implemented chat long-polling and optimistic updates, centralized notification management, optimized avatar caching

lib/widget/user_avatar.dart

@@ -29,15 +29,18 @@ class _AvatarPayload {
   _AvatarPayload(this.bytes, this.isSvg);
 }
 
-final Map<String, Future<_AvatarPayload?>> _avatarCache = {};
+// Resolved payloads are cached so re-mounts render synchronously; in-flight
+// requests are deduped so concurrent mounts share one HTTP call.
+final Map<String, _AvatarPayload?> _resolvedAvatars = {};
+final Map<String, Future<_AvatarPayload?>> _pendingAvatars = {};
 
 class _UserAvatarState extends State<UserAvatar> {
-  late Future<_AvatarPayload?> _payload;
+  _AvatarPayload? _payload;
 
   @override
   void initState() {
     super.initState();
-    _payload = _load();
+    _attach();
   }
 
   @override
@@ -46,7 +49,7 @@ class _UserAvatarState extends State<UserAvatar> {
     if (oldWidget.id != widget.id ||
         oldWidget.isGroup != widget.isGroup ||
         oldWidget.size != widget.size) {
-      _payload = _load();
+      _attach();
     }
   }
 
@@ -58,9 +61,20 @@ class _UserAvatarState extends State<UserAvatar> {
     return 'https://$host/avatar/${widget.id}/${widget.size}';
   }
 
-  Future<_AvatarPayload?> _load() {
+  void _attach() {
     final url = _url();
-    return _avatarCache.putIfAbsent(url, () => _fetch(url));
+    if (_resolvedAvatars.containsKey(url)) {
+      _payload = _resolvedAvatars[url];
+      return;
+    }
+    _payload = null;
+    final pending = _pendingAvatars.putIfAbsent(url, () => _fetch(url));
+    pending.then((p) {
+      _resolvedAvatars[url] = p;
+      _pendingAvatars.remove(url);
+      if (!mounted || _url() != url) return;
+      setState(() => _payload = p);
+    });
   }
 
   Future<_AvatarPayload?> _fetch(String url) async {
@@ -97,49 +111,45 @@ class _UserAvatarState extends State<UserAvatar> {
   Widget build(BuildContext context) {
     final radius = widget.size.toDouble();
     final theme = Theme.of(context);
+    final payload = _payload;
 
-    return FutureBuilder<_AvatarPayload?>(
-      future: _payload,
-      builder: (context, snapshot) {
-        final payload = snapshot.data;
-
-        Widget content;
-        if (payload == null) {
-          content = Icon(
-            widget.isGroup ? Icons.group : Icons.person,
-            size: radius,
-            color: Colors.white,
-          );
-        } else if (payload.isSvg) {
-          content = SvgPicture.memory(
-            payload.bytes,
-            width: radius * 2,
-            height: radius * 2,
-            fit: BoxFit.cover,
-          );
-        } else {
-          content = Image.memory(
-            payload.bytes,
-            width: radius * 2,
-            height: radius * 2,
-            fit: BoxFit.cover,
-            gaplessPlayback: true,
-          );
-        }
-
-        return CircleAvatar(
-          radius: radius,
-          backgroundColor: theme.primaryColor,
-          foregroundColor: Colors.white,
-          child: ClipOval(
-            child: SizedBox(
-              width: radius * 2,
-              height: radius * 2,
-              child: content,
-            ),
-          ),
+    Widget content;
+    if (payload != null) {
+      if (payload.isSvg) {
+        content = SvgPicture.memory(
+          payload.bytes,
+          width: radius * 2,
+          height: radius * 2,
+          fit: BoxFit.cover,
         );
-      },
+      } else {
+        content = Image.memory(
+          payload.bytes,
+          width: radius * 2,
+          height: radius * 2,
+          fit: BoxFit.cover,
+          gaplessPlayback: true,
+        );
+      }
+    } else {
+      content = Icon(
+        widget.isGroup ? Icons.group : Icons.person,
+        size: radius,
+        color: Colors.white,
+      );
+    }
+
+    return CircleAvatar(
+      radius: radius,
+      backgroundColor: theme.primaryColor,
+      foregroundColor: Colors.white,
+      child: ClipOval(
+        child: SizedBox(
+          width: radius * 2,
+          height: radius * 2,
+          child: content,
+        ),
+      ),
     );
   }
 }