multitap.dart

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:ui' show Offset;

import 'arena.dart';
import 'binding.dart';
import 'constants.dart';
import 'events.dart';
import 'pointer_router.dart';
import 'recognizer.dart';
import 'tap.dart';

/// Signature for callback when the user has tapped the screen at the same
/// location twice in quick succession.
typedef GestureDoubleTapCallback = void Function();

/// Signature used by [MultiTapGestureRecognizer] for when a pointer that might
/// cause a tap has contacted the screen at a particular location.
typedef GestureMultiTapDownCallback = void Function(int pointer, TapDownDetails details);

/// Signature used by [MultiTapGestureRecognizer] for when a pointer that will
/// trigger a tap has stopped contacting the screen at a particular location.
typedef GestureMultiTapUpCallback = void Function(int pointer, TapUpDetails details);

/// Signature used by [MultiTapGestureRecognizer] for when a tap has occurred.
typedef GestureMultiTapCallback = void Function(int pointer);

/// Signature for when the pointer that previously triggered a
/// [GestureMultiTapDownCallback] will not end up causing a tap.
typedef GestureMultiTapCancelCallback = void Function(int pointer);

/// TapTracker helps track individual tap sequences as part of a
/// larger gesture.
class _TapTracker {
  _TapTracker({ PointerDownEvent event, this.entry })
    : pointer = event.pointer,
      _initialPosition = event.position;

  final int pointer;
  final GestureArenaEntry entry;
  final Offset _initialPosition;

  bool _isTrackingPointer = false;

  void startTrackingPointer(PointerRoute route) {
    if (!_isTrackingPointer) {
      _isTrackingPointer = true;
      GestureBinding.instance.pointerRouter.addRoute(pointer, route);
    }
  }

  void stopTrackingPointer(PointerRoute route) {
    if (_isTrackingPointer) {
      _isTrackingPointer = false;
      GestureBinding.instance.pointerRouter.removeRoute(pointer, route);
    }
  }

  bool isWithinTolerance(PointerEvent event, double tolerance) {
    final Offset offset = event.position - _initialPosition;
    return offset.distance <= tolerance;
  }
}

/// Recognizes when the user has tapped the screen at the same location twice in
/// quick succession.
class DoubleTapGestureRecognizer extends GestureRecognizer {
  /// Create a gesture recognizer for double taps.
  DoubleTapGestureRecognizer({ Object debugOwner }) : super(debugOwner: debugOwner);

  // Implementation notes:
  // The double tap recognizer can be in one of four states. There's no
  // explicit enum for the states, because they are already captured by
  // the state of existing fields. Specifically:
  // Waiting on first tap: In this state, the _trackers list is empty, and
  // _firstTap is null.
  // First tap in progress: In this state, the _trackers list contains all
  // the states for taps that have begun but not completed. This list can
  // have more than one entry if two pointers begin to tap.
  // Waiting on second tap: In this state, one of the in-progress taps has
  // completed successfully. The _trackers list is again empty, and
  // _firstTap records the successful tap.
  // Second tap in progress: Much like the "first tap in progress" state, but
  // _firstTap is non-null. If a tap completes successfully while in this
  // state, the callback is called and the state is reset.
  // There are various other scenarios that cause the state to reset:
  // - All in-progress taps are rejected (by time, distance, pointercancel, etc)
  // - The long timer between taps expires
  // - The gesture arena decides we have been rejected wholesale

  /// Called when the user has tapped the screen at the same location twice in
  /// quick succession.
  GestureDoubleTapCallback onDoubleTap;

  Timer _doubleTapTimer;
  _TapTracker _firstTap;
  final Map<int, _TapTracker> _trackers = <int, _TapTracker>{};

  @override
  void addPointer(PointerEvent event) {
    // Ignore out-of-bounds second taps.
    if (_firstTap != null &&
        !_firstTap.isWithinTolerance(event, kDoubleTapSlop))
      return;
    _stopDoubleTapTimer();
    final _TapTracker tracker = _TapTracker(
      event: event,
      entry: GestureBinding.instance.gestureArena.add(event.pointer, this)
    );
    _trackers[event.pointer] = tracker;
    tracker.startTrackingPointer(_handleEvent);
  }

  void _handleEvent(PointerEvent event) {
    final _TapTracker tracker = _trackers[event.pointer];
    assert(tracker != null);
    if (event is PointerUpEvent) {
      if (_firstTap == null)
        _registerFirstTap(tracker);
      else
        _registerSecondTap(tracker);
    } else if (event is PointerMoveEvent) {
      if (!tracker.isWithinTolerance(event, kDoubleTapTouchSlop))
        _reject(tracker);
    } else if (event is PointerCancelEvent) {
      _reject(tracker);
    }
  }

  @override
  void acceptGesture(int pointer) { }

  @override
  void rejectGesture(int pointer) {
    _TapTracker tracker = _trackers[pointer];
    // If tracker isn't in the list, check if this is the first tap tracker
    if (tracker == null &&
        _firstTap != null &&
        _firstTap.pointer == pointer)
      tracker = _firstTap;
    // If tracker is still null, we rejected ourselves already
    if (tracker != null)
      _reject(tracker);
  }

  void _reject(_TapTracker tracker) {
    _trackers.remove(tracker.pointer);
    tracker.entry.resolve(GestureDisposition.rejected);
    _freezeTracker(tracker);
    // If the first tap is in progress, and we've run out of taps to track,
    // reset won't have any work to do. But if we're in the second tap, we need
    // to clear intermediate state.
    if (_firstTap != null &&
        (_trackers.isEmpty || tracker == _firstTap))
      _reset();
  }

  @override
  void dispose() {
    _reset();
    super.dispose();
  }

  void _reset() {
    _stopDoubleTapTimer();
    if (_firstTap != null) {
      // Note, order is important below in order for the resolve -> reject logic
      // to work properly.
      final _TapTracker tracker = _firstTap;
      _firstTap = null;
      _reject(tracker);
      GestureBinding.instance.gestureArena.release(tracker.pointer);
    }
    _clearTrackers();
  }

  void _registerFirstTap(_TapTracker tracker) {
    _startDoubleTapTimer();
    GestureBinding.instance.gestureArena.hold(tracker.pointer);
    // Note, order is important below in order for the clear -> reject logic to
    // work properly.
    _freezeTracker(tracker);
    _trackers.remove(tracker.pointer);
    _clearTrackers();
    _firstTap = tracker;
  }

  void _registerSecondTap(_TapTracker tracker) {
    _firstTap.entry.resolve(GestureDisposition.accepted);
    tracker.entry.resolve(GestureDisposition.accepted);
    _freezeTracker(tracker);
    _trackers.remove(tracker.pointer);
    if (onDoubleTap != null)
      invokeCallback<void>('onDoubleTap', onDoubleTap);
    _reset();
  }

  void _clearTrackers() {
    _trackers.values.toList().forEach(_reject);
    assert(_trackers.isEmpty);
  }

  void _freezeTracker(_TapTracker tracker) {
    tracker.stopTrackingPointer(_handleEvent);
  }

  void _startDoubleTapTimer() {
    _doubleTapTimer ??= Timer(kDoubleTapTimeout, _reset);
  }

  void _stopDoubleTapTimer() {
    if (_doubleTapTimer != null) {
      _doubleTapTimer.cancel();
      _doubleTapTimer = null;
    }
  }

  @override
  String get debugDescription => 'double tap';
}

/// TapGesture represents a full gesture resulting from a single tap sequence,
/// as part of a [MultiTapGestureRecognizer]. Tap gestures are passive, meaning
/// that they will not preempt any other arena member in play.
class _TapGesture extends _TapTracker {

  _TapGesture({
    this.gestureRecognizer,
    PointerEvent event,
    Duration longTapDelay
  }) : _lastPosition = event.position,
       super(
    event: event,
    entry: GestureBinding.instance.gestureArena.add(event.pointer, gestureRecognizer)
  ) {
    startTrackingPointer(handleEvent);
    if (longTapDelay > Duration.zero) {
      _timer = Timer(longTapDelay, () {
        _timer = null;
        gestureRecognizer._dispatchLongTap(event.pointer, _lastPosition);
      });
    }
  }

  final MultiTapGestureRecognizer gestureRecognizer;

  bool _wonArena = false;
  Timer _timer;

  Offset _lastPosition;
  Offset _finalPosition;

  void handleEvent(PointerEvent event) {
    assert(event.pointer == pointer);
    if (event is PointerMoveEvent) {
      if (!isWithinTolerance(event, kTouchSlop))
        cancel();
      else
        _lastPosition = event.position;
    } else if (event is PointerCancelEvent) {
      cancel();
    } else if (event is PointerUpEvent) {
      stopTrackingPointer(handleEvent);
      _finalPosition = event.position;
      _check();
    }
  }

  @override
  void stopTrackingPointer(PointerRoute route) {
    _timer?.cancel();
    _timer = null;
    super.stopTrackingPointer(route);
  }

  void accept() {
    _wonArena = true;
    _check();
  }

  void reject() {
    stopTrackingPointer(handleEvent);
    gestureRecognizer._dispatchCancel(pointer);
  }

  void cancel() {
    // If we won the arena already, then entry is resolved, so resolving
    // again is a no-op. But we still need to clean up our own state.
    if (_wonArena)
      reject();
    else
      entry.resolve(GestureDisposition.rejected); // eventually calls reject()
  }

  void _check() {
    if (_wonArena && _finalPosition != null)
      gestureRecognizer._dispatchTap(pointer, _finalPosition);
  }
}

/// Recognizes taps on a per-pointer basis.
///
/// [MultiTapGestureRecognizer] considers each sequence of pointer events that
/// could constitute a tap independently of other pointers: For example, down-1,
/// down-2, up-1, up-2 produces two taps, on up-1 and up-2.
///
/// See also:
///
///  * [TapGestureRecognizer]
class MultiTapGestureRecognizer extends GestureRecognizer {
  /// Creates a multi-tap gesture recognizer.
  ///
  /// The [longTapDelay] defaults to [Duration.zero], which means
  /// [onLongTapDown] is called immediately after [onTapDown].
  MultiTapGestureRecognizer({
    this.longTapDelay = Duration.zero,
    Object debugOwner,
  }) : super(debugOwner: debugOwner);

  /// A pointer that might cause a tap has contacted the screen at a particular
  /// location.
  GestureMultiTapDownCallback onTapDown;

  /// A pointer that will trigger a tap has stopped contacting the screen at a
  /// particular location.
  GestureMultiTapUpCallback onTapUp;

  /// A tap has occurred.
  GestureMultiTapCallback onTap;

  /// The pointer that previously triggered [onTapDown] will not end up causing
  /// a tap.
  GestureMultiTapCancelCallback onTapCancel;

  /// The amount of time between [onTapDown] and [onLongTapDown].
  Duration longTapDelay;

  /// A pointer that might cause a tap is still in contact with the screen at a
  /// particular location after [longTapDelay].
  GestureMultiTapDownCallback onLongTapDown;

  final Map<int, _TapGesture> _gestureMap = <int, _TapGesture>{};

  @override
  void addPointer(PointerEvent event) {
    assert(!_gestureMap.containsKey(event.pointer));
    _gestureMap[event.pointer] = _TapGesture(
      gestureRecognizer: this,
      event: event,
      longTapDelay: longTapDelay
    );
    if (onTapDown != null)
      invokeCallback<void>('onTapDown', () => onTapDown(event.pointer, TapDownDetails(globalPosition: event.position)));
  }

  @override
  void acceptGesture(int pointer) {
    assert(_gestureMap.containsKey(pointer));
    _gestureMap[pointer].accept();
  }

  @override
  void rejectGesture(int pointer) {
    assert(_gestureMap.containsKey(pointer));
    _gestureMap[pointer].reject();
    assert(!_gestureMap.containsKey(pointer));
  }

  void _dispatchCancel(int pointer) {
    assert(_gestureMap.containsKey(pointer));
    _gestureMap.remove(pointer);
    if (onTapCancel != null)
      invokeCallback<void>('onTapCancel', () => onTapCancel(pointer));
  }

  void _dispatchTap(int pointer, Offset globalPosition) {
    assert(_gestureMap.containsKey(pointer));
    _gestureMap.remove(pointer);
    if (onTapUp != null)
      invokeCallback<void>('onTapUp', () => onTapUp(pointer, TapUpDetails(globalPosition: globalPosition)));
    if (onTap != null)
      invokeCallback<void>('onTap', () => onTap(pointer));
  }

  void _dispatchLongTap(int pointer, Offset lastPosition) {
    assert(_gestureMap.containsKey(pointer));
    if (onLongTapDown != null)
      invokeCallback<void>('onLongTapDown', () => onLongTapDown(pointer, TapDownDetails(globalPosition: lastPosition)));
  }

  @override
  void dispose() {
    final List<_TapGesture> localGestures = List<_TapGesture>.from(_gestureMap.values);
    for (_TapGesture gesture in localGestures)
      gesture.cancel();
    // Rejection of each gesture should cause it to be removed from our map
    assert(_gestureMap.isEmpty);
    super.dispose();
  }

  @override
  String get debugDescription => 'multitap';
}