using System.Windows.Markup;

namespace Melskin.Layout;

/// <summary>
/// StackPanel 类继承自 Panel，用于在用户界面中以垂直或水平方式排列子元素。它支持设置子元素之间的间距、方向以及单个子项的填充方式。
/// </summary>
[ContentProperty(nameof(Children))]
public class StackPanel : Panel
{
    /// <summary>
    /// 设置某子项附加属性，控制其是否填充到当前StackPanel所在的面板（控制单个子项的在面板填充方式）
    /// </summary>
    public static readonly DependencyProperty FillProperty = DependencyProperty.RegisterAttached(
        "Fill",
        typeof(FillType),
        typeof(StackPanel),
        new FrameworkPropertyMetadata(
            FillType.Auto,
            FrameworkPropertyMetadataOptions.AffectsArrange |
                FrameworkPropertyMetadataOptions.AffectsMeasure |
                FrameworkPropertyMetadataOptions.AffectsParentArrange |
                FrameworkPropertyMetadataOptions.AffectsParentMeasure));

    /// <summary>
    /// 定义 StackPanel 的排列方向，可以设置为水平或垂直。此属性影响子元素的布局方式。
    /// </summary>
    public static readonly DependencyProperty OrientationProperty = DependencyProperty.Register(
        nameof(Orientation),
        typeof(Orientation),
        typeof(StackPanel),
        new FrameworkPropertyMetadata(
            Orientation.Vertical,
            FrameworkPropertyMetadataOptions.AffectsArrange | FrameworkPropertyMetadataOptions.AffectsMeasure));

    /// <summary>
    /// 定义子元素之间的间距。此属性允许用户指定StackPanel中相邻子元素间的距离。
    /// </summary>
    public static readonly DependencyProperty SpacingProperty = DependencyProperty.Register(
        nameof(Spacing),
        typeof(double),
        typeof(StackPanel),
        new FrameworkPropertyMetadata(
            0.0,
            FrameworkPropertyMetadataOptions.AffectsArrange | FrameworkPropertyMetadataOptions.AffectsMeasure));

    static double CalculateTotalMarginToAdd(UIElementCollection children, double marginBetweenChildren)
    {
        //可见的子项数量
        var visibleChildrenCount = children
            .OfType<UIElement>()
            .Count(x => x.Visibility != Visibility.Collapsed && GetFill(x) != FillType.Ignored);
        var marginMultiplier = Math.Max(visibleChildrenCount - 1, 0);
        var totalMarginToAdd = marginBetweenChildren * marginMultiplier;
        return totalMarginToAdd;
    }

    /// <inheritdoc />
    protected override Size ArrangeOverride(Size arrangeSize)
    {
        var children = InternalChildren;
        var totalChildrenCount = children.Count;

        double accumulatedLeft = 0;
        double accumulatedTop = 0;

        var isHorizontal = Orientation == Orientation.Horizontal;
        var spacing = Spacing;

        var totalMarginToAdd = CalculateTotalMarginToAdd(children, spacing);

        var allAutoSizedSum = 0.0;
        var countOfFillTypes = 0;
        foreach (var child in children.OfType<UIElement>())
        {
            var fillType = GetFill(child);
            if (fillType != FillType.Auto)
            {
                if (child.Visibility != Visibility.Collapsed && fillType != FillType.Ignored)
                    countOfFillTypes += 1;
            }
            else
            {
                var desiredSize = isHorizontal ? child.DesiredSize.Width : child.DesiredSize.Height;
                allAutoSizedSum += desiredSize;
            }
        }

        var remainingForFillTypes = isHorizontal
            ? Math.Max(0, arrangeSize.Width - allAutoSizedSum - totalMarginToAdd)
            : Math.Max(0, arrangeSize.Height - allAutoSizedSum - totalMarginToAdd);
        var fillTypeSize = remainingForFillTypes / countOfFillTypes;

        for (var i = 0; i < totalChildrenCount; ++i)
        {
            var child = children[i];
            if (child == null)
            {
                continue;
            }
            var childDesiredSize = child.DesiredSize;
            var fillType = GetFill(child);
            var isCollapsed = child.Visibility == Visibility.Collapsed || fillType == FillType.Ignored;
            var isLastChild = i == totalChildrenCount - 1;
            var marginToAdd = isLastChild || isCollapsed ? 0 : spacing;

            var rcChild = new Rect(
                accumulatedLeft,
                accumulatedTop,
                Math.Max(0.0, arrangeSize.Width - accumulatedLeft),
                Math.Max(0.0, arrangeSize.Height - accumulatedTop));

            if (isHorizontal)
            {
                rcChild.Width = fillType == FillType.Auto || isCollapsed ? childDesiredSize.Width : fillTypeSize;
                rcChild.Height = arrangeSize.Height;
                accumulatedLeft += rcChild.Width + marginToAdd;
            }
            else
            {
                rcChild.Width = arrangeSize.Width;
                rcChild.Height = fillType == FillType.Auto || isCollapsed ? childDesiredSize.Height : fillTypeSize;
                accumulatedTop += rcChild.Height + marginToAdd;
            }

            child.Arrange(rcChild);
        }

        return arrangeSize;
    }

    /// <inheritdoc />
    protected override Size MeasureOverride(Size constraint)
    {
        var children = InternalChildren;

        double parentWidth = 0;
        double parentHeight = 0;
        double accumulatedWidth = 0;
        double accumulatedHeight = 0;

        var isHorizontal = Orientation == Orientation.Horizontal;
        var totalMarginToAdd = CalculateTotalMarginToAdd(children, Spacing);

        for (var i = 0; i < children.Count; i++)
        {
            var child = children[i];

            if (child == null)
            {
                continue;
            }

            // 先处理Auto的情况，再计算Fill的剩余空间
            if (GetFill(child) != FillType.Auto)
            {
                continue;
            }

            // 子项约束为剩余大小; 即总大小减去前一个子项目消耗的大小。
            var childConstraint = new Size(
                Math.Max(0.0, constraint.Width - accumulatedWidth),
                Math.Max(0.0, constraint.Height - accumulatedHeight));

            // 计算子项
            child.Measure(childConstraint);
            var childDesiredSize = child.DesiredSize;

            if (isHorizontal)
            {
                accumulatedWidth += childDesiredSize.Width;
                parentHeight = Math.Max(parentHeight, accumulatedHeight + childDesiredSize.Height);
            }
            else
            {
                parentWidth = Math.Max(parentWidth, accumulatedWidth + childDesiredSize.Width);
                accumulatedHeight += childDesiredSize.Height;
            }
        }

        // 在计算剩余空间之前，将所有边距添加到累积大小中，以便填充元素。
        if (isHorizontal)
        {
            accumulatedWidth += totalMarginToAdd;
        }
        else
        {
            accumulatedHeight += totalMarginToAdd;
        }
        //Fill类型的总数量
        var totalCountOfFillTypes = children
            .OfType<UIElement>()
            .Count(x => GetFill(x) == FillType.Fill && x.Visibility != Visibility.Collapsed);
        //可用的剩余空间
        var availableSpaceRemaining = isHorizontal
            ? Math.Max(0, constraint.Width - accumulatedWidth)
            : Math.Max(0, constraint.Height - accumulatedHeight);

        var eachFillTypeSize = totalCountOfFillTypes > 0 ? availableSpaceRemaining / totalCountOfFillTypes : 0;

        for (var i = 0; i < children.Count; i++)
        {
            var child = children[i];

            if (child == null)
            {
                continue;
            }

            // 处理所有的填充，给它们一部分剩余空间
            if (GetFill(child) != FillType.Fill)
            {
                continue;
            }

            // 子项限制是剩余大小；即总大小减去前一个子项限制所消耗的大小。
            var childConstraint = isHorizontal
                ? new Size(eachFillTypeSize, Math.Max(0.0, constraint.Height - accumulatedHeight))
                : new Size(Math.Max(0.0, constraint.Width - accumulatedWidth), eachFillTypeSize);

            // 测量子项.
            child.Measure(childConstraint);
            var childDesiredSize = child.DesiredSize;

            if (isHorizontal)
            {
                accumulatedWidth += childDesiredSize.Width;
                parentHeight = Math.Max(parentHeight, accumulatedHeight + childDesiredSize.Height);
            }
            else
            {
                parentWidth = Math.Max(parentWidth, accumulatedWidth + childDesiredSize.Width);
                accumulatedHeight += childDesiredSize.Height;
            }
        }

        // 确保最终累积的大小反映在 parentSize 中。
        parentWidth = Math.Max(parentWidth, accumulatedWidth);
        parentHeight = Math.Max(parentHeight, accumulatedHeight);
        var parent = new Size(parentWidth, parentHeight);

        return parent;
    }

    /// <summary>
    /// 获取指定元素的填充类型。
    /// </summary>
    /// <param name="element">要获取填充类型的依赖对象。</param>
    /// <returns>返回指定元素的填充类型。</returns>
    public static FillType GetFill(DependencyObject element)
    {
        return (FillType)element.GetValue(FillProperty); }

    /// <summary>
    /// 设置指定元素的填充方式属性。
    /// </summary>
    /// <param name="element">要设置填充方式的依赖对象。</param>
    /// <param name="value">要设置的填充类型值，可以是Auto、Fill或Ignored。</param>
    public static void SetFill(DependencyObject element, FillType value)
    {
        element.SetValue(FillProperty, value); }

    /// <summary>
    /// 堆叠方向
    /// </summary>
    public Orientation Orientation
    {
        get => (Orientation)GetValue(OrientationProperty);
        set => SetValue(OrientationProperty, value);
    }

    /// <summary>
    /// 子项间距
    /// </summary>
    public double Spacing
    {
        get => (double)GetValue(SpacingProperty);
        set => SetValue(SpacingProperty, value);
    }
}
/// <summary>
/// 
/// </summary>
public enum FillType
{
    /// <summary>
    /// 实际大小填充
    /// </summary>
    Auto,
    /// <summary>
    /// 填充剩余空间相当于Stretch
    /// </summary>
    Fill,
    /// <summary>
    /// 忽略当前项
    /// </summary>
    Ignored
}