feat: add connectivity check for multiplayer training and retry logic for sync

lib/src/core/utils/connectivity_helper.dart

@@ -0,0 +1,12 @@
+import 'dart:io';
+
+class ConnectivityHelper {
+  static Future<bool> hasConnection() async {
+    try {
+      final result = await InternetAddress.lookup('8.8.8.8');
+      return result.isNotEmpty && result[0].rawAddress.isNotEmpty;
+    } on SocketException catch (_) {
+      return false;
+    }
+  }
+}

lib/src/features/dashboard/presentation/screens/hub_screen.dart

@@ -25,6 +25,7 @@ import '../widgets/level_display.dart';
 import '../widgets/start_raid_button.dart';
 import '../../../gamification/application/quest_service.dart';
 import '../../../workout_runner/application/workout_generator_service.dart';
+import '../../../../core/utils/connectivity_helper.dart';
 
 class HubScreen extends ConsumerStatefulWidget {
   const HubScreen({super.key});
@@ -51,6 +52,26 @@ class _HubScreenState extends ConsumerState<HubScreen> {
     });
   }
 
+  Future<void> _handleMultiplayerPress() async {
+    final hasInternet = await ConnectivityHelper.hasConnection();
+
+    if (!hasInternet) {
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          const SnackBar(
+            content: Text(
+                'Für Multiplayer wird eine aktive Internetverbindung benötigt.'), //TODO: make this in l10n
+            backgroundColor: AppTheme.errorColor,
+            behavior: SnackBarBehavior.floating,
+          ),
+        );
+      }
+      return;
+    }
+
+    if (mounted) _showMultiplayerDialog();
+  }
+
   Future<void> _startNextWorkout(
       CycleCollection cycle, UserCollection user) async {
     try {
@@ -422,7 +443,7 @@ class _HubScreenState extends ConsumerState<HubScreen> {
                             icon: const Icon(Icons.groups,
                                 color: AppTheme.secondaryColor),
                             tooltip: 'Multiplayer Lobby',
-                            onPressed: _showMultiplayerDialog,
+                            onPressed: _handleMultiplayerPress,
                           ),
                         ],
                       ),

lib/src/shared/data/remote/sync_service.dart

@@ -1,10 +1,14 @@
+import 'dart:async';
 import 'dart:developer';
+import 'dart:io';
+
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:drift/drift.dart';
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 
 import '../../../../main.dart';
 import '../../../core/constants/app_constants.dart';
+import '../../../core/utils/connectivity_helper.dart';
 import '../local/app_database.dart';
 import '../repositories/user_repository.dart';
 import 'api_client.dart';
@@ -25,9 +29,25 @@ class SyncService {
 
   Future<void> sync() async {
     if (_isSyncing) return;
+
+    if (!await ConnectivityHelper.hasConnection()) {
+      log('Sync skipped: No internet connection');
+      return;
+    }
+
     _isSyncing = true;
 
     try {
+      await _retry(_performSync, maxAttempts: 3);
+      log('✅ Sync completed successfully');
+    } catch (e) {
+      log('❌ Sync failed finally: $e');
+    } finally {
+      _isSyncing = false;
+    }
+  }
+
+  Future<void> _performSync() async {
     log('🔄 Starting Sync...');
 
     final dirtyCycles = await (db.select(db.cycles)
@@ -35,7 +55,6 @@ class SyncService {
         .get();
 
     for (var cycle in dirtyCycles) {
-        try {
       if (cycle.serverId == null) {
         log('📤 Pushing new cycle ${cycle.cycleNumber}...');
         final tmsMap = cycle.trainingMaxes
@@ -67,9 +86,6 @@ class SyncService {
         await (db.update(db.cycles)..where((c) => c.id.equals(cycle.id)))
             .write(const CyclesCompanion(isDirty: Value(false)));
       }
-        } catch (e) {
-          log('❌ Failed to sync cycle ${cycle.id}: $e');
-        }
     }
 
     final dirtyUser = await (db.select(db.users)
@@ -108,9 +124,9 @@ class SyncService {
 
     final lastSync = await _storage.read(key: AppConstants.keyLastSync);
 
-      if ((pushData['workouts'] as List).isNotEmpty ||
+    // if ((pushData['workouts'] as List).isNotEmpty || pushData['user_stats'] != null) { ... }
-          pushData['user_stats'] != null) {
+
-        log('📤 Pushing data...');
+    log('Checking for updates...');
     final response = await apiClient.sync(
       lastSyncTimestamp: lastSync ?? '',
       pushData: pushData,
@@ -220,16 +236,34 @@ class SyncService {
 
     if (response['server_timestamp'] != null) {
       await _storage.write(
-              key: AppConstants.keyLastSync,
+          key: AppConstants.keyLastSync, value: response['server_timestamp']);
-              value: response['server_timestamp']);
     }
   }
-      log('✅ Sync completed successfully');
+
-    } catch (e, stack) {
+  Future<T> _retry<T>(
-      log('❌ Sync failed: $e');
+    Future<T> Function() function, {
-      log(stack.toString());
+    int maxAttempts = 3,
-    } finally {
+    Duration initialDelay = const Duration(seconds: 2),
-      _isSyncing = false;
+  }) async {
+    int attempts = 0;
+    while (true) {
+      try {
+        attempts++;
+        return await function();
+      } catch (e) {
+        final shouldRetry = (e is SocketException) ||
+            (e.toString().contains('500')) ||
+            (e.toString().contains('502')) ||
+            (e.toString().contains('timeout'));
+
+        if (attempts >= maxAttempts || !shouldRetry) {
+          rethrow;
+        }
+
+        final delay = initialDelay * (1 << (attempts - 1)); // 2s, 4s, 8s
+        log('⚠️ Sync attempt $attempts failed. Retrying in ${delay.inSeconds}s... Error: $e');
+        await Future.delayed(delay);
+      }
     }
   }
 }