HandyControl/src/Shared/HandyControl_Shared/Controls/Panel/ElementGroup.cs

using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using HandyControl.Data;
using HandyControl.Tools;

namespace HandyControl.Controls
{
    public class ElementGroup : ItemsControl
    {
        private static readonly Dictionary<Orientation, Dictionary<ChildLocation, CornerRadius>> CornerRadiusDict;

        public static readonly DependencyProperty OrientationProperty =
            StackPanel.OrientationProperty.AddOwner(typeof(ElementGroup),
                new FrameworkPropertyMetadata(ValueBoxes.HorizontalBox, FrameworkPropertyMetadataOptions.AffectsMeasure));

        public Orientation Orientation
        {
            get => (Orientation) GetValue(OrientationProperty);
            set => SetValue(OrientationProperty, ValueBoxes.OrientationBox(value));
        }

        public static readonly DependencyProperty LayoutProperty = DependencyProperty.Register(
            "Layout", typeof(LinearLayout), typeof(ElementGroup),
            new FrameworkPropertyMetadata(LinearLayout.Uniform, FrameworkPropertyMetadataOptions.AffectsMeasure));

        public LinearLayout Layout
        {
            get => (LinearLayout) GetValue(LayoutProperty);
            set => SetValue(LayoutProperty, value);
        }

        static ElementGroup()
        {
            var defaultCornerRadius = ResourceHelper.GetResourceInternal<CornerRadius>("DefaultCornerRadius");

            CornerRadiusDict = new Dictionary<Orientation, Dictionary<ChildLocation, CornerRadius>>
            {
                [Orientation.Horizontal] = new()
                {
                    [ChildLocation.Single] = defaultCornerRadius,
                    [ChildLocation.First] = new CornerRadius(defaultCornerRadius.TopLeft, 0, 0, defaultCornerRadius.BottomLeft),
                    [ChildLocation.Middle] = new CornerRadius(),
                    [ChildLocation.Last] = new CornerRadius(0, defaultCornerRadius.TopRight, defaultCornerRadius.BottomRight, 0)
                },
                [Orientation.Vertical] = new()
                {
                    [ChildLocation.Single] = defaultCornerRadius,
                    [ChildLocation.First] = new CornerRadius(defaultCornerRadius.TopLeft, defaultCornerRadius.TopRight, 0, 0),
                    [ChildLocation.Middle] = new CornerRadius(),
                    [ChildLocation.Last] = new CornerRadius(0, 0, defaultCornerRadius.BottomRight, defaultCornerRadius.BottomLeft)
                }
            };
        }

        protected override void OnVisualChildrenChanged(DependencyObject visualAdded, DependencyObject visualRemoved)
        {
            base.OnVisualChildrenChanged(visualAdded, visualRemoved);

            if (visualAdded is UIElement elementAdded)
            {
                elementAdded.GotFocus += ElementAdded_GotFocus;
                elementAdded.LostFocus += ElementAdded_LostFocus;
                elementAdded.IsVisibleChanged += ElementAdded_IsVisibleChanged;
            }

            if (visualRemoved is UIElement elementRemoved)
            {
                elementRemoved.GotFocus -= ElementAdded_GotFocus;
                elementRemoved.LostFocus -= ElementAdded_LostFocus;
                elementRemoved.IsVisibleChanged -= ElementAdded_IsVisibleChanged;
            }
        }

        protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e) => UpdateChildrenCornerRadius();

        protected override void OnRender(DrawingContext drawingContext) => UpdateChildrenCornerRadius();

        private void UpdateChildrenCornerRadius()
        {
            var visibleChildren = GetVisibleChildrenCount();
            var count = visibleChildren.Count;
            if (count == 0)
            {
                return;
            }

            var orientation = Orientation;

            if (count == 1)
            {
                UpdateChildCornerRadius(visibleChildren[0], CornerRadiusDict[orientation][ChildLocation.Single]);
            }
            else
            {
                UpdateChildCornerRadius(visibleChildren[0], CornerRadiusDict[orientation][ChildLocation.First]);

                var childMargin = orientation == Orientation.Horizontal
                    ? new Thickness(-1, 0, 0, 0)
                    : new Thickness(0, -1, 0, 0);

                for (var childIndex = 1; childIndex < count; childIndex++)
                {
                    var child = visibleChildren[childIndex];
                    child.SetCurrentValue(MarginProperty, childMargin);
                    UpdateChildCornerRadius(child, CornerRadiusDict[orientation][ChildLocation.Middle]);
                }

                var lastChild = visibleChildren[count - 1];
                lastChild.SetCurrentValue(MarginProperty, childMargin);
                UpdateChildCornerRadius(lastChild, CornerRadiusDict[orientation][ChildLocation.Last]);
            }
        }

        private List<UIElement> GetVisibleChildrenCount()
        {
            return Items.OfType<UIElement>().Where(element => element.Visibility == Visibility.Visible).ToList();
        }

        private static void UpdateChildCornerRadius(DependencyObject child, CornerRadius cornerRadius)
        {
            if (child is Border border)
            {
                border.SetCurrentValue(Border.CornerRadiusProperty, cornerRadius);
            }
            else
            {
                BorderElement.SetCornerRadius(child, cornerRadius);
            }
        }

        private void ElementAdded_LostFocus(object sender, RoutedEventArgs e) => ResetElementZIndex(e.OriginalSource);

        private void ElementAdded_GotFocus(object sender, RoutedEventArgs e) => MaximizeElementZIndex(e.OriginalSource);

        private static void ResetElementZIndex(object element) => Panel.SetZIndex((UIElement) element, 0);

        private static void MaximizeElementZIndex(object element) => Panel.SetZIndex((UIElement) element, int.MaxValue);

        private void ElementAdded_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e) => UpdateChildrenCornerRadius();

        private enum ChildLocation
        {
            Single,
            First,
            Middle,
            Last
        }
    }
}