using System;
using DG.Tweening; // 引入 DOTween
using UnityEngine;
using SLSUtilities.UI;

namespace Cielonos.Core.UI
{
    // 继承 UIElementBase，同时实现简单的单例逻辑
    public class ScreenFader : UIElementBase
    {
        public static ScreenFader Instance { get; private set; }

        [Header("Settings")]
        [SerializeField] private float defaultDuration = 0.5f;
        [SerializeField] private bool startBlack = true;
        [SerializeField] private Ease fadeEase = Ease.InOutQuad; // 暴露曲线设置，比 SmoothStep 更灵活

        private Tween currentTween; // 记录当前动画，防止冲突

        private void Awake()
        {
            // --- 单例逻辑 ---
            if (Instance != null && Instance != this)
            {
                Destroy(gameObject);
                return;
            }
            Instance = this;
            // ----------------
            
            // 初始化状态
            if (canvasGroup == null) canvasGroup = GetComponent<CanvasGroup>();
            
            if (startBlack)
            {
                canvasGroup.alpha = 1f;
                canvasGroup.blocksRaycasts = true;
            }
            else
            {
                canvasGroup.alpha = 0f;
                canvasGroup.blocksRaycasts = false;
            }
        }

        private void OnDestroy()
        {
            // 这是一个好习惯：销毁时杀掉所有未完成的动画，防止报错
            currentTween?.Kill();
        }

        /// <summary>
        /// 变黑 (Fade Out / 遮挡屏幕)
        /// </summary>
        public Tween FadeToBlack(float duration = -1, Action onComplete = null)
        {
            return FadeTo(1f, duration, onComplete);
        }

        /// <summary>
        /// 变亮 (Fade In / 显示屏幕)
        /// </summary>
        public Tween FadeToClear(float duration = -1, float delay = 1, Action onComplete = null)
        {
            return FadeTo(0f, duration, onComplete).SetDelay(delay);
        }

        /// <summary>
        /// 通用淡入淡出逻辑
        /// 返回 Tween 对象，允许外部使用 yield return tween.WaitForCompletion();
        /// </summary>
        private Tween FadeTo(float targetAlpha, float duration, Action onComplete)
        {
            // 1. 如果有正在运行的动画，立刻杀掉，确保从当前 alpha 开始新的变化
            currentTween?.Kill();

            float d = duration < 0 ? defaultDuration : duration;

            // 2. 只有在变黑（alpha -> 1）开始时，才阻挡射线
            // 这样防止玩家在变黑过程中还能点击后面的按钮
            if (targetAlpha > 0.5f) 
            {
                canvasGroup.blocksRaycasts = true;
            }

            // 3. 使用 DOTween
            currentTween = canvasGroup.DOFade(targetAlpha, d)
                .SetEase(fadeEase)
                .SetUpdate(true) // 【关键】忽略 TimeScale，游戏暂停时依然可以淡入淡出
                .OnComplete(() =>
                {
                    // 只有在完全变亮（alpha -> 0）结束后，才取消阻挡
                    if (targetAlpha < 0.01f)
                    {
                        canvasGroup.blocksRaycasts = false;
                    }
                    onComplete?.Invoke();
                });

            return currentTween;
        }
    }
}