using System;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
using UnityEngine;
using UnityEngine.SceneManagement;

public class SceneLoadManager : MonoBehaviour
{
    public static SceneLoadManager Instance;

    [SerializeField] private GameObject _loadingRoot;
    [SerializeField] private Camera _loadingCam;
    [SerializeField] private Transform _loadingCamTargetTransform;
    [SerializeField] private LoadingScreen _loadingScreen;

    private void Awake()
    {
        if (Instance == null)
        {
            Instance = this; //만들어진 자신을 인스턴스로 설정
        }
        else
        {
            Destroy(gameObject); //이미 인스턴스가 있으면 자신을 파괴
        }    
    
        _loadingScreen = _loadingCam.GetComponentInChildren<LoadingScreen>();
    }

    private void Start()
    {
        SceneManager.sceneLoaded += OnSceneLoaded;
    }

    private void Update()
    {
        if(_loadingCamTargetTransform != null)
        {
            _loadingCam.transform.position = _loadingCamTargetTransform.position;
            _loadingCam.transform.rotation = _loadingCamTargetTransform.rotation;
        }
    }

    private void OnSceneLoaded(Scene scene, LoadSceneMode mode)
    {
        // 씬이 로드될 때마다
        
    }

    public async Awaitable FadeLoadingCanvas(bool isOut,float fadeTime)
    {
        float startAlpha = isOut ? 1f : 0f;
        float endAlpha = isOut ? 0f : 1f;

        float timer = 0;
        _loadingScreen.LoadingScreenCanvasGroup.alpha = startAlpha;

        while(timer < fadeTime)
        {
            timer += Time.deltaTime;
            _loadingScreen.LoadingScreenCanvasGroup.alpha = Mathf.Lerp(startAlpha, endAlpha, timer / fadeTime);
            await Awaitable.NextFrameAsync(this.destroyCancellationToken); 
        }

        _loadingScreen.LoadingScreenCanvasGroup.alpha = endAlpha;
    }

    public async Task SetSceneLoadingActive(bool isActive,float alphaTime)
    {
        if (isActive)
            _loadingRoot.SetActive(true);

        if (alphaTime > 0f)
        {
            await FadeLoadingCanvas(!isActive,alphaTime);
        }

        if (!isActive)
            _loadingRoot.SetActive(false);
    }

    public void SetSceneLoadingActive(bool isActive)
    {
        _ = SetSceneLoadingActive(isActive, 0f);
    }

    public void SetSceneLoadingProgressValue(float value)
    {
        _loadingScreen.LoadingImage.fillAmount = value;
        _loadingScreen.LoadingTextMeshProUGUI.text = $"{(value * 100):F0}% 로딩 중...";
    }
    public void SetSceneLoadingProgressValue(float value,string loadingText)
    {
        _loadingScreen.LoadingImage.fillAmount = value;
        _loadingScreen.LoadingTextMeshProUGUI.text = loadingText;
    }

    public void RequestSceneChange(string sceneName)
    {
        _ = SceneChange(sceneName);
    }

    private async Awaitable SceneChange(string sceneName)
    {
        try
        {
            SetSceneLoadingProgressValue(0f);

            await SetSceneLoadingActive(true,1f);

            AsyncOperation op = SceneManager.LoadSceneAsync(sceneName);

            //자동 전환을 하고 싶지 않을 경우 해당값을 false로 두었다가 true로 바꾸면 그 때 전환됨
            op.allowSceneActivation = false;

            //화면에 보여줄 로딩 수치
            float displayProgress = 0f;

            //op.progress 0.9가 데이터 로딩이 끝난 기준 allowSceneActivation이 트루면 바로 다음으로 넘어가면서 op.isDone이 true가 된다.
            while (op.progress < 0.9f) 
            {
                //실제 로딩 수치
                float realProgress = Mathf.Clamp01(op.progress / 0.9f);

                //보여줄 값을 실제값을 향해 부드럽게 이동
                displayProgress = Mathf.MoveTowards(displayProgress, realProgress, Time.deltaTime * 0.5f);

                // UI에 적용
                SetSceneLoadingProgressValue(displayProgress);

                await Awaitable.NextFrameAsync(this.destroyCancellationToken); //자기자신이 파괴될때 토큰에 취소요청을 보냄
            }

            SetSceneLoadingProgressValue(1);

            // 잠시 대기했다가 전환
            await Awaitable.WaitForSecondsAsync(1.0f, this.destroyCancellationToken);

            //로딩 끝
            op.allowSceneActivation = true;

            // 씬 활성화가 완전히 끝날 때까지 대기
            // allowSceneActivation가 true가 되고 완전히 전환되기까지는 몇프레임 걸림. op.isDone 은 이 과정이 끝난 뒤에 true가 됨.
            while(!op.isDone)
            {
                await Awaitable.NextFrameAsync(this.destroyCancellationToken);
            }

            //VR용 로직
            //트래킹이 중단되면 안되기 때문에 카메라를 유지해야 한다
            _loadingCamTargetTransform = Camera.main.transform; // 새로운 씬의 메인카메라를 따라가게끔 설정
            await SetSceneLoadingActive(false,1f);
            //-------------------------------------------------------------------------------

            Debug.Log("씬 전환됨");
        }
        catch (OperationCanceledException)
        {
            Debug.Log("씬 전환 작업이 취소됨");
        }
    }
}