Avalonia/tests/Avalonia.Controls.UnitTests/PullToRefresh/ScrollablePullGestureRecognizerTests.cs

using System.Collections.Generic;
using Avalonia.Controls.Primitives;
using Avalonia.Controls.PullToRefresh;
using Avalonia.Input;
using Avalonia.UnitTests;
using Xunit;

namespace Avalonia.Controls.UnitTests.PullToRefresh;

public class ScrollablePullGestureRecognizerTests : ScopedTestBase
{
    // Repro for the "PointerCaptureLost doesn't clean up state" bug.
    //
    // PointerReleased clears _pullInProgress, _tracking, _initialPosition.
    // PointerCaptureLost only raises EndPull (so the PullGestureEnded event fires)
    // but leaves _pullInProgress == true and _tracking pointing at the lost pointer.
    // The next gesture re-enters PointerMoved with (_pullInProgress=true, pulling=true)
    // and goes straight to HandlePull, skipping BeginPull. This reuses the OLD _gestureId
    // for the next PullGestureEvent - the same id that was just used in the
    // PullGestureEndedEvent for the previous gesture.
    [Fact]
    public void Gesture_After_PointerCaptureLost_Uses_A_New_Id()
    {
        var scrollable = new TestScrollable();
        var recognizer = new ScrollablePullGestureRecognizer(PullDirection.TopToBottom, isMouseEnabled: true);
        scrollable.GestureRecognizers.Add(recognizer);

        var root = new TestRoot(scrollable);

        var pullIds = new List<int>();
        var endedIds = new List<int>();
        root.AddHandler(InputElement.PullGestureEvent, (_, e) => pullIds.Add(e.Id));
        root.AddHandler(InputElement.PullGestureEndedEvent, (_, e) => endedIds.Add(e.Id));

        var touch = new TouchTestHelper();

        // First gesture: start pulling downwards so the recognizer begins a pull and captures the pointer.
        touch.Down(scrollable, new Point(10, 20));
        touch.Move(scrollable, new Point(10, 70));

        Assert.Single(pullIds);
        var firstGestureId = pullIds[0];

        // Capture is lost (e.g. another control steals it, or the visual is detached mid-gesture)
        touch.Cancel();

        Assert.Equal([firstGestureId], endedIds);

        // Second gesture must begin cleanly (BeginPull, not HandlePull) and therefore get a fresh id.
        touch.Down(scrollable, new Point(10, 20));
        touch.Move(scrollable, new Point(10, 70));

        Assert.Equal(2, pullIds.Count);
        Assert.NotEqual(firstGestureId, pullIds[1]);
    }

    private sealed class TestScrollable : Decorator, IScrollable
    {
        public Size Extent => new(100, 1000);
        public Vector Offset { get; set; }
        public Size Viewport => new(100, 100);
        public bool CanHorizontallyScroll { get => false; }
        public bool CanVerticallyScroll { get => true; }
    }
}