using System.Collections;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Input;

namespace VariaStudio.Controls
{
    /// <summary>
    /// AutoComplete 控件提供了一个文本框，用户可以在其中输入文本，并从一个下拉列表中选择建议项。该控件适用于需要快速完成或查找功能的场景。
    /// </summary>
    /// <remarks>
    /// 通过设置 ItemsSource 属性，可以为 AutoComplete 控件提供数据源，用于填充建议列表。当用户在文本框中输入时，会根据输入的内容显示匹配的建议项。
    /// </remarks>
    [TemplatePart(Name = "PART_TextBox", Type = typeof(TextBox))]
    [TemplatePart(Name = "PART_Popup", Type = typeof(Popup))]
    [TemplatePart(Name = "PART_ListBox", Type = typeof(ListBox))]
    public class AutoComplete : Control
    {
        private TextBox? textBox;
        private Popup? popup;
        private ListBox? listBox;

        private bool isSelectionChanging = false;

        private const int filterDelay = 200;
        private CancellationTokenSource? cts;
        #region Dependency Properties

        /// <summary>
        /// 用于设置或获取 AutoComplete 控件的数据源。该属性接受实现了 IEnumerable 接口的任何集合，这些数据将作为建议项显示给用户。
        /// </summary>
        public static readonly DependencyProperty ItemsSourceProperty =
            DependencyProperty.Register(nameof(ItemsSource), typeof(IEnumerable), typeof(AutoComplete), new PropertyMetadata(null, OnItemsSourceChanged));

        /// <summary>
        /// 用于设置或获取 AutoComplete 控件的数据源。该属性接受实现了 IEnumerable 接口的任何集合，这些数据将作为建议项显示给用户。
        /// </summary>
        public IEnumerable ItemsSource
        {
            get => (IEnumerable)GetValue(ItemsSourceProperty);
            set => SetValue(ItemsSourceProperty, value);
        }

        /// <summary>
        /// 用于设置或获取 AutoComplete 控件中文本框显示的文本。此属性支持双向数据绑定，允许在控件与数据源之间同步文本内容。
        /// </summary>
        public static readonly DependencyProperty TextProperty =
            DependencyProperty.Register(nameof(Text), typeof(string), typeof(AutoComplete), new FrameworkPropertyMetadata(string.Empty, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnTextChanged));

        /// <summary>
        /// 用于获取或设置 AutoComplete 控件中显示的文本。此属性支持双向数据绑定，允许用户输入的文本与外部数据源之间进行同步。
        /// </summary>
        public string Text
        {
            get => (string)GetValue(TextProperty);
            set => SetValue(TextProperty, value);
        }

        /// <summary>
        /// 用于设置或获取 AutoComplete 控件中当前选中的项。该属性支持双向数据绑定，可以用来反映用户从建议列表中选择的项目。
        /// </summary>
        public static readonly DependencyProperty SelectedItemProperty =
            DependencyProperty.Register(nameof(SelectedItem), typeof(object), typeof(AutoComplete), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

        /// <summary>
        /// 获取或设置当前在 AutoComplete 控件中选中的项。此属性支持双向数据绑定，允许用户选择的项能够被外部逻辑访问和修改。
        /// </summary>
        public object? SelectedItem
        {
            get => GetValue(SelectedItemProperty);
            set => SetValue(SelectedItemProperty, value);
        }

        /// <summary>
        /// 用于设置或获取 AutoComplete 控件的下拉列表是否展开的状态。该属性为布尔值，当设置为 true 时，表示下拉列表处于打开状态；反之则关闭。
        /// </summary>
        public static readonly DependencyProperty IsDropDownOpenProperty =
            DependencyProperty.Register(nameof(IsDropDownOpen), typeof(bool), typeof(AutoComplete), new PropertyMetadata(false));

        /// <summary>
        /// 
        /// </summary>
        public bool IsDropDownOpen
        {
            get => (bool)GetValue(IsDropDownOpenProperty);
            set => SetValue(IsDropDownOpenProperty, value);
        }

        /// <summary>
        /// 
        /// </summary>
        public static readonly DependencyProperty PlaceholderTextProperty =
            DependencyProperty.Register(nameof(PlaceholderText), typeof(string), typeof(AutoComplete), new PropertyMetadata(string.Empty));

        /// <summary>
        /// 
        /// </summary>
        public string PlaceholderText
        {
            get => (string)GetValue(PlaceholderTextProperty);
            set => SetValue(PlaceholderTextProperty, value);
        }
        #endregion

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

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

            if (textBox != null)
            {
                textBox.TextChanged -= OnTextBoxTextChanged;
                textBox.PreviewKeyDown -= OnTextBoxPreviewKeyDown;
            }
            if (listBox != null)
            {
                listBox.SelectionChanged -= OnListBoxSelectionChanged;
            }

            textBox = GetTemplateChild("PART_TextBox") as TextBox;
            popup = GetTemplateChild("PART_Popup") as Popup;
            listBox = GetTemplateChild("PART_ListBox") as ListBox;

            if (textBox != null)
            {
                textBox.TextChanged += OnTextBoxTextChanged;
                textBox.PreviewKeyDown += OnTextBoxPreviewKeyDown;
            }

            if (listBox != null)
            {
                listBox.SelectionChanged += OnListBoxSelectionChanged;
            }
        }

        private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var control = (AutoComplete)d;
            if (control.listBox != null)
            {
                control.listBox.ItemsSource = e.NewValue as IEnumerable;
            }
        }

        private static async void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var control = (AutoComplete)d;
            if (control.isSelectionChanging) return;

            if (control.textBox != null && control.textBox.Text != (string)e.NewValue)
            {
                control.textBox.Text = (string)e.NewValue;
            }

            control.cts?.Cancel();
            control.cts = new CancellationTokenSource();

            try
            {
                await Task.Delay(filterDelay, control.cts.Token).ConfigureAwait(true);
                control.FilterItemsSource();
            }
            catch (TaskCanceledException)
            {
                // Ignore cancellation
            }
        }

        private void OnTextBoxTextChanged(object sender, TextChangedEventArgs e)
        {
            if (isSelectionChanging) return;

            // 同步Text属性
            if (textBox != null && Text != textBox.Text)
            {
                Text = textBox.Text;
            }

            // 清空我们自己控件的选中项
            SelectedItem = null;

            // 同时清空ListBox内部的选中项
            if (listBox is { SelectedItem: not null })
            {
                listBox.SelectedItem = null;
            }
        }

        private void OnTextBoxPreviewKeyDown(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Down && listBox is { Items.Count: > 0 })
            {
                listBox.Focus();
                listBox.SelectedIndex = 0;
            }
            else if (e.Key == Key.Escape)
            {
                IsDropDownOpen = false;
            }
        }

        private void OnListBoxSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (e.AddedItems.Count == 0 || listBox?.SelectedItem == null) return;

            isSelectionChanging = true;

            SelectedItem = listBox.SelectedItem;
            Text = SelectedItem?.ToString() ?? string.Empty;
            IsDropDownOpen = false;

            textBox?.Focus();
            textBox?.Select(textBox.Text.Length, 0);

            isSelectionChanging = false;
        }

        private void FilterItemsSource()
        {
            if (ItemsSource == null) return;

            var view = CollectionViewSource.GetDefaultView(ItemsSource);
            if (string.IsNullOrEmpty(Text))
            {
                view.Filter = null;
            }
            else
            {
                view.Filter = item => item.ToString()?.IndexOf(Text, StringComparison.OrdinalIgnoreCase) >= 0;
            }
            view.Refresh();

            // !string.IsNullOrEmpty(Text) 的判断
            if (!string.IsNullOrEmpty(Text) && !view.IsEmpty && textBox is { IsKeyboardFocused: true })
            {
                IsDropDownOpen = true;
            }
            else
            {
                IsDropDownOpen = false;
            }
        }
    }
}