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protected internal override async void OnMapMouseDown(MouseButtonEventArgs e)
{
    base.OnMapMouseDown(e);

    var target = Target;
    if (target == null)
        return;
    if (e.ChangedButton != MouseButton.Left)
        return;

    if (inMouseDown)
        return;
    inMouseDown = true;
    try
    {
        using var uScope = Map.Document?.UndoManager.BeginScope();
        var token = InputCancellationToken;

        var p = e.GetPosition(Layer);
        mouseDownLoc = target.Walls.Location(p.X, p.Y);

        var isMouseStillDown = true;
        await foreach (var (click, isIn) in GetClicksAsync(e, token))
        {
            isMouseStillDown = isIn;
            Trace.WriteLine($"Got One: ({click}, {isIn})");
        }
        if (token.IsCancellationRequested)
            return;

        if (isMouseStillDown)
        {
            await foreach (var move in MapMouseDragAsync(e, token))
            {

            }
        }
        else
        {
            var anchor = new AnchorPoint(0.5, 0);
            MapUtils.SetAutobounds(textEditor, () => p + anchor.OffsetFor(textEditor.TextBox, textEditor));
            await MapUtils.EditAsync(Map, textEditor, token);
        }
    }
    catch (TaskCanceledException) { }
    finally
    {
        inMouseDown = false;
    }
    Trace.WriteLine("OnMapMouseDown over");
}
bool inMouseDown;
DD.TileLocation mouseDownLoc;

Subject<EventArgs> mMapLeave = new();
Subject<MouseButtonEventArgs> mMapMouseUp = new();
Subject<MouseEventArgs> mMapMouseMove = new();

public IObservable<EventArgs> MapLeave => mMapLeave;
public IObservable<MouseButtonEventArgs> MapMouseUp => mMapMouseUp;
public IObservable<MouseEventArgs> MapMouseMove => mMapMouseMove;

protected internal virtual void OnMapLeave()
{
    mMapLeave.OnNext(EventArgs.Empty);
    mInputCancellationToken?.Cancel();
    mInputCancellationToken = null;
}
protected internal virtual void OnMapMouseUp(MouseButtonEventArgs e) => mMapMouseUp.OnNext(e);
protected internal virtual void OnMapMouseMove(MouseEventArgs e) => mMapMouseMove.OnNext(e);

public async IAsyncEnumerable<MouseEventArgs> MapMouseDragAsync(MouseButtonEventArgs e, [EnumeratorCancellation] CancellationToken token)
{
    if (e.ChangedButton != MouseButton.Left || Map.IsMouseCaptured)
        yield break;

    var captured = Map.CaptureMouse();
    try
    {
        var events = this.MapMouseMove
            .TakeUntil(this.MapMouseUp.Where(z => z.ChangedButton == MouseButton.Left))
            .TakeUntil(this.MapLeave)
            .ToAsyncEnumerable(token);

        await foreach (var ev in events)
            yield return ev;
    }
    finally
    {
        if (captured)
            Map.ReleaseMouseCapture();
    }
}