feat(stream_chat_v1): implement foreground notifications

packages/stream_chat_v1/lib/home_page.dart

@@ -1,9 +1,56 @@
+import 'dart:async';
+
+import 'package:example/channel_page.dart';
+import 'package:example/notifications_service.dart';
 import 'package:example/routes/app_routes.dart';
 import 'package:example/routes/routes.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:stream_chat_flutter/stream_chat_flutter.dart';
 
+class MyObserver extends NavigatorObserver {
+  Route? currentRoute;
+  late final StreamSubscription _subscription;
+
+  MyObserver(StreamChatClient client, BuildContext context) {
+    _subscription = client.on(EventType.messageNew).listen((event) {
+      final channelId = event.channelId;
+      if (currentRoute?.settings.name == Routes.CHANNEL_PAGE) {
+        final args = currentRoute?.settings.arguments as ChannelPageArgs;
+        if (args.channel?.id == channelId) {
+          return;
+        }
+      }
+
+      showLocalNotification(event, client.state.currentUser!.id, context);
+    });
+  }
+
+  @override
+  void didPop(Route route, Route? previousRoute) {
+    currentRoute = route;
+  }
+
+  @override
+  void didPush(Route route, Route? previousRoute) {
+    currentRoute = route;
+  }
+
+  @override
+  void didRemove(Route route, Route? previousRoute) {
+    currentRoute = route;
+  }
+
+  @override
+  void didReplace({Route? newRoute, Route? oldRoute}) {
+    currentRoute = newRoute;
+  }
+
+  void dispose() {
+    _subscription.cancel();
+  }
+}
+
 class HomePageArgs {
   final StreamChatClient chatClient;
 
@@ -24,6 +71,7 @@ class HomePage extends StatefulWidget {
 
 class _HomePageState extends State<HomePage> {
   final GlobalKey<NavigatorState> _navigatorKey = GlobalKey();
+  MyObserver? _observer;
 
   @override
   Widget build(BuildContext context) {
@@ -38,8 +86,16 @@ class _HomePageState extends State<HomePage> {
           key: _navigatorKey,
           onGenerateRoute: AppRoutes.generateRoute,
           initialRoute: Routes.CHANNEL_LIST_PAGE,
+          observers: [_observer!],
         ),
       ),
     );
   }
+
+  @override
+  void didChangeDependencies() {
+    _observer?.dispose();
+    _observer = MyObserver(widget.chatClient, context);
+    super.didChangeDependencies();
+  }
 }