step

lib/shared/services/backup_service.dart

@@ -0,0 +1,72 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+class BackupData {
+  final String ownerPurchaseToken;
+  final DateTime createdAt;
+  final Map<String, dynamic> payload;
+
+  const BackupData({
+    required this.ownerPurchaseToken,
+    required this.createdAt,
+    required this.payload,
+  });
+
+  Map<String, dynamic> toJson() => {
+        'owner_purchase_token': ownerPurchaseToken,
+        'created_at': createdAt.toIso8601String(),
+        'payload': payload,
+      };
+
+  factory BackupData.fromJson(Map<String, dynamic> json) {
+    return BackupData(
+      ownerPurchaseToken: json['owner_purchase_token'] as String? ?? '',
+      createdAt: DateTime.tryParse(json['created_at'] as String? ?? '') ??
+          DateTime.now(),
+      payload: json['payload'] as Map<String, dynamic>? ?? {},
+    );
+  }
+}
+
+enum BackupVerifyResult { ok, tokenMismatch, noToken, invalidFormat }
+
+class BackupService {
+  String _currentPurchaseToken;
+
+  BackupService(this._currentPurchaseToken);
+
+  void updatePurchaseToken(String token) {
+    _currentPurchaseToken = token;
+  }
+
+  String get currentPurchaseToken => _currentPurchaseToken;
+
+  Uint8List createBackup(Map<String, dynamic> payload) {
+    final data = BackupData(
+      ownerPurchaseToken: _currentPurchaseToken,
+      createdAt: DateTime.now(),
+      payload: payload,
+    );
+    final json = jsonEncode(data.toJson());
+    return Uint8List.fromList(utf8.encode(json));
+  }
+
+  (BackupVerifyResult, BackupData?) verifyAndParse(Uint8List raw) {
+    try {
+      final json = jsonDecode(utf8.decode(raw)) as Map<String, dynamic>;
+      final data = BackupData.fromJson(json);
+
+      if (data.ownerPurchaseToken.isEmpty) {
+        return (BackupVerifyResult.noToken, null);
+      }
+
+      if (data.ownerPurchaseToken != _currentPurchaseToken) {
+        return (BackupVerifyResult.tokenMismatch, null);
+      }
+
+      return (BackupVerifyResult.ok, data);
+    } catch (e) {
+      return (BackupVerifyResult.invalidFormat, null);
+    }
+  }
+}