// Copyright 2018 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:ui' show Offset;

import 'package:flutter/foundation.dart';

import 'arena.dart';
import 'constants.dart';
import 'events.dart';
import 'recognizer.dart';

enum _ForceState {
  // No pointer has touched down and the detector is ready for a pointer down to occur.
  ready,

  // A pointer has touched down, but a force press gesture has not yet been detected.
  possible,

  // A pointer is down and a force press gesture has been detected. However, if
  // the ForcePressGestureRecognizer is the only recognizer in the arena, thus
  // accepted as soon as the gesture state is possible, the gesture will not
  // yet have started.
  accepted,

  // A pointer is down and the gesture has started, ie. the pressure of the pointer
  // has just become greater than the ForcePressGestureRecognizer.startPressure.
  started,

  // A pointer is down and the pressure of the pointer has just become greater
  // than the ForcePressGestureRecognizer.peakPressure. Even after a pointer
  // crosses this threshold, onUpdate callbacks will still be sent.
  peaked,
}

/// Details object for callbacks that use [GestureForcePressStartCallback],
/// [GestureForcePressPeakCallback], [GestureForcePressEndCallback] or
/// [GestureForcePressUpdateCallback].
///
/// See also:
///
///  * [ForcePressGestureRecognizer.onStart], [ForcePressGestureRecognizer.onPeak],
///    [ForcePressGestureRecognizer.onEnd], and [ForcePressGestureRecognizer.onUpdate]
///    which use [ForcePressDetails].
///  * [ForcePressUpdateDetails], the details for [ForcePressUpdateCallback].
class ForcePressDetails {
  /// Creates details for a [GestureForcePressStartCallback],
  /// [GestureForcePressPeakCallback] or [GestureForcePressEndCallback].
  ///
  /// The [globalPosition] argument must not be null.
  ForcePressDetails({
    @required this.globalPosition,
    @required this.pressure,
  }) : assert(globalPosition != null),
       assert(pressure != null);

  /// The global position at which the function was called.
  final Offset globalPosition;

  /// The pressure of the pointer on the screen.
  final double pressure;
}

/// Signature used by a [ForcePressGestureRecognizer] for when a pointer has
/// pressed with at least [ForcePressGestureRecognizer.startPressure].
typedef GestureForcePressStartCallback = void Function(ForcePressDetails details);

/// Signature used by [ForcePressGestureRecognizer] for when a pointer that has
/// pressed with at least [ForcePressGestureRecognizer.peakPressure].
typedef GestureForcePressPeakCallback = void Function(ForcePressDetails details);

/// Signature used by [ForcePressGestureRecognizer] during the frames
/// after the triggering of a [ForcePressGestureRecognizer.onStart] callback.
typedef GestureForcePressUpdateCallback = void Function(ForcePressDetails details);

/// Signature for when the pointer that previously triggered a
/// [ForcePressGestureRecognizer.onStart] callback is no longer in contact
/// with the screen.
typedef GestureForcePressEndCallback = void Function(ForcePressDetails details);

/// Signature used by [ForcePressGestureRecognizer] for interpolating the raw
/// device pressure to a value in the range [0, 1] given the device's pressure
/// min and pressure max.
typedef GestureForceInterpolation = double Function(double pressureMin, double pressureMax, double pressure);

/// Recognizes a force press on devices that have force sensors.
///
/// Only the force from a single pointer is used to invoke events. A tap
/// recognizer will win against this recognizer on pointer up as long as the
/// pointer has not pressed with a force greater than
/// [ForcePressGestureRecognizer.startPressure]. A long press recognizer will
/// win when the press down time exceeds the threshold time as long as the
/// pointer's pressure was never greater than
/// [ForcePressGestureRecognizer.startPressure] in that duration.
///
/// As of November, 2018 iPhone devices of generation 6S and higher have
/// force touch functionality, with the exception of the iPhone XR. In addition,
/// a small handful of Android devices have this functionality as well.
///
/// Reported pressure will always be in the range [0.0, 1.0], where 1.0 is
/// maximum pressure and 0.0 is minimum pressure. If using a non-linear
/// interpolation equation, the pressure reported will correspond with the
/// custom curve. (ie. if the interpolation maps t(0.5) -> 0.1, a value of 0.1
/// will be reported at a device pressure value of 0.5).
///
class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
  /// Creates a force press gesture recognizer.
  ///
  /// The [startPressure] defaults to 0.4, and [peakPressure] defaults to 0.85
  /// where a value of 0.0 is no pressure and a value of 1.0 is maximum pressure.
  ///
  /// [startPressure], [peakPressure] and [interpolation] must not be null.
  /// [peakPressure] must be greater than [startPressure]. [interpolation] must
  /// always return a value in the range [0.0, 1.0] where
  /// pressureMin <= pressure <= pressureMax.
  ForcePressGestureRecognizer({
    this.startPressure = 0.4,
    this.peakPressure = 0.85,
    this.interpolation = _inverseLerp,
    Object debugOwner,
  }) : assert(startPressure != null),
       assert(peakPressure != null),
       assert(interpolation != null),
       assert(peakPressure > startPressure),
       super(debugOwner: debugOwner);

  /// A pointer is in contact with the screen and has just pressed with a force
  /// exceeding the [startPressure]. Consequently, if there were other gesture
  /// detectors, only the force press gesture will be detected and all others
  /// will be rejected.
  ///
  /// The position of the pointer is provided in the callback's `details`
  /// argument, which is a [ForcePressDetails] object.
  GestureForcePressStartCallback onStart;

  /// A pointer is in contact with the screen and is either moving on the plane
  /// of the screen, pressing the screen with varying forces or both
  /// simultaneously.
  ///
  /// This callback will be invoked for every pointer event after the invocation
  /// of [onStart] and/or [onPeak] and before the invocation of [onEnd], no
  /// matter what the pressure is during this time period. The position and
  /// pressure of the pointer is provided in the callback's `details` argument,
  /// which is a [ForcePressUpdateDetails] object.
  GestureForcePressUpdateCallback onUpdate;

  /// A pointer is in contact with the screen and has just pressed with a force
  /// exceeding the [peakPressure]. This is an arbitrary second level action
  /// threshold and isn't necessarily the maximum possible device pressure
  /// (which is 1.0).
  ///
  /// The position of the pointer is provided in the callback's `details`
  /// argument, which is a [ForcePressDetails] object.
  GestureForcePressPeakCallback onPeak;

  /// A pointer is no longer in contact with the screen.
  ///
  /// The position of the pointer is provided in the callback's `details`
  /// argument, which is a [ForcePressDetails] object.
  GestureForcePressEndCallback onEnd;

  /// The pressure of the press required to initiate a force press.
  ///
  /// A value of 0.0 is no pressure, and 1.0 is maximum pressure.
  final double startPressure;

  /// The pressure of the press required to peak a force press.
  ///
  /// A value of 0.0 is no pressure, and 1.0 is maximum pressure. This value
  /// must be greater than [startPressure].
  final double peakPressure;

  /// The function used to convert the raw device pressure values into a value
  /// in the range [0, 1].
  ///
  /// The function takes in the device's min, max and raw touch
  /// pressure and returns a value in the range [0.0, 1.0] denoting the
  /// interpolated touch pressure.
  ///
  /// This function must always return values in the range [0, 1] when
  /// pressureMin <= pressure <= pressureMax.
  ///
  /// By default, the the function is a simple linear interpolation, however,
  /// changing the function could be useful to accommodate variations in the way
  /// different devices respond to pressure, change how animations from pressure
  /// feedback are rendered or for other custom functionality.
  ///
  /// For example, an ease in curve can be used to determine the interpolated
  /// value:
  ///
  /// ```dart
  /// static double interpolateWithEasing(double min, double max, double t) {
  ///    final double lerp = (t - min) / (max - min);
  ///    return Curves.easeIn.transform(lerp);
  /// }
  /// ```
  final GestureForceInterpolation interpolation;

  Offset _lastPosition;
  double _lastPressure;
  _ForceState _state = _ForceState.ready;

  @override
  void addPointer(PointerEvent event) {
    startTrackingPointer(event.pointer);
    if (_state == _ForceState.ready) {
      _state = _ForceState.possible;
      _lastPosition = event.position;
    }
  }

  @override
  void handleEvent(PointerEvent event) {
    assert(_state != _ForceState.ready);
    // A static pointer with changes in pressure creates PointerMoveEvent events.
    if (event is PointerMoveEvent || event is PointerDownEvent) {
      final double pressure = interpolation(event.pressureMin, event.pressureMax, event.pressure);
      assert(pressure.isNaN ? true : (pressure <= 1.0 && pressure >= 0.0));
      _lastPosition = event.position;
      _lastPressure = pressure;

      if (_state == _ForceState.possible) {
        if (pressure > startPressure) {
          _state = _ForceState.started;
          resolve(GestureDisposition.accepted);
        } else if (event.delta.distanceSquared > kTouchSlop) {
          resolve(GestureDisposition.rejected);
        }
      }
      // In case this is the only gesture detector we still don't want to start
      // the gesture until the pressure is greater than the startPressure.
      if (pressure > startPressure && _state == _ForceState.accepted) {
        _state = _ForceState.started;
        if (onStart != null) {
          invokeCallback<void>('onStart', () => onStart(ForcePressDetails(
            pressure: pressure,
            globalPosition: _lastPosition,
          )));
        }
      }
      if (onPeak != null && pressure > peakPressure &&
         (_state == _ForceState.started)) {
        _state = _ForceState.peaked;
        if (onPeak != null) {
          invokeCallback<void>('onPeak', () => onPeak(ForcePressDetails(
            pressure: pressure,
            globalPosition: event.position,
          )));
        }
      }
      if (onUpdate != null &&
         (_state == _ForceState.started || _state == _ForceState.peaked)) {
        if (onUpdate != null) {
          invokeCallback<void>('onUpdate', () => onUpdate(ForcePressDetails(
            pressure: pressure,
            globalPosition: event.position,
          )));
        }
      }
    }
    stopTrackingIfPointerNoLongerDown(event);
  }

  @override
  void acceptGesture(int pointer) {
    if (_state == _ForceState.possible)
      _state = _ForceState.accepted;

    if (onStart != null && _state == _ForceState.started) {
      invokeCallback<void>('onStart', () => onStart(ForcePressDetails(
        pressure: _lastPressure,
        globalPosition: _lastPosition,
      )));
    }
  }

  @override
  void didStopTrackingLastPointer(int pointer) {
    final bool wasAccepted = _state == _ForceState.started || _state == _ForceState.peaked;
    if (_state == _ForceState.possible) {
      resolve(GestureDisposition.rejected);
      return;
    }
    if (wasAccepted && onEnd != null) {
      if (onEnd != null) {
        invokeCallback<void>('onEnd', () => onEnd(ForcePressDetails(
          pressure: 0.0,
          globalPosition: _lastPosition,
        )));
      }
    }
    _state = _ForceState.ready;
  }

  @override
  void rejectGesture(int pointer) {
    stopTrackingPointer(pointer);
    didStopTrackingLastPointer(pointer);
  }

  static double _inverseLerp(double min, double max, double t) {
    return (t - min) / (max - min);
  }

  @override
  String get debugDescription => 'force press';
}
