feat: Implement database migration

This allows the user to give a legacyDatabaseBuilder to the client object
and in the init proccess the client checks by itself if there is old data in the legacy
database. If yes then it migrates them and
then deletes the old database. This uses the database_api and is agnostic to
the database implementation.

lib/src/client.dart

@@ -57,7 +57,9 @@ class Client extends MatrixApi {
   int get id => _id;
 
   final FutureOr<DatabaseApi> Function(Client) databaseBuilder;
+  final FutureOr<DatabaseApi> Function(Client) legacyDatabaseBuilder;
   final FutureOr<void> Function(Client) databaseDestroyer;
+  final FutureOr<void> Function(Client) legacyDatabaseDestroyer;
   DatabaseApi _database;
 
   DatabaseApi get database => _database;
@@ -94,6 +96,7 @@ class Client extends MatrixApi {
   /// Create a client
   /// [clientName] = unique identifier of this client
   /// [databaseBuilder]: A function that creates the database instance, that will be used.
+  /// [legacyDatabaseBuilder]: Use this for your old database implementation to perform an automatic migration
   /// [databaseDestroyer]: A function that can be used to destroy a database instance, for example by deleting files from disk.
   /// [enableE2eeRecovery]: Enable additional logic to try to recover from bad e2ee sessions
   /// [verificationMethods]: A set of all the verification methods this client can handle. Includes:
@@ -128,6 +131,8 @@ class Client extends MatrixApi {
     this.clientName, {
     this.databaseBuilder,
     this.databaseDestroyer,
+    this.legacyDatabaseBuilder,
+    this.legacyDatabaseDestroyer,
     this.enableE2eeRecovery = false,
     this.verificationMethods,
     http.Client httpClient,
@@ -877,6 +882,52 @@ class Client extends MatrixApi {
         onLoginStateChanged.add(LoginState.loggedOut);
         Logs().i('User is not logged in.');
         _initLock = false;
+        if (legacyDatabaseBuilder != null) {
+          Logs().i('Check legacy database for migration data');
+          final legacyDatabase = await legacyDatabaseBuilder(this);
+          final migrateClient = await legacyDatabase.getClient(clientName);
+          if (migrateClient != null) {
+            Logs().i('Found data in the legacy database');
+            _id = migrateClient['client_id'];
+            await database.insertClient(
+              clientName,
+              migrateClient['homeserver_url'],
+              migrateClient['token'],
+              migrateClient['user_id'],
+              migrateClient['device_id'],
+              migrateClient['device_name'],
+              null,
+              migrateClient['olm_account'],
+            );
+            for (final type in cacheTypes) {
+              Logs().i('Migrate $type');
+              final ssssCache = await legacyDatabase.getSSSSCache(_id, type);
+              if (ssssCache != null) {
+                await database.storeSSSSCache(
+                  _id,
+                  type,
+                  ssssCache.keyId,
+                  ssssCache.ciphertext,
+                  ssssCache.content,
+                );
+              }
+            }
+
+            await legacyDatabase.clear(_id);
+            await legacyDatabaseDestroyer?.call(this);
+          }
+          await legacyDatabase.close();
+          if (migrateClient != null) {
+            return init(
+              newToken: migrateClient['token'],
+              newHomeserver: Uri.parse(migrateClient['homeserver_url']),
+              newUserID: migrateClient['user_id'],
+              newDeviceID: migrateClient['device_id'],
+              newDeviceName: migrateClient['device_name'],
+              newOlmAccount: migrateClient['olm_account'],
+            );
+          }
+        }
         return;
       }
       _initLock = false;

test/client_test.dart

@@ -634,5 +634,37 @@ void main() {
     test('dispose', () async {
       await matrix.dispose(closeDatabase: true);
     });
+
+    test('Database Migration', () async {
+      final database = await getDatabase(null);
+      final moorClient = Client(
+        'testclient',
+        httpClient: FakeMatrixApi(),
+        databaseBuilder: (_) => database,
+      );
+      FakeMatrixApi.client = moorClient;
+      await moorClient.checkHomeserver('https://fakeServer.notExisting',
+          checkWellKnown: false);
+      await moorClient.init(
+        newToken: 'abcd',
+        newUserID: '@test:fakeServer.notExisting',
+        newHomeserver: moorClient.homeserver,
+        newDeviceName: 'Text Matrix Client',
+        newDeviceID: 'GHTYAJCE',
+        newOlmAccount: pickledOlmAccount,
+      );
+      await Future.delayed(Duration(milliseconds: 200));
+      await moorClient.dispose(closeDatabase: false);
+
+      final hiveClient = Client(
+        'testclient',
+        httpClient: FakeMatrixApi(),
+        databaseBuilder: getDatabase,
+        legacyDatabaseBuilder: (_) => database,
+      );
+      await hiveClient.init();
+      await Future.delayed(Duration(milliseconds: 200));
+      expect(hiveClient.isLogged(), true);
+    });
   });
 }