using System.Collections;
using UnityEngine;
using BaseGames.Core.Events;

namespace BaseGames.UI
{
    /// <summary>
    /// 全屏黑幕渐入渐出遮罩（架构 10_UIModule §8）。
    /// 由 SceneLoader 通过 EVT_LoadingOverlay BoolEventChannelSO 触发。
    /// true = 淡入（遮挡场景），false = 淡出（显示场景）。
    /// </summary>
    [RequireComponent(typeof(CanvasGroup))]
    public class LoadingOverlay : MonoBehaviour
    {
        [SerializeField] private CanvasGroup        _canvasGroup;
        [SerializeField] private float              _fadeDuration = 0.3f;

        [Header("Event Channel")]
        [SerializeField] private BoolEventChannelSO _onLoadingOverlayRequested;  // EVT_LoadingOverlay

        private Coroutine _fadeCoroutine;
        private readonly CompositeDisposable _subs = new();

        private void Awake()
        {
            if (_canvasGroup == null)
                _canvasGroup = GetComponent<CanvasGroup>();
            // 初始状态：完全透明，不阻挡射线
            _canvasGroup.alpha         = 0f;
            _canvasGroup.blocksRaycasts = false;
        }

        private void OnEnable()  => _onLoadingOverlayRequested?.Subscribe(SetVisible).AddTo(_subs);
        private void OnDisable() => _subs.Clear();

        public void SetVisible(bool visible)
        {
            if (_fadeCoroutine != null) StopCoroutine(_fadeCoroutine);
            _fadeCoroutine = StartCoroutine(FadeCoroutine(visible ? 1f : 0f));
        }

        private IEnumerator FadeCoroutine(float target)
        {
            float start = _canvasGroup.alpha;
            float elapsed = 0f;

            // 遮挡时立刻阻挡射线，让开时完成后再放开
            if (target > 0.5f) _canvasGroup.blocksRaycasts = true;

            while (elapsed < _fadeDuration)
            {
                _canvasGroup.alpha = Mathf.Lerp(start, target, elapsed / _fadeDuration);
                elapsed += Time.unscaledDeltaTime;
                yield return null;
            }
            _canvasGroup.alpha         = target;
            _canvasGroup.blocksRaycasts = target > 0.5f;
        }
    }
}