lib/web_ui/lib/src/engine/pointer_binding.dart

// 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.

// @dart = 2.6
part of engine;

/// Set this flag to true to see all the fired events in the console.
const bool _debugLogPointerEvents = false;

/// The signature of a callback that handles pointer events.
typedef _PointerDataCallback = void Function(Iterable<ui.PointerData>);

// The mask for the bitfield of event buttons. Buttons not contained in this
// mask are cut off.
//
// In Flutter we used `kMaxUnsignedSMI`, but since that value is not available
// here, we use an already very large number (30 bits).
const int _kButtonsMask = 0x3FFFFFFF;

// Intentionally set to -1 so it doesn't conflict with other device IDs.
const int _mouseDeviceId = -1;

const int _kPrimaryMouseButton = 0x1;
const int _kSecondaryMouseButton = 0x2;
const int _kMiddleMouseButton =0x4;

int _nthButton(int n) => 0x1 << n;

/// Convert the `button` property of PointerEvent or MouseEvent to a bit mask of
/// its `buttons` property.
///
/// The `button` property is a integer describing the button changed in an event,
/// which is sequentially 0 for LMB, 1 for MMB, 2 for RMB, 3 for backward and
/// 4 for forward, etc.
///
/// The `buttons` property is a bitfield describing the buttons pressed after an
/// event, which is 0x1 for LMB, 0x4 for MMB, 0x2 for RMB, 0x8 for backward
/// and 0x10 for forward, etc.
@visibleForTesting
int convertButtonToButtons(int button) {
  assert(button >= 0, 'Unexpected negative button $button.');
  switch(button) {
    case 0:
      return _kPrimaryMouseButton;
    case 1:
      return _kMiddleMouseButton;
    case 2:
      return _kSecondaryMouseButton;
    default:
      return _nthButton(button);
  }
}

class PointerBinding {
  /// The singleton instance of this object.
  static PointerBinding get instance => _instance;
  static PointerBinding _instance;

  static void initInstance(html.Element glassPaneElement) {
    if (_instance == null) {
      _instance = PointerBinding._(glassPaneElement);
      assert(() {
        registerHotRestartListener(() {
          _instance._adapter?.clearListeners();
          _instance._pointerDataConverter?.clearPointerState();
        });
        return true;
      }());
    }
  }

  PointerBinding._(this.glassPaneElement) {
    _pointerDataConverter = PointerDataConverter();
    _detector = const PointerSupportDetector();
    _adapter = _createAdapter();
  }

  final html.Element glassPaneElement;

  PointerSupportDetector _detector;
  _BaseAdapter _adapter;
  PointerDataConverter _pointerDataConverter;

  /// Should be used in tests to define custom detection of pointer support.
  ///
  /// ```dart
  /// // Forces PointerBinding to use mouse events.
  /// class MyTestDetector extends PointerSupportDetector {
  ///   @override
  ///   final bool hasPointerEvents = false;
  ///
  ///   @override
  ///   final bool hasTouchEvents = false;
  ///
  ///   @override
  ///   final bool hasMouseEvents = true;
  /// }
  ///
  /// PointerBinding.instance.debugOverrideDetector(MyTestDetector());
  /// ```
  void debugOverrideDetector(PointerSupportDetector newDetector) {
    newDetector ??= const PointerSupportDetector();
    // When changing the detector, we need to swap the adapter.
    if (newDetector != _detector) {
      _detector = newDetector;
      _adapter?.clearListeners();
      _adapter = _createAdapter();
      _pointerDataConverter?.clearPointerState();
    }
  }

  _BaseAdapter _createAdapter() {
    if (_detector.hasPointerEvents) {
      return _PointerAdapter(_onPointerData, glassPaneElement, _pointerDataConverter);
    }
    if (_detector.hasTouchEvents) {
      return _TouchAdapter(_onPointerData, glassPaneElement, _pointerDataConverter);
    }
    if (_detector.hasMouseEvents) {
      return _MouseAdapter(_onPointerData, glassPaneElement, _pointerDataConverter);
    }
    return null;
  }

  void _onPointerData(Iterable<ui.PointerData> data) {
    final ui.PointerDataPacket packet = ui.PointerDataPacket(data: data.toList());
    if (window._onPointerDataPacket != null) {
      window.invokeOnPointerDataPacket(packet);
    }
  }
}

class PointerSupportDetector {
  const PointerSupportDetector();

  bool get hasPointerEvents => js_util.hasProperty(html.window, 'PointerEvent');
  bool get hasTouchEvents => js_util.hasProperty(html.window, 'TouchEvent');
  bool get hasMouseEvents => js_util.hasProperty(html.window, 'MouseEvent');

  @override
  String toString() =>
      'pointers:$hasPointerEvents, touch:$hasTouchEvents, mouse:$hasMouseEvents';
}

/// Common functionality that's shared among adapters.
abstract class _BaseAdapter {
  _BaseAdapter(this._callback, this.glassPaneElement, this._pointerDataConverter) {
    setup();
  }

  /// Listeners that are registered through dart to js api.
  static final Map<String, html.EventListener> _listeners =
    <String, html.EventListener>{};
  /// Listeners that are registered through native javascript api.
  static final Map<String, html.EventListener> _nativeListeners =
    <String, html.EventListener>{};
  final html.Element glassPaneElement;
  _PointerDataCallback _callback;
  PointerDataConverter _pointerDataConverter;

  /// Each subclass is expected to override this method to attach its own event
  /// listeners and convert events into pointer events.
  void setup();

  /// Remove all active event listeners.
  void clearListeners() {
    _listeners.forEach((String eventName, html.EventListener listener) {
        html.window.removeEventListener(eventName, listener, true);
    });
    // For native listener, we will need to remove it through native javascript
    // api.
    _nativeListeners.forEach((String eventName, html.EventListener listener) {
      js_util.callMethod(
        glassPaneElement,
        'removeEventListener', <dynamic>[
          'wheel',
          listener,
        ]
      );
    });
    _listeners.clear();
    _nativeListeners.clear();
  }

  /// Adds a listener to the given [eventName].
  ///
  /// The event listener is attached to [html.window] but only events that have
  /// [glassPaneElement] as a target will be let through by default.
  ///
  /// If [acceptOutsideGlasspane] is set to true, events outside of the
  /// glasspane will also invoke the [handler].
  void addEventListener(
    String eventName,
    html.EventListener handler, {
    bool acceptOutsideGlasspane = false,
  }) {
    final html.EventListener loggedHandler = (html.Event event) {
      if (!acceptOutsideGlasspane && !glassPaneElement.contains(event.target)) {
        return;
      }

      if (_debugLogPointerEvents) {
        print(event.type);
      }
      // Report the event to semantics. This information is used to debounce
      // browser gestures. Semantics tells us whether it is safe to forward
      // the event to the framework.
      if (EngineSemanticsOwner.instance.receiveGlobalEvent(event)) {
        handler(event);
      }
    };
    _listeners[eventName] = loggedHandler;
    // We have to attach the event listener on the window instead of the
    // glasspane element. That's because "up" events that occur outside the
    // browser are only reported on window, not on DOM elements.
    // See: https://github.com/flutter/flutter/issues/52827
    html.window.addEventListener(eventName, loggedHandler, true);
  }

  /// Converts a floating number timestamp (in milliseconds) to a [Duration] by
  /// splitting it into two integer components: milliseconds + microseconds.
  static Duration _eventTimeStampToDuration(num milliseconds) {
    final int ms = milliseconds.toInt();
    final int micro =
    ((milliseconds - ms) * Duration.microsecondsPerMillisecond).toInt();
    return Duration(milliseconds: ms, microseconds: micro);
  }
}

mixin _WheelEventListenerMixin on _BaseAdapter {
  List<ui.PointerData> _convertWheelEventToPointerData(
    html.WheelEvent event
  ) {
    const int domDeltaPixel = 0x00;
    const int domDeltaLine = 0x01;
    const int domDeltaPage = 0x02;

    // Flutter only supports pixel scroll delta. Convert deltaMode values
    // to pixels.
    double deltaX = event.deltaX;
    double deltaY = event.deltaY;
    switch (event.deltaMode) {
      case domDeltaLine:
        deltaX *= 32.0;
        deltaY *= 32.0;
        break;
      case domDeltaPage:
        deltaX *= ui.window.physicalSize.width;
        deltaY *= ui.window.physicalSize.height;
        break;
      case domDeltaPixel:
      default:
        break;
    }
    final List<ui.PointerData> data = <ui.PointerData>[];
    _pointerDataConverter.convert(
      data,
      change: ui.PointerChange.hover,
      timeStamp: _BaseAdapter._eventTimeStampToDuration(event.timeStamp),
      kind: ui.PointerDeviceKind.mouse,
      signalKind: ui.PointerSignalKind.scroll,
      device: _mouseDeviceId,
      physicalX: event.client.x * ui.window.devicePixelRatio,
      physicalY: event.client.y * ui.window.devicePixelRatio,
      buttons: event.buttons,
      pressure: 1.0,
      pressureMin: 0.0,
      pressureMax: 1.0,
      scrollDeltaX: deltaX,
      scrollDeltaY: deltaY,
    );
    return data;
  }

  void _addWheelEventListener(html.EventListener handler) {
    final dynamic eventOptions = js_util.newObject();
    final html.EventListener jsHandler = js.allowInterop((html.Event event) => handler(event));
    _BaseAdapter._nativeListeners['wheel'] = jsHandler;
    js_util.setProperty(eventOptions, 'passive', false);
    js_util.callMethod(
      glassPaneElement,
      'addEventListener', <dynamic>[
        'wheel',
        jsHandler,
        eventOptions
      ]
    );
  }
}

@immutable
class _SanitizedDetails {
  const _SanitizedDetails({
    @required this.buttons,
    @required this.change,
  });

  final ui.PointerChange change;
  final int buttons;

  @override
  String toString() => '$runtimeType(change: $change, buttons: $buttons)';
}

class _ButtonSanitizer {
  int _pressedButtons = 0;

  /// Transform [html.PointerEvent.buttons] to Flutter's PointerEvent buttons.
  int _htmlButtonsToFlutterButtons(int buttons) {
    // Flutter's button definition conveniently matches that of JavaScript
    // from primary button (0x1) to forward button (0x10), which allows us to
    // avoid transforming it bit by bit.
    return buttons & _kButtonsMask;
  }

  /// Given [html.PointerEvent.button] and [html.PointerEvent.buttons], tries to
  /// infer the correct value for Flutter buttons.
  int _inferDownFlutterButtons(int button, int buttons) {
    if (buttons == 0 && button > -1) {
      // In some cases, the browser sends `buttons:0` in a down event. In such
      // case, we try to infer the value from `button`.
      buttons = convertButtonToButtons(button);
    }
    return _htmlButtonsToFlutterButtons(buttons);
  }

  _SanitizedDetails sanitizeDownEvent({
    @required int button,
    @required int buttons,
  }) {
    // If the pointer is already down, we just send a move event with the new
    // `buttons` value.
    if (_pressedButtons != 0) {
      return sanitizeMoveEvent(buttons: buttons);
    }

    _pressedButtons = _inferDownFlutterButtons(button, buttons);
    return _SanitizedDetails(
      change: ui.PointerChange.down,
      buttons: _pressedButtons,
    );
  }

  _SanitizedDetails sanitizeMoveEvent({@required int buttons}) {
    final int newPressedButtons = _htmlButtonsToFlutterButtons(buttons);
    // This could happen when the context menu is active and the user clicks
    // RMB somewhere else. The browser sends a down event with `buttons:0`.
    //
    // In this case, we keep the old `buttons` value so we don't confuse the
    // framework.
    if (_pressedButtons != 0 && newPressedButtons == 0) {
      return _SanitizedDetails(
        change: ui.PointerChange.move,
        buttons: _pressedButtons,
      );
    }

    // This could happen when the user clicks RMB then moves the mouse quickly.
    // The brower sends a move event with `buttons:2` even though there's no
    // buttons down yet.
    if (_pressedButtons == 0 && newPressedButtons != 0) {
      return _SanitizedDetails(
        change: ui.PointerChange.hover,
        buttons: _pressedButtons,
      );
    }

    _pressedButtons = newPressedButtons;
    return _SanitizedDetails(
      change: _pressedButtons == 0
          ? ui.PointerChange.hover
          : ui.PointerChange.move,
      buttons: _pressedButtons,
    );
  }

  _SanitizedDetails sanitizeUpEvent() {
    // The pointer could have been released by a `pointerout` event, in which
    // case `pointerup` should have no effect.
    if (_pressedButtons == 0) {
      return null;
    }
    _pressedButtons = 0;
    return _SanitizedDetails(
      change: ui.PointerChange.up,
      buttons: _pressedButtons,
    );
  }

  _SanitizedDetails sanitizeCancelEvent() {
    _pressedButtons = 0;
    return _SanitizedDetails(
      change: ui.PointerChange.cancel,
      buttons: _pressedButtons,
    );
  }
}

typedef _PointerEventListener = dynamic Function(html.PointerEvent event);

/// Adapter class to be used with browsers that support native pointer events.
///
/// For the difference between MouseEvent and PointerEvent, see _MouseAdapter.
class _PointerAdapter extends _BaseAdapter with _WheelEventListenerMixin {
  _PointerAdapter(
    _PointerDataCallback callback,
    html.Element glassPaneElement,
    PointerDataConverter _pointerDataConverter
  ) : super(callback, glassPaneElement, _pointerDataConverter);

  final Map<int, _ButtonSanitizer> _sanitizers = <int, _ButtonSanitizer>{};

  @visibleForTesting
  Iterable<int> debugTrackedDevices() => _sanitizers.keys;

  _ButtonSanitizer _ensureSanitizer(int device) {
    return _sanitizers.putIfAbsent(device, () => _ButtonSanitizer());
  }

  _ButtonSanitizer _getSanitizer(int device) {
    final _ButtonSanitizer sanitizer = _sanitizers[device];
    assert(sanitizer != null);
    return sanitizer;
  }

  void _removePointerIfUnhoverable(html.PointerEvent event) {
    if (event.pointerType == 'touch') {
      _sanitizers.remove(event.pointerId);
    }
  }

  void _addPointerEventListener(
    String eventName,
    _PointerEventListener handler, {
    bool acceptOutsideGlasspane = false,
  }) {
    addEventListener(eventName, (html.Event event) {
      final html.PointerEvent pointerEvent = event;
      return handler(pointerEvent);
    }, acceptOutsideGlasspane: acceptOutsideGlasspane);
  }

  @override
  void setup() {
    _addPointerEventListener('pointerdown', (html.PointerEvent event) {
      final int device = event.pointerId;
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final _SanitizedDetails details =
        _ensureSanitizer(device).sanitizeDownEvent(
          button: event.button,
          buttons: event.buttons,
        );
      _convertEventsToPointerData(data: pointerData, event: event, details: details);
      _callback(pointerData);
    });

    _addPointerEventListener('pointermove', (html.PointerEvent event) {
      final int device = event.pointerId;
      final _ButtonSanitizer sanitizer = _ensureSanitizer(device);
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final Iterable<_SanitizedDetails> detailsList = _expandEvents(event).map(
        (html.PointerEvent expandedEvent) => sanitizer.sanitizeMoveEvent(buttons: expandedEvent.buttons),
      );
      for (_SanitizedDetails details in detailsList) {
        _convertEventsToPointerData(data: pointerData, event: event, details: details);
      }
      _callback(pointerData);
    }, acceptOutsideGlasspane: true);

    _addPointerEventListener('pointerup', (html.PointerEvent event) {
      final int device = event.pointerId;
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final _SanitizedDetails details = _getSanitizer(device).sanitizeUpEvent();
      _removePointerIfUnhoverable(event);
      if (details != null) {
        _convertEventsToPointerData(data: pointerData, event: event, details: details);
      }
      _callback(pointerData);
    }, acceptOutsideGlasspane: true);

    // A browser fires cancel event if it concludes the pointer will no longer
    // be able to generate events (example: device is deactivated)
    _addPointerEventListener('pointercancel', (html.PointerEvent event) {
      final int device = event.pointerId;
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final _SanitizedDetails details = _getSanitizer(device).sanitizeCancelEvent();
      _removePointerIfUnhoverable(event);
      _convertEventsToPointerData(data: pointerData, event: event, details: details);
      _callback(pointerData);
    });

    _addWheelEventListener((html.Event event) {
      assert(event is html.WheelEvent);
      if (_debugLogPointerEvents) {
        print(event.type);
      }
      _callback(_convertWheelEventToPointerData(event));
      // Prevent default so mouse wheel event doesn't get converted to
      // a scroll event that semantic nodes would process.
      event.preventDefault();
    });
  }

  // For each event that is de-coalesced from `event` and described in
  // `details`, convert it to pointer data and store in `data`.
  void _convertEventsToPointerData({
    @required List<ui.PointerData> data,
    @required html.PointerEvent event,
    @required _SanitizedDetails details,
  }) {
    assert(data != null);
    assert(event != null);
    assert(details != null);
    final ui.PointerDeviceKind kind = _pointerTypeToDeviceKind(event.pointerType);
    // We force `device: _mouseDeviceId` on mouse pointers because Wheel events
    // might come before any PointerEvents, and since wheel events don't contain
    // pointerId we always assign `device: _mouseDeviceId` to them.
    final int device = kind == ui.PointerDeviceKind.mouse ? _mouseDeviceId : event.pointerId;
    final double tilt = _computeHighestTilt(event);
    final Duration timeStamp = _BaseAdapter._eventTimeStampToDuration(event.timeStamp);
    _pointerDataConverter.convert(
      data,
      change: details.change,
      timeStamp: timeStamp,
      kind: kind,
      signalKind: ui.PointerSignalKind.none,
      device: device,
      physicalX: event.client.x * ui.window.devicePixelRatio,
      physicalY: event.client.y * ui.window.devicePixelRatio,
      buttons: details.buttons,
      pressure: event.pressure,
      pressureMin: 0.0,
      pressureMax: 1.0,
      tilt: tilt,
    );
  }

  List<html.PointerEvent> _expandEvents(html.PointerEvent event) {
    // For browsers that don't support `getCoalescedEvents`, we fallback to
    // using the original event.
    if (js_util.hasProperty(event, 'getCoalescedEvents')) {
      final List<html.PointerEvent> coalescedEvents =
          event.getCoalescedEvents().cast<html.PointerEvent>();
      // Some events don't perform coalescing, so they return an empty list. In
      // that case, we also fallback to using the original event.
      if (coalescedEvents.isNotEmpty) {
        return coalescedEvents;
      }
    }
    return <html.PointerEvent>[event];
  }

  ui.PointerDeviceKind _pointerTypeToDeviceKind(String pointerType) {
    switch (pointerType) {
      case 'mouse':
        return ui.PointerDeviceKind.mouse;
      case 'pen':
        return ui.PointerDeviceKind.stylus;
      case 'touch':
        return ui.PointerDeviceKind.touch;
      default:
        return ui.PointerDeviceKind.unknown;
    }
  }

  /// Tilt angle is -90 to + 90. Take maximum deflection and convert to radians.
  double _computeHighestTilt(html.PointerEvent e) =>
      (e.tiltX.abs() > e.tiltY.abs() ? e.tiltX : e.tiltY).toDouble() /
      180.0 *
      math.pi;
}

typedef _TouchEventListener = dynamic Function(html.TouchEvent event);

/// Adapter to be used with browsers that support touch events.
class _TouchAdapter extends _BaseAdapter {
  _TouchAdapter(
    _PointerDataCallback callback,
    html.Element glassPaneElement,
    PointerDataConverter _pointerDataConverter
  ) : super(callback, glassPaneElement, _pointerDataConverter);

  final Set<int> _pressedTouches = <int>{};
  bool _isTouchPressed(int identifier) => _pressedTouches.contains(identifier);
  void _pressTouch(int identifier) { _pressedTouches.add(identifier); }
  void _unpressTouch(int identifier) { _pressedTouches.remove(identifier); }

  void _addTouchEventListener(String eventName, _TouchEventListener handler) {
    addEventListener(eventName, (html.Event event) {
      final html.TouchEvent touchEvent = event;
      return handler(touchEvent);
    });
  }

  @override
  void setup() {
    _addTouchEventListener('touchstart', (html.TouchEvent event) {
      final Duration timeStamp = _BaseAdapter._eventTimeStampToDuration(event.timeStamp);
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      for (html.Touch touch in event.changedTouches) {
        final nowPressed = _isTouchPressed(touch.identifier);
        if (!nowPressed) {
          _pressTouch(touch.identifier);
          _convertEventToPointerData(
            data: pointerData,
            change: ui.PointerChange.down,
            touch: touch,
            pressed: true,
            timeStamp: timeStamp,
          );
        }
      }
      _callback(pointerData);
    });

    _addTouchEventListener('touchmove', (html.TouchEvent event) {
      event.preventDefault(); // Prevents standard overscroll on iOS/Webkit.
      final Duration timeStamp = _BaseAdapter._eventTimeStampToDuration(event.timeStamp);
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      for (html.Touch touch in event.changedTouches) {
        final nowPressed = _isTouchPressed(touch.identifier);
        if (nowPressed) {
          _convertEventToPointerData(
            data: pointerData,
            change: ui.PointerChange.move,
            touch: touch,
            pressed: true,
            timeStamp: timeStamp,
          );
        }
      }
      _callback(pointerData);
    });

    _addTouchEventListener('touchend', (html.TouchEvent event) {
      // On Safari Mobile, the keyboard does not show unless this line is
      // added.
      event.preventDefault();
      final Duration timeStamp = _BaseAdapter._eventTimeStampToDuration(event.timeStamp);
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      for (html.Touch touch in event.changedTouches) {
        final nowPressed = _isTouchPressed(touch.identifier);
        if (nowPressed) {
          _unpressTouch(touch.identifier);
          _convertEventToPointerData(
            data: pointerData,
            change: ui.PointerChange.up,
            touch: touch,
            pressed: false,
            timeStamp: timeStamp,
          );
        }
      }
      _callback(pointerData);
    });

    _addTouchEventListener('touchcancel', (html.TouchEvent event) {
      final Duration timeStamp = _BaseAdapter._eventTimeStampToDuration(event.timeStamp);
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      for (html.Touch touch in event.changedTouches) {
        final nowPressed = _isTouchPressed(touch.identifier);
        if (nowPressed) {
          _unpressTouch(touch.identifier);
          _convertEventToPointerData(
            data: pointerData,
            change: ui.PointerChange.cancel,
            touch: touch,
            pressed: false,
            timeStamp: timeStamp,
          );
        }
      }
      _callback(pointerData);
    });
  }

  void _convertEventToPointerData({
    @required List<ui.PointerData> data,
    @required ui.PointerChange change,
    @required html.Touch touch,
    @required bool pressed,
    @required Duration timeStamp,
  }) {
    _pointerDataConverter.convert(
      data,
      change: change,
      timeStamp: timeStamp,
      kind: ui.PointerDeviceKind.touch,
      signalKind: ui.PointerSignalKind.none,
      device: touch.identifier,
      physicalX: touch.client.x * ui.window.devicePixelRatio,
      physicalY: touch.client.y * ui.window.devicePixelRatio,
      buttons: pressed ? _kPrimaryMouseButton : 0,
      pressure: 1.0,
      pressureMin: 0.0,
      pressureMax: 1.0,
    );
  }
}

typedef _MouseEventListener = dynamic Function(html.MouseEvent event);

/// Adapter to be used with browsers that support mouse events.
///
/// The difference between MouseEvent and PointerEvent can be illustrated using
/// a scenario of changing buttons during a drag sequence: LMB down, RMB down,
/// move, LMB up, RMB up, hover.
///
///                 LMB down    RMB down      move      LMB up      RMB up     hover
/// PntEvt type | pointerdown pointermove pointermove pointermove pointerup pointermove
///      button |      0           2           -1         0           2          -1
///     buttons |     0x1         0x3         0x3        0x2         0x0        0x0
/// MosEvt type |  mousedown   mousedown   mousemove   mouseup     mouseup   mousemove
///      button |      0           2           0          0           2          0
///     buttons |     0x1         0x3         0x3        0x2         0x0        0x0
///
/// The major differences are:
///
///  * The type of events for changing buttons during a drag sequence.
///  * The `button` for dragging or hovering.
class _MouseAdapter extends _BaseAdapter with _WheelEventListenerMixin {
  _MouseAdapter(
    _PointerDataCallback callback,
    html.Element glassPaneElement,
    PointerDataConverter _pointerDataConverter
  ) : super(callback, glassPaneElement, _pointerDataConverter);

  final _ButtonSanitizer _sanitizer = _ButtonSanitizer();

  void _addMouseEventListener(
    String eventName,
    _MouseEventListener handler, {
    bool acceptOutsideGlasspane = false,
  }) {
    addEventListener(eventName, (html.Event event) {
      final html.MouseEvent mouseEvent = event;
      return handler(mouseEvent);
    }, acceptOutsideGlasspane: acceptOutsideGlasspane);
  }

  @override
  void setup() {
    _addMouseEventListener('mousedown', (html.MouseEvent event) {
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final _SanitizedDetails sanitizedDetails =
        _sanitizer.sanitizeDownEvent(
          button: event.button,
          buttons: event.buttons,
        );
      _convertEventsToPointerData(data: pointerData, event: event, details: sanitizedDetails);
      _callback(pointerData);
    });

    _addMouseEventListener('mousemove', (html.MouseEvent event) {
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final _SanitizedDetails sanitizedDetails = _sanitizer.sanitizeMoveEvent(buttons: event.buttons);
      _convertEventsToPointerData(data: pointerData, event: event, details: sanitizedDetails);
      _callback(pointerData);
    }, acceptOutsideGlasspane: true);

    _addMouseEventListener('mouseup', (html.MouseEvent event) {
      final List<ui.PointerData> pointerData = <ui.PointerData>[];
      final bool isEndOfDrag = event.buttons == 0;
      final _SanitizedDetails sanitizedDetails = isEndOfDrag ?
        _sanitizer.sanitizeUpEvent() :
        _sanitizer.sanitizeMoveEvent(buttons: event.buttons);
      _convertEventsToPointerData(data: pointerData, event: event, details: sanitizedDetails);
      _callback(pointerData);
    }, acceptOutsideGlasspane: true);

    _addWheelEventListener((html.Event event) {
      assert(event is html.WheelEvent);
      if (_debugLogPointerEvents) {
        print(event.type);
      }
      _callback(_convertWheelEventToPointerData(event));
      // Prevent default so mouse wheel event doesn't get converted to
      // a scroll event that semantic nodes would process.
      event.preventDefault();
    });
  }

  // For each event that is de-coalesced from `event` and described in
  // `detailsList`, convert it to pointer data and store in `data`.
  void _convertEventsToPointerData({
    @required List<ui.PointerData> data,
    @required html.MouseEvent event,
    @required _SanitizedDetails details,
  }) {
    assert(data != null);
    assert(event != null);
    assert(details != null);
    _pointerDataConverter.convert(
      data,
      change: details.change,
      timeStamp: _BaseAdapter._eventTimeStampToDuration(event.timeStamp),
      kind: ui.PointerDeviceKind.mouse,
      signalKind: ui.PointerSignalKind.none,
      device: _mouseDeviceId,
      physicalX: event.client.x * ui.window.devicePixelRatio,
      physicalY: event.client.y * ui.window.devicePixelRatio,
      buttons: details.buttons,
      pressure: 1.0,
      pressureMin: 0.0,
      pressureMax: 1.0,
    );
  }
}