Trigger background sync on connectivity recovery

lib/features/sync/sync_background_runner.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:relationship_saver/core/config/app_config.dart';
+import 'package:relationship_saver/core/network/reachability/network_reachability.dart';
 import 'package:relationship_saver/core/network/reachability/network_reachability_provider.dart';
 import 'package:relationship_saver/features/sync/sync_auto_trigger_controller.dart';
 import 'package:relationship_saver/features/sync/sync_coordinator.dart';
@@ -22,10 +23,13 @@ class _SyncBackgroundRunnerState extends ConsumerState<SyncBackgroundRunner>
     with WidgetsBindingObserver {
   late final SyncAutoTriggerController _controller;
   Timer? _periodicTimer;
+  StreamSubscription<bool>? _reachabilitySubscription;
+  bool? _lastReachable;
 
   @override
   void initState() {
     super.initState();
+    final reachability = ref.read(networkReachabilityProvider);
     _controller = SyncAutoTriggerController(
       syncNow: () => ref.read(syncCoordinatorProvider).syncNow(),
       now: DateTime.now,
@@ -36,11 +40,12 @@ class _SyncBackgroundRunnerState extends ConsumerState<SyncBackgroundRunner>
         if (AppConfig.useFakeBackend) {
           return true;
         }
-        return ref.read(networkReachabilityProvider).isReachable();
+        return reachability.isReachable();
       },
     );
     WidgetsBinding.instance.addObserver(this);
     _configurePeriodicRunner();
+    _configureReachabilityRunner(reachability);
     if (AppConfig.enableBackgroundSync) {
       unawaited(_controller.trigger(ignoreCooldown: true));
     }
@@ -60,6 +65,7 @@ class _SyncBackgroundRunnerState extends ConsumerState<SyncBackgroundRunner>
   void dispose() {
     WidgetsBinding.instance.removeObserver(this);
     _periodicTimer?.cancel();
+    _reachabilitySubscription?.cancel();
     super.dispose();
   }
 
@@ -80,4 +86,22 @@ class _SyncBackgroundRunnerState extends ConsumerState<SyncBackgroundRunner>
       unawaited(_controller.trigger());
     });
   }
+
+  void _configureReachabilityRunner(NetworkReachability reachability) {
+    if (!AppConfig.enableBackgroundSync) {
+      return;
+    }
+    _reachabilitySubscription = reachability.watch().listen((bool reachable) {
+      final bool? previous = _lastReachable;
+      _lastReachable = reachable;
+      if (reachable && previous == false) {
+        unawaited(_controller.trigger(ignoreCooldown: true));
+      }
+    });
+    unawaited(_primeReachabilityState(reachability));
+  }
+
+  Future<void> _primeReachabilityState(NetworkReachability reachability) async {
+    _lastReachable = await reachability.isReachable();
+  }
 }