fix unavailable settings

@@ -18,7 +18,22 @@ final class MediaTrackConstraintsDelegate {
 
     final MediaStreamTrack? track = tracks.first as MediaStreamTrack?;
 
-    return track?.getSettings();
+    if (track == null) {
+      return null;
+    }
+
+    final MediaTrackSettings settings = track.getSettings();
+
+    return MediaTrackSettings(
+      width: settings.width,
+      height: settings.height,
+      zoom: settings.zoomNullable ?? 1.0,
+      facingMode: settings.facingModeNullable ?? '',
+      focusMode: settings.focusModeNullable ?? 'none',
+      torch: settings.torchNullable ?? false,
+      focusDistance: settings.focusDistanceNullable ?? 0.0,
+      aspectRatio: settings.aspectRatio,
+    );
   }
 
   /// Returns a list of supported flashlight modes for the given [mediaStream].
@@ -95,3 +110,24 @@ final class MediaTrackConstraintsDelegate {
     }
   }
 }
+
+// TODO: turn this extension into an extension type when Dart 3.3 releases.
+
+// This extension exists because the Web IDL bindings for MediaTrackSettings
+// do not account for unavailable properties.
+extension _NullableMediaTrackSettings on MediaTrackSettings {
+  @JS('facingMode')
+  external String? get facingModeNullable;
+
+  @JS('focusDistance')
+  external num? get focusDistanceNullable;
+
+  @JS('focusMode')
+  external String? get focusModeNullable;
+
+  @JS('torch')
+  external bool? get torchNullable;
+
+  @JS('zoom')
+  external num? get zoomNullable;
+}

-import 'dart:js_interop';
-
-import 'package:web/web.dart';
-
-/// This class defines the settings for a video track.
-///
-/// Since the [MediaTrackSettings] type is the full union of both the base MediaTrackSettings,
-/// the tracks settings for audio tracks, and the tracks settings for video tracks,
-/// this class only keeps track of the video track settings.
-///
-/// See also:
-///  * https://www.w3.org/TR/mediacapture-streams/#media-track-settings
-///  * https://www.w3.org/TR/image-capture/#mediatracksettings-section
-class VideoTrackSettings {
-  /// Creates a [VideoTrackSettings] instance from a [MediaStreamTrack].
-  ///
-  /// Since the actual track settings might not have specify all required properties,
-  /// query the capabilities before using specific settings.
-  ///
-  /// Unsupported values fall back to their defaults.
-  factory VideoTrackSettings(MediaStreamTrack videoTrack) {
-    assert(videoTrack.kind == 'video', 'The given track is not a video track.');
-
-    final MediaTrackSettings settings = videoTrack.getSettings();
-    final MediaTrackCapabilities capabilities = videoTrack.getCapabilities();
-
-    final JSAny? facingModeCapability = capabilities.facingMode as JSAny?;
-    final JSAny? focusDistanceCapability = capabilities.focusDistance as JSAny?;
-    final JSAny? focusModeCapability = capabilities.focusMode as JSAny?;
-    final JSAny? torchCapability = capabilities.torch as JSAny?;
-    final JSAny? zoomCapability = capabilities.zoom as JSAny?;
-
-    // The width and height are always supported.
-    return VideoTrackSettings._(
-      width: settings.width,
-      height: settings.height,
-      facingMode:
-          facingModeCapability.isDefinedAndNotNull ? settings.facingMode : '',
-      focusDistance: focusDistanceCapability.isDefinedAndNotNull
-          ? settings.focusDistance.toDouble()
-          : -1.0,
-      focusMode:
-          focusModeCapability.isDefinedAndNotNull ? settings.focusMode : 'none',
-      torch: torchCapability.isDefinedAndNotNull && settings.torch,
-      zoom: zoomCapability.isDefinedAndNotNull ? settings.zoom.toDouble() : 1.0,
-    );
-  }
-
-  /// The private constructor.
-  const VideoTrackSettings._({
-    required this.facingMode,
-    required this.focusDistance,
-    required this.focusMode,
-    required this.height,
-    required this.torch,
-    required this.width,
-    required this.zoom,
-  });
-
-  final String facingMode;
-  final double focusDistance;
-  final String focusMode;
-  final int height;
-  final bool torch;
-  final int width;
-  final double zoom;
-}