login: Support logging out of an account

Fixes: zulip#463

assets/l10n/app_en.arb

@@ -19,6 +19,10 @@
   "@chooseAccountPageTitle": {
     "description": "Title for ChooseAccountPage"
   },
+  "chooseAccountPageLogOutButton": "Log out",
+  "@chooseAccountPageLogOutButton": {
+    "description": "Label for the 'Log out' button for an account on the choose-account page"
+  },
   "chooseAccountButtonAddAnAccount": "Add an account",
   "@chooseAccountButtonAddAnAccount": {
     "description": "Label for ChooseAccountPage button to add an account"

lib/widgets/app.dart

@@ -8,6 +8,8 @@ import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 import '../log.dart';
 import '../model/localizations.dart';
 import '../model/narrow.dart';
+import '../model/store.dart';
+import '../notifications/receive.dart';
 import 'about_zulip.dart';
 import 'app_bar.dart';
 import 'dialog.dart';
@@ -221,15 +223,64 @@ class ChooseAccountPage extends StatelessWidget {
     required Widget title,
     Widget? subtitle,
   }) {
+    final designVariables = DesignVariables.of(context);
+    final zulipLocalizations = ZulipLocalizations.of(context);
     return Card(
       clipBehavior: Clip.hardEdge,
       child: ListTile(
         title: title,
         subtitle: subtitle,
+        trailing: PopupMenuButton<AccountItemOverflowMenuItem>(
+          iconColor: designVariables.icon,
+          itemBuilder: (context) => [
+            PopupMenuItem(
+              value: AccountItemOverflowMenuItem.logOut,
+              child: Text(zulipLocalizations.chooseAccountPageLogOutButton)),
+          ],
+          onSelected: (item) async {
+            switch (item) {
+              case AccountItemOverflowMenuItem.logOut: {
+                unawaited(_logOutAccount(context, accountId));
+              }
+            }
+          }),
+        // The default trailing padding with M3 is 24px. Decrease by 12 because
+        // PopupMenuButton adds 12px padding on all sides of the "…" icon.
+        contentPadding: const EdgeInsetsDirectional.only(start: 16, end: 12),
         onTap: () => Navigator.push(context,
           HomePage.buildRoute(accountId: accountId))));
   }
 
+  Future<void> _logOutAccount(BuildContext context, int accountId) async {
+    final globalStore = GlobalStoreWidget.of(context);
+
+    final account = globalStore.getAccount(accountId);
+    if (account == null) return; // TODO(log)
+
+    // Unawaited, to not block removing the account on this request.
+    unawaited(_unregisterToken(globalStore, account));
+
+    await globalStore.removeAccount(accountId);
+  }
+
+  Future<void> _unregisterToken(GlobalStore globalStore, Account account) async {
+    // TODO(#322) use actual acked push token; until #322, this is just null.
+    final token = account.ackedPushToken
+      // Try the current token as a fallback; maybe the server has registered
+      // it and we just haven't recorded that fact in the client.
+      ?? NotificationService.instance.token.value;
+    if (token == null) return;
+
+    final connection = globalStore.apiConnectionFromAccount(account);
+    try {
+      await NotificationService.unregisterToken(connection, token: token);
+    } catch (e) {
+      // TODO retry? handle failures?
+    } finally {
+      connection.close();
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     final zulipLocalizations = ZulipLocalizations.of(context);
@@ -286,6 +337,8 @@ class ChooseAccountPageOverflowButton extends StatelessWidget {
   }
 }
 
+enum AccountItemOverflowMenuItem { logOut }
+
 class HomePage extends StatelessWidget {
   const HomePage({super.key});
 

lib/widgets/page.dart

@@ -40,6 +40,7 @@ mixin AccountPageRouteMixin<T extends Object?> on PageRoute<T> {
     return PerAccountStoreWidget(
       accountId: accountId,
       placeholder: const LoadingPlaceholderPage(),
+      routeToRemoveOnLogout: this,
       child: super.buildPage(context, animation, secondaryAnimation));
   }
 }

lib/widgets/store.dart

@@ -1,7 +1,9 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/scheduler.dart';
 
 import '../model/binding.dart';
 import '../model/store.dart';
+import 'page.dart';
 
 /// Provides access to the app's data.
 ///
@@ -112,11 +114,19 @@ class PerAccountStoreWidget extends StatefulWidget {
     super.key,
     required this.accountId,
     this.placeholder = const LoadingPlaceholder(),
+    this.routeToRemoveOnLogout,
     required this.child,
   });
 
   final int accountId;
   final Widget placeholder;
+
+  /// A per-account [Route] that should be removed on logout.
+  ///
+  /// Use this when the widget is a page on a route that should go away
+  /// when the account is logged out, instead of lingering with [placeholder].
+  final AccountPageRouteMixin? routeToRemoveOnLogout;
+
   final Widget child;
 
   /// The user's data for the relevant Zulip account for this widget.
@@ -195,6 +205,16 @@ class _PerAccountStoreWidgetState extends State<PerAccountStoreWidget> {
   void didChangeDependencies() {
     super.didChangeDependencies();
     final globalStore = GlobalStoreWidget.of(context);
+    final accountExists = globalStore.getAccount(widget.accountId) != null;
+    if (!accountExists) {
+      // logged out
+      _setStore(null);
+      if (widget.routeToRemoveOnLogout != null) {
+        SchedulerBinding.instance.addPostFrameCallback(
+          (_) => Navigator.of(context).removeRoute(widget.routeToRemoveOnLogout!));
+      }
+      return;
+    }
     // If we already have data, get it immediately. This avoids showing one
     // frame of loading indicator each time we have a new PerAccountStoreWidget.
     final store = globalStore.perAccountSync(widget.accountId);
@@ -212,13 +232,13 @@ class _PerAccountStoreWidgetState extends State<PerAccountStoreWidget> {
           // The account was logged out while its store was loading.
           // This widget will be showing [placeholder] perpetually,
           // but that's OK as long as other code will be removing it from the UI
-          // (for example by removing a per-account route from the nav).
+          // (usually by using [routeToRemoveOnLogout]).
         }
       }();
     }
   }
 
-  void _setStore(PerAccountStore store) {
+  void _setStore(PerAccountStore? store) {
     if (store != this.store) {
       setState(() {
         this.store = store;