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

namespace UVC.UIToolkit
{
    /// <summary>
    /// 드롭다운 메뉴 컴포넌트.
    /// Unity DropdownField를 래핑하여 커스텀 스타일을 적용합니다.
    /// </summary>
    /// <example>
    /// <para><b>C# 코드에서 사용:</b></para>
    /// <code>
    /// // 기본 드롭다운
    /// var dropdown = new UTKDropdown();
    /// dropdown.Label = "국가 선택";
    /// dropdown.SetChoices(new List<string> { "한국", "미국", "일본" });
    /// dropdown.OnSelectionChanged += (index, value) => Debug.Log($"선택: {value}");
    /// 
    /// // 기본값 설정
    /// dropdown.value = "한국";
    /// dropdown.index = 0;
    /// </code>
    /// <para><b>UXML에서 사용:</b></para>
    /// <code>
    /// <ui:UXML xmlns:utk="UVC.UIToolkit">
    ///     <!-- 기본 드롭다운 -->
    ///     <utk:UTKDropdown label="정렬" choices="이름,날짜,크기" />
    ///     
    ///     <!-- 기본값 지정 -->
    ///     <utk:UTKDropdown label="언어" choices="한국어,English,日本語" index="0" />
    ///     
    ///     <!-- 비활성화 -->
    ///     <utk:UTKDropdown label="선택" IsEnabled="false" />
    /// </ui:UXML>
    /// </code>
    /// </example>
    [UxmlElement]
    public partial class UTKDropdown : DropdownField, IDisposable
    {
        #region Constants
        private const string USS_PATH = "UIToolkit/Dropdown/UTKDropdown";
        #endregion

        #region Fields
        private bool _disposed;
        private bool _isEnabled = true;
        #endregion

        #region Events
        /// <summary>선택 변경 이벤트</summary>
        public event Action<int, string>? OnSelectionChanged;
        #endregion

        #region Properties
        /// <summary>선택된 인덱스</summary>
        public int SelectedIndex
        {
            get => index;
            set => index = value;
        }

        /// <summary>선택된 값</summary>
        public string? SelectedValue => value;

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

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

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

            SetupStyles();
            SetupEvents();
            SubscribeToThemeChanges();
        }

        public UTKDropdown(string label, List<string>? options = null) : this()
        {
            this.label = label;
            if (options != null)
            {
                choices = options;
            }
        }
        #endregion

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

        private void SetupEvents()
        {
            this.RegisterValueChangedCallback(OnDropdownValueChanged);
        }

        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 OnDropdownValueChanged(ChangeEvent<string> evt)
        {
            OnSelectionChanged?.Invoke(index, evt.newValue);
        }
        #endregion

        #region Methods
        /// <summary>
        /// 옵션 목록 설정
        /// </summary>
        public void SetOptions(List<string> options)
        {
            choices = options ?? new List<string>();
        }

        /// <summary>
        /// 옵션 추가
        /// </summary>
        public void AddOption(string option)
        {
            var list = new List<string>(choices) { option };
            choices = list;
        }

        /// <summary>
        /// 값으로 선택
        /// </summary>
        public void SetSelectedValue(string? selectedValue, bool notify = true)
        {
            if (selectedValue == null)
            {
                index = -1;
                return;
            }

            var idx = choices.IndexOf(selectedValue);
            if (idx >= 0)
            {
                if (notify)
                {
                    index = idx;
                }
                else
                {
                    SetValueWithoutNotify(selectedValue);
                }
            }
        }
        #endregion

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

            UTKThemeManager.Instance.OnThemeChanged -= OnThemeChanged;
            OnSelectionChanged = null;
        }
        #endregion
    }
}