Add error handle for login page

lib/globals.dart

@@ -106,3 +106,5 @@ EHApi get api {
 
 final AuthInfo auth = AuthInfo();
 final Path platformPath = Path();
+final GlobalKey<ScaffoldMessengerState> rootScaffoldMessengerKey =
+    GlobalKey<ScaffoldMessengerState>();

lib/l10n/app_en.arb

@@ -6,5 +6,8 @@
     "password": "Password",
     "save": "Save",
     "login": "Login",
-    "titleBar": "EH Downloader"
+    "titleBar": "EH Downloader",
+    "incorrectUserPassword": "Incorrect username or password.",
+    "networkError": "Network error.",
+    "internalError": "Some internal error occurred. Please send the log file to the developer."
 }

lib/l10n/app_zh.arb

@@ -6,5 +6,8 @@
     "password": "密码",
     "save": "保存",
     "login": "登录",
-    "titleBar": "EH 下载器"
+    "titleBar": "EH 下载器",
+    "incorrectUserPassword": "不正确的用户名或密码。",
+    "networkError": "网络错误。",
+    "internalError": "出现了内部错误，请将日志发送给开发者。"
 }

lib/login.dart

@@ -70,7 +70,9 @@ class _LoginPageState extends State<LoginPage> {
         setCookie: true,
         httpOnly: true,
         secure: u.scheme == 'https');
-    return re.ok;
+    if (re.ok) return true;
+    if (re.status == 4) return false;
+    throw re.unwrapErr();
   }
 
   void _checkStatus(BuildContext build) {
@@ -147,12 +149,27 @@ class _LoginPageState extends State<LoginPage> {
                                   if (re) {
                                     context.go("/");
                                   } else {
+                                    final snackBar = SnackBar(
+                                        content: Text(
+                                            AppLocalizations.of(context)!
+                                                .incorrectUserPassword));
+                                    ScaffoldMessenger.of(context)
+                                        .showSnackBar(snackBar);
                                     setState(() {
                                       _isLogin = false;
                                     });
                                   }
                                 }).catchError((e) {
                                   _log.severe("Failed to login:", e);
+                                  final isNetworkError = e is! (int, String);
+                                  final snackBar = SnackBar(
+                                      content: Text(isNetworkError
+                                          ? AppLocalizations.of(context)!
+                                              .networkError
+                                          : AppLocalizations.of(context)!
+                                              .internalError));
+                                  ScaffoldMessenger.of(context)
+                                      .showSnackBar(snackBar);
                                   setState(() {
                                     _isLogin = false;
                                   });

lib/main.dart

@@ -123,6 +123,7 @@ class _MainApp extends State<MainApp> {
       theme: _themeData,
       darkTheme: _darkThemeData,
       themeMode: _themeMode,
+      scaffoldMessengerKey: rootScaffoldMessengerKey,
     );
   }