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

namespace UVC.UIToolkit
{
    /// <summary>
    /// Enum 선택 드롭다운 컴포넌트.
    /// 여러 옵션 중 하나를 선택할 수 있는 UI 컨트롤입니다.
    /// 선택된 항목은 체크 아이콘으로 표시됩니다.
    /// </summary>
    /// <remarks>
    /// <para><b>Enum 드롭다운이란?</b></para>
    /// <para>
    /// Enum 드롭다운은 C#의 열거형(Enum) 타입을 자동으로 드롭다운 목록으로 만들어주는 컴포넌트입니다.
    /// 문자열 목록을 수동으로 관리할 필요 없이, Enum 정의만으로 타입 안전한 선택 UI를 구현합니다.
    /// </para>
    ///
    /// <para><b>Enum이란?</b></para>
    /// <para>
    /// Enum(열거형)은 관련된 상수들을 묶어 명명된 값의 집합을 정의합니다.
    /// 예를 들어, 게임 난이도를 <c>Easy</c>, <c>Normal</c>, <c>Hard</c>로 정의할 수 있습니다.
    /// </para>
    ///
    /// <para><b>문자열 드롭다운 vs Enum 드롭다운:</b></para>
    /// <list type="bullet">
    /// <item><description>문자열: 유연하지만 오타 위험, 컴파일 타임 검증 불가</description></item>
    /// <item><description>Enum: 타입 안전, 자동 완성 지원, 리팩토링 용이</description></item>
    /// </list>
    ///
    /// <para><b>주요 속성:</b></para>
    /// <list type="bullet">
    /// <item><description><c>Label</c> - 드롭다운 라벨 텍스트</description></item>
    /// <item><description><c>Value</c> - 현재 선택된 Enum 값</description></item>
    /// <item><description><c>Placeholder</c> - 선택되지 않았을 때 표시되는 텍스트</description></item>
    /// <item><description><c>IsEnabled</c> - 활성화/비활성화 상태</description></item>
    /// </list>
    ///
    /// <para><b>주요 메서드:</b></para>
    /// <list type="bullet">
    /// <item><description><c>Init(Enum)</c> - Enum 타입과 기본값으로 초기화 (필수!)</description></item>
    /// <item><description><c>SetValue(Enum, bool)</c> - 값 설정 (notify: 이벤트 발생 여부)</description></item>
    /// </list>
    ///
    /// <para><b>주요 이벤트:</b></para>
    /// <list type="bullet">
    /// <item><description><c>OnValueChanged</c> - 선택 변경 시 발생 (Enum 값 전달)</description></item>
    /// </list>
    ///
    /// <para><b>UXML 사용 시 주의:</b></para>
    /// <para>
    /// UXML에서는 Enum 타입을 지정할 수 없으므로, 반드시 C# 코드에서 <c>Init()</c>을 호출해야 합니다.
    /// </para>
    ///
    /// <para><b>실제 활용 예시:</b></para>
    /// <list type="bullet">
    /// <item><description>게임 난이도 - Easy, Normal, Hard, Expert</description></item>
    /// <item><description>정렬 방식 - Ascending, Descending</description></item>
    /// <item><description>파일 형식 - PNG, JPG, GIF, BMP</description></item>
    /// <item><description>품질 설정 - Low, Medium, High, Ultra</description></item>
    /// <item><description>애니메이션 상태 - Idle, Walk, Run, Jump</description></item>
    /// </list>
    /// </remarks>
    /// <example>
    /// <para><b>Enum 정의:</b></para>
    /// <code>
    /// // 게임 난이도 Enum
    /// public enum Difficulty { Easy, Normal, Hard, Expert }
    ///
    /// // 품질 설정 Enum
    /// public enum QualityLevel { Low, Medium, High, Ultra }
    /// </code>
    /// <para><b>C# 코드에서 사용:</b></para>
    /// <code>
    /// // 난이도 선택 드롭다운
    /// var difficultyDropdown = new UTKEnumDropDown();
    /// difficultyDropdown.Label = "난이도";
    /// difficultyDropdown.Init(Difficulty.Normal);  // 기본값: Normal
    ///
    /// // 값 변경 이벤트
    /// difficultyDropdown.OnValueChanged += (value) => {
    ///     var difficulty = (Difficulty)value;
    ///     Debug.Log($"난이도 변경: {difficulty}");
    ///     ApplyDifficulty(difficulty);
    /// };
    ///
    /// // 생성자로 한 번에 설정
    /// var qualityDropdown = new UTKEnumDropDown("품질", QualityLevel.High);
    ///
    /// // 현재 값 읽기 (캐스팅 필요)
    /// var currentQuality = (QualityLevel)qualityDropdown.Value;
    ///
    /// // 프로그래밍으로 값 변경
    /// difficultyDropdown.Value = Difficulty.Hard;
    /// </code>
    /// <para><b>UXML에서 사용:</b></para>
    /// <code>
    /// <!-- UXML에서는 name과 label만 지정 -->
    /// <utk:UTKEnumDropDown name="difficulty-dropdown" label="난이도" placeholder="난이도를 선택하세요" />
    /// <utk:UTKEnumDropDown name="quality-dropdown" label="품질" />
    /// </code>
    /// <para><b>UXML 로드 후 C#에서 초기화:</b></para>
    /// <code>
    /// // UXML 로드 후 반드시 Init() 호출
    /// var diffDropdown = root.Q<UTKEnumDropDown>("difficulty-dropdown");
    /// diffDropdown.Init(Difficulty.Normal);
    ///
    /// var qualityDropdown = root.Q<UTKEnumDropDown>("quality-dropdown");
    /// qualityDropdown.Init(QualityLevel.High);
    /// </code>
    /// </example>
    [UxmlElement]
    public partial class UTKEnumDropDown : VisualElement, IDisposable
    {
        #region Constants
        private const string USS_PATH = "UIToolkit/Dropdown/UTKEnumDropDownUss";
        private const string DEFAULT_PLACEHOLDER = "Select";
        #endregion

        #region Fields
        private bool _disposed;
        private Label? _labelElement;
        private VisualElement? _inputContainer;
        private Label? _displayLabel;
        private VisualElement? _dropdownIconContainer;
        private UTKLabel? _dropdownIcon;
        private VisualElement? _popupContainer;
        private ScrollView? _optionsScrollView;

        private string _label = "";
        private Type? _enumType;
        private Enum? _value;
        private string _placeholder = DEFAULT_PLACEHOLDER;
        private bool _isEnabled = true;
        private bool _isPopupOpen;

        private readonly StyleSheet? _loadedUss;

        // 옵션 항목과 체크 아이콘 추적
        private readonly List<(VisualElement container, UTKLabel checkIcon, Enum enumValue)> _optionItems = new();
        #endregion

        #region Events
        /// <summary>값 변경 이벤트 (선택된 Enum 값)</summary>
        public event Action<Enum?>? OnValueChanged;
        #endregion

        #region Properties
        /// <summary>라벨 텍스트</summary>
        [UxmlAttribute("label")]
        public string Label
        {
            get => _label;
            set
            {
                _label = value;
                if (_labelElement != null)
                    _labelElement.text = value;
            }
        }

        /// <summary>현재 선택된 Enum 값</summary>
        public Enum? Value
        {
            get => _value;
            set
            {
                if (_value?.Equals(value) == true) return;
                _value = value;
                UpdateDisplayText();
                UpdateCheckIcons();
            }
        }

        /// <summary>플레이스홀더 텍스트 (선택되지 않았을 때 표시)</summary>
        [UxmlAttribute("placeholder")]
        public string Placeholder
        {
            get => _placeholder;
            set
            {
                _placeholder = value;
                UpdateDisplayText();
            }
        }

        /// <summary>활성화 상태</summary>
        [UxmlAttribute("is-enabled")]
        public bool IsEnabled
        {
            get => _isEnabled;
            set
            {
                _isEnabled = value;
                SetEnabled(value);
                EnableInClassList("utk-enum-dropdown--disabled", !value);
            }
        }
        #endregion

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

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

            CreateUI();
            SubscribeToThemeChanges();
        }

        public UTKEnumDropDown(string label, Enum defaultValue) : this()
        {
            Label = label;
            Init(defaultValue);
        }
        #endregion

        #region Setup
        private void CreateUI()
        {
            AddToClassList("utk-enum-dropdown");

            // Label
            _labelElement = new Label(_label);
            _labelElement.AddToClassList("utk-enum-dropdown__label");
            Add(_labelElement);

            // Input Container
            _inputContainer = new VisualElement();
            _inputContainer.AddToClassList("utk-enum-dropdown__input");
            Add(_inputContainer);

            // Display Label
            _displayLabel = new Label(_placeholder);
            _displayLabel.AddToClassList("utk-enum-dropdown__display");
            _displayLabel.AddToClassList("utk-enum-dropdown__display--placeholder");
            _inputContainer.Add(_displayLabel);

            // Icon Container
            _dropdownIconContainer = new VisualElement();
            _dropdownIconContainer.AddToClassList("utk-enum-dropdown__icon-container");
            _inputContainer.Add(_dropdownIconContainer);

            // Dropdown Icon
            _dropdownIcon = new UTKLabel(UTKMaterialIcons.ArrowDropDown, 24);
            _dropdownIcon.AddToClassList("utk-enum-dropdown__icon");
            _dropdownIconContainer.Add(_dropdownIcon);

            // Popup Container
            _popupContainer = new VisualElement();
            _popupContainer.AddToClassList("utk-enum-dropdown__popup");
            _popupContainer.style.display = DisplayStyle.None;
            _popupContainer.style.position = Position.Absolute;

            // Options ScrollView
            _optionsScrollView = new ScrollView(ScrollViewMode.Vertical);
            _optionsScrollView.AddToClassList("utk-enum-dropdown__options");
            _popupContainer.Add(_optionsScrollView);

            // Events
            _inputContainer.RegisterCallback<ClickEvent>(OnInputClicked);
            RegisterCallback<AttachToPanelEvent>(OnAttachedToPanel);
            RegisterCallback<DetachFromPanelEvent>(OnDetachedFromPanel);
        }

        private void SubscribeToThemeChanges()
        {
            UTKThemeManager.Instance.OnThemeChanged += OnThemeChanged;
            RegisterCallback<AttachToPanelEvent>(OnAttachToPanelForTheme);
            RegisterCallback<DetachFromPanelEvent>(OnDetachFromPanelForTheme);
        }

        private void OnAttachToPanelForTheme(AttachToPanelEvent evt)
        {
            UTKThemeManager.Instance.OnThemeChanged -= OnThemeChanged;
            UTKThemeManager.Instance.OnThemeChanged += OnThemeChanged;
            UTKThemeManager.Instance.ApplyThemeToElement(this);
        }

        private void OnDetachFromPanelForTheme(DetachFromPanelEvent evt)
        {
            UTKThemeManager.Instance.OnThemeChanged -= OnThemeChanged;
        }

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

        private void OnAttachedToPanel(AttachToPanelEvent evt)
        {
            if (panel != null)
            {
                panel.visualTree.RegisterCallback<PointerDownEvent>(OnPanelPointerDown, TrickleDown.TrickleDown);
            }
        }

        private void OnDetachedFromPanel(DetachFromPanelEvent evt)
        {
            if (panel != null)
            {
                panel.visualTree.UnregisterCallback<PointerDownEvent>(OnPanelPointerDown, TrickleDown.TrickleDown);
            }
        }
        #endregion

        #region Public Methods
        /// <summary>
        /// Enum 타입과 기본값으로 초기화합니다.
        /// </summary>
        /// <param name="defaultValue">기본값으로 설정할 Enum 값</param>
        public void Init(Enum defaultValue)
        {
            _enumType = defaultValue.GetType();
            _value = defaultValue;

            RebuildOptions();
            UpdateDisplayText();
        }

        /// <summary>
        /// 현재 값을 특정 Enum 값으로 설정합니다.
        /// </summary>
        /// <param name="enumValue">설정할 Enum 값</param>
        /// <param name="notify">이벤트 발생 여부</param>
        public void SetValue(Enum? enumValue, bool notify = true)
        {
            if (_value?.Equals(enumValue) == true) return;
            _value = enumValue;
            UpdateDisplayText();
            UpdateCheckIcons();

            if (notify)
            {
                OnValueChanged?.Invoke(_value);
            }
        }
        #endregion

        #region Private Methods
        private void RebuildOptions()
        {
            if (_optionsScrollView == null || _enumType == null) return;

            // Clear existing options
            _optionsScrollView.Clear();
            _optionItems.Clear();

            // Get all enum values
            var enumValues = Enum.GetValues(_enumType);

            // Create option for each enum value
            foreach (Enum enumValue in enumValues)
            {
                var optionContainer = new VisualElement();
                optionContainer.AddToClassList("utk-enum-dropdown__option");

                // Check icon
                var checkIcon = new UTKLabel(UTKMaterialIcons.Check, 16);
                checkIcon.AddToClassList("utk-enum-dropdown__check-icon");
                checkIcon.style.display = _value?.Equals(enumValue) == true ? DisplayStyle.Flex : DisplayStyle.None;
                optionContainer.Add(checkIcon);

                // Option label
                var optionLabel = new Label(enumValue.ToString());
                optionLabel.AddToClassList("utk-enum-dropdown__option-label");
                optionContainer.Add(optionLabel);

                // Click event
                optionContainer.RegisterCallback<ClickEvent>(evt =>
                {
                    evt.StopPropagation();
                    OnOptionSelected(enumValue);
                });

                // 마우스 호버 이벤트
                optionContainer.RegisterCallback<MouseEnterEvent>(_ =>
                {
                    optionContainer.AddToClassList("utk-enum-dropdown__option--hover");
                });
                optionContainer.RegisterCallback<MouseLeaveEvent>(_ =>
                {
                    optionContainer.RemoveFromClassList("utk-enum-dropdown__option--hover");
                });

                _optionsScrollView.Add(optionContainer);
                _optionItems.Add((optionContainer, checkIcon, enumValue));
            }
        }

        private void UpdateDisplayText()
        {
            if (_displayLabel == null) return;

            if (_value != null)
            {
                _displayLabel.text = _value.ToString();
                _displayLabel.RemoveFromClassList("utk-enum-dropdown__display--placeholder");
            }
            else
            {
                _displayLabel.text = _placeholder;
                _displayLabel.AddToClassList("utk-enum-dropdown__display--placeholder");
            }
        }

        private void UpdateCheckIcons()
        {
            foreach (var (_, checkIcon, enumValue) in _optionItems)
            {
                checkIcon.style.display = _value?.Equals(enumValue) == true ? DisplayStyle.Flex : DisplayStyle.None;
            }
        }

        private void OnOptionSelected(Enum enumValue)
        {
            SetValue(enumValue, notify: true);
            ClosePopup();
        }

        private void OnInputClicked(ClickEvent evt)
        {
            if (!_isEnabled) return;

            _isPopupOpen = !_isPopupOpen;

            if (_popupContainer != null)
            {
                if (_isPopupOpen)
                {
                    OpenPopup();
                }
                else
                {
                    ClosePopup();
                }
            }

            EnableInClassList("utk-enum-dropdown--open", _isPopupOpen);

            evt.StopPropagation();
        }

        private void OpenPopup()
        {
            if (_popupContainer == null || _inputContainer == null || panel == null) return;

            // 아이콘 변경
            if (_dropdownIcon is UTKLabel iconLabel)
            {
                iconLabel.SetMaterialIcon(UTKMaterialIcons.ArrowDropUp);
            }

            // 팝업을 루트로 이동
            if (_popupContainer.parent != panel.visualTree)
            {
                _popupContainer.RemoveFromHierarchy();
                panel.visualTree.Add(_popupContainer);
                UTKThemeManager.Instance.ApplyThemeToElement(_popupContainer);
                if (_loadedUss != null)
                {
                    _popupContainer.styleSheets.Add(_loadedUss);
                }
            }

            // 드롭다운의 월드 위치 계산
            var inputBounds = _inputContainer.worldBound;

            _popupContainer.style.position = Position.Absolute;
            _popupContainer.style.left = inputBounds.x;
            _popupContainer.style.top = inputBounds.yMax + 2; // 2px 간격
            _popupContainer.style.width = inputBounds.width;
            _popupContainer.style.display = DisplayStyle.Flex;
        }

        private void ClosePopup()
        {
            _isPopupOpen = false;

            // 아이콘 복원
            if (_dropdownIcon is UTKLabel iconLabel)
            {
                iconLabel.SetMaterialIcon(UTKMaterialIcons.ArrowDropDown);
            }

            if (_popupContainer != null)
            {
                _popupContainer.style.display = DisplayStyle.None;

                // 팝업을 원래 위치(드롭다운 내부)로 되돌림
                if (_popupContainer.parent != this)
                {
                    _popupContainer.RemoveFromHierarchy();
                    Add(_popupContainer);
                }
            }

            // 포커스 상태 클래스 제거
            EnableInClassList("utk-enum-dropdown--open", false);
        }

        private void OnPanelPointerDown(PointerDownEvent evt)
        {
            if (!_isPopupOpen) return;

            var target = evt.target as VisualElement;
            if (target == null) return;

            // 입력 컨테이너 클릭 확인
            if (_inputContainer != null && target.FindCommonAncestor(_inputContainer) == _inputContainer)
            {
                return; // 입력 영역 클릭이면 무시
            }

            // 팝업 컨테이너 클릭 확인
            if (_popupContainer != null && target.FindCommonAncestor(_popupContainer) == _popupContainer)
            {
                return; // 팝업 내부 클릭이면 무시
            }

            // 외부 클릭이면 팝업 닫기
            ClosePopup();
        }
        #endregion

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

            UTKThemeManager.Instance.OnThemeChanged -= OnThemeChanged;
            UnregisterCallback<AttachToPanelEvent>(OnAttachToPanelForTheme);
            UnregisterCallback<DetachFromPanelEvent>(OnDetachFromPanelForTheme);
            OnValueChanged = null;

            _inputContainer?.UnregisterCallback<ClickEvent>(OnInputClicked);

            if (panel != null)
            {
                panel.visualTree.UnregisterCallback<PointerDownEvent>(OnPanelPointerDown);
            }

            foreach (var (container, checkIcon, _) in _optionItems)
            {
                checkIcon.Dispose();
            }
            _optionItems.Clear();
        }
        #endregion
    }
}