Avalonia/src/Avalonia.Controls/Primitives/PopupRoot.cs

using System;
using Avalonia.Automation.Peers;
using Avalonia.Controls.Primitives.PopupPositioning;
using Avalonia.Interactivity;
using Avalonia.Media;
using Avalonia.Platform;
using Avalonia.Styling;
using Avalonia.VisualTree;

namespace Avalonia.Controls.Primitives
{
    /// <summary>
    /// The root window of a <see cref="Popup"/>.
    /// </summary>
    public sealed class PopupRoot : WindowBase, IInteractive, IHostedVisualTreeRoot, IDisposable, IStyleHost, IPopupHost
    {
        /// <summary>
        /// Defines the <see cref="Transform"/> property.
        /// </summary>
        public static readonly StyledProperty<Transform?> TransformProperty =
            AvaloniaProperty.Register<PopupRoot, Transform?>(nameof(Transform));

        private PopupPositionerParameters _positionerParameters;        

        /// <summary>
        /// Initializes static members of the <see cref="PopupRoot"/> class.
        /// </summary>
        static PopupRoot()
        {
            BackgroundProperty.OverrideDefaultValue(typeof(PopupRoot), Brushes.White);            
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="PopupRoot"/> class.
        /// </summary>
        public PopupRoot(TopLevel parent, IPopupImpl impl)
            : this(parent, impl,null)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="PopupRoot"/> class.
        /// </summary>
        /// <param name="parent">The popup parent.</param>
        /// <param name="impl">The popup implementation.</param>
        /// <param name="dependencyResolver">
        /// The dependency resolver to use. If null the default dependency resolver will be used.
        /// </param>
        public PopupRoot(TopLevel parent, IPopupImpl impl, IAvaloniaDependencyResolver? dependencyResolver)
            : base(impl, dependencyResolver)
        {
            ParentTopLevel = parent;
        }

        /// <summary>
        /// Gets the platform-specific window implementation.
        /// </summary>
        public new IPopupImpl? PlatformImpl => (IPopupImpl?)base.PlatformImpl;               

        /// <summary>
        /// Gets or sets a transform that will be applied to the popup.
        /// </summary>
        public Transform? Transform
        {
            get => GetValue(TransformProperty);
            set => SetValue(TransformProperty, value);
        }

        /// <summary>
        /// Gets the parent control in the event route.
        /// </summary>
        /// <remarks>
        /// Popup events are passed to their parent window. This facilitates this.
        /// </remarks>
        IInteractive? IInteractive.InteractiveParent => Parent;

        /// <summary>
        /// Gets the control that is hosting the popup root.
        /// </summary>
        IVisual? IHostedVisualTreeRoot.Host => Parent;

        /// <summary>
        /// Gets the styling parent of the popup root.
        /// </summary>
        IStyleHost? IStyleHost.StylingParent => Parent;

        public TopLevel ParentTopLevel { get; }

        /// <inheritdoc/>
        public void Dispose()
        {
            PlatformImpl?.Dispose();
            HandleClosed();
        }

        private void UpdatePosition()
        {
            PlatformImpl?.PopupPositioner.Update(_positionerParameters);
        }

        public void ConfigurePosition(IVisual target, PlacementMode placement, Point offset,
            PopupAnchor anchor = PopupAnchor.None,
            PopupGravity gravity = PopupGravity.None,
            PopupPositionerConstraintAdjustment constraintAdjustment = PopupPositionerConstraintAdjustment.All,
            Rect? rect = null)
        {
            _positionerParameters.ConfigurePosition(ParentTopLevel, target,
                placement, offset, anchor, gravity, constraintAdjustment, rect, FlowDirection);

            if (_positionerParameters.Size != default)
                UpdatePosition();
        }

        public void SetChild(IControl? control) => Content = control;

        IVisual IPopupHost.HostedVisualTreeRoot => this;
        
        protected override Size MeasureOverride(Size availableSize)
        {
            var maxAutoSize = PlatformImpl?.MaxAutoSizeHint ?? Size.Infinity;
            var constraint = availableSize;

            if (double.IsInfinity(constraint.Width))
            {
                constraint = constraint.WithWidth(maxAutoSize.Width);
            }

            if (double.IsInfinity(constraint.Height))
            {
                constraint = constraint.WithHeight(maxAutoSize.Height);
            }

            var measured = base.MeasureOverride(constraint);
            var width = measured.Width;
            var height = measured.Height;
            var widthCache = Width;
            var heightCache = Height;

            if (!double.IsNaN(widthCache))
            {
                width = widthCache;
            }

            width = Math.Min(width, MaxWidth);
            width = Math.Max(width, MinWidth);

            if (!double.IsNaN(heightCache))
            {
                height = heightCache;
            }

            height = Math.Min(height, MaxHeight);
            height = Math.Max(height, MinHeight);

            return new Size(width, height);
        }

        protected override sealed Size ArrangeSetBounds(Size size)
        {
            _positionerParameters.Size = size;
            UpdatePosition();
            return ClientSize;
        }

        protected override AutomationPeer OnCreateAutomationPeer()
        {
            return new PopupRootAutomationPeer(this);
        }
    }
}