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。
    ///
    /// 搭建：把 SceneLoader 挂到一个空物体上（放第一个场景 MainMenu 里），
    /// 它会 DontDestroyOnLoad。transitionImage 是它子物体 Canvas 上的 Image（全屏黑），
    /// Canvas 设为 Screen Space - Overlay、sortingOrder 设很高（如 1000）。
    /// </summary>
    public class SceneLoader : PersistentSingleton<SceneLoader>
    {
        [Header("过渡")]
        [SerializeField] private Image transitionImage;
        [SerializeField] private float fadeTime = 1.5f;

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

        private Color color;

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

        private IEnumerator LoadingCoroutine(string sceneName)
        {
            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
                while (color.a < 1f)
                {
                    color.a = Mathf.Clamp01(color.a + Time.unscaledDeltaTime / fadeTime);
                    transitionImage.color = color;
                    yield return null;
                }
            }

            // 等异步加载到 90%
            yield return new WaitUntil(() => loadingOperation.progress >= 0.9f);

            loadingOperation.allowSceneActivation = true;

            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);
            }
        }
    }
}