fix pending permission request breaking the controller start sequence

@@ -11,7 +11,8 @@ export 'src/enums/phone_type.dart';
 export 'src/enums/torch_state.dart';
 export 'src/mobile_scanner.dart';
 export 'src/mobile_scanner_controller.dart';
-export 'src/mobile_scanner_exception.dart';
+export 'src/mobile_scanner_exception.dart'
+    hide PermissionRequestPendingException;
 export 'src/mobile_scanner_platform_interface.dart';
 export 'src/objects/address.dart';
 export 'src/objects/barcode.dart';

@@ -290,6 +290,8 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
           zoomScale: 1.0,
         );
       }
+    } on PermissionRequestPendingException catch (_) {
+      // If a permission request was already pending, do nothing.
     }
   }
 

@@ -39,3 +39,10 @@ class MobileScannerErrorDetails {
   /// The error message from the [PlatformException].
   final String? message;
 }
+
+/// This class represents an exception that is thrown
+/// when the scanner was (re)started while a permission request was pending.
+///
+/// This exception type is only used internally,
+/// and is not part of the public API.
+class PermissionRequestPendingException implements Exception {}

@@ -39,6 +39,18 @@ class MobileScannerWeb extends MobileScannerPlatform {
   /// This container element is used by the barcode reader.
   HTMLDivElement? _divElement;
 
+  /// This [Completer] is used to prevent additional calls to the [start] method.
+  ///
+  /// To handle lifecycle changes properly,
+  /// the scanner is stopped when the application is inactive,
+  /// and restarted when the application gains focus.
+  ///
+  /// However, when the camera permission is requested,
+  /// the application is put in the inactive state due to the permission popup gaining focus.
+  /// Thus, as long as the permission status is not known,
+  /// any calls to the [start] method are ignored.
+  Completer<void>? _cameraPermissionCompleter;
+
   /// The stream controller for the media track settings stream.
   final StreamController<MediaTrackSettings> _settingsController =
       StreamController.broadcast();
@@ -50,6 +62,11 @@ class MobileScannerWeb extends MobileScannerPlatform {
     MobileScannerPlatform.instance = MobileScannerWeb();
   }
 
+  bool get _hasPendingPermissionRequest {
+    return _cameraPermissionCompleter != null &&
+        !_cameraPermissionCompleter!.isCompleted;
+  }
+
   @override
   Stream<BarcodeCapture?> get barcodesStream => _barcodesController.stream;
 
@@ -174,6 +191,13 @@ class MobileScannerWeb extends MobileScannerPlatform {
 
   @override
   Future<MobileScannerViewAttributes> start(StartOptions startOptions) async {
+    // If the permission request has not yet completed,
+    // the camera view is not ready yet.
+    // Prevent the permission popup from triggering a restart of the scanner.
+    if (_hasPendingPermissionRequest) {
+      throw PermissionRequestPendingException();
+    }
+
     await _barcodeReader.maybeLoadLibrary(
       alternateScriptUrl: _alternateScriptUrl,
     );