Add dark mode support

lib/home.dart

@@ -1,11 +1,19 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_gen/gen_l10n/app_localizations.dart';
 import 'package:flutter_hooks/flutter_hooks.dart';
 import 'package:go_router/go_router.dart';
 import 'package:logging/logging.dart';
 import 'globals.dart';
+import 'main.dart';
 
 final _log = Logger("HomePage");
 
+ThemeMode _themeModeNext(ThemeMode mode) {
+  if (mode == ThemeMode.system) return ThemeMode.light;
+  if (mode == ThemeMode.dark) return ThemeMode.system;
+  return ThemeMode.dark;
+}
+
 class HomePage extends HookWidget {
   const HomePage({Key? key}) : super(key: key);
 
@@ -26,8 +34,26 @@ class HomePage extends HookWidget {
       }
       return;
     }, []);
-    return const Scaffold(
-      body: Center(
+    var mode = useState(MainApp.of(context).themeMode);
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(AppLocalizations.of(context)!.titleBar),
+        actions: [
+          IconButton(
+              onPressed: () {
+                final n = _themeModeNext(mode.value);
+                MainApp.of(context).changeThemeMode(n);
+                mode.value = n;
+              },
+              icon: Icon(mode.value == ThemeMode.system
+                  ? Icons.brightness_auto
+                  : mode.value == ThemeMode.dark
+                      ? Icons.dark_mode
+                      : Icons.light_mode)),
+          const IconButton(onPressed: null, icon: Icon(Icons.more_vert)),
+        ],
+      ),
+      body: const Center(
         child: Text('Hello World!'),
       ),
     );

lib/l10n/app_en.arb

@@ -5,5 +5,6 @@
     "username": "Username",
     "password": "Password",
     "save": "Save",
-    "login": "Login"
+    "login": "Login",
+    "titleBar": "EH Downloader"
 }

lib/l10n/app_zh.arb

@@ -5,5 +5,6 @@
     "username": "用户名",
     "password": "密码",
     "save": "保存",
-    "login": "登录"
+    "login": "登录",
+    "titleBar": "EH 下载器"
 }

lib/main.dart

@@ -75,12 +75,40 @@ void main() async {
   runApp(const MainApp());
 }
 
-class MainApp extends StatelessWidget {
+final _log = Logger("MainApp");
+
+class MainApp extends StatefulWidget {
   const MainApp({super.key});
 
+  @override
+  State<MainApp> createState() => _MainApp();
+  // ignore: library_private_types_in_public_api
+  static _MainApp of(BuildContext context) =>
+      context.findAncestorStateOfType<_MainApp>()!;
+}
+
+class _MainApp extends State<MainApp> {
+  ThemeMode _themeMode = ThemeMode.system;
+  ThemeData _themeData = ThemeData();
+  ThemeData _darkThemeData = ThemeData.dark();
+  ThemeMode get themeMode => _themeMode;
+
+  @override
+  void initState() {
+    super.initState();
+    try {
+      _themeMode = ThemeMode.values[prefs.getInt("themeMode") ?? 0];
+    } catch (e) {
+      _log.warning("Failed to read themeMode from prefs:", e);
+    }
+    if (kIsWeb || isWindows) {
+      _themeData = _themeData.useSystemChineseFont();
+      _darkThemeData = _darkThemeData.useSystemChineseFont();
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
-    var theme = ThemeData();
     return MaterialApp.router(
       routerConfig: _router,
       onGenerateTitle: (context) {
@@ -92,7 +120,16 @@ class MainApp extends StatelessWidget {
       },
       localizationsDelegates: AppLocalizations.localizationsDelegates,
       supportedLocales: AppLocalizations.supportedLocales,
-      theme: (kIsWeb || isWindows) ? theme.useSystemChineseFont() : theme,
+      theme: _themeData,
+      darkTheme: _darkThemeData,
+      themeMode: _themeMode,
     );
   }
+
+  void changeThemeMode(ThemeMode mode) {
+    prefs.setInt("themeMode", mode.index);
+    setState(() {
+      _themeMode = mode;
+    });
+  }
 }