Fix double camera permission request on OS back and refactor qr scanner

CHANGELOG.md

@@ -56,6 +56,7 @@ and this project adheres to Calendar Versioning (CalVer).
 - Fix deleting all app data reusing a closed Whitenoise database instance [PR #662](https://github.com/marmot-protocol/whitenoise/pull/662)
 - Fixed QR scanner not showing camera on first attempt after giving permission [PR #654](https://github.com/marmot-protocol/whitenoise/pull/654)
 - Fix show author name in last message of pending invites in chat list [PR #668](https://github.com/marmot-protocol/whitenoise/pull/668)
+- Fix double camera permission request on OS back [PR #655](https://github.com/marmot-protocol/whitenoise/pull/655)
 
 ### Security
 

lib/hooks/use_qr_scanner.dart

@@ -0,0 +1,197 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_hooks/flutter_hooks.dart';
+import 'package:mobile_scanner/mobile_scanner.dart';
+import 'package:permission_handler/permission_handler.dart';
+
+class _Injectable<T extends Function> {
+  final T _default;
+  late T _current;
+  _Injectable(this._default) : _current = _default;
+  T get value => _current;
+  void set(T v) => _current = v;
+  void reset() => _current = _default;
+}
+
+final _controllerFactory = _Injectable<MobileScannerController Function()>(
+  () => MobileScannerController(
+    formats: [BarcodeFormat.qrCode],
+    autoStart: false,
+  ),
+);
+final _permissionRequester = _Injectable<Future<PermissionStatus> Function()>(
+  () => Permission.camera.request(),
+);
+final _permissionStatusChecker = _Injectable<Future<PermissionStatus> Function()>(
+  () => Permission.camera.status,
+);
+
+MobileScannerController createScannerController() => _controllerFactory.value();
+Future<PermissionStatus> requestCameraPermission() => _permissionRequester.value();
+Future<PermissionStatus> checkCameraPermissionStatus() => _permissionStatusChecker.value();
+
+void setScannerControllerFactory(MobileScannerController Function() factory) =>
+    _controllerFactory.set(factory);
+void resetScannerControllerFactory() => _controllerFactory.reset();
+void setPermissionRequester(Future<PermissionStatus> Function() requester) =>
+    _permissionRequester.set(requester);
+void resetPermissionRequester() => _permissionRequester.reset();
+void setPermissionStatusChecker(Future<PermissionStatus> Function() checker) =>
+    _permissionStatusChecker.set(checker);
+void resetPermissionStatusChecker() => _permissionStatusChecker.reset();
+
+enum ScannerState { loading, ready, permissionDenied, initError, error }
+
+void _useCameraPermission({
+  required UniqueKey retryKey,
+  required ObjectRef<bool> isMounted,
+  required VoidCallback onGranted,
+  required VoidCallback onDenied,
+  required VoidCallback retryScanner,
+}) {
+  final isDenied = useRef(false);
+  final permissionStatusAtDenial = useRef<PermissionStatus?>(null);
+
+  useEffect(() {
+    Future<void> checkPermission() async {
+      final status = await requestCameraPermission();
+      if (!isMounted.value) return;
+
+      if (status.isGranted || status.isLimited) {
+        isDenied.value = false;
+        permissionStatusAtDenial.value = null;
+        onGranted();
+      } else {
+        final currentStatus = await checkCameraPermissionStatus();
+        if (!isMounted.value) return;
+        isDenied.value = true;
+        permissionStatusAtDenial.value = currentStatus;
+        onDenied();
+      }
+    }
+
+    unawaited(checkPermission());
+    return null;
+  }, [retryKey]);
+
+  useOnAppLifecycleStateChange((previous, current) {
+    if (current != AppLifecycleState.resumed || !isMounted.value) return;
+    if (!isDenied.value) return;
+
+    Future<void> checkAndRetry() async {
+      final cameraPermissionStatus = await checkCameraPermissionStatus();
+      if (!isMounted.value) return;
+      final snapshotWasDenied =
+          permissionStatusAtDenial.value != null &&
+          !(permissionStatusAtDenial.value!.isGranted || permissionStatusAtDenial.value!.isLimited);
+      if (snapshotWasDenied &&
+          (cameraPermissionStatus.isGranted || cameraPermissionStatus.isLimited)) {
+        retryScanner();
+      }
+    }
+
+    unawaited(checkAndRetry());
+  });
+}
+
+({
+  ScannerState scannerState,
+  MobileScannerController controller,
+  VoidCallback retryScanner,
+  void Function(ScannerState) setErrorState,
+})
+useQrScanner({required void Function(String) onQrCodeDetected}) {
+  final isProcessing = useState(false);
+  final scannerRetryKey = useState(UniqueKey());
+  final isMounted = useRef(true);
+  final scannerState = useState(ScannerState.loading);
+
+  useEffect(() {
+    isMounted.value = true;
+    return () => isMounted.value = false;
+  }, const []);
+
+  void retryScanner() {
+    scannerState.value = ScannerState.loading;
+    scannerRetryKey.value = UniqueKey();
+  }
+
+  _useCameraPermission(
+    retryKey: scannerRetryKey.value,
+    isMounted: isMounted,
+    onGranted: () => scannerState.value = ScannerState.ready,
+    onDenied: () => scannerState.value = ScannerState.permissionDenied,
+    retryScanner: retryScanner,
+  );
+
+  final controller = useMemoized(createScannerController, [
+    scannerRetryKey.value,
+  ]);
+
+  useEffect(() {
+    if (scannerState.value != ScannerState.ready) return null;
+
+    var startCalled = false;
+
+    void handleQrCode(BarcodeCapture capture) {
+      if (capture.barcodes.isEmpty) return;
+      if (isProcessing.value) return;
+      final barcode = capture.barcodes.first;
+      final rawValue = barcode.rawValue ?? '';
+      if (rawValue.isEmpty) return;
+      isProcessing.value = true;
+      onQrCodeDetected(rawValue.trim());
+      Future.delayed(const Duration(milliseconds: 500), () {
+        if (isMounted.value) isProcessing.value = false;
+      });
+    }
+
+    Future<void> startController() async {
+      if (startCalled) return;
+      startCalled = true;
+      try {
+        await controller.start();
+      } on MobileScannerException {
+        if (isMounted.value) scannerState.value = ScannerState.initError;
+      }
+    }
+
+    final subscription = controller.barcodes.listen(handleQrCode);
+    unawaited(startController());
+
+    return () {
+      unawaited(subscription.cancel());
+      unawaited(controller.dispose());
+    };
+  }, [controller, scannerState.value]);
+
+  useOnAppLifecycleStateChange((previous, current) {
+    if (current != AppLifecycleState.resumed || !isMounted.value) return;
+    if (scannerState.value == ScannerState.permissionDenied) return;
+
+    if (scannerState.value == ScannerState.loading) {
+      unawaited(() async {
+        final status = await checkCameraPermissionStatus();
+        if (!isMounted.value) return;
+        if (status.isGranted || status.isLimited) {
+          retryScanner();
+        }
+      }());
+      return;
+    }
+
+    retryScanner();
+  });
+
+  void setErrorState(ScannerState state) {
+    if (isMounted.value) scannerState.value = state;
+  }
+
+  return (
+    scannerState: scannerState.value,
+    controller: controller,
+    retryScanner: retryScanner,
+    setErrorState: setErrorState,
+  );
+}

lib/screens/scan_npub_screen.dart

@@ -21,7 +21,7 @@ class ScanNpubScreen extends HookWidget {
     final l10n = context.l10n;
     final showInvalidNpubError = useState(false);
 
-    void onBarcodeDetected(String value) {
+    void onQrCodeDetected(String value) {
       final deepLinkTarget = DeepLinks.parseString(value);
       if (deepLinkTarget != null) {
         Routes.goBack(context);
@@ -51,11 +51,7 @@ class ScanNpubScreen extends HookWidget {
             child: Column(
               crossAxisAlignment: CrossAxisAlignment.stretch,
               children: [
-                Expanded(
-                  child: QrScanner(
-                    onBarcodeDetected: onBarcodeDetected,
-                  ),
-                ),
+                Expanded(child: QrScanner(onQrCodeDetected: onQrCodeDetected)),
                 Gap(12.h),
                 Text(
                   showInvalidNpubError.value ? l10n.invalidNpub : l10n.scanNpubHint,

lib/screens/scan_nsec_screen.dart

@@ -42,7 +42,7 @@ class ScanNsecScreen extends StatelessWidget {
                   children: [
                     Expanded(
                       child: QrScanner(
-                        onBarcodeDetected: (value) => GoRouter.of(context).pop(value),
+                        onQrCodeDetected: (value) => GoRouter.of(context).pop(value),
                       ),
                     ),
                     Gap(12.h),