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

/// <summary>
/// Throttled preload: uses queues and concurrency limits to load scenes and Resources in small time slices
/// to avoid long frames on low-end devices.
/// - scenesToPreload: names of scenes included in Build Settings to preload additively (allowSceneActivation=false)
/// - resourcesToPreload: paths under Resources/ to load via Resources.LoadAsync
/// </summary>
public class preload_allScene : MonoBehaviour
{
    [Header("Preload settings")]
    public string[] resourcesToPreload = new string[0];

    [Header("UI")]
    public Text progressText;
    [Tooltip("Optional Image whose fillAmount will be driven by the overall progress (0..1)")]
    public Image progressFillImage;
    [Tooltip("Optional Text to show current loading item: '���ڼ��أ�xxx'")]
    public Text loadingInfoText;

    [Header("Behavior")]
    public bool startOnAwake = true;

    [Header("Fade-out on complete")]
    [Tooltip("GameObject to disable after fade completes")] public GameObject fadeOutObject;
    [Tooltip("CanvasGroup to fade (if null and fadeOutObject assigned, will search for one on it)")] public CanvasGroup fadeCanvasGroup;
    [Tooltip("Duration of fade-out in seconds")] public float fadeOutDuration = 0.5f;
    [Tooltip("Delay before starting fade-out after completion")] public float fadeOutDelay = 0f;

    [Header("Throttle")]
    public int maxConcurrentResourceLoads = 2;
    [Tooltip("Max milliseconds spent per frame on driver work (approx)")]
    public int maxMilliSecondsPerFrame = 4;

    // internal queues and trackers
    private Queue<string> resourceQueue = new Queue<string>();

    private List<(string path, ResourceRequest rr)> activeResourceReqs = new List<(string, ResourceRequest)>();

    private List<Object> loadedResources = new List<Object>();

    private Coroutine preloadCoroutine;

    void Awake()
    {
        Debug.Log("[preload_allScene] Awake called. Forcing Time.timeScale = 1.");
        Time.timeScale = 1f; // Ensure time is running so fades and DOTween work

        if (fadeOutObject != null)
        {
            fadeOutObject.SetActive(true);
        }
        else
        {
            Debug.LogWarning("[preload_allScene] fadeOutObject is not assigned!");
        }
        
        // if UI not assigned, try to auto-find Text components
        if (progressText == null)
        {
            progressText = GetComponentInChildren<Text>(true);
        }

        if (loadingInfoText == null)
        {
            // try to find a different Text child (avoid using same as progressText)
            var texts = GetComponentsInChildren<Text>(true);
            foreach (var t in texts)
            {
                if (t != progressText)
                {
                    loadingInfoText = t;
                    break;
                }
            }
        }

        // If a fade object is set but no CanvasGroup assigned, try to find one on the object
        if (fadeOutObject != null && fadeCanvasGroup == null)
        {
            fadeCanvasGroup = fadeOutObject.GetComponent<CanvasGroup>() ?? fadeOutObject.GetComponentInChildren<CanvasGroup>(true);
        }
    }

    void Start()
    {
        Debug.Log("[preload_allScene] Start called. resourcesToPreload count: " + (resourcesToPreload?.Length ?? 0));
        // Always call StartPreload to ensure the screen fades out even if no resources are listed
        StartPreload();
    }

    public void StartPreload()
    {
        if (preloadCoroutine != null) return;

        // fill queues
        resourceQueue.Clear();

        if (resourcesToPreload != null)
        {
            foreach (var r in resourcesToPreload)
                if (!string.IsNullOrWhiteSpace(r)) resourceQueue.Enqueue(r);
        }

        Debug.Log($"Preload starting. Resources queued: {resourceQueue.Count}");

        // ensure UI shows 0%
        UpdateProgressText(0f);
        UpdateLoadingInfo("");

        // If nothing to preload, just show 100% and fade out immediately
        if (resourceQueue.Count == 0)
        {
            UpdateProgressText(1f);
            UpdateLoadingInfo("Loading Complete");
            if (fadeOutObject != null)
            {
                StartCoroutine(FadeAndDisableCoroutine());
            }
            return;
        }

        preloadCoroutine = StartCoroutine(PreloadRoutine());
    }

    public void StopPreload()
    {
        if (preloadCoroutine != null)
        {
            StopCoroutine(preloadCoroutine);
            preloadCoroutine = null;
        }
    }

    private IEnumerator PreloadRoutine()
    {
        // Start initial batch
        while (resourceQueue.Count > 0 || activeResourceReqs.Count > 0)
        {
            float frameStart = Time.realtimeSinceStartup;

            // start resource reqs up to concurrency
            while (activeResourceReqs.Count < maxConcurrentResourceLoads && resourceQueue.Count > 0)
            {
                string path = resourceQueue.Dequeue();
                UpdateLoadingInfo($"Loading: {path}");
                ResourceRequest rr = null;
                try
                {
                    rr = Resources.LoadAsync<Object>(path);
                }
                catch (System.Exception ex)
                {
                    Debug.LogWarning($"Preload: failed to start loading resource '{path}': {ex}");
                }

                if (rr != null)
                {
                    activeResourceReqs.Add((path, rr));
                    Debug.Log($"Preload: started resource load '{path}'");
                }

                if ((Time.realtimeSinceStartup - frameStart) * 1000f > maxMilliSecondsPerFrame) break;
            }

            // Poll progress and collect finished resources
            for (int i = activeResourceReqs.Count - 1; i >= 0; i--)
            {
                var tuple = activeResourceReqs[i];
                var rr = tuple.rr;
                if (rr.isDone)
                {
                    if (rr.asset != null)
                        loadedResources.Add(rr.asset);
                    Debug.Log($"Preload: resource loaded '{tuple.path}'");
                    activeResourceReqs.RemoveAt(i);
                }

                if ((Time.realtimeSinceStartup - frameStart) * 1000f > maxMilliSecondsPerFrame) break;
            }

            // Update progress calculation
            float overall = CalculateOverallProgress();
            UpdateProgressText(overall);

            // If there are no active resource requests and no queued resources, we're done
            bool anyActiveResources = activeResourceReqs.Count > 0 || resourceQueue.Count > 0;

            if (!anyActiveResources)
            {
                UpdateProgressText(1f);
                UpdateLoadingInfo("Loading Complete");
                preloadCoroutine = null;
                Debug.Log("Preload complete (throttled). Resources cached: " + loadedResources.Count);

                // start fade+disable if configured
                if (fadeOutObject != null)
                {
                    StartCoroutine(FadeAndDisableCoroutine());
                }

                yield break;
            }

            // yield one frame to respect budget
            yield return null;
        }

        // if we exit loop, also mark complete
        UpdateProgressText(1f);
        UpdateLoadingInfo("Loading Complete");
        preloadCoroutine = null;
        if (fadeOutObject != null)
        {
            StartCoroutine(FadeAndDisableCoroutine());
        }
    }

    private float CalculateOverallProgress()
    {
        float sum = 0f;
        int items = 0;

        items += resourceQueue.Count + activeResourceReqs.Count;

        if (items == 0) return 1f;

        foreach (var (path, rr) in activeResourceReqs)
        {
            sum += rr.progress; // 0..1
        }

        return Mathf.Clamp01(sum / (float)items);
    }

    private void UpdateProgressText(float t)
    {
        int percent = Mathf.RoundToInt(t * 100f);

        // update fill image if present
        if (progressFillImage != null)
        {
            // clamp to 0..1
            progressFillImage.fillAmount = Mathf.Clamp01(t);
        }

        if (progressText != null)
        {
            progressText.text = percent + "%";
            return;
        }

        // If no UI assigned, try to find any in children and cache it
        var tcomp = GetComponentInChildren<Text>(true);
        if (tcomp != null)
        {
            progressText = tcomp;
            progressText.text = percent + "%";
        }
    }

    // helper to update loading info text
    private void UpdateLoadingInfo(string message)
    {
        if (loadingInfoText != null)
        {
            loadingInfoText.text = message;
            return;
        }

        // try to find and cache a Text child that is not the progress text
        var texts = GetComponentsInChildren<Text>(true);
        foreach (var t in texts)
        {
            if (t != progressText)
            {
                loadingInfoText = t;
                loadingInfoText.text = message;
                return;
            }
        }
    }

    private IEnumerator FadeAndDisableCoroutine()
    {
        // ensure we have a CanvasGroup reference
        if (fadeOutObject == null) yield break;

        if (fadeCanvasGroup == null)
        {
            fadeCanvasGroup = fadeOutObject.GetComponent<CanvasGroup>() ?? fadeOutObject.GetComponentInChildren<CanvasGroup>(true);
        }

        // if there's no CanvasGroup, just disable after delay
        if (fadeCanvasGroup == null)
        {
            if (fadeOutDelay > 0f) yield return new WaitForSecondsRealtime(fadeOutDelay);
            fadeOutObject.SetActive(false);
            yield break;
        }

        // optionally wait before fading
        if (fadeOutDelay > 0f) yield return new WaitForSecondsRealtime(fadeOutDelay);

        float startAlpha = fadeCanvasGroup.alpha;
        float elapsed = 0f;
        while (elapsed < fadeOutDuration)
        {
            elapsed += Time.unscaledDeltaTime;
            float frac = Mathf.Clamp01(elapsed / Mathf.Max(0.0001f, fadeOutDuration));
            fadeCanvasGroup.alpha = Mathf.Lerp(startAlpha, 0f, frac);
            yield return null;
        }

        fadeCanvasGroup.alpha = 0f;
        // disable raycasts and interaction
        fadeCanvasGroup.blocksRaycasts = false;
        fadeCanvasGroup.interactable = false;

        // finally disable the GameObject
        fadeOutObject.SetActive(false);
    }
}