firka_wear: add error screen

Closes #12

firka_wear/lib/app/app_state.dart

@@ -9,6 +9,10 @@ import 'package:firka_wear/services/wear_sync_store.dart';
 late final Logger logger;
 
 final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+
+/// When non-null, the app should show [WearErrorScreen] with this error.
+final ValueNotifier<FlutterErrorDetails?> globalErrorNotifier =
+    ValueNotifier<FlutterErrorDetails?>(null);
 late WearAppInitialization initData;
 bool initDone = false;
 

firka_wear/lib/app/initialization_screen.dart

@@ -1,13 +1,13 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
-import 'package:wear_plus/wear_plus.dart';
 
 import 'package:firka_wear/app/app_state.dart';
 import 'package:firka_wear/app/initialization.dart';
 import 'package:firka_wear/core/bloc/wear_sync_cubit.dart';
 import 'package:firka_wear/l10n/app_localizations.dart';
 import 'package:firka_wear/ui/theme/style.dart';
+import 'package:firka_wear/ui/wear/screens/error/error_screen.dart';
 import 'package:firka_wear/ui/wear/screens/home/home_screen.dart';
 import 'package:firka_wear/ui/wear/screens/login/login_screen.dart';
 
@@ -25,25 +25,7 @@ class WearInitializationScreen extends StatelessWidget {
           if (snapshot.hasError) {
             return MaterialApp(
               key: ValueKey('firkaErrorPage'),
-              home: Scaffold(
-                body: Center(
-                  child: WatchShape(
-                    builder: (context, shape, child) {
-                      return Column(
-                        mainAxisAlignment: MainAxisAlignment.center,
-                        children: <Widget>[
-                          Text(
-                            'Error initializing app: ${snapshot.error}',
-                            style: TextStyle(color: Colors.red),
-                          ),
-                          child!,
-                        ],
-                      );
-                    },
-                    child: SizedBox(),
-                  ),
-                ),
-              ),
+              home: WearErrorScreen(exception: snapshot.error!),
             );
           }
 

firka_wear/lib/main.dart

@@ -1,7 +1,9 @@
+import 'dart:async';
 import 'dart:io';
 
 import 'package:firka_wear/app/app_state.dart';
 import 'package:firka_wear/app/initialization_screen.dart';
+import 'package:firka_wear/ui/wear/screens/error/error_screen.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_screenutil/flutter_screenutil.dart';
 import 'package:logging/logging.dart';
@@ -26,5 +28,49 @@ void main() async {
 
   await ScreenUtil.ensureScreenSize();
 
-  runApp(WearInitializationScreen());
+  FlutterError.onError = (FlutterErrorDetails details) {
+    FlutterError.presentError(details);
+    if (_isFatalError(details.exception)) {
+      globalErrorNotifier.value = details;
+    }
+  };
+
+  runZonedGuarded(() => runApp(const _WearAppWrapper()), (
+    Object error,
+    StackTrace stackTrace,
+  ) {
+    if (_isFatalError(error)) {
+      globalErrorNotifier.value = FlutterErrorDetails(
+        exception: error,
+        stack: stackTrace,
+        library: 'firka_wear',
+      );
+    }
+  });
+}
+
+bool _isFatalError(Object error) {
+  return error is! AssertionError;
+}
+
+class _WearAppWrapper extends StatelessWidget {
+  const _WearAppWrapper();
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder<FlutterErrorDetails?>(
+      valueListenable: globalErrorNotifier,
+      builder: (context, error, _) {
+        if (error != null) {
+          return MaterialApp(
+            home: WearErrorScreen(
+              exception: error.exception,
+              stackTrace: error.stack,
+            ),
+          );
+        }
+        return WearInitializationScreen();
+      },
+    );
+  }
 }

firka_wear/lib/ui/wear/screens/error/error_screen.dart

@@ -0,0 +1,65 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_screenutil/flutter_screenutil.dart';
+import 'package:qr_flutter/qr_flutter.dart';
+import 'package:wear_plus/wear_plus.dart';
+
+import 'package:firka_wear/ui/theme/style.dart';
+
+final int _kMaxQrPayloadChars = 410;
+
+String errorPayload(Object exception, [StackTrace? stackTrace]) {
+  final buffer = StringBuffer();
+  buffer.writeln(exception.toString());
+  if (stackTrace != null) buffer.write(stackTrace.toString());
+  final s = buffer.toString();
+  return s.length > _kMaxQrPayloadChars
+      ? s.substring(0, _kMaxQrPayloadChars)
+      : s;
+}
+
+/// Full-screen error UI: encodes [exception] (and [stackTrace]) into a QR code
+/// scaled to fit the watch's circular display so it is not clipped.
+class WearErrorScreen extends StatelessWidget {
+  final Object exception;
+  final StackTrace? stackTrace;
+
+  const WearErrorScreen({super.key, required this.exception, this.stackTrace});
+
+  @override
+  Widget build(BuildContext context) {
+    ScreenUtil.init(context);
+
+    final payload = errorPayload(exception, stackTrace);
+    return Scaffold(
+      backgroundColor: wearStyle.colors.background,
+      body: LayoutBuilder(
+        builder: (context, constraints) {
+          return Center(
+            child: WatchShape(
+              builder: (context, shape, child) {
+                return SizedBox(
+                  width: 350.w,
+                  height: 350.h,
+                  child: QrImageView(
+                    data: payload,
+                    version: 13,
+                    backgroundColor: wearStyle.colors.background,
+                    eyeStyle: QrEyeStyle(
+                      eyeShape: QrEyeShape.square,
+                      color: wearStyle.colors.textPrimary,
+                    ),
+                    dataModuleStyle: QrDataModuleStyle(
+                      dataModuleShape: QrDataModuleShape.square,
+                      color: wearStyle.colors.textPrimary,
+                    ),
+                  ),
+                );
+              },
+              child: const SizedBox.shrink(),
+            ),
+          );
+        },
+      ),
+    );
+  }
+}

firka_wear/pubspec.yaml

@@ -62,6 +62,7 @@ dependencies:
   flutter_svg: ^1.1.6
   logging: ^1.3.0
   flutter_bloc: ^9.0.0
+  qr_flutter: ^4.1.0
 
 dev_dependencies:
   build_runner: any