TapGestureRecognizer.cs

using System.Drawing;
using Gondwana.Timers;
 
namespace Gondwana.Input.Touch.Gestures;

public sealed class TapGestureRecognizer : IDisposable
{
    private readonly ITouchInput _touchInput;
 
    // Per-touch tracking: key = touch ID
    private readonly Dictionary<int, TapState> _activeTaps = new();
    private readonly HashSet<int> _activeContacts = new();
    private bool _isMultiTouchSequence;
 
    internal SwipeGestureRecognizer? CompetingSwipeRecognizer { get; set; }
 
    private bool _isDisposed;

    public double MaxTapDurationSeconds { get; set; } = 0.3;

    public double MaxTapMovementPixels { get; set; } = 20;

    public event EventHandler<TappedEventArgs>? Tapped;

    public TapGestureRecognizer(ITouchInput touchInput)
    {
        _touchInput = touchInput ?? throw new ArgumentNullException(nameof(touchInput));
        _touchInput.TouchBegan += OnTouchBegan;
        _touchInput.TouchMoved += OnTouchMoved;
        _touchInput.TouchEnded += OnTouchEnded;
    }
 
    private void OnTouchBegan(object? sender, TouchEventArgs e)
    {
        _activeContacts.Add(e.Touch.Id);
 
        if (_activeContacts.Count > 1)
        {
            _isMultiTouchSequence = true;
            _activeTaps.Clear();
            return;
        }
 
        if (!_isMultiTouchSequence)
            _activeTaps[e.Touch.Id] = new TapState(e.Touch.Position, e.Tick);
    }
 
    private void OnTouchMoved(object? sender, TouchEventArgs e)
    {
        if (!_activeTaps.TryGetValue(e.Touch.Id, out var state))
            return;
 
        if (state.Cancelled)
            return;
 
        var dx = e.Touch.Position.X - state.StartPosition.X;
        var dy = e.Touch.Position.Y - state.StartPosition.Y;
        var distance = Math.Sqrt(dx * dx + dy * dy);
 
        if (distance > MaxTapMovementPixels)
            _activeTaps[e.Touch.Id] = state with { Cancelled = true };
    }
 
    private void OnTouchEnded(object? sender, TouchEventArgs e)
    {
        _activeContacts.Remove(e.Touch.Id);
 
        if (_isMultiTouchSequence)
        {
            _activeTaps.Remove(e.Touch.Id);
            if (_activeContacts.Count == 0)
                _isMultiTouchSequence = false;
            return;
        }
 
        if (!_activeTaps.TryGetValue(e.Touch.Id, out var state))
            return;
 
        _activeTaps.Remove(e.Touch.Id);
 
        // A system-cancelled contact (e.g. incoming call) must never fire Tapped.
        if (state.Cancelled || e.Touch.Phase == TouchPhase.Cancelled)
            return;
 
        var dx = e.Touch.Position.X - state.StartPosition.X;
        var dy = e.Touch.Position.Y - state.StartPosition.Y;
        var distance = Math.Sqrt(dx * dx + dy * dy);
        var elapsed = HighResTimer.GetDuration(state.StartTick, e.Tick);
 
        if (distance <= MaxTapMovementPixels &&
            elapsed <= MaxTapDurationSeconds &&
            !(CompetingSwipeRecognizer?.WouldRecognize(distance, elapsed) ?? false))
        {
            Tapped?.Invoke(this, new TappedEventArgs(e.Touch.Id, state.StartPosition));
        }
    }

    public void Dispose()
    {
        if (_isDisposed) return;
        _isDisposed = true;
 
        _touchInput.TouchBegan -= OnTouchBegan;
        _touchInput.TouchMoved -= OnTouchMoved;
        _touchInput.TouchEnded -= OnTouchEnded;
        Reset();
    }
 
    internal void Reset()
    {
        _activeTaps.Clear();
        _activeContacts.Clear();
        _isMultiTouchSequence = false;
    }
 
    private record struct TapState(Point StartPosition, long StartTick, bool Cancelled)
    {
        public TapState(Point startPosition, long startTick) : this(startPosition, startTick, false) { }
    }
}