feat: Cashu improvements

packages/ndk/lib/domain_layer/usecases/cashu/cashu.dart

@@ -19,6 +19,7 @@ import '../../repositories/cache_manager.dart';
 import '../../repositories/cashu_key_derivation.dart';
 import '../../repositories/cashu_repo.dart';
 import '../../repositories/wallets_repo.dart';
+import 'cashu_backup.dart';
 import 'cashu_bdhke.dart';
 import 'cashu_cache_decorator.dart';
 import 'cashu_keysets.dart';
@@ -39,6 +40,8 @@ class Cashu {
 
   late final CashuSeed _cashuSeed;
 
+  late final CashuBackup _cashuBackup;
+
   final CashuKeyDerivation _cashuKeyDerivation;
 
   Cashu({
@@ -64,6 +67,12 @@ class Cashu {
     _cashuSeed = CashuSeed(
       userSeedPhrase: cashuUserSeedphrase,
     );
+    _cashuBackup = CashuBackup(
+      cacheManagerCashu: _cacheManagerCashu,
+      cacheManager: _cacheManager,
+      walletsRepo: _walletsRepo,
+      cashuSeed: _cashuSeed,
+    );
     if (cashuUserSeedphrase == null) {
       Logger.log.w(() =>
           'Cashu initialized without user seed phrase, cashu features will not work \nSet the seed phrase using NdkConfig or Cashu.setCashuSeedPhrase()');
@@ -100,6 +109,72 @@ class Cashu {
     return _cashuSeed;
   }
 
+  /// Export a full backup of the local cashu database (proofs, keysets, mint
+  /// infos, derivation counters and transactions) as a JSON map.
+  ///
+  /// The global seed phrase is NOT included by default — it is wallet
+  /// independent and should be backed up separately. Set [includeSeedPhrase]
+  /// true only for a single self-contained backup, and then treat the result
+  /// like a private key. See [CashuBackup].
+  Future<Map<String, dynamic>> exportBackup({
+    bool includeSeedPhrase = false,
+    bool includeTransactions = true,
+  }) {
+    return _cashuBackup.exportToMap(
+      includeSeedPhrase: includeSeedPhrase,
+      includeTransactions: includeTransactions,
+    );
+  }
+
+  /// Export a full backup of all local cashu state as a JSON string.
+  /// See [exportBackup].
+  Future<String> exportBackupJsonString({
+    bool includeSeedPhrase = false,
+    bool includeTransactions = true,
+    bool pretty = true,
+  }) {
+    return _cashuBackup.exportToJsonString(
+      includeSeedPhrase: includeSeedPhrase,
+      includeTransactions: includeTransactions,
+      pretty: pretty,
+    );
+  }
+
+  /// Restore cashu state from a backup map produced by [exportBackup].
+  ///
+  /// NOTE: the restored seed phrase is only loaded into memory; persist
+  /// [CashuBackupRestoreResult.seedPhrase] to secure storage to finish the
+  /// restore. After restoring you may want to call [restore] to re-sync proofs
+  /// from each mint. See [CashuBackup].
+  Future<CashuBackupRestoreResult> importBackup(
+    Map<String, dynamic> json, {
+    bool restoreSeedPhrase = true,
+    bool restoreTransactions = true,
+  }) async {
+    final result = await _cashuBackup.importFromMap(
+      json,
+      restoreSeedPhrase: restoreSeedPhrase,
+      restoreTransactions: restoreTransactions,
+    );
+    await _updateBalances();
+    return result;
+  }
+
+  /// Restore cashu state from a backup JSON string. See [importBackup].
+  Future<CashuBackupRestoreResult> importBackupJsonString(
+    String jsonString, {
+    bool restoreSeedPhrase = true,
+    bool restoreTransactions = true,
+  }) async {
+    final result = await _cashuBackup.importFromJsonString(
+      jsonString,
+      restoreSeedPhrase: restoreSeedPhrase,
+      restoreTransactions: restoreTransactions,
+    );
+    await _updateBalances();
+    return result;
+  }
+
   /// Restores proofs from a mint using the wallet's seed phrase.
   ///
   /// This implements NUT-09 (Restore) using NUT-13 (Deterministic Secrets).