using System.Collections;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

namespace GameFramework
{
    /// <summary>
    /// 场景异步加载器（持久化单例）。带黑色淡入淡出过渡。
    /// 场景名可在 Inspector 配置，默认 MainMenu / Gameplay / Scoring。
    ///
    /// 修复：协程结束后将 isLoading 重置为 false，允许后续加载。
    /// </summary>
    public class SceneLoader : PersistentSingleton<SceneLoader>
    {
        [Header("过渡")]
        [SerializeField] private Image transitionImage;
        [SerializeField] private float fadeTime = 1.5f;

        [Header("场景名（按你工程中的实际名称填）")]
        [SerializeField] private string mainMenuScene = "MainMenu";
        [SerializeField] private string gameplayScene = "Gameplay";
        [SerializeField] private string scoringScene = "Scoring";

        private Color color;
        private bool isLoading = false;

        public void LoadGameplayScene() => Load(gameplayScene);
        public void LoadMainMenuScene() => Load(mainMenuScene);
        public void LoadScoringScene() => Load(scoringScene);
        public void Load(string sceneName)
        {
            if (isLoading) return;
            isLoading = true;
            StopAllCoroutines();
            StartCoroutine(LoadingCoroutine(sceneName));
        }

        private IEnumerator LoadingCoroutine(string sceneName)
        {
            if (transitionImage == null)
            {
                Debug.LogWarning("[SceneLoader] transitionImage 未赋值! " +
                    "请在 SceneLoader 子物体上创建 Canvas (Overlay, SortOrder=9999) + 全屏黑色 Image，" +
                    "拖到 SceneLoader 的 transitionImage 字段。");
            }

            var loadingOperation = SceneManager.LoadSceneAsync(sceneName);
            loadingOperation.allowSceneActivation = false;

            if (transitionImage != null)
            {
                transitionImage.gameObject.SetActive(true);
                color = transitionImage.color;
                color.a = 0f;

                // 淡入到黑（LoadSceneAsync 在后台并行加载）
                while (color.a < 1f)
                {
                    color.a = Mathf.Clamp01(color.a + Time.unscaledDeltaTime / fadeTime);
                    transitionImage.color = color;
                    yield return null;
                }
                color.a = 1f;
                transitionImage.color = color;

                // 淡入完成后，确保场景已加载就绪（大多数情况下已经加载好了）
                yield return new WaitUntil(() => loadingOperation.progress >= 0.9f);
            }
            else
            {
                // 没有过渡图，直接等加载
                yield return new WaitUntil(() => loadingOperation.progress >= 0.9f);
            }

            loadingOperation.allowSceneActivation = true;

            // 等待场景切换完全完成（旧场景卸载 + 新场景渲染就绪）
            // 没有这一步会在场景交接时闪一帧旧场景的内容
            yield return null;
            yield return null;

            if (transitionImage != null)
            {
                // 淡出到透明
                while (color.a > 0f)
                {
                    color.a = Mathf.Clamp01(color.a - Time.unscaledDeltaTime / fadeTime);
                    transitionImage.color = color;
                    yield return null;
                }
                transitionImage.gameObject.SetActive(false);
            }

            // 加载完成，重置标志，允许下一次加载
            isLoading = false;
        }
    }
}