Add chat topic feature

lib/views/chat_details.dart

@@ -14,6 +14,7 @@ import 'package:fluffychat/views/invitation_selection.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:image_picker/image_picker.dart';
+import 'package:link_text/link_text.dart';
 import 'package:toast/toast.dart';
 
 class ChatDetails extends StatefulWidget {
@@ -27,6 +28,7 @@ class ChatDetails extends StatefulWidget {
 
 class _ChatDetailsState extends State<ChatDetails> {
   List<User> members;
+  bool topicEditMode = false;
   void setDisplaynameAction(BuildContext context, String displayname) async {
     final MatrixState matrix = Matrix.of(context);
     final success = await matrix.tryRequestWithLoadingDialog(
@@ -41,6 +43,21 @@ class _ChatDetailsState extends State<ChatDetails> {
     }
   }
 
+  void setTopicAction(BuildContext context, String displayname) async {
+    setState(() => topicEditMode = false);
+    final MatrixState matrix = Matrix.of(context);
+    final success = await matrix.tryRequestWithLoadingDialog(
+      widget.room.setDescription(displayname),
+    );
+    if (success != false) {
+      Toast.show(
+        "Group description has been changed",
+        context,
+        duration: Toast.LENGTH_LONG,
+      );
+    }
+  }
+
   void setAvatarAction(BuildContext context) async {
     final File tempFile = await ImagePicker.pickImage(
         source: ImageSource.gallery,
@@ -111,30 +128,63 @@ class _ChatDetailsState extends State<ChatDetails> {
                   children: <Widget>[
                     ContentBanner(widget.room.avatar),
                     Divider(height: 1),
-                    widget.room.canSendEvent("m.room.avatar") && !kIsWeb
+                    if (widget.room.canSendEvent("m.room.avatar") && !kIsWeb)
-                        ? ListTile(
+                      ListTile(
                         title: Text("Upload group avatar"),
                         leading: Icon(Icons.camera),
                         onTap: () => setAvatarAction(context),
-                          )
+                      ),
-                        : Container(),
+                    if (widget.room.canSendEvent("m.room.name"))
-                    widget.room.canSendEvent("m.room.name")
+                      ListTile(
-                        ? ListTile(
                         leading: Icon(Icons.edit),
                         title: TextField(
                           textInputAction: TextInputAction.done,
-                              onSubmitted: (s) =>
+                          onSubmitted: (s) => setDisplaynameAction(context, s),
-                                  setDisplaynameAction(context, s),
                           decoration: InputDecoration(
                             border: InputBorder.none,
                             labelText: "Set group name",
                             labelStyle: TextStyle(color: Colors.black),
-                                hintText:
+                            hintText: (RoomNameCalculator(widget.room).name),
-                                    (RoomNameCalculator(widget.room).name),
+                          ),
+                        ),
+                      ),
+                    topicEditMode
+                        ? ListTile(
+                            title: TextField(
+                              textInputAction: TextInputAction.done,
+                              onSubmitted: (s) => setTopicAction(context, s),
+                              autofocus: true,
+                              minLines: 1,
+                              maxLines: 4,
+                              decoration: InputDecoration(
+                                border: InputBorder.none,
+                                labelText: "Group description:",
+                                labelStyle: TextStyle(
+                                    color: Theme.of(context).primaryColor,
+                                    fontWeight: FontWeight.bold),
+                                hintText: widget.room.topic ??
+                                    "Set group description",
                               ),
                             ),
                           )
-                        : Container(),
+                        : ListTile(
+                            title: Text("Group description:",
+                                style: TextStyle(
+                                    color: Theme.of(context).primaryColor,
+                                    fontWeight: FontWeight.bold)),
+                            subtitle: LinkText(
+                              text: widget.room.topic?.isEmpty ?? true
+                                  ? "Add a group description"
+                                  : widget.room.topic,
+                              textStyle: TextStyle(
+                                fontSize: 14,
+                                color: Colors.black,
+                              ),
+                            ),
+                            onTap: widget.room.canSendEvent("m.room.topic")
+                                ? () => setState(() => topicEditMode = true)
+                                : null,
+                          ),
                     ListTile(
                       title: Text(
                         "$actualMembersCount participant" +