// Cascader.cs
using System.Collections;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using Melskin.Utilities;

namespace Melskin.Controls;

/// <summary>
/// 用于实现级联选择器功能的控件类。该控件允许用户从多层级的数据源中选择一个值，通常应用于需要按类别或层级进行选择的场景。
/// </summary>
[TemplatePart(Name = "PART_Popup", Type = typeof(Popup))]
public class Cascader : Control
{
    private static readonly DependencyPropertyKey FilteredItemsSourcePropertyKey = DependencyProperty.RegisterReadOnly("FilteredItemsSource", typeof(IEnumerable), typeof(Cascader), new PropertyMetadata(null));

    /// <summary>
    /// 用于获取经过筛选后的项集合。此属性为只读，其值由控件内部逻辑根据当前搜索条件自动更新。
    /// </summary>
    public static readonly DependencyProperty FilteredItemsSourceProperty = FilteredItemsSourcePropertyKey.DependencyProperty;
    /// <summary>
    /// 控制是否启用搜索功能的开关
    /// </summary>
    public static readonly DependencyProperty IsSearchableProperty =
        DependencyProperty.Register(nameof(IsSearchable), typeof(bool), typeof(Cascader), new PropertyMetadata(true));

    /// <summary>
    /// 定义一个依赖属性，用于接收来自 XAML 的 ListBox 样式
    /// </summary>
    public static readonly DependencyProperty PanelStyleProperty =
        DependencyProperty.Register(nameof(PanelStyle), typeof(Style), typeof(Cascader), new PropertyMetadata(null));

    /// <summary>
    /// 用于存储或获取搜索框中的文本，支持双向数据绑定。
    /// </summary>
    public static readonly DependencyProperty SearchTextProperty = DependencyProperty.Register(nameof(SearchText), typeof(string), typeof(Cascader), new FrameworkPropertyMetadata("", FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSearchTextChanged));

    private readonly List<object> selectedPath = [];

    static Cascader()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(Cascader), new FrameworkPropertyMetadata(typeof(Cascader)));
    }

    /// <summary>
    /// Cascader 控件用于在用户界面中显示级联选择菜单。该控件支持从数据源动态加载选项，并允许用户通过多级菜单进行选择。
    /// </summary>
    /// <remarks>
    /// 该控件包含多个依赖属性，如 ItemsSource、SelectedValue 和 DisplayMemberPath 等，以支持数据绑定和自定义显示。
    /// 另外，Cascader 控件还支持搜索功能（通过 IsSearchable 属性控制），并且可以自定义弹出面板的样式（通过 PanelStyle 属性）。
    /// </remarks>
    public Cascader()
    {
        SelectSearchResultCommand = new RelayCommand<CascaderSearchResult>(ExecuteSelectSearchResult);
    }

    private ListBox CreateItemsControl(IEnumerable items)
    {
        var itemsControl = new ListBox
        {
            Style = PanelStyle,
            ItemsSource = items,
            //DisplayMemberPath = DisplayMemberPath
        };
        itemsControl.SelectionChanged += OnSelectionChanged;
        return itemsControl;
    }
    private void ExecuteSelectSearchResult(CascaderSearchResult? result)
    {
        if (result == null) return;
        selectedPath.Clear();
        selectedPath.AddRange(result.FullPath);
        SelectedValue = result.TargetItem;
        UpdateSelectedText();
        IsDropDownOpen = false;
        SearchText = "";
    }

    private IEnumerable? GetChildren(object? item)
    {
        if (item == null || string.IsNullOrEmpty(SubmenuMemberPath)) return null;
        var property = item.GetType().GetProperty(SubmenuMemberPath);
        return property?.GetValue(item) as IEnumerable;
    }

    private string GetObjectDisplayText(object? item)
    {
        if (item == null) return string.Empty;
        if (!string.IsNullOrEmpty(DisplayMemberPath))
        {
            var prop = item.GetType().GetProperty(DisplayMemberPath);
            return prop?.GetValue(item)?.ToString() ?? string.Empty;
        }
        return item.ToString()!;
    }

    // 创建了完整的、非空的 CascadingPanel
    private void InitializeCascadingPanel()
    {
        selectedPath.Clear();
        UpdateSelectedText();

        // 1. 创建一个水平 StackPanel 作为根容器。这就是 CascadingPanel 的实体。
        var panel = new StackPanel { Orientation = Orientation.Horizontal };

        if (ItemsSource != null && ItemsSource.Cast<object>().Any())
        {
            // 2. 创建第一级菜单 (ListBox)
            var firstLevelMenu = CreateItemsControl(ItemsSource);
            // 3. 将第一级菜单添加到 Panel 中
            panel.Children.Add(firstLevelMenu);
        }

        // 4. 将这个构建好的、包含内容的 Panel 赋值给依赖属性，让 XAML 可以找到它。
        CascadingPanel = panel;
    }

    private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (Cascader)d;
        control.InitializeCascadingPanel();
        control.UpdateFilteredItems();
    }
    private static void OnSearchTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (Cascader)d;
        control.UpdateFilteredItems();
    }

    private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (e.AddedItems.Count == 0) return;
        var selectedItem = e.AddedItems[0]!;
        var currentMenu = sender as ItemsControl;
        var parentPanel = CascadingPanel;
        if (parentPanel == null) return;
        var currentIndex = parentPanel.Children.IndexOf(currentMenu);
        while (selectedPath.Count > currentIndex) selectedPath.RemoveAt(selectedPath.Count - 1);
        selectedPath.Add(selectedItem);
        while (parentPanel.Children.Count > currentIndex + 1) parentPanel.Children.RemoveAt(parentPanel.Children.Count - 1);
        var children = GetChildren(selectedItem);
        if (children != null && children.Cast<object>().Any())
        {
            var newMenu = CreateItemsControl(children);
            parentPanel.Children.Add(newMenu);
            UpdateSelectedText();
        }
        else
        {
            SelectedValue = selectedItem;
            UpdateSelectedText();
            IsDropDownOpen = false;
        }
    }

    private void SearchRecursive(IEnumerable? nodes, List<object> currentPath, List<CascaderSearchResult> results)
    {
        if (nodes == null) return;

        foreach (var node in nodes)
        {
            var newPath = new List<object>(currentPath) { node };
            var displayText = GetObjectDisplayText(node);

            if (displayText.IndexOf(SearchText, StringComparison.OrdinalIgnoreCase) >= 0)
            {
                var fullPathText = string.Join(Separator, newPath.Select(GetObjectDisplayText));
                results.Add(new CascaderSearchResult(fullPathText, node, newPath));
            }

            var children = GetChildren(node);
            if (children != null)
            {
                SearchRecursive(children, newPath, results);
            }
        }
    }
    private void UpdateFilteredItems()
    {
        if (string.IsNullOrWhiteSpace(SearchText) || ItemsSource == null)
        {
            FilteredItemsSource = null;
            return;
        }

        var results = new List<CascaderSearchResult>();
        SearchRecursive(ItemsSource, [], results);
        FilteredItemsSource = results;
    }

    private void UpdateSelectedText()
    {
        SelectedText = string.Join(Separator, selectedPath.Select(GetObjectDisplayText));
    }

    /// <inheritdoc />
    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        InitializeCascadingPanel();
    }

    /// <summary>
    /// 
    /// </summary>
    public IEnumerable? FilteredItemsSource { get => (IEnumerable)GetValue(FilteredItemsSourceProperty); protected set => SetValue(FilteredItemsSourcePropertyKey, value); }

    /// <summary>
    /// 获取或设置一个值，指示是否允许搜索功能。当设置为 true 时，用户可以使用搜索框来过滤选项；如果设置为 false，则禁用搜索功能。
    /// </summary>
    public bool IsSearchable { get => (bool)GetValue(IsSearchableProperty); set => SetValue(IsSearchableProperty, value); }

    /// <summary>
    /// 用于设置或获取级联控件面板的样式
    /// </summary>
    public Style PanelStyle
    {
        get => (Style)GetValue(PanelStyleProperty);
        set => SetValue(PanelStyleProperty, value);
    }

    /// <summary>
    /// 用于存储或获取当前搜索框中的文本，支持双向绑定。
    /// </summary>
    public string SearchText { get => (string)GetValue(SearchTextProperty); set => SetValue(SearchTextProperty, value); }

    /// <summary>
    /// 用于选择搜索结果的命令。此命令绑定到UI元素上，当用户触发时，将执行与选择搜索结果相关的操作。
    /// </summary>
    public ICommand SelectSearchResultCommand { get; private set; }

    #region 依赖属性

    /// <summary>
    /// 用于设置或获取级联选择器的数据源。
    /// </summary>
    public static readonly DependencyProperty ItemsSourceProperty =
        DependencyProperty.Register(
        nameof(ItemsSource),
        typeof(IEnumerable),
        typeof(Cascader),
        new PropertyMetadata(null, OnItemsSourceChanged));

    /// <summary>
    /// 获取或设置用于显示的项集合。
    /// </summary>
    public IEnumerable ItemsSource
    {
        get => (IEnumerable)GetValue(ItemsSourceProperty);
        set => SetValue(ItemsSourceProperty, value);
    }

    /// <summary>
    /// 用于获取或设置当前选中的值。此属性支持双向数据绑定。
    /// </summary>
    public static readonly DependencyProperty SelectedValueProperty =
        DependencyProperty.Register(
        nameof(SelectedValue),
        typeof(object),
        typeof(Cascader),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

    /// <summary>
    /// 获取或设置当前选中的值。
    /// 该属性支持双向数据绑定，可以用于在Cascader控件与其数据源之间同步选定的项。
    /// </summary>
    public object SelectedValue
    {
        get => GetValue(SelectedValueProperty);
        set => SetValue(SelectedValueProperty, value);
    }

    /// <summary>
    /// 用于指定在显示项时使用的属性路径。
    /// </summary>
    public static readonly DependencyProperty DisplayMemberPathProperty =
        DependencyProperty.Register(nameof(DisplayMemberPath), typeof(string), typeof(Cascader), new PropertyMetadata(""));

    /// <summary>
    /// 用于指定在显示项时，用来表示对象的属性路径。当设置此属性后，控件将使用该属性的值来展示列表中的每个项目。
    /// </summary>
    public string DisplayMemberPath
    {
        get => (string)GetValue(DisplayMemberPathProperty);
        set => SetValue(DisplayMemberPathProperty, value);
    }

    /// <summary>
    /// 用于指定子菜单成员路径的属性，该属性指示了在数据源中如何查找子项。
    /// </summary>
    public static readonly DependencyProperty SubmenuMemberPathProperty =
        DependencyProperty.Register(
        nameof(SubmenuMemberPath),
        typeof(string),
        typeof(Cascader),
        new PropertyMetadata("Children"));

    /// <summary>
    /// 用于指定子菜单项的属性路径，该属性路径指向的数据应为可枚举类型，表示当前项下的子项集合。
    /// </summary>
    public string SubmenuMemberPath
    {
        get => (string)GetValue(SubmenuMemberPathProperty);
        set => SetValue(SubmenuMemberPathProperty, value);
    }

    /// <summary>
    /// 用于获取或设置与控件关联的输入绑定集合
    /// </summary>
    public static readonly DependencyProperty InputBindingsProperty =
            DependencyProperty.RegisterAttached("InputBindings", typeof(InputBindingCollection), typeof(Cascader),
                new FrameworkPropertyMetadata(new InputBindingCollection(), OnInputBindingsChanged));

    /// <summary>
    /// 获取指定元素的输入绑定集合。
    /// </summary>
    /// <param name="element">要获取输入绑定集合的UI元素。</param>
    /// <returns>返回指定元素的输入绑定集合。</returns>
    public static InputBindingCollection GetInputBindings(UIElement element) => (InputBindingCollection)element.GetValue(InputBindingsProperty);

    /// <summary>
    /// 设置指定元素的输入绑定集合。
    /// </summary>
    /// <param name="element">要设置输入绑定的UI元素。</param>
    /// <param name="value">要分配给元素的输入绑定集合。</param>
    public static void SetInputBindings(UIElement element, InputBindingCollection value) => element.SetValue(InputBindingsProperty, value);

    private static void OnInputBindingsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is not UIElement uiElement) return;
        uiElement.InputBindings.Clear();
        if (e.NewValue is InputBindingCollection bindings)
        {
            uiElement.InputBindings.AddRange(bindings);
        }
    }

    /// <summary>
    /// 用于设置或获取分隔符字符串，该字符串用于在显示层级结构时分隔不同层级的文本。
    /// </summary>
    public static readonly DependencyProperty SeparatorProperty =
        DependencyProperty.Register(nameof(Separator), typeof(string), typeof(Cascader), new PropertyMetadata(" / "));

    /// <summary>
    /// 用于连接路径中各个元素的分隔符字符串
    /// </summary>
    public string Separator
    { get => (string)GetValue(SeparatorProperty); set => SetValue(SeparatorProperty, value); }

    /// <summary>
    /// 控制下拉菜单是否展开的属性
    /// </summary>
    public static readonly DependencyProperty IsDropDownOpenProperty =
        DependencyProperty.Register(
        nameof(IsDropDownOpen),
        typeof(bool),
        typeof(Cascader),
        new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

    /// <summary>
    /// 获取或设置一个值，表示下拉菜单是否处于打开状态。此属性支持双向数据绑定。
    /// </summary>
    public bool IsDropDownOpen
    {
        get => (bool)GetValue(IsDropDownOpenProperty);
        set => SetValue(IsDropDownOpenProperty, value);
    }

    private static readonly DependencyPropertyKey SelectedTextPropertyKey =
        DependencyProperty.RegisterReadOnly("SelectedText", typeof(string), typeof(Cascader), new PropertyMetadata(""));

    /// <summary>
    /// 获取或设置当前选中的文本。
    /// </summary>
    public static readonly DependencyProperty SelectedTextProperty = SelectedTextPropertyKey.DependencyProperty;

    /// <summary>
    /// 获取或设置当前选中的文本，该文本通常由用户选择的级联项组成。
    /// </summary>
    public string SelectedText
    {
        get => (string)GetValue(SelectedTextProperty);
        protected set => SetValue(SelectedTextPropertyKey, value);
    }

    // 【核心概念】这里定义了 CascadingPanel 属性，它是一个“舞台”的蓝图
    internal static readonly DependencyProperty CascadingPanelProperty =
        DependencyProperty.Register(nameof(CascadingPanel), typeof(Panel), typeof(Cascader), new PropertyMetadata(null));

    internal Panel CascadingPanel
    {
        get => (Panel)GetValue(CascadingPanelProperty);
        set => SetValue(CascadingPanelProperty, value);
    }
    #endregion
}
/// <summary>
/// 用于封装级联选择器搜索结果的类
/// </summary>
/// <remarks>
/// 用于封装级联选择器搜索结果的类。此类包含了展示文本、目标项以及完整的路径信息。
/// </remarks>
public class CascaderSearchResult(string displayText, object targetItem, List<object> fullPath)
{

    /// <summary>
    /// 用于在UI上显示的完整路径文本
    /// </summary>
    public string DisplayText { get; } = displayText;

    /// <summary>
    /// 构成完整路径的原始数据对象列表
    /// </summary>
    public List<object> FullPath { get; } = fullPath;

    /// <summary>
    /// 路径中的最后一项，即匹配到的原始数据对象
    /// </summary>
    public object TargetItem { get; } = targetItem;
}