#nullable enable
using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UIElements;

namespace UVC.UIToolkit
{
    /// <summary>
    /// 트리 뷰 컴포넌트.
    /// Unity TreeView를 래핑하여 커스텀 스타일을 적용합니다.
    /// </summary>
    /// <example>
    /// <para><b>C# 코드에서 사용:</b></para>
    /// <code>
    /// // 트리 뷰 생성
    /// var treeView = new UTKTreeView();
    /// 
    /// // 데이터 구조 설정
    /// var rootItems = new List<TreeViewItemData<string>> {
    ///     new TreeViewItemData<string>(0, "루트 1", new List<TreeViewItemData<string>> {
    ///         new TreeViewItemData<string>(1, "자식 1-1"),
    ///         new TreeViewItemData<string>(2, "자식 1-2")
    ///     }),
    ///     new TreeViewItemData<string>(3, "루트 2")
    /// };
    /// treeView.SetRootItems(rootItems);
    /// 
    /// // 아이템 렌더링
    /// treeView.makeItem = () => new Label();
    /// treeView.bindItem = (element, index) => {
    ///     var item = treeView.GetItemDataForIndex<string>(index);
    ///     (element as Label).text = item;
    /// };
    /// 
    /// // 선택 이벤트
    /// treeView.OnItemSelected += (index) => Debug.Log($"선택: {index}");
    /// </code>
    /// <para><b>UXML에서 사용:</b></para>
    /// <code>
    /// <ui:UXML xmlns:utk="UVC.UIToolkit">
    ///     <utk:UTKTreeView fixed-item-height="24" />
    /// </ui:UXML>
    /// </code>
    /// </example>
    [UxmlElement]
    public partial class UTKTreeView : TreeView, IDisposable
    {
        #region Constants
        private const string USS_PATH = "UIToolkit/List/UTKTreeView";
        #endregion

        #region Fields
        private bool _disposed;
        #endregion

        #region Events
        /// <summary>아이템 선택 이벤트</summary>
        public event Action<int>? OnItemSelected;
        /// <summary>아이템 더블클릭 이벤트</summary>
        public event Action<int>? OnItemDoubleClicked;
        #endregion

        #region Constructor
        public UTKTreeView() : base()
        {
            UTKThemeManager.Instance.ApplyThemeToElement(this);

            var uss = Resources.Load<StyleSheet>(USS_PATH);
            if (uss != null)
            {
                styleSheets.Add(uss);
            }

            SetupStyles();
            SetupEvents();
            SubscribeToThemeChanges();
        }
        #endregion

        #region Setup
        private void SetupStyles()
        {
            AddToClassList("utk-treeview");
        }

        private void SetupEvents()
        {
            selectionChanged += OnSelectionChanged;
            itemsChosen += OnItemsChosen;
        }

        private void SubscribeToThemeChanges()
        {
            UTKThemeManager.Instance.OnThemeChanged += OnThemeChanged;
            RegisterCallback<DetachFromPanelEvent>(_ =>
            {
                UTKThemeManager.Instance.OnThemeChanged -= OnThemeChanged;
            });
        }

        private void OnThemeChanged(UTKTheme theme)
        {
            UTKThemeManager.Instance.ApplyThemeToElement(this);
        }
        #endregion

        #region Event Handlers
        private void OnSelectionChanged(IEnumerable<object> items)
        {
            OnItemSelected?.Invoke(selectedIndex);
        }

        private void OnItemsChosen(IEnumerable<object> items)
        {
            OnItemDoubleClicked?.Invoke(selectedIndex);
        }
        #endregion

        #region IDisposable
        public void Dispose()
        {
            if (_disposed) return;
            _disposed = true;

            selectionChanged -= OnSelectionChanged;
            itemsChosen -= OnItemsChosen;
            UTKThemeManager.Instance.OnThemeChanged -= OnThemeChanged;
            OnItemSelected = null;
            OnItemDoubleClicked = null;
        }
        #endregion
    }
}