// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
part of dart.ui;

/// Signature of callbacks that have no arguments and return no data.
typedef VoidCallback = void Function();

/// Signature for [PlatformDispatcher.onBeginFrame].
typedef FrameCallback = void Function(Duration duration);

/// Signature for [PlatformDispatcher.onReportTimings].
///
/// {@template dart.ui.TimingsCallback.list}
/// The callback takes a list of [FrameTiming] because it may not be
/// immediately triggered after each frame. Instead, Flutter tries to batch
/// frames together and send all their timings at once to decrease the
/// overhead (as this is available in the release mode). The list is sorted in
/// ascending order of time (earliest frame first). The timing of any frame
/// will be sent within about 1 second (100ms if in the profile/debug mode)
/// even if there are no later frames to batch. The timing of the first frame
/// will be sent immediately without batching.
/// {@endtemplate}
typedef TimingsCallback = void Function(List<FrameTiming> timings);

/// Signature for [PlatformDispatcher.onPointerDataPacket].
typedef PointerDataPacketCallback = void Function(PointerDataPacket packet);

/// Signature for [PlatformDispatcher.onKeyData].
///
/// The callback should return true if the key event has been handled by the
/// framework and should not be propagated further.
typedef KeyDataCallback = bool Function(KeyData data);

/// Signature for [PlatformDispatcher.onSemanticsAction].
typedef SemanticsActionCallback = void Function(int id, SemanticsAction action, ByteData? args);

/// Signature for responses to platform messages.
///
/// Used as a parameter to [PlatformDispatcher.sendPlatformMessage] and
/// [PlatformDispatcher.onPlatformMessage].
typedef PlatformMessageResponseCallback = void Function(ByteData? data);

/// Signature for [PlatformDispatcher.onPlatformMessage].
// TODO(ianh): deprecate once framework uses [ChannelBuffers.setListener].
typedef PlatformMessageCallback = void Function(String name, ByteData? data, PlatformMessageResponseCallback? callback);

// Signature for _setNeedsReportTimings.
typedef _SetNeedsReportTimingsFunc = void Function(bool value);

/// Signature for [PlatformDispatcher.onConfigurationChanged].
typedef PlatformConfigurationChangedCallback = void Function(PlatformConfiguration configuration);

/// Signature for [PlatformDispatcher.onError].
///
/// If this method returns false, the engine may use some fallback method to
/// provide information about the error.
///
/// After calling this method, the process or the VM may terminate. Some severe
/// unhandled errors may not be able to call this method either, such as Dart
/// compilation errors or process terminating errors.
typedef ErrorCallback = bool Function(Object exception, StackTrace stackTrace);

// A gesture setting value that indicates it has not been set by the engine.
const double _kUnsetGestureSetting = -1.0;

// A message channel to receive KeyData from the platform.
//
// See embedder.cc::kFlutterKeyDataChannel for more information.
const String _kFlutterKeyDataChannel = 'flutter/keydata';

@pragma('vm:entry-point')
ByteData? _wrapUnmodifiableByteData(ByteData? byteData) =>
    byteData == null ? null : UnmodifiableByteDataView(byteData);

/// A token that represents a root isolate.
class RootIsolateToken {
  RootIsolateToken._(this._token);

  /// An enumeration representing the root isolate (0 if not a root isolate).
  final int _token;

  /// The token for the root isolate that is executing this Dart code.  If this
  /// Dart code is not executing on a root isolate [instance] will be null.
  static final RootIsolateToken? instance = () {
    final int token = __getRootIsolateToken();
    return token == 0 ? null : RootIsolateToken._(token);
  }();

  @FfiNative<Int64 Function()>('PlatformConfigurationNativeApi::GetRootIsolateToken')
  external static int __getRootIsolateToken();
}

/// Platform event dispatcher singleton.
///
/// The most basic interface to the host operating system's interface.
///
/// This is the central entry point for platform messages and configuration
/// events from the platform.
///
/// It exposes the core scheduler API, the input event callback, the graphics
/// drawing API, and other such core services.
///
/// It manages the list of the application's [views] and the [screens] attached
/// to the device, as well as the [configuration] of various platform
/// attributes.
///
/// Consider avoiding static references to this singleton through
/// [PlatformDispatcher.instance] and instead prefer using a binding for
/// dependency resolution such as `WidgetsBinding.instance.platformDispatcher`.
/// See [PlatformDispatcher.instance] for more information about why this is
/// preferred.
class PlatformDispatcher {
  /// Private constructor, since only dart:ui is supposed to create one of
  /// these. Use [instance] to access the singleton.
  PlatformDispatcher._() {
    _setNeedsReportTimings = _nativeSetNeedsReportTimings;
  }

  /// The [PlatformDispatcher] singleton.
  ///
  /// Consider avoiding static references to this singleton though
  /// [PlatformDispatcher.instance] and instead prefer using a binding for
  /// dependency resolution such as `WidgetsBinding.instance.platformDispatcher`.
  ///
  /// Static access of this object means that Flutter has few, if any options to
  /// fake or mock the given object in tests. Even in cases where Dart offers
  /// special language constructs to forcefully shadow such properties, those
  /// mechanisms would only be reasonable for tests and they would not be
  /// reasonable for a future of Flutter where we legitimately want to select an
  /// appropriate implementation at runtime.
  ///
  /// The only place that `WidgetsBinding.instance.platformDispatcher` is
  /// inappropriate is if access to these APIs is required before the binding is
  /// initialized by invoking `runApp()` or
  /// `WidgetsFlutterBinding.instance.ensureInitialized()`. In that case, it is
  /// necessary (though unfortunate) to use the [PlatformDispatcher.instance]
  /// object statically.
  static PlatformDispatcher get instance => _instance;
  static final PlatformDispatcher _instance = PlatformDispatcher._();

  /// The current platform configuration.
  ///
  /// If values in this configuration change, [onPlatformConfigurationChanged]
  /// will be called.
  PlatformConfiguration get configuration => _configuration;
  PlatformConfiguration _configuration = const PlatformConfiguration();

  /// Called when the platform configuration changes.
  ///
  /// The engine invokes this callback in the same zone in which the callback
  /// was set.
  VoidCallback? get onPlatformConfigurationChanged => _onPlatformConfigurationChanged;
  VoidCallback? _onPlatformConfigurationChanged;
  Zone _onPlatformConfigurationChangedZone = Zone.root;
  set onPlatformConfigurationChanged(VoidCallback? callback) {
    _onPlatformConfigurationChanged = callback;
    _onPlatformConfigurationChangedZone = Zone.current;
  }

  /// The current list of views, including top level platform windows used by
  /// the application.
  ///
  /// If any of their configurations change, [onMetricsChanged] will be called.
  Iterable<FlutterView> get views => _views.values;
  final Map<Object, FlutterView> _views = <Object, FlutterView>{};

  // A map of opaque platform view identifiers to view configurations.
  final Map<Object, ViewConfiguration> _viewConfigurations = <Object, ViewConfiguration>{};

  /// A callback that is invoked whenever the [ViewConfiguration] of any of the
  /// [views] changes.
  ///
  /// For example when the device is rotated or when the application is resized
  /// (e.g. when showing applications side-by-side on Android),
  /// `onMetricsChanged` is called.
  ///
  /// The engine invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// The framework registers with this callback and updates the layout
  /// appropriately.
  ///
  /// See also:
  ///
  /// * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///   register for notifications when this is called.
  /// * [MediaQuery.of], a simpler mechanism for the same.
  VoidCallback? get onMetricsChanged => _onMetricsChanged;
  VoidCallback? _onMetricsChanged;
  Zone _onMetricsChangedZone = Zone.root;
  set onMetricsChanged(VoidCallback? callback) {
    _onMetricsChanged = callback;
    _onMetricsChangedZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  //
  // Updates the metrics of the window with the given id.
  void _updateWindowMetrics(
    Object id,
    double devicePixelRatio,
    double width,
    double height,
    double viewPaddingTop,
    double viewPaddingRight,
    double viewPaddingBottom,
    double viewPaddingLeft,
    double viewInsetTop,
    double viewInsetRight,
    double viewInsetBottom,
    double viewInsetLeft,
    double systemGestureInsetTop,
    double systemGestureInsetRight,
    double systemGestureInsetBottom,
    double systemGestureInsetLeft,
    double physicalTouchSlop,
    List<double> displayFeaturesBounds,
    List<int> displayFeaturesType,
    List<int> displayFeaturesState,
  ) {
    final ViewConfiguration previousConfiguration =
        _viewConfigurations[id] ?? const ViewConfiguration();
    if (!_views.containsKey(id)) {
      _views[id] = FlutterWindow._(id, this);
    }
    _viewConfigurations[id] = previousConfiguration.copyWith(
      window: _views[id],
      devicePixelRatio: devicePixelRatio,
      geometry: Rect.fromLTWH(0.0, 0.0, width, height),
      viewPadding: WindowPadding._(
        top: viewPaddingTop,
        right: viewPaddingRight,
        bottom: viewPaddingBottom,
        left: viewPaddingLeft,
      ),
      viewInsets: WindowPadding._(
        top: viewInsetTop,
        right: viewInsetRight,
        bottom: viewInsetBottom,
        left: viewInsetLeft,
      ),
      padding: WindowPadding._(
        top: math.max(0.0, viewPaddingTop - viewInsetTop),
        right: math.max(0.0, viewPaddingRight - viewInsetRight),
        bottom: math.max(0.0, viewPaddingBottom - viewInsetBottom),
        left: math.max(0.0, viewPaddingLeft - viewInsetLeft),
      ),
      systemGestureInsets: WindowPadding._(
        top: math.max(0.0, systemGestureInsetTop),
        right: math.max(0.0, systemGestureInsetRight),
        bottom: math.max(0.0, systemGestureInsetBottom),
        left: math.max(0.0, systemGestureInsetLeft),
      ),
      // -1 is used as a sentinel for an undefined touch slop
      gestureSettings: GestureSettings(
        physicalTouchSlop: physicalTouchSlop == _kUnsetGestureSetting ? null : physicalTouchSlop,
      ),
      displayFeatures: _decodeDisplayFeatures(
        bounds: displayFeaturesBounds,
        type: displayFeaturesType,
        state: displayFeaturesState,
        devicePixelRatio: devicePixelRatio,
      ),
    );
    _invoke(onMetricsChanged, _onMetricsChangedZone);
  }

  List<DisplayFeature> _decodeDisplayFeatures({
    required List<double> bounds,
    required List<int> type,
    required List<int> state,
    required double devicePixelRatio,
  }) {
    assert(bounds.length / 4 == type.length, 'Bounds are rectangles, requiring 4 measurements each');
    assert(type.length == state.length);
    final List<DisplayFeature> result = <DisplayFeature>[];
    for(int i = 0; i < type.length; i++) {
      final int rectOffset = i * 4;
      result.add(DisplayFeature(
        bounds: Rect.fromLTRB(
          bounds[rectOffset] / devicePixelRatio,
          bounds[rectOffset + 1] / devicePixelRatio,
          bounds[rectOffset + 2] / devicePixelRatio,
          bounds[rectOffset + 3] / devicePixelRatio,
        ),
        type: DisplayFeatureType.values[type[i]],
        state: state[i] < DisplayFeatureState.values.length
            ? DisplayFeatureState.values[state[i]]
            : DisplayFeatureState.unknown,
      ));
    }
    return result;
  }

  /// A callback invoked when any view begins a frame.
  ///
  /// A callback that is invoked to notify the application that it is an
  /// appropriate time to provide a scene using the [SceneBuilder] API and the
  /// [FlutterView.render] method.
  ///
  /// When possible, this is driven by the hardware VSync signal of the attached
  /// screen with the highest VSync rate. This is only called if
  /// [PlatformDispatcher.scheduleFrame] has been called since the last time
  /// this callback was invoked.
  FrameCallback? get onBeginFrame => _onBeginFrame;
  FrameCallback? _onBeginFrame;
  Zone _onBeginFrameZone = Zone.root;
  set onBeginFrame(FrameCallback? callback) {
    _onBeginFrame = callback;
    _onBeginFrameZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _beginFrame(int microseconds) {
    _invoke1<Duration>(
      onBeginFrame,
      _onBeginFrameZone,
      Duration(microseconds: microseconds),
    );
  }

  /// A callback that is invoked for each frame after [onBeginFrame] has
  /// completed and after the microtask queue has been drained.
  ///
  /// This can be used to implement a second phase of frame rendering that
  /// happens after any deferred work queued by the [onBeginFrame] phase.
  VoidCallback? get onDrawFrame => _onDrawFrame;
  VoidCallback? _onDrawFrame;
  Zone _onDrawFrameZone = Zone.root;
  set onDrawFrame(VoidCallback? callback) {
    _onDrawFrame = callback;
    _onDrawFrameZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _drawFrame() {
    _invoke(onDrawFrame, _onDrawFrameZone);
  }

  /// A callback that is invoked when pointer data is available.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// See also:
  ///
  ///  * [GestureBinding], the Flutter framework class which manages pointer
  ///    events.
  PointerDataPacketCallback? get onPointerDataPacket => _onPointerDataPacket;
  PointerDataPacketCallback? _onPointerDataPacket;
  Zone _onPointerDataPacketZone = Zone.root;
  set onPointerDataPacket(PointerDataPacketCallback? callback) {
    _onPointerDataPacket = callback;
    _onPointerDataPacketZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _dispatchPointerDataPacket(ByteData packet) {
    if (onPointerDataPacket != null) {
      _invoke1<PointerDataPacket>(
        onPointerDataPacket,
        _onPointerDataPacketZone,
        _unpackPointerDataPacket(packet),
      );
    }
  }

  // If this value changes, update the encoding code in the following files:
  //
  //  * pointer_data.cc
  //  * pointer.dart
  //  * AndroidTouchProcessor.java
  static const int _kPointerDataFieldCount = 35;

  static PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
    const int kStride = Int64List.bytesPerElement;
    const int kBytesPerPointerData = _kPointerDataFieldCount * kStride;
    final int length = packet.lengthInBytes ~/ kBytesPerPointerData;
    assert(length * kBytesPerPointerData == packet.lengthInBytes);
    final List<PointerData> data = <PointerData>[];
    for (int i = 0; i < length; ++i) {
      int offset = i * _kPointerDataFieldCount;
      data.add(PointerData(
        embedderId: packet.getInt64(kStride * offset++, _kFakeHostEndian),
        timeStamp: Duration(microseconds: packet.getInt64(kStride * offset++, _kFakeHostEndian)),
        change: PointerChange.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
        kind: PointerDeviceKind.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
        signalKind: PointerSignalKind.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
        device: packet.getInt64(kStride * offset++, _kFakeHostEndian),
        pointerIdentifier: packet.getInt64(kStride * offset++, _kFakeHostEndian),
        physicalX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        physicalY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        physicalDeltaX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        physicalDeltaY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        buttons: packet.getInt64(kStride * offset++, _kFakeHostEndian),
        obscured: packet.getInt64(kStride * offset++, _kFakeHostEndian) != 0,
        synthesized: packet.getInt64(kStride * offset++, _kFakeHostEndian) != 0,
        pressure: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        pressureMin: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        pressureMax: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        distance: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        distanceMax: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        size: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        radiusMajor: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        radiusMinor: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        radiusMin: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        radiusMax: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        orientation: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        tilt: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        platformData: packet.getInt64(kStride * offset++, _kFakeHostEndian),
        scrollDeltaX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        scrollDeltaY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        panX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        panY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        panDeltaX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        panDeltaY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        scale: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
        rotation: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
      ));
      assert(offset == (i + 1) * _kPointerDataFieldCount);
    }
    return PointerDataPacket(data: data);
  }

  static ChannelCallback _keyDataListener(KeyDataCallback onKeyData, Zone zone) =>
    (ByteData? packet, PlatformMessageResponseCallback callback) {
      _invoke1<KeyData>(
        (KeyData keyData) {
          final bool handled = onKeyData(keyData);
          final Uint8List response = Uint8List(1);
          response[0] = handled ? 1 : 0;
          callback(response.buffer.asByteData());
        },
        zone,
        _unpackKeyData(packet!),
      );
    };

  /// A callback that is invoked when key data is available.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// The callback should return true if the key event has been handled by the
  /// framework and should not be propagated further.
  KeyDataCallback? get onKeyData => _onKeyData;
  KeyDataCallback? _onKeyData;
  set onKeyData(KeyDataCallback? callback) {
    _onKeyData = callback;
    if (callback != null) {
      channelBuffers.setListener(_kFlutterKeyDataChannel, _keyDataListener(callback, Zone.current));
    } else {
      channelBuffers.clearListener(_kFlutterKeyDataChannel);
    }
  }

  // If this value changes, update the encoding code in the following files:
  //
  //  * key_data.h
  //  * key.dart (ui)
  //  * key.dart (web_ui)
  //  * HardwareKeyboard.java
  static const int _kKeyDataFieldCount = 5;

  // The packet structure is described in `key_data_packet.h`.
  static KeyData _unpackKeyData(ByteData packet) {
    const int kStride = Int64List.bytesPerElement;

    int offset = 0;
    final int charDataSize = packet.getUint64(kStride * offset++, _kFakeHostEndian);
    final String? character = charDataSize == 0 ? null : utf8.decoder.convert(
          packet.buffer.asUint8List(kStride * (offset + _kKeyDataFieldCount), charDataSize));

    final KeyData keyData = KeyData(
      timeStamp: Duration(microseconds: packet.getUint64(kStride * offset++, _kFakeHostEndian)),
      type: KeyEventType.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
      physical: packet.getUint64(kStride * offset++, _kFakeHostEndian),
      logical: packet.getUint64(kStride * offset++, _kFakeHostEndian),
      character: character,
      synthesized: packet.getUint64(kStride * offset++, _kFakeHostEndian) != 0,
    );

    return keyData;
  }

  /// A callback that is invoked to report the [FrameTiming] of recently
  /// rasterized frames.
  ///
  /// It's preferred to use [SchedulerBinding.addTimingsCallback] than to use
  /// [onReportTimings] directly because [SchedulerBinding.addTimingsCallback]
  /// allows multiple callbacks.
  ///
  /// This can be used to see if the application has missed frames (through
  /// [FrameTiming.buildDuration] and [FrameTiming.rasterDuration]), or high
  /// latencies (through [FrameTiming.totalSpan]).
  ///
  /// Unlike [Timeline], the timing information here is available in the release
  /// mode (additional to the profile and the debug mode). Hence this can be
  /// used to monitor the application's performance in the wild.
  ///
  /// {@macro dart.ui.TimingsCallback.list}
  ///
  /// If this is null, no additional work will be done. If this is not null,
  /// Flutter spends less than 0.1ms every 1 second to report the timings
  /// (measured on iPhone6S). The 0.1ms is about 0.6% of 16ms (frame budget for
  /// 60fps), or 0.01% CPU usage per second.
  TimingsCallback? get onReportTimings => _onReportTimings;
  TimingsCallback? _onReportTimings;
  Zone _onReportTimingsZone = Zone.root;
  set onReportTimings(TimingsCallback? callback) {
    if ((callback == null) != (_onReportTimings == null)) {
      _setNeedsReportTimings(callback != null);
    }
    _onReportTimings = callback;
    _onReportTimingsZone = Zone.current;
  }

  late _SetNeedsReportTimingsFunc _setNeedsReportTimings;

  void _nativeSetNeedsReportTimings(bool value) => __nativeSetNeedsReportTimings(value);

  @FfiNative<Void Function(Bool)>('PlatformConfigurationNativeApi::SetNeedsReportTimings')
  external static void __nativeSetNeedsReportTimings(bool value);

  // Called from the engine, via hooks.dart
  void _reportTimings(List<int> timings) {
    assert(timings.length % FrameTiming._dataLength == 0);
    final List<FrameTiming> frameTimings = <FrameTiming>[];
    for (int i = 0; i < timings.length; i += FrameTiming._dataLength) {
      frameTimings.add(FrameTiming._(timings.sublist(i, i + FrameTiming._dataLength)));
    }
    _invoke1(onReportTimings, _onReportTimingsZone, frameTimings);
  }

  /// Sends a message to a platform-specific plugin.
  ///
  /// The `name` parameter determines which plugin receives the message. The
  /// `data` parameter contains the message payload and is typically UTF-8
  /// encoded JSON but can be arbitrary data. If the plugin replies to the
  /// message, `callback` will be called with the response.
  ///
  /// The framework invokes [callback] in the same zone in which this method was
  /// called.
  void sendPlatformMessage(String name, ByteData? data, PlatformMessageResponseCallback? callback) {
    final String? error =
        _sendPlatformMessage(name, _zonedPlatformMessageResponseCallback(callback), data);
    if (error != null) {
      throw Exception(error);
    }
  }

  String? _sendPlatformMessage(String name, PlatformMessageResponseCallback? callback, ByteData? data) =>
      __sendPlatformMessage(name, callback, data);

  @FfiNative<Handle Function(Handle, Handle, Handle)>('PlatformConfigurationNativeApi::SendPlatformMessage')
  external static String? __sendPlatformMessage(String name, PlatformMessageResponseCallback? callback, ByteData? data);

  /// Sends a message to a platform-specific plugin via a [SendPort].
  ///
  /// This operates similarly to [sendPlatformMessage] but is used when sending
  /// messages from background isolates. The [port] parameter allows Flutter to
  /// know which isolate to send the result to. The [name] parameter is the name
  /// of the channel communication will happen on. The [data] parameter is the
  /// payload of the message. The [identifier] parameter is a unique integer
  /// assigned to the message.
  void sendPortPlatformMessage(
    String name,
    ByteData? data,
    int identifier,
    SendPort port) {
    final String? error =
        _sendPortPlatformMessage(name, identifier, port.nativePort, data);
    if (error != null) {
      throw Exception(error);
    }
  }

  String? _sendPortPlatformMessage(String name, int identifier, int port, ByteData? data) =>
      __sendPortPlatformMessage(name, identifier, port, data);

  @FfiNative<Handle Function(Handle, Handle, Handle, Handle)>('PlatformConfigurationNativeApi::SendPortPlatformMessage')
  external static String? __sendPortPlatformMessage(String name, int identifier, int port, ByteData? data);

  /// Registers the current isolate with the isolate identified with by the
  /// [token]. This is required if platform channels are to be used on a
  /// background isolate.
  void registerBackgroundIsolate(RootIsolateToken token) {
    if (!Platform.isIOS) {
      // Issue: https://github.com/flutter/flutter/issues/13937
      throw UnimplementedError("Platform doesn't yet support platform channels on background isolates.");
    }
    __registerBackgroundIsolate(token._token);
  }
  @FfiNative<Void Function(Int64)>('PlatformConfigurationNativeApi::RegisterBackgroundIsolate')
  external static void __registerBackgroundIsolate(int rootIsolateId);

  /// Called whenever this platform dispatcher receives a message from a
  /// platform-specific plugin.
  ///
  /// The `name` parameter determines which plugin sent the message. The `data`
  /// parameter is the payload and is typically UTF-8 encoded JSON but can be
  /// arbitrary data.
  ///
  /// Message handlers must call the function given in the `callback` parameter.
  /// If the handler does not need to respond, the handler should pass null to
  /// the callback.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  // TODO(ianh): Deprecate onPlatformMessage once the framework is moved over
  // to using channel buffers exclusively.
  PlatformMessageCallback? get onPlatformMessage => _onPlatformMessage;
  PlatformMessageCallback? _onPlatformMessage;
  Zone _onPlatformMessageZone = Zone.root;
  set onPlatformMessage(PlatformMessageCallback? callback) {
    _onPlatformMessage = callback;
    _onPlatformMessageZone = Zone.current;
  }

  /// Called by [_dispatchPlatformMessage].
  void _respondToPlatformMessage(int responseId, ByteData? data) => __respondToPlatformMessage(responseId, data);

  @FfiNative<Void Function(IntPtr, Handle)>('PlatformConfigurationNativeApi::RespondToPlatformMessage')
  external static void __respondToPlatformMessage(int responseId, ByteData? data);

  /// Wraps the given [callback] in another callback that ensures that the
  /// original callback is called in the zone it was registered in.
  static PlatformMessageResponseCallback? _zonedPlatformMessageResponseCallback(
    PlatformMessageResponseCallback? callback,
  ) {
    if (callback == null) {
      return null;
    }

    // Store the zone in which the callback is being registered.
    final Zone registrationZone = Zone.current;

    return (ByteData? data) {
      registrationZone.runUnaryGuarded(callback, data);
    };
  }

  /// Send a message to the framework using the [ChannelBuffers].
  ///
  /// This method constructs the appropriate callback to respond
  /// with the given `responseId`. It should only be called for messages
  /// from the platform.
  void _dispatchPlatformMessage(String name, ByteData? data, int responseId) {
    if (name == ChannelBuffers.kControlChannelName) {
      try {
        channelBuffers.handleMessage(data!);
      } finally {
        _respondToPlatformMessage(responseId, null);
      }
    } else if (onPlatformMessage != null) {
      _invoke3<String, ByteData?, PlatformMessageResponseCallback>(
        onPlatformMessage,
        _onPlatformMessageZone,
        name,
        data,
        (ByteData? responseData) {
          _respondToPlatformMessage(responseId, responseData);
        },
      );
    } else {
      channelBuffers.push(name, data, (ByteData? responseData) {
        _respondToPlatformMessage(responseId, responseData);
      });
    }
  }

  /// Set the debug name associated with this platform dispatcher's root
  /// isolate.
  ///
  /// Normally debug names are automatically generated from the Dart port, entry
  /// point, and source file. For example: `main.dart$main-1234`.
  ///
  /// This can be combined with flutter tools `--isolate-filter` flag to debug
  /// specific root isolates. For example: `flutter attach --isolate-filter=[name]`.
  /// Note that this does not rename any child isolates of the root.
  void setIsolateDebugName(String name) => _setIsolateDebugName(name);

  @FfiNative<Void Function(Handle)>('PlatformConfigurationNativeApi::SetIsolateDebugName')
  external static void _setIsolateDebugName(String name);

  /// Requests the Dart VM to adjusts the GC heuristics based on the requested `performance_mode`.
  ///
  /// This operation is a no-op of web. The request to change a performance may be ignored by the
  /// engine or not resolve in a predictable way.
  ///
  /// See [DartPerformanceMode] for more information on individual performance modes.
  void requestDartPerformanceMode(DartPerformanceMode mode) {
    _requestDartPerformanceMode(mode.index);
  }

  @FfiNative<Int Function(Int)>('PlatformConfigurationNativeApi::RequestDartPerformanceMode')
  external static int _requestDartPerformanceMode(int mode);

  /// The embedder can specify data that the isolate can request synchronously
  /// on launch. This accessor fetches that data.
  ///
  /// This data is persistent for the duration of the Flutter application and is
  /// available even after isolate restarts. Because of this lifecycle, the size
  /// of this data must be kept to a minimum.
  ///
  /// For asynchronous communication between the embedder and isolate, a
  /// platform channel may be used.
  ByteData? getPersistentIsolateData() => _getPersistentIsolateData();

  @FfiNative<Handle Function()>('PlatformConfigurationNativeApi::GetPersistentIsolateData')
  external static ByteData? _getPersistentIsolateData();

  /// Requests that, at the next appropriate opportunity, the [onBeginFrame] and
  /// [onDrawFrame] callbacks be invoked.
  ///
  /// See also:
  ///
  ///  * [SchedulerBinding], the Flutter framework class which manages the
  ///    scheduling of frames.
  void scheduleFrame() => _scheduleFrame();

  @FfiNative<Void Function()>('PlatformConfigurationNativeApi::ScheduleFrame')
  external static void _scheduleFrame();

  /// Additional accessibility features that may be enabled by the platform.
  AccessibilityFeatures get accessibilityFeatures => configuration.accessibilityFeatures;

  /// A callback that is invoked when the value of [accessibilityFeatures]
  /// changes.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  VoidCallback? get onAccessibilityFeaturesChanged => _onAccessibilityFeaturesChanged;
  VoidCallback? _onAccessibilityFeaturesChanged;
  Zone _onAccessibilityFeaturesChangedZone = Zone.root;
  set onAccessibilityFeaturesChanged(VoidCallback? callback) {
    _onAccessibilityFeaturesChanged = callback;
    _onAccessibilityFeaturesChangedZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _updateAccessibilityFeatures(int values) {
    final AccessibilityFeatures newFeatures = AccessibilityFeatures._(values);
    final PlatformConfiguration previousConfiguration = configuration;
    if (newFeatures == previousConfiguration.accessibilityFeatures) {
      return;
    }
    _configuration = previousConfiguration.copyWith(
      accessibilityFeatures: newFeatures,
    );
    _invoke(onPlatformConfigurationChanged, _onPlatformConfigurationChangedZone,);
    _invoke(onAccessibilityFeaturesChanged, _onAccessibilityFeaturesChangedZone,);
  }

  /// Change the retained semantics data about this platform dispatcher.
  ///
  /// If [semanticsEnabled] is true, the user has requested that this function
  /// be called whenever the semantic content of this platform dispatcher
  /// changes.
  ///
  /// In either case, this function disposes the given update, which means the
  /// semantics update cannot be used further.
  void updateSemantics(SemanticsUpdate update) => _updateSemantics(update);

  @FfiNative<Void Function(Pointer<Void>)>('PlatformConfigurationNativeApi::UpdateSemantics')
  external static void _updateSemantics(SemanticsUpdate update);

  /// The system-reported default locale of the device.
  ///
  /// This establishes the language and formatting conventions that application
  /// should, if possible, use to render their user interface.
  ///
  /// This is the first locale selected by the user and is the user's primary
  /// locale (the locale the device UI is displayed in)
  ///
  /// This is equivalent to `locales.first`, except that it will provide an
  /// undefined (using the language tag "und") non-null locale if the [locales]
  /// list has not been set or is empty.
  Locale get locale => locales.isEmpty ? const Locale.fromSubtags() : locales.first;

  /// The full system-reported supported locales of the device.
  ///
  /// This establishes the language and formatting conventions that application
  /// should, if possible, use to render their user interface.
  ///
  /// The list is ordered in order of priority, with lower-indexed locales being
  /// preferred over higher-indexed ones. The first element is the primary
  /// [locale].
  ///
  /// The [onLocaleChanged] callback is called whenever this value changes.
  ///
  /// See also:
  ///
  ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///    observe when this value changes.
  List<Locale> get locales => configuration.locales;

  /// Performs the platform-native locale resolution.
  ///
  /// Each platform may return different results.
  ///
  /// If the platform fails to resolve a locale, then this will return null.
  ///
  /// This method returns synchronously and is a direct call to
  /// platform specific APIs without invoking method channels.
  Locale? computePlatformResolvedLocale(List<Locale> supportedLocales) {
    final List<String?> supportedLocalesData = <String?>[];
    for (final Locale locale in supportedLocales) {
      supportedLocalesData.add(locale.languageCode);
      supportedLocalesData.add(locale.countryCode);
      supportedLocalesData.add(locale.scriptCode);
    }

    final List<String> result = _computePlatformResolvedLocale(supportedLocalesData);

    if (result.isNotEmpty) {
      return Locale.fromSubtags(
        languageCode: result[0],
        countryCode: result[1] == '' ? null : result[1],
        scriptCode: result[2] == '' ? null : result[2]);
    }
    return null;
  }

  List<String> _computePlatformResolvedLocale(List<String?> supportedLocalesData) => __computePlatformResolvedLocale(supportedLocalesData);

  @FfiNative<Handle Function(Handle)>('PlatformConfigurationNativeApi::ComputePlatformResolvedLocale')
  external static List<String> __computePlatformResolvedLocale(List<String?> supportedLocalesData);

  /// A callback that is invoked whenever [locale] changes value.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// See also:
  ///
  ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///    observe when this callback is invoked.
  VoidCallback? get onLocaleChanged => _onLocaleChanged;
  VoidCallback? _onLocaleChanged;
  Zone _onLocaleChangedZone = Zone.root;
  set onLocaleChanged(VoidCallback? callback) {
    _onLocaleChanged = callback;
    _onLocaleChangedZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _updateLocales(List<String> locales) {
    const int stringsPerLocale = 4;
    final int numLocales = locales.length ~/ stringsPerLocale;
    final PlatformConfiguration previousConfiguration = configuration;
    final List<Locale> newLocales = <Locale>[];
    bool localesDiffer = numLocales != previousConfiguration.locales.length;
    for (int localeIndex = 0; localeIndex < numLocales; localeIndex++) {
      final String countryCode = locales[localeIndex * stringsPerLocale + 1];
      final String scriptCode = locales[localeIndex * stringsPerLocale + 2];

      newLocales.add(Locale.fromSubtags(
        languageCode: locales[localeIndex * stringsPerLocale],
        countryCode: countryCode.isEmpty ? null : countryCode,
        scriptCode: scriptCode.isEmpty ? null : scriptCode,
      ));
      if (!localesDiffer && newLocales[localeIndex] != previousConfiguration.locales[localeIndex]) {
        localesDiffer = true;
      }
    }
    if (!localesDiffer) {
      return;
    }
    _configuration = previousConfiguration.copyWith(locales: newLocales);
    _invoke(onPlatformConfigurationChanged, _onPlatformConfigurationChangedZone);
    _invoke(onLocaleChanged, _onLocaleChangedZone);
  }

  // Called from the engine, via hooks.dart
  String _localeClosure() => locale.toString();

  /// The lifecycle state immediately after dart isolate initialization.
  ///
  /// This property will not be updated as the lifecycle changes.
  ///
  /// It is used to initialize [SchedulerBinding.lifecycleState] at startup with
  /// any buffered lifecycle state events.
  String get initialLifecycleState {
    _initialLifecycleStateAccessed = true;
    return _initialLifecycleState;
  }

  late String _initialLifecycleState;

  /// Tracks if the initial state has been accessed. Once accessed, we will stop
  /// updating the [initialLifecycleState], as it is not the preferred way to
  /// access the state.
  bool _initialLifecycleStateAccessed = false;

  // Called from the engine, via hooks.dart
  void _updateLifecycleState(String state) {
    // We do not update the state if the state has already been used to initialize
    // the lifecycleState.
    if (!_initialLifecycleStateAccessed) {
      _initialLifecycleState = state;
    }
  }

  /// The setting indicating whether time should always be shown in the 24-hour
  /// format.
  ///
  /// This option is used by [showTimePicker].
  bool get alwaysUse24HourFormat => configuration.alwaysUse24HourFormat;

  /// The system-reported text scale.
  ///
  /// This establishes the text scaling factor to use when rendering text,
  /// according to the user's platform preferences.
  ///
  /// The [onTextScaleFactorChanged] callback is called whenever this value
  /// changes.
  ///
  /// See also:
  ///
  ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///    observe when this value changes.
  double get textScaleFactor => configuration.textScaleFactor;

  /// A callback that is invoked whenever [textScaleFactor] changes value.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// See also:
  ///
  ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///    observe when this callback is invoked.
  VoidCallback? get onTextScaleFactorChanged => _onTextScaleFactorChanged;
  VoidCallback? _onTextScaleFactorChanged;
  Zone _onTextScaleFactorChangedZone = Zone.root;
  set onTextScaleFactorChanged(VoidCallback? callback) {
    _onTextScaleFactorChanged = callback;
    _onTextScaleFactorChangedZone = Zone.current;
  }

  /// Whether the spell check service is supported on the current platform.
  ///
  /// This option is used by [EditableTextState] to define its
  /// [SpellCheckConfiguration] when a default spell check service
  /// is requested.
  bool get nativeSpellCheckServiceDefined => _nativeSpellCheckServiceDefined;
  bool _nativeSpellCheckServiceDefined = false;

  /// Whether briefly displaying the characters as you type in obscured text
  /// fields is enabled in system settings.
  ///
  /// See also:
  ///
  ///  * [EditableText.obscureText], which when set to true hides the text in
  ///    the text field.
  bool get brieflyShowPassword => _brieflyShowPassword;
  bool _brieflyShowPassword = true;

  /// The setting indicating the current brightness mode of the host platform.
  /// If the platform has no preference, [platformBrightness] defaults to
  /// [Brightness.light].
  Brightness get platformBrightness => configuration.platformBrightness;

  /// A callback that is invoked whenever [platformBrightness] changes value.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// See also:
  ///
  ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///    observe when this callback is invoked.
  VoidCallback? get onPlatformBrightnessChanged => _onPlatformBrightnessChanged;
  VoidCallback? _onPlatformBrightnessChanged;
  Zone _onPlatformBrightnessChangedZone = Zone.root;
  set onPlatformBrightnessChanged(VoidCallback? callback) {
    _onPlatformBrightnessChanged = callback;
    _onPlatformBrightnessChangedZone = Zone.current;
  }

  /// The setting indicating the current system font of the host platform.
  String? get systemFontFamily => configuration.systemFontFamily;

  /// A callback that is invoked whenever [systemFontFamily] changes value.
  ///
  /// The framework invokes this callback in the same zone in which the callback
  /// was set.
  ///
  /// See also:
  ///
  ///  * [WidgetsBindingObserver], for a mechanism at the widgets layer to
  ///    observe when this callback is invoked.
  VoidCallback? get onSystemFontFamilyChanged => _onSystemFontFamilyChanged;
  VoidCallback? _onSystemFontFamilyChanged;
  Zone _onSystemFontFamilyChangedZone = Zone.root;
  set onSystemFontFamilyChanged(VoidCallback? callback) {
    _onSystemFontFamilyChanged = callback;
    _onSystemFontFamilyChangedZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _updateUserSettingsData(String jsonData) {
    final Map<String, Object?> data = json.decode(jsonData) as Map<String, Object?>;
    if (data.isEmpty) {
      return;
    }

    final double textScaleFactor = (data['textScaleFactor']! as num).toDouble();
    final bool alwaysUse24HourFormat = data['alwaysUse24HourFormat']! as bool;
    final bool? nativeSpellCheckServiceDefined = data['nativeSpellCheckServiceDefined'] as bool?;
    if (nativeSpellCheckServiceDefined != null) {
      _nativeSpellCheckServiceDefined = nativeSpellCheckServiceDefined;
    } else {
      _nativeSpellCheckServiceDefined = false;
    }
    // This field is optional.
    final bool? brieflyShowPassword = data['brieflyShowPassword'] as bool?;
    if (brieflyShowPassword != null) {
      _brieflyShowPassword = brieflyShowPassword;
    }
    final Brightness platformBrightness =
    data['platformBrightness']! as String == 'dark' ? Brightness.dark : Brightness.light;
    final String? systemFontFamily = data['systemFontFamily'] as String?;
    final PlatformConfiguration previousConfiguration = configuration;
    final bool platformBrightnessChanged = previousConfiguration.platformBrightness != platformBrightness;
    final bool textScaleFactorChanged = previousConfiguration.textScaleFactor != textScaleFactor;
    final bool alwaysUse24HourFormatChanged =
        previousConfiguration.alwaysUse24HourFormat != alwaysUse24HourFormat;
    final bool systemFontFamilyChanged =
        previousConfiguration.systemFontFamily != systemFontFamily;
    if (!platformBrightnessChanged && !textScaleFactorChanged && !alwaysUse24HourFormatChanged && !systemFontFamilyChanged) {
      return;
    }
    _configuration = previousConfiguration.copyWith(
      textScaleFactor: textScaleFactor,
      alwaysUse24HourFormat: alwaysUse24HourFormat,
      platformBrightness: platformBrightness,
      systemFontFamily: systemFontFamily,
    );
    _invoke(onPlatformConfigurationChanged, _onPlatformConfigurationChangedZone);
    if (textScaleFactorChanged) {
      _invoke(onTextScaleFactorChanged, _onTextScaleFactorChangedZone);
    }
    if (platformBrightnessChanged) {
      _invoke(onPlatformBrightnessChanged, _onPlatformBrightnessChangedZone);
    }
    if (systemFontFamilyChanged) {
      _invoke(onSystemFontFamilyChanged, _onSystemFontFamilyChangedZone);
    }
  }

  /// Whether the user has requested that [updateSemantics] be called when the
  /// semantic contents of a view changes.
  ///
  /// The [onSemanticsEnabledChanged] callback is called whenever this value
  /// changes.
  bool get semanticsEnabled => configuration.semanticsEnabled;

  /// A callback that is invoked when the value of [semanticsEnabled] changes.
  ///
  /// The framework invokes this callback in the same zone in which the
  /// callback was set.
  VoidCallback? get onSemanticsEnabledChanged => _onSemanticsEnabledChanged;
  VoidCallback? _onSemanticsEnabledChanged;
  Zone _onSemanticsEnabledChangedZone = Zone.root;
  set onSemanticsEnabledChanged(VoidCallback? callback) {
    _onSemanticsEnabledChanged = callback;
    _onSemanticsEnabledChangedZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _updateSemanticsEnabled(bool enabled) {
    final PlatformConfiguration previousConfiguration = configuration;
    if (previousConfiguration.semanticsEnabled == enabled) {
      return;
    }
    _configuration = previousConfiguration.copyWith(
      semanticsEnabled: enabled,
    );
    _invoke(onPlatformConfigurationChanged, _onPlatformConfigurationChangedZone);
    _invoke(onSemanticsEnabledChanged, _onSemanticsEnabledChangedZone);
  }

  /// A callback that is invoked whenever the user requests an action to be
  /// performed.
  ///
  /// This callback is used when the user expresses the action they wish to
  /// perform based on the semantics supplied by [updateSemantics].
  ///
  /// The framework invokes this callback in the same zone in which the
  /// callback was set.
  SemanticsActionCallback? get onSemanticsAction => _onSemanticsAction;
  SemanticsActionCallback? _onSemanticsAction;
  Zone _onSemanticsActionZone = Zone.root;
  set onSemanticsAction(SemanticsActionCallback? callback) {
    _onSemanticsAction = callback;
    _onSemanticsActionZone = Zone.current;
  }

  // Called from the engine via hooks.dart.
  void _updateFrameData(int frameNumber) {
    final FrameData previous = _frameData;
    if (previous.frameNumber == frameNumber) {
      return;
    }
    _frameData = FrameData._(frameNumber: frameNumber);
    _invoke(onFrameDataChanged, _onFrameDataChangedZone);
  }

  /// The [FrameData] object for the current frame.
  FrameData get frameData => _frameData;
  FrameData _frameData = const FrameData._();

  /// A callback that is invoked when the window updates the [FrameData].
  VoidCallback? get onFrameDataChanged => _onFrameDataChanged;
  VoidCallback? _onFrameDataChanged;
  Zone _onFrameDataChangedZone = Zone.root;
  set onFrameDataChanged(VoidCallback? callback) {
    _onFrameDataChanged = callback;
    _onFrameDataChangedZone = Zone.current;
  }

  // Called from the engine, via hooks.dart
  void _dispatchSemanticsAction(int id, int action, ByteData? args) {
    _invoke3<int, SemanticsAction, ByteData?>(
      onSemanticsAction,
      _onSemanticsActionZone,
      id,
      SemanticsAction.values[action]!,
      args,
    );
  }

  ErrorCallback? _onError;
  Zone? _onErrorZone;

  /// A callback that is invoked when an unhandled error occurs in the root
  /// isolate.
  ///
  /// This callback must return `true` if it has handled the error. Otherwise,
  /// it must return `false` and a fallback mechanism such as printing to stderr
  /// will be used, as configured by the specific platform embedding via
  /// `Settings::unhandled_exception_callback`.
  ///
  /// The VM or the process may exit or become unresponsive after calling this
  /// callback. The callback will not be called for exceptions that cause the VM
  /// or process to terminate or become unresponsive before the callback can be
  /// invoked.
  ///
  /// This callback is not directly invoked by errors in child isolates of the
  /// root isolate. Programs that create new isolates must listen for errors on
  /// those isolates and forward the errors to the root isolate. An example of
  /// this can be found in the Flutter framework's `compute` function.
  ErrorCallback? get onError => _onError;
  set onError(ErrorCallback? callback) {
    _onError = callback;
    _onErrorZone = Zone.current;
  }

  bool _dispatchError(Object error, StackTrace stackTrace) {
    if (_onError == null) {
      return false;
    }
    assert(_onErrorZone != null);

    if (identical(_onErrorZone, Zone.current)) {
      return _onError!(error, stackTrace);
    } else {
      try {
        return _onErrorZone!.runBinary<bool, Object, StackTrace>(_onError!, error, stackTrace);
      } catch (e, s) {
        _onErrorZone!.handleUncaughtError(e, s);
        return false;
      }
    }
  }

  /// The route or path that the embedder requested when the application was
  /// launched.
  ///
  /// This will be the string "`/`" if no particular route was requested.
  ///
  /// ## Android
  ///
  /// On Android, calling
  /// [`FlutterView.setInitialRoute`](/javadoc/io/flutter/view/FlutterView.html#setInitialRoute-java.lang.String-)
  /// will set this value. The value must be set sufficiently early, i.e. before
  /// the [runApp] call is executed in Dart, for this to have any effect on the
  /// framework. The `createFlutterView` method in your `FlutterActivity`
  /// subclass is a suitable time to set the value. The application's
  /// `AndroidManifest.xml` file must also be updated to have a suitable
  /// [`<intent-filter>`](https://developer.android.com/guide/topics/manifest/intent-filter-element.html).
  ///
  /// ## iOS
  ///
  /// On iOS, calling
  /// [`FlutterViewController.setInitialRoute`](/objcdoc/Classes/FlutterViewController.html#/c:objc%28cs%29FlutterViewController%28im%29setInitialRoute:)
  /// will set this value. The value must be set sufficiently early, i.e. before
  /// the [runApp] call is executed in Dart, for this to have any effect on the
  /// framework. The `application:didFinishLaunchingWithOptions:` method is a
  /// suitable time to set this value.
  ///
  /// See also:
  ///
  ///  * [Navigator], a widget that handles routing.
  ///  * [SystemChannels.navigation], which handles subsequent navigation
  ///    requests from the embedder.
  String get defaultRouteName => _defaultRouteName();

  @FfiNative<Handle Function()>('PlatformConfigurationNativeApi::DefaultRouteName')
  external static String _defaultRouteName();
}

/// Configuration of the platform.
///
/// Immutable class (but can't use @immutable in dart:ui)
class PlatformConfiguration {
  /// Const constructor for [PlatformConfiguration].
  const PlatformConfiguration({
    this.accessibilityFeatures = const AccessibilityFeatures._(0),
    this.alwaysUse24HourFormat = false,
    this.semanticsEnabled = false,
    this.platformBrightness = Brightness.light,
    this.textScaleFactor = 1.0,
    this.locales = const <Locale>[],
    this.defaultRouteName,
    this.systemFontFamily,
  });

  /// Copy a [PlatformConfiguration] with some fields replaced.
  PlatformConfiguration copyWith({
    AccessibilityFeatures? accessibilityFeatures,
    bool? alwaysUse24HourFormat,
    bool? semanticsEnabled,
    Brightness? platformBrightness,
    double? textScaleFactor,
    List<Locale>? locales,
    String? defaultRouteName,
    String? systemFontFamily,
  }) {
    return PlatformConfiguration(
      accessibilityFeatures: accessibilityFeatures ?? this.accessibilityFeatures,
      alwaysUse24HourFormat: alwaysUse24HourFormat ?? this.alwaysUse24HourFormat,
      semanticsEnabled: semanticsEnabled ?? this.semanticsEnabled,
      platformBrightness: platformBrightness ?? this.platformBrightness,
      textScaleFactor: textScaleFactor ?? this.textScaleFactor,
      locales: locales ?? this.locales,
      defaultRouteName: defaultRouteName ?? this.defaultRouteName,
      systemFontFamily: systemFontFamily ?? this.systemFontFamily,
    );
  }

  /// Additional accessibility features that may be enabled by the platform.
  final AccessibilityFeatures accessibilityFeatures;

  /// The setting indicating whether time should always be shown in the 24-hour
  /// format.
  final bool alwaysUse24HourFormat;

  /// Whether the user has requested that [updateSemantics] be called when the
  /// semantic contents of a view changes.
  final bool semanticsEnabled;

  /// The setting indicating the current brightness mode of the host platform.
  /// If the platform has no preference, [platformBrightness] defaults to
  /// [Brightness.light].
  final Brightness platformBrightness;

  /// The system-reported text scale.
  final double textScaleFactor;

  /// The full system-reported supported locales of the device.
  final List<Locale> locales;

  /// The route or path that the embedder requested when the application was
  /// launched.
  final String? defaultRouteName;

  /// The system-reported default font family.
  final String? systemFontFamily;
}

/// An immutable view configuration.
class ViewConfiguration {
  /// A const constructor for an immutable [ViewConfiguration].
  const ViewConfiguration({
    this.window,
    this.devicePixelRatio = 1.0,
    this.geometry = Rect.zero,
    this.visible = false,
    this.viewInsets = WindowPadding.zero,
    this.viewPadding = WindowPadding.zero,
    this.systemGestureInsets = WindowPadding.zero,
    this.padding = WindowPadding.zero,
    this.gestureSettings = const GestureSettings(),
    this.displayFeatures = const <DisplayFeature>[],
  });

  /// Copy this configuration with some fields replaced.
  ViewConfiguration copyWith({
    FlutterView? window,
    double? devicePixelRatio,
    Rect? geometry,
    bool? visible,
    WindowPadding? viewInsets,
    WindowPadding? viewPadding,
    WindowPadding? systemGestureInsets,
    WindowPadding? padding,
    GestureSettings? gestureSettings,
    List<DisplayFeature>? displayFeatures,
  }) {
    return ViewConfiguration(
      window: window ?? this.window,
      devicePixelRatio: devicePixelRatio ?? this.devicePixelRatio,
      geometry: geometry ?? this.geometry,
      visible: visible ?? this.visible,
      viewInsets: viewInsets ?? this.viewInsets,
      viewPadding: viewPadding ?? this.viewPadding,
      systemGestureInsets: systemGestureInsets ?? this.systemGestureInsets,
      padding: padding ?? this.padding,
      gestureSettings: gestureSettings ?? this.gestureSettings,
      displayFeatures: displayFeatures ?? this.displayFeatures,
    );
  }

  /// The top level view into which the view is placed and its geometry is
  /// relative to.
  ///
  /// If null, then this configuration represents a top level view itself.
  final FlutterView? window;

  /// The pixel density of the output surface.
  final double devicePixelRatio;

  /// The geometry requested for the view on the screen or within its parent
  /// window, in logical pixels.
  final Rect geometry;

  /// Whether or not the view is currently visible on the screen.
  final bool visible;

  /// The view insets, as it intersects with [Screen.viewInsets] for the screen
  /// it is on.
  ///
  /// For instance, if the view doesn't overlap the
  /// [ScreenConfiguration.viewInsets] area, [viewInsets] will be
  /// [WindowPadding.zero].
  ///
  /// The number of physical pixels on each side of this view rectangle into
  /// which the application can draw, but over which the operating system will
  /// likely place system UI, such as the keyboard or system menus, that fully
  /// obscures any content.
  final WindowPadding viewInsets;

  /// The view insets, as it intersects with [ScreenConfiguration.viewPadding]
  /// for the screen it is on.
  ///
  /// For instance, if the view doesn't overlap the
  /// [ScreenConfiguration.viewPadding] area, [viewPadding] will be
  /// [WindowPadding.zero].
  ///
  /// The number of physical pixels on each side of this screen rectangle into
  /// which the application can place a view, but which may be partially
  /// obscured by system UI (such as the system notification area), or physical
  /// intrusions in the display (e.g. overscan regions on television screens or
  /// phone sensor housings).
  final WindowPadding viewPadding;

  /// The view insets, as it intersects with
  /// [ScreenConfiguration.systemGestureInsets] for the screen it is on.
  ///
  /// For instance, if the view doesn't overlap the
  /// [ScreenConfiguration.systemGestureInsets] area, [systemGestureInsets] will
  /// be [WindowPadding.zero].
  ///
  /// The number of physical pixels on each side of this screen rectangle into
  /// which the application can place a view, but where the operating system
  /// will consume input gestures for the sake of system navigation.
  final WindowPadding systemGestureInsets;

  /// The view insets, as it intersects with [ScreenConfiguration.padding] for
  /// the screen it is on.
  ///
  /// For instance, if the view doesn't overlap the
  /// [ScreenConfiguration.padding] area, [padding] will be
  /// [WindowPadding.zero].
  ///
  /// The number of physical pixels on each side of this screen rectangle into
  /// which the application can place a view, but which may be partially
  /// obscured by system UI (such as the system notification area), or physical
  /// intrusions in the display (e.g. overscan regions on television screens or
  /// phone sensor housings).
  final WindowPadding padding;

  /// Additional configuration for touch gestures performed on this view.
  ///
  /// For example, the touch slop defined in physical pixels may be provided
  /// by the gesture settings and should be preferred over the framework
  /// touch slop constant.
  final GestureSettings gestureSettings;

  /// {@template dart.ui.ViewConfiguration.displayFeatures}
  /// Areas of the display that are obstructed by hardware features.
  ///
  /// This list is populated only on Android. If the device has no display
  /// features, this list is empty.
  ///
  /// The coordinate space in which the [DisplayFeature.bounds] are defined spans
  /// across the screens currently in use. This means that the space between the screens
  /// is virtually part of the Flutter view space, with the [DisplayFeature.bounds]
  /// of the display feature as an obstructed area. The [DisplayFeature.type] can
  /// be used to determine if this display feature obstructs the screen or not.
  /// For example, [DisplayFeatureType.hinge] and [DisplayFeatureType.cutout] both
  /// obstruct the display, while [DisplayFeatureType.fold] is a crease in the display.
  ///
  /// Folding [DisplayFeature]s like the [DisplayFeatureType.hinge] and
  /// [DisplayFeatureType.fold] also have a [DisplayFeature.state] which can be
  /// used to determine the posture the device is in.
  /// {@endtemplate}
  final List<DisplayFeature> displayFeatures;

  @override
  String toString() {
    return '$runtimeType[window: $window, geometry: $geometry]';
  }
}

/// Various important time points in the lifetime of a frame.
///
/// [FrameTiming] records a timestamp of each phase for performance analysis.
enum FramePhase {
  /// The timestamp of the vsync signal given by the operating system.
  ///
  /// See also [FrameTiming.vsyncOverhead].
  vsyncStart,

  /// When the UI thread starts building a frame.
  ///
  /// See also [FrameTiming.buildDuration].
  buildStart,

  /// When the UI thread finishes building a frame.
  ///
  /// See also [FrameTiming.buildDuration].
  buildFinish,

  /// When the raster thread starts rasterizing a frame.
  ///
  /// See also [FrameTiming.rasterDuration].
  rasterStart,

  /// When the raster thread finishes rasterizing a frame.
  ///
  /// See also [FrameTiming.rasterDuration].
  rasterFinish,

  /// When the raster thread finished rasterizing a frame in wall-time.
  ///
  /// This is useful for correlating time raster finish time with the system
  /// clock to integrate with other profiling tools.
  rasterFinishWallTime,
}

enum _FrameTimingInfo {
  /// The number of engine layers cached in the raster cache during the frame.
  layerCacheCount,

  /// The number of bytes used to cache engine layers during the frame.
  layerCacheBytes,

  /// The number of picture layers cached in the raster cache during the frame.
  pictureCacheCount,

  /// The number of bytes used to cache pictures during the frame.
  pictureCacheBytes,

  /// The frame number of the frame.
  frameNumber,
}

/// Time-related performance metrics of a frame.
///
/// If you're using the whole Flutter framework, please use
/// [SchedulerBinding.addTimingsCallback] to get this. It's preferred over using
/// [PlatformDispatcher.onReportTimings] directly because
/// [SchedulerBinding.addTimingsCallback] allows multiple callbacks. If
/// [SchedulerBinding] is unavailable, then see [PlatformDispatcher.onReportTimings]
/// for how to get this.
///
/// The metrics in debug mode (`flutter run` without any flags) may be very
/// different from those in profile and release modes due to the debug overhead.
/// Therefore it's recommended to only monitor and analyze performance metrics
/// in profile and release modes.
class FrameTiming {
  /// Construct [FrameTiming] with raw timestamps in microseconds.
  ///
  /// This constructor is used for unit test only. Real [FrameTiming]s should
  /// be retrieved from [PlatformDispatcher.onReportTimings].
  ///
  /// If the [frameNumber] is not provided, it defaults to `-1`.
  factory FrameTiming({
    required int vsyncStart,
    required int buildStart,
    required int buildFinish,
    required int rasterStart,
    required int rasterFinish,
    required int rasterFinishWallTime,
    int layerCacheCount = 0,
    int layerCacheBytes = 0,
    int pictureCacheCount = 0,
    int pictureCacheBytes = 0,
    int frameNumber = -1,
  }) {
    return FrameTiming._(<int>[
      vsyncStart,
      buildStart,
      buildFinish,
      rasterStart,
      rasterFinish,
      rasterFinishWallTime,
      layerCacheCount,
      layerCacheBytes,
      pictureCacheCount,
      pictureCacheBytes,
      frameNumber,
    ]);
  }

  /// Construct [FrameTiming] with raw timestamps in microseconds.
  ///
  /// List [timestamps] must have the same number of elements as
  /// [FramePhase.values].
  ///
  /// This constructor is usually only called by the Flutter engine, or a test.
  /// To get the [FrameTiming] of your app, see [PlatformDispatcher.onReportTimings].
  FrameTiming._(this._data) : assert(_data.length == _dataLength);

  static final int _dataLength = FramePhase.values.length + _FrameTimingInfo.values.length;

  /// This is a raw timestamp in microseconds from some epoch. The epoch in all
  /// [FrameTiming] is the same, but it may not match [DateTime]'s epoch.
  int timestampInMicroseconds(FramePhase phase) => _data[phase.index];

  Duration _rawDuration(FramePhase phase) => Duration(microseconds: _data[phase.index]);

  int _rawInfo(_FrameTimingInfo info) => _data[FramePhase.values.length + info.index];

  /// The duration to build the frame on the UI thread.
  ///
  /// The build starts approximately when [PlatformDispatcher.onBeginFrame] is
  /// called. The [Duration] in the [PlatformDispatcher.onBeginFrame] callback
  /// is exactly the `Duration(microseconds:
  /// timestampInMicroseconds(FramePhase.buildStart))`.
  ///
  /// The build finishes when [FlutterView.render] is called.
  ///
  /// {@template dart.ui.FrameTiming.fps_smoothness_milliseconds}
  /// To ensure smooth animations of X fps, this should not exceed 1000/X
  /// milliseconds.
  /// {@endtemplate}
  /// {@template dart.ui.FrameTiming.fps_milliseconds}
  /// That's about 16ms for 60fps, and 8ms for 120fps.
  /// {@endtemplate}
  Duration get buildDuration => _rawDuration(FramePhase.buildFinish) - _rawDuration(FramePhase.buildStart);

  /// The duration to rasterize the frame on the raster thread.
  ///
  /// {@macro dart.ui.FrameTiming.fps_smoothness_milliseconds}
  /// {@macro dart.ui.FrameTiming.fps_milliseconds}
  Duration get rasterDuration => _rawDuration(FramePhase.rasterFinish) - _rawDuration(FramePhase.rasterStart);

  /// The duration between receiving the vsync signal and starting building the
  /// frame.
  Duration get vsyncOverhead => _rawDuration(FramePhase.buildStart) - _rawDuration(FramePhase.vsyncStart);

  /// The timespan between vsync start and raster finish.
  ///
  /// To achieve the lowest latency on an X fps display, this should not exceed
  /// 1000/X milliseconds.
  /// {@macro dart.ui.FrameTiming.fps_milliseconds}
  ///
  /// See also [vsyncOverhead], [buildDuration] and [rasterDuration].
  Duration get totalSpan => _rawDuration(FramePhase.rasterFinish) - _rawDuration(FramePhase.vsyncStart);

  /// The number of layers stored in the raster cache during the frame.
  ///
  /// See also [layerCacheBytes], [pictureCacheCount] and [pictureCacheBytes].
  int get layerCacheCount => _rawInfo(_FrameTimingInfo.layerCacheCount);

  /// The number of bytes of image data used to cache layers during the frame.
  ///
  /// See also [layerCacheCount], [layerCacheMegabytes], [pictureCacheCount] and [pictureCacheBytes].
  int get layerCacheBytes => _rawInfo(_FrameTimingInfo.layerCacheBytes);

  /// The number of megabytes of image data used to cache layers during the frame.
  ///
  /// See also [layerCacheCount], [layerCacheBytes], [pictureCacheCount] and [pictureCacheBytes].
  double get layerCacheMegabytes => layerCacheBytes / 1024.0 / 1024.0;

  /// The number of pictures stored in the raster cache during the frame.
  ///
  /// See also [layerCacheCount], [layerCacheBytes] and [pictureCacheBytes].
  int get pictureCacheCount => _rawInfo(_FrameTimingInfo.pictureCacheCount);

  /// The number of bytes of image data used to cache pictures during the frame.
  ///
  /// See also [layerCacheCount], [layerCacheBytes], [pictureCacheCount] and [pictureCacheMegabytes].
  int get pictureCacheBytes => _rawInfo(_FrameTimingInfo.pictureCacheBytes);

  /// The number of megabytes of image data used to cache pictures during the frame.
  ///
  /// See also [layerCacheCount], [layerCacheBytes], [pictureCacheCount] and [pictureCacheBytes].
  double get pictureCacheMegabytes => pictureCacheBytes / 1024.0 / 1024.0;

  /// The frame key associated with this frame measurement.
  int get frameNumber => _data.last;

  final List<int> _data; // some elements in microseconds, some in bytes, some are counts

  String _formatMS(Duration duration) => '${duration.inMicroseconds * 0.001}ms';

  @override
  String toString() {
    return '$runtimeType(buildDuration: ${_formatMS(buildDuration)}, '
        'rasterDuration: ${_formatMS(rasterDuration)}, '
        'vsyncOverhead: ${_formatMS(vsyncOverhead)}, '
        'totalSpan: ${_formatMS(totalSpan)}, '
        'layerCacheCount: $layerCacheCount, '
        'layerCacheBytes: $layerCacheBytes, '
        'pictureCacheCount: $pictureCacheCount, '
        'pictureCacheBytes: $pictureCacheBytes, '
        'frameNumber: ${_data.last})';
  }
}

/// States that an application can be in.
///
/// The values below describe notifications from the operating system.
/// Applications should not expect to always receive all possible
/// notifications. For example, if the users pulls out the battery from the
/// device, no notification will be sent before the application is suddenly
/// terminated, along with the rest of the operating system.
///
/// See also:
///
///  * [WidgetsBindingObserver], for a mechanism to observe the lifecycle state
///    from the widgets layer.
enum AppLifecycleState {
  /// The application is visible and responding to user input.
  resumed,

  /// The application is in an inactive state and is not receiving user input.
  ///
  /// On iOS, this state corresponds to an app or the Flutter host view running
  /// in the foreground inactive state. Apps transition to this state when in
  /// a phone call, responding to a TouchID request, when entering the app
  /// switcher or the control center, or when the UIViewController hosting the
  /// Flutter app is transitioning.
  ///
  /// On Android, this corresponds to an app or the Flutter host view running
  /// in the foreground inactive state.  Apps transition to this state when
  /// another activity is focused, such as a split-screen app, a phone call,
  /// a picture-in-picture app, a system dialog, or another window.
  ///
  /// Apps in this state should assume that they may be [paused] at any time.
  inactive,

  /// The application is not currently visible to the user, not responding to
  /// user input, and running in the background.
  ///
  /// When the application is in this state, the engine will not call the
  /// [PlatformDispatcher.onBeginFrame] and [PlatformDispatcher.onDrawFrame]
  /// callbacks.
  paused,

  /// The application is still hosted on a flutter engine but is detached from
  /// any host views.
  ///
  /// When the application is in this state, the engine is running without
  /// a view. It can either be in the progress of attaching a view when engine
  /// was first initializes, or after the view being destroyed due to a Navigator
  /// pop.
  detached,
}

/// A representation of distances for each of the four edges of a rectangle,
/// used to encode the view insets and padding that applications should place
/// around their user interface, as exposed by [FlutterView.viewInsets] and
/// [FlutterView.padding]. View insets and padding are preferably read via
/// [MediaQuery.of].
///
/// For a generic class that represents distances around a rectangle, see the
/// [EdgeInsets] class.
///
/// See also:
///
///  * [WidgetsBindingObserver], for a widgets layer mechanism to receive
///    notifications when the padding changes.
///  * [MediaQuery.of], for the preferred mechanism for accessing these values.
///  * [Scaffold], which automatically applies the padding in material design
///    applications.
class WindowPadding {
  const WindowPadding._({ required this.left, required this.top, required this.right, required this.bottom });

  /// The distance from the left edge to the first unpadded pixel, in physical pixels.
  final double left;

  /// The distance from the top edge to the first unpadded pixel, in physical pixels.
  final double top;

  /// The distance from the right edge to the first unpadded pixel, in physical pixels.
  final double right;

  /// The distance from the bottom edge to the first unpadded pixel, in physical pixels.
  final double bottom;

  /// A window padding that has zeros for each edge.
  static const WindowPadding zero = WindowPadding._(left: 0.0, top: 0.0, right: 0.0, bottom: 0.0);

  @override
  String toString() {
    return 'WindowPadding(left: $left, top: $top, right: $right, bottom: $bottom)';
  }
}

/// Area of the display that may be obstructed by a hardware feature.
///
/// This is populated only on Android.
///
/// The [bounds] are measured in logical pixels. On devices with two screens the
/// coordinate system starts with [0,0] in the top-left corner of the left or top screen
/// and expands to include both screens and the visual space between them.
///
/// The [type] describes the behaviour and if [DisplayFeature] obstructs the display.
/// For example, [DisplayFeatureType.hinge] and [DisplayFeatureType.cutout] both obstruct the display,
/// while [DisplayFeatureType.fold] does not.
///
/// ![Device with a hinge display feature](https://flutter.github.io/assets-for-api-docs/assets/hardware/display_feature_hinge.png)
///
/// ![Device with a fold display feature](https://flutter.github.io/assets-for-api-docs/assets/hardware/display_feature_fold.png)
///
/// ![Device with a cutout display feature](https://flutter.github.io/assets-for-api-docs/assets/hardware/display_feature_cutout.png)
///
/// The [state] contains information about the posture for foldable features
/// ([DisplayFeatureType.hinge] and [DisplayFeatureType.fold]). The posture is
/// the shape of the display, for example [DisplayFeatureState.postureFlat] or
/// [DisplayFeatureState.postureHalfOpened]. For [DisplayFeatureType.cutout],
/// the state is not used and has the [DisplayFeatureState.unknown] value.
class DisplayFeature {
  const DisplayFeature({
    required this.bounds,
    required this.type,
    required this.state,
  }) : assert(!identical(type, DisplayFeatureType.cutout) || identical(state, DisplayFeatureState.unknown));

  /// The area of the flutter view occupied by this display feature, measured in logical pixels.
  ///
  /// On devices with two screens, the Flutter view spans from the top-left corner
  /// of the left or top screen to the bottom-right corner of the right or bottom screen,
  /// including the visual area occupied by any display feature. Bounds of display
  /// features are reported in this coordinate system.
  ///
  /// For example, on a dual screen device in portrait mode:
  ///
  /// * [bounds.left] gives you the size of left screen, in logical pixels.
  /// * [bounds.right] gives you the size of the left screen + the hinge width.
  final Rect bounds;

  /// Type of display feature, e.g. hinge, fold, cutout.
  final DisplayFeatureType type;

  /// Posture of display feature, which is populated only for folds and hinges.
  ///
  /// For cutouts, this is [DisplayFeatureState.unknown]
  final DisplayFeatureState state;

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) {
      return true;
    }
    if (other.runtimeType != runtimeType) {
      return false;
    }
    return other is DisplayFeature
        && bounds == other.bounds
        && type == other.type
        && state == other.state;
  }

  @override
  int get hashCode => Object.hash(bounds, type, state);

  @override
  String toString() {
    return 'DisplayFeature(rect: $bounds, type: $type, state: $state)';
  }
}

/// Type of [DisplayFeature], describing the [DisplayFeature] behaviour and if
/// it obstructs the display.
///
/// Some types of [DisplayFeature], like [DisplayFeatureType.fold], can be
/// reported without actually impeding drawing on the screen. They are useful
/// for knowing where the display is bent or has a crease. The
/// [DisplayFeature.bounds] can be 0-width in such cases.
///
/// The shape formed by the screens for types [DisplayFeatureType.fold] and
/// [DisplayFeatureType.hinge] is called the posture and is exposed in
/// [DisplayFeature.state]. For example, the [DisplayFeatureState.postureFlat] posture
/// means the screens form a flat surface, while [DisplayFeatureState.postureFlipped]
/// posture means the screens are facing opposite directions.
///
/// ![Device with a hinge display feature](https://flutter.github.io/assets-for-api-docs/assets/hardware/display_feature_hinge.png)
///
/// ![Device with a fold display feature](https://flutter.github.io/assets-for-api-docs/assets/hardware/display_feature_fold.png)
///
/// ![Device with a cutout display feature](https://flutter.github.io/assets-for-api-docs/assets/hardware/display_feature_cutout.png)
enum DisplayFeatureType {
  /// [DisplayFeature] type is new and not yet known to Flutter.
  unknown,
  /// A fold in the flexible screen without a physical gap.
  ///
  /// The bounds for this display feature type indicate where the display makes a crease.
  fold,
  /// A physical separation with a hinge that allows two display panels to fold.
  hinge,
  /// A non-displaying area of the screen, usually housing cameras or sensors.
  cutout,
}

/// State of the display feature, which contains information about the posture
/// for foldable features.
///
/// The posture is the shape made by the parts of the flexible screen or
/// physical screen panels. They are inspired by and similar to
/// [Android Postures](https://developer.android.com/guide/topics/ui/foldables#postures).
///
/// * For [DisplayFeatureType.fold]s & [DisplayFeatureType.hinge]s, the state is
///   the posture.
/// * For [DisplayFeatureType.cutout]s, the state is not used and has the
/// [DisplayFeatureState.unknown] value.
enum DisplayFeatureState {
  /// The display feature is a [DisplayFeatureType.cutout] or this state is new
  /// and not yet known to Flutter.
  unknown,
  /// The foldable device is completely open.
  ///
  /// The screen space that is presented to the user is flat.
  postureFlat,
  /// Fold angle is in an intermediate position between opened and closed state.
  ///
  /// There is a non-flat angle between parts of the flexible screen or between
  /// physical screen panels such that the screens start to face each other.
  postureHalfOpened,
}

/// An identifier used to select a user's language and formatting preferences.
///
/// This represents a [Unicode Language
/// Identifier](https://www.unicode.org/reports/tr35/#Unicode_language_identifier)
/// (i.e. without Locale extensions), except variants are not supported.
///
/// Locales are canonicalized according to the "preferred value" entries in the
/// [IANA Language Subtag
/// Registry](https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry).
/// For example, `const Locale('he')` and `const Locale('iw')` are equal and
/// both have the [languageCode] `he`, because `iw` is a deprecated language
/// subtag that was replaced by the subtag `he`.
///
/// See also:
///
///  * [PlatformDispatcher.locale], which specifies the system's currently selected
///    [Locale].
class Locale {
  /// Creates a new Locale object. The first argument is the
  /// primary language subtag, the second is the region (also
  /// referred to as 'country') subtag.
  ///
  /// For example:
  ///
  /// ```dart
  /// const Locale swissFrench = Locale('fr', 'CH');
  /// const Locale canadianFrench = Locale('fr', 'CA');
  /// ```
  ///
  /// The primary language subtag must not be null. The region subtag is
  /// optional. When there is no region/country subtag, the parameter should
  /// be omitted or passed `null` instead of an empty-string.
  ///
  /// The subtag values are _case sensitive_ and must be one of the valid
  /// subtags according to CLDR supplemental data:
  /// [language](https://github.com/unicode-org/cldr/blob/master/common/validity/language.xml),
  /// [region](https://github.com/unicode-org/cldr/blob/master/common/validity/region.xml). The
  /// primary language subtag must be at least two and at most eight lowercase
  /// letters, but not four letters. The region region subtag must be two
  /// uppercase letters or three digits. See the [Unicode Language
  /// Identifier](https://www.unicode.org/reports/tr35/#Unicode_language_identifier)
  /// specification.
  ///
  /// Validity is not checked by default, but some methods may throw away
  /// invalid data.
  ///
  /// See also:
  ///
  ///  * [Locale.fromSubtags], which also allows a [scriptCode] to be
  ///    specified.
  const Locale(
    this._languageCode, [
    this._countryCode,
  ]) : assert(_languageCode != null),
       assert(_languageCode != ''),
       scriptCode = null;

  /// Creates a new Locale object.
  ///
  /// The keyword arguments specify the subtags of the Locale.
  ///
  /// The subtag values are _case sensitive_ and must be valid subtags according
  /// to CLDR supplemental data:
  /// [language](https://github.com/unicode-org/cldr/blob/master/common/validity/language.xml),
  /// [script](https://github.com/unicode-org/cldr/blob/master/common/validity/script.xml) and
  /// [region](https://github.com/unicode-org/cldr/blob/master/common/validity/region.xml) for
  /// each of languageCode, scriptCode and countryCode respectively.
  ///
  /// The [languageCode] subtag is optional. When there is no language subtag,
  /// the parameter should be omitted or set to "und". When not supplied, the
  /// [languageCode] defaults to "und", an undefined language code.
  ///
  /// The [countryCode] subtag is optional. When there is no country subtag,
  /// the parameter should be omitted or passed `null` instead of an empty-string.
  ///
  /// Validity is not checked by default, but some methods may throw away
  /// invalid data.
  const Locale.fromSubtags({
    String languageCode = 'und',
    this.scriptCode,
    String? countryCode,
  }) : assert(languageCode != null),
       assert(languageCode != ''),
       _languageCode = languageCode,
       assert(scriptCode != ''),
       assert(countryCode != ''),
       _countryCode = countryCode;

  /// The primary language subtag for the locale.
  ///
  /// This must not be null. It may be 'und', representing 'undefined'.
  ///
  /// This is expected to be string registered in the [IANA Language Subtag
  /// Registry](https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry)
  /// with the type "language". The string specified must match the case of the
  /// string in the registry.
  ///
  /// Language subtags that are deprecated in the registry and have a preferred
  /// code are changed to their preferred code. For example, `const
  /// Locale('he')` and `const Locale('iw')` are equal, and both have the
  /// [languageCode] `he`, because `iw` is a deprecated language subtag that was
  /// replaced by the subtag `he`.
  ///
  /// This must be a valid Unicode Language subtag as listed in [Unicode CLDR
  /// supplemental
  /// data](https://github.com/unicode-org/cldr/blob/master/common/validity/language.xml).
  ///
  /// See also:
  ///
  ///  * [Locale.fromSubtags], which describes the conventions for creating
  ///    [Locale] objects.
  String get languageCode => _deprecatedLanguageSubtagMap[_languageCode] ?? _languageCode;
  final String _languageCode;

  // This map is generated by //flutter/tools/gen_locale.dart
  // Mappings generated for language subtag registry as of 2019-02-27.
  static const Map<String, String> _deprecatedLanguageSubtagMap = <String, String>{
    'in': 'id', // Indonesian; deprecated 1989-01-01
    'iw': 'he', // Hebrew; deprecated 1989-01-01
    'ji': 'yi', // Yiddish; deprecated 1989-01-01
    'jw': 'jv', // Javanese; deprecated 2001-08-13
    'mo': 'ro', // Moldavian, Moldovan; deprecated 2008-11-22
    'aam': 'aas', // Aramanik; deprecated 2015-02-12
    'adp': 'dz', // Adap; deprecated 2015-02-12
    'aue': 'ktz', // ǂKxʼauǁʼein; deprecated 2015-02-12
    'ayx': 'nun', // Ayi (China); deprecated 2011-08-16
    'bgm': 'bcg', // Baga Mboteni; deprecated 2016-05-30
    'bjd': 'drl', // Bandjigali; deprecated 2012-08-12
    'ccq': 'rki', // Chaungtha; deprecated 2012-08-12
    'cjr': 'mom', // Chorotega; deprecated 2010-03-11
    'cka': 'cmr', // Khumi Awa Chin; deprecated 2012-08-12
    'cmk': 'xch', // Chimakum; deprecated 2010-03-11
    'coy': 'pij', // Coyaima; deprecated 2016-05-30
    'cqu': 'quh', // Chilean Quechua; deprecated 2016-05-30
    'drh': 'khk', // Darkhat; deprecated 2010-03-11
    'drw': 'prs', // Darwazi; deprecated 2010-03-11
    'gav': 'dev', // Gabutamon; deprecated 2010-03-11
    'gfx': 'vaj', // Mangetti Dune ǃXung; deprecated 2015-02-12
    'ggn': 'gvr', // Eastern Gurung; deprecated 2016-05-30
    'gti': 'nyc', // Gbati-ri; deprecated 2015-02-12
    'guv': 'duz', // Gey; deprecated 2016-05-30
    'hrr': 'jal', // Horuru; deprecated 2012-08-12
    'ibi': 'opa', // Ibilo; deprecated 2012-08-12
    'ilw': 'gal', // Talur; deprecated 2013-09-10
    'jeg': 'oyb', // Jeng; deprecated 2017-02-23
    'kgc': 'tdf', // Kasseng; deprecated 2016-05-30
    'kgh': 'kml', // Upper Tanudan Kalinga; deprecated 2012-08-12
    'koj': 'kwv', // Sara Dunjo; deprecated 2015-02-12
    'krm': 'bmf', // Krim; deprecated 2017-02-23
    'ktr': 'dtp', // Kota Marudu Tinagas; deprecated 2016-05-30
    'kvs': 'gdj', // Kunggara; deprecated 2016-05-30
    'kwq': 'yam', // Kwak; deprecated 2015-02-12
    'kxe': 'tvd', // Kakihum; deprecated 2015-02-12
    'kzj': 'dtp', // Coastal Kadazan; deprecated 2016-05-30
    'kzt': 'dtp', // Tambunan Dusun; deprecated 2016-05-30
    'lii': 'raq', // Lingkhim; deprecated 2015-02-12
    'lmm': 'rmx', // Lamam; deprecated 2014-02-28
    'meg': 'cir', // Mea; deprecated 2013-09-10
    'mst': 'mry', // Cataelano Mandaya; deprecated 2010-03-11
    'mwj': 'vaj', // Maligo; deprecated 2015-02-12
    'myt': 'mry', // Sangab Mandaya; deprecated 2010-03-11
    'nad': 'xny', // Nijadali; deprecated 2016-05-30
    'ncp': 'kdz', // Ndaktup; deprecated 2018-03-08
    'nnx': 'ngv', // Ngong; deprecated 2015-02-12
    'nts': 'pij', // Natagaimas; deprecated 2016-05-30
    'oun': 'vaj', // ǃOǃung; deprecated 2015-02-12
    'pcr': 'adx', // Panang; deprecated 2013-09-10
    'pmc': 'huw', // Palumata; deprecated 2016-05-30
    'pmu': 'phr', // Mirpur Panjabi; deprecated 2015-02-12
    'ppa': 'bfy', // Pao; deprecated 2016-05-30
    'ppr': 'lcq', // Piru; deprecated 2013-09-10
    'pry': 'prt', // Pray 3; deprecated 2016-05-30
    'puz': 'pub', // Purum Naga; deprecated 2014-02-28
    'sca': 'hle', // Sansu; deprecated 2012-08-12
    'skk': 'oyb', // Sok; deprecated 2017-02-23
    'tdu': 'dtp', // Tempasuk Dusun; deprecated 2016-05-30
    'thc': 'tpo', // Tai Hang Tong; deprecated 2016-05-30
    'thx': 'oyb', // The; deprecated 2015-02-12
    'tie': 'ras', // Tingal; deprecated 2011-08-16
    'tkk': 'twm', // Takpa; deprecated 2011-08-16
    'tlw': 'weo', // South Wemale; deprecated 2012-08-12
    'tmp': 'tyj', // Tai Mène; deprecated 2016-05-30
    'tne': 'kak', // Tinoc Kallahan; deprecated 2016-05-30
    'tnf': 'prs', // Tangshewi; deprecated 2010-03-11
    'tsf': 'taj', // Southwestern Tamang; deprecated 2015-02-12
    'uok': 'ema', // Uokha; deprecated 2015-02-12
    'xba': 'cax', // Kamba (Brazil); deprecated 2016-05-30
    'xia': 'acn', // Xiandao; deprecated 2013-09-10
    'xkh': 'waw', // Karahawyana; deprecated 2016-05-30
    'xsj': 'suj', // Subi; deprecated 2015-02-12
    'ybd': 'rki', // Yangbye; deprecated 2012-08-12
    'yma': 'lrr', // Yamphe; deprecated 2012-08-12
    'ymt': 'mtm', // Mator-Taygi-Karagas; deprecated 2015-02-12
    'yos': 'zom', // Yos; deprecated 2013-09-10
    'yuu': 'yug', // Yugh; deprecated 2014-02-28
  };

  /// The script subtag for the locale.
  ///
  /// This may be null, indicating that there is no specified script subtag.
  ///
  /// This must be a valid Unicode Language Identifier script subtag as listed
  /// in [Unicode CLDR supplemental
  /// data](https://github.com/unicode-org/cldr/blob/master/common/validity/script.xml).
  ///
  /// See also:
  ///
  ///  * [Locale.fromSubtags], which describes the conventions for creating
  ///    [Locale] objects.
  final String? scriptCode;

  /// The region subtag for the locale.
  ///
  /// This may be null, indicating that there is no specified region subtag.
  ///
  /// This is expected to be string registered in the [IANA Language Subtag
  /// Registry](https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry)
  /// with the type "region". The string specified must match the case of the
  /// string in the registry.
  ///
  /// Region subtags that are deprecated in the registry and have a preferred
  /// code are changed to their preferred code. For example, `const Locale('de',
  /// 'DE')` and `const Locale('de', 'DD')` are equal, and both have the
  /// [countryCode] `DE`, because `DD` is a deprecated language subtag that was
  /// replaced by the subtag `DE`.
  ///
  /// See also:
  ///
  ///  * [Locale.fromSubtags], which describes the conventions for creating
  ///    [Locale] objects.
  String? get countryCode => _deprecatedRegionSubtagMap[_countryCode] ?? _countryCode;
  final String? _countryCode;

  // This map is generated by //flutter/tools/gen_locale.dart
  // Mappings generated for language subtag registry as of 2019-02-27.
  static const Map<String, String> _deprecatedRegionSubtagMap = <String, String>{
    'BU': 'MM', // Burma; deprecated 1989-12-05
    'DD': 'DE', // German Democratic Republic; deprecated 1990-10-30
    'FX': 'FR', // Metropolitan France; deprecated 1997-07-14
    'TP': 'TL', // East Timor; deprecated 2002-05-20
    'YD': 'YE', // Democratic Yemen; deprecated 1990-08-14
    'ZR': 'CD', // Zaire; deprecated 1997-07-14
  };

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) {
      return true;
    }
    if (other is! Locale) {
      return false;
    }
    final String? thisCountryCode = countryCode;
    final String? otherCountryCode = other.countryCode;
    return other.languageCode == languageCode
        && other.scriptCode == scriptCode // scriptCode cannot be ''
        && (other.countryCode == thisCountryCode // Treat '' as equal to null.
            || otherCountryCode != null && otherCountryCode.isEmpty && thisCountryCode == null
            || thisCountryCode != null && thisCountryCode.isEmpty && other.countryCode == null);
  }

  @override
  int get hashCode => Object.hash(languageCode, scriptCode, countryCode == '' ? null : countryCode);

  static Locale? _cachedLocale;
  static String? _cachedLocaleString;

  /// Returns a string representing the locale.
  ///
  /// This identifier happens to be a valid Unicode Locale Identifier using
  /// underscores as separator, however it is intended to be used for debugging
  /// purposes only. For parsable results, use [toLanguageTag] instead.
  @keepToString
  @override
  String toString() {
    if (!identical(_cachedLocale, this)) {
      _cachedLocale = this;
      _cachedLocaleString = _rawToString('_');
    }
    return _cachedLocaleString!;
  }

  /// Returns a syntactically valid Unicode BCP47 Locale Identifier.
  ///
  /// Some examples of such identifiers: "en", "es-419", "hi-Deva-IN" and
  /// "zh-Hans-CN". See http://www.unicode.org/reports/tr35/ for technical
  /// details.
  String toLanguageTag() => _rawToString('-');

  String _rawToString(String separator) {
    final StringBuffer out = StringBuffer(languageCode);
    if (scriptCode != null && scriptCode!.isNotEmpty) {
      out.write('$separator$scriptCode');
    }
    if (_countryCode != null && _countryCode!.isNotEmpty) {
      out.write('$separator$countryCode');
    }
    return out.toString();
  }
}

/// Various performance modes for tuning the Dart VM's GC performance.
///
/// For the editor of this enum, please keep the order in sync with `Dart_PerformanceMode`
/// in [dart_api.h](https://github.com/dart-lang/sdk/blob/main/runtime/include/dart_api.h#L1302).
enum DartPerformanceMode {
  /// This is the default mode that the Dart VM is in.
  balanced,

  /// Optimize for low latency, at the expense of throughput and memory overhead
  /// by performing work in smaller batches (requiring more overhead) or by
  /// delaying work (requiring more memory). An embedder should not remain in
  /// this mode indefinitely.
  latency,

  /// Optimize for high throughput, at the expense of latency and memory overhead
  /// by performing work in larger batches with more intervening growth.
  throughput,

  /// Optimize for low memory, at the expensive of throughput and latency by more
  /// frequently performing work.
  memory,
}