neon: add NeonTabBar widget

packages/neon/neon/lib/src/widgets/app_tab_bar.dart

@@ -0,0 +1,120 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:meta/meta.dart';
+import 'package:neon/neon.dart';
+import 'package:neon/src/widgets/app_bar.dart';
+import 'package:neon/src/widgets/drawer_destination.dart';
+import 'package:provider/provider.dart';
+
+@internal
+class NeonTabBar extends StatelessWidget {
+  const NeonTabBar({
+    super.key,
+  });
+
+  @override
+  Widget build(final BuildContext context) {
+    final theme = Theme.of(context);
+    final accountsBloc = Provider.of<AccountsBloc>(context, listen: false);
+    final appsBloc = accountsBloc.activeAppsBloc;
+
+    final tabbar = ResultBuilder.behaviorSubject(
+      stream: appsBloc.appImplementations,
+      builder: (final context, final snapshot) {
+        if (!snapshot.hasData) {
+          return const SizedBox.shrink();
+        }
+
+        return _NeonTabBar(
+          apps: snapshot.requireData,
+        );
+      },
+    );
+
+    return DecoratedBox(
+      decoration: BoxDecoration(
+        border: Border(
+          bottom: BorderSide(
+            color: theme.dividerColor,
+          ),
+        ),
+      ),
+      child: Row(
+        children: [
+          Expanded(
+            child: tabbar,
+          ),
+          const NotificationIconButton(),
+          const AccountSwitcherButton(),
+        ],
+      ),
+    );
+  }
+}
+
+class _NeonTabBar extends StatefulWidget {
+  const _NeonTabBar({
+    required this.apps,
+  });
+
+  final Iterable<AppImplementation> apps;
+
+  @override
+  State<_NeonTabBar> createState() => __NeonTabBarState();
+}
+
+class __NeonTabBarState extends State<_NeonTabBar> with SingleTickerProviderStateMixin {
+  late TabController _tabController;
+  late AccountsBloc _accountsBloc;
+  late AppsBloc _appsBloc;
+  late List<AppImplementation> _apps;
+
+  @override
+  void initState() {
+    super.initState();
+
+    _accountsBloc = Provider.of<AccountsBloc>(context, listen: false);
+    _appsBloc = _accountsBloc.activeAppsBloc;
+
+    _apps = widget.apps.toList();
+    final initialIndex = _apps.indexWhere((final app) => app.id == _appsBloc.activeApp.valueOrNull?.id);
+
+    _tabController = TabController(
+      initialIndex: initialIndex,
+      vsync: this,
+      length: widget.apps.length,
+    );
+  }
+
+  @override
+  void dispose() {
+    _tabController.dispose();
+    super.dispose();
+  }
+
+  void onAppChange(final int index) {
+    _tabController.animateTo(index);
+
+    unawaited(_appsBloc.setActiveApp(_apps[index].id));
+  }
+
+  @override
+  Widget build(final BuildContext context) {
+    final appDestinations = _apps.map(
+      (final app) => TabExtension.fromNeonDestination(
+        app.destination(context),
+      ),
+    );
+
+    final drawer = TabBar(
+      controller: _tabController,
+      tabs: appDestinations.toList(),
+      onTap: onAppChange,
+      isScrollable: true,
+      dividerColor: Colors.transparent,
+    );
+
+    return drawer;
+  }
+}