inabox/InABox.Avalonia/Dialogs/MessageDialog/PopupPositioner.cs

using Avalonia;
using Avalonia.Layout;
using DialogHostAvalonia.Positioners;
using InABox.Avalonia;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace InABox.Avalonia.Dialogs;

public class PopupPositioner : AvaloniaObject, IDialogPopupPositioner, IDialogPopupPositionerConstrainable
{
    public static readonly StyledProperty<Thickness> MarginProperty
        = Layoutable.MarginProperty.AddOwner<AlignmentDialogPopupPositioner>();

    public static readonly StyledProperty<object?> ContentProperty
        = AvaloniaProperty.Register<PopupPositioner, object?>(nameof(Content));

    public Thickness Margin
    {
        get => GetValue(MarginProperty);
        set => SetValue(MarginProperty, value);
    }
    public object? Content
    {
        get => GetValue(ContentProperty);
        set => SetValue(ContentProperty, value);
    }

    private HorizontalAlignment GetHorizontalAlignment()
    {
        return (Content as IAlignedPopup)?.HorizontalAlignment ?? HorizontalAlignment.Center;
    }
    private VerticalAlignment GetVerticalAlignment()
    {
        return (Content as IAlignedPopup)?.VerticalAlignment ?? VerticalAlignment.Center;
    }

    public Rect Update(Size anchorRectangle, Size size) {
        var margin = GetValue(MarginProperty);

        var availableSpaceRect = new Rect(anchorRectangle);
        var constrainRect = availableSpaceRect.Deflate(margin);
        var rect = new Rect(size);

        var hAlign = GetHorizontalAlignment();
        var vAlign = GetVerticalAlignment();

        if (hAlign == HorizontalAlignment.Stretch) rect = rect.WithWidth(0);
        if (vAlign == VerticalAlignment.Stretch) rect = rect.WithHeight(0);
        var aligned = rect.Align(constrainRect, hAlign, vAlign);
        return new Rect(margin.Left + aligned.Left, margin.Top + aligned.Top, aligned.Width, aligned.Height);
    }

    public Size Constrain(Size availableSize)
    {
        return availableSize.Deflate(Margin);
    }
}