsJson == null) {
+      throw StateError('Backup file is missing settings or records.');
+    }
+
+    _settings = AppSettings.fromJson(settingsJson);
+    final restoredRecords = <String, MonthlyRentRecord>{};
+    for (final item in recordsJson) {
+      final record = MonthlyRentRecord.fromJson(item as Map<String, dynamic>);
+      restoredRecords[record.key] = record;
+    }
+    _records = restoredRecords;
+
+    await _storageService.saveSettings(_settings);
+    await _storageService.saveRecords(_records);
+    await _notificationService.cancelAll();
+    await _syncNotificationScheduleForCurrentMonth();
+    notifyListeners();
+  }
+
+  Future<String> importBackupFromFile(String filePath) async {
+    _errorMessage = null;
+    _setLoading(true);
+
+    try {
+      final file = File(filePath);
+      if (!await file.exists()) {
+        throw StateError('Selected backup file could not be found.');
+      }
+
+      final raw = await file.readAsString();
+      final payload = jsonDecode(raw) as Map<String, dynamic>;
+
+      await _restoreFromPayload(payload);
+
+      return file.path;
+    } catch (err, stackTrace) {
+      if (kDebugMode) {
+        debugPrint('[RentController] importBackupFromFile failed: $err');
+        debugPrint(stackTrace.toString());
+      }
+      _errorMessage = err.toString();
+      rethrow;
+    } finally {
+      _setLoading(false);
+    }
+  }
+
   List<RentTableRow> buildRowsForSelectedYear() {
     final now = DateTime.now();
     final maxMonth = _selectedYear < now.year