feat: chat mentions

closes #17

lib/widgets/chat_write.dart

@@ -1,8 +1,12 @@
+import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:ndk/ndk.dart';
+import 'package:ndk/shared/nips/nip19/nip19.dart';
 import 'package:zap_stream_flutter/main.dart';
 import 'package:zap_stream_flutter/theme.dart';
 import 'package:zap_stream_flutter/utils.dart';
+import 'package:zap_stream_flutter/widgets/avatar.dart';
+import 'package:zap_stream_flutter/widgets/profile.dart';
 
 class WriteMessageWidget extends StatefulWidget {
   final StreamEvent stream;
@@ -15,11 +19,128 @@ class WriteMessageWidget extends StatefulWidget {
 
 class __WriteMessageWidget extends State<WriteMessageWidget> {
   late final TextEditingController _controller;
+  OverlayEntry? _entry;
+  late FocusNode _focusNode;
 
   @override
   void initState() {
     super.initState();
+    _focusNode = FocusNode();
+    _focusNode.addListener(() {
+      if (!_focusNode.hasFocus && _entry != null) {
+        _entry!.remove();
+        _entry = null;
+      }
+    });
     _controller = TextEditingController();
+    _controller.addListener(() {
+      if (_controller.text.endsWith("@")) {
+        // start auto-complete
+        _showAutoComplete();
+      }
+    });
+  }
+
+  @override
+  void dispose() {
+    if (_entry != null) {
+      _entry!.remove();
+    }
+    _controller.dispose();
+    super.dispose();
+  }
+
+  void _showAutoComplete() {
+    if (_entry != null) {
+      _entry!.remove();
+      _entry = null;
+    }
+
+    final pos = context.findRenderObject() as RenderBox?;
+    _entry = OverlayEntry(
+      builder: (context) {
+        return ValueListenableBuilder(
+          valueListenable: _controller,
+          builder: (context, v, _) {
+            final selectionStart = v.text.lastIndexOf("@");
+            if (selectionStart == -1) {
+              _entry!.remove();
+              _entry = null;
+              return SizedBox();
+            }
+            final search = v.text.substring(selectionStart + 1, v.text.length);
+            if (search.isEmpty) {
+              return SizedBox();
+            }
+            return Stack(
+              children: [
+                Positioned(
+                  left: 0,
+                  bottom: (pos?.paintBounds.bottom ?? 0),
+                  width: MediaQuery.of(context).size.width,
+                  child: Container(
+                    padding: EdgeInsets.symmetric(horizontal: 4, vertical: 8),
+                    decoration: BoxDecoration(
+                      color: LAYER_2,
+                      borderRadius: DEFAULT_BR,
+                    ),
+                    child: FutureBuilder(
+                      future: ndkCache.searchMetadatas(search, 5),
+                      builder: (context, state) {
+                        if (state.data?.isEmpty ?? true) {
+                          return Text("No user found");
+                        }
+
+                        return Column(
+                          spacing: 4,
+                          children:
+                              (state.data ?? [])
+                                  .groupListsBy((m) => m.pubKey)
+                                  .entries
+                                  .map(
+                                    (m) => GestureDetector(
+                                      onTap: () {
+                                        // replace search string with npub
+                                        _controller
+                                            .text = _controller.text.replaceRange(
+                                          selectionStart,
+                                          _controller.text.length,
+                                          "nostr:${Nip19.encodePubKey(m.value.first.pubKey)}",
+                                        );
+                                        _entry!.remove();
+                                        _entry = null;
+                                      },
+                                      child: Row(
+                                        spacing: 4,
+                                        children: [
+                                          AvatarWidget(
+                                            profile: m.value.first,
+                                            size: 30,
+                                          ),
+                                          Expanded(
+                                            child: Text(
+                                              ProfileNameWidget.nameFromProfile(
+                                                m.value.first,
+                                              ),
+                                            ),
+                                          ),
+                                        ],
+                                      ),
+                                    ),
+                                  )
+                                  .toList(),
+                        );
+                      },
+                    ),
+                  ),
+                ),
+              ],
+            );
+          },
+        );
+      },
+    );
+    Overlay.of(context).insert(_entry!);
   }
 
   Future<void> _sendMessage(BuildContext context) async {
@@ -35,7 +156,7 @@ class __WriteMessageWidget extends State<WriteMessageWidget> {
       ],
     );
     _controller.clear();
-    FocusScope.of(context).unfocus();
+    _focusNode.unfocus();
     final res = ndk.broadcast.broadcast(nostrEvent: chatMsg);
     await res.broadcastDoneFuture;
   }
@@ -55,6 +176,9 @@ class __WriteMessageWidget extends State<WriteMessageWidget> {
                 children: [
                   Expanded(
                     child: TextField(
+                      maxLines: 3,
+                      minLines: 1,
+                      focusNode: _focusNode,
                       controller: _controller,
                       onSubmitted: (_) => _sendMessage(context),
                       decoration: InputDecoration(