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

namespace BaseGames.UI
{
    /// <summary>
    /// 右下角存档进行中提示（架构 10_UIModule §7.6）。
    /// 订阅 EVT_SaveIndicatorVisible（BoolEventChannelSO）：true = 淡入，false = 淡出。
    /// </summary>
    [RequireComponent(typeof(CanvasGroup))]
    public class SaveIndicator : MonoBehaviour
    {
        [SerializeField] private CanvasGroup        _cg;
        [SerializeField] private float              _fadeDuration = 0.2f;

        [Header("Event Channel")]
        [SerializeField] private BoolEventChannelSO _onSaveIndicatorVisible;  // EVT_SaveIndicatorVisible

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

        private void Awake()
        {
            if (_cg == null) _cg = GetComponent<CanvasGroup>();
            _cg.alpha = 0f;
        }

        private void OnEnable()
        {
            _onSaveIndicatorVisible?.Subscribe(OnVisibilityChanged).AddTo(_subs);
        }
        private void OnDisable()
        {
            _subs.Clear();
        }

        private void OnVisibilityChanged(bool visible) => FadeTo(visible ? 1f : 0f);

        private void FadeTo(float target)
        {
            if (_fadeCoroutine != null) StopCoroutine(_fadeCoroutine);
            _fadeCoroutine = StartCoroutine(FadeCoroutine(target));
        }

        private IEnumerator FadeCoroutine(float target)
        {
            float start   = _cg.alpha;
            float elapsed = 0f;
            while (elapsed < _fadeDuration)
            {
                _cg.alpha = Mathf.Lerp(start, target, elapsed / _fadeDuration);
                elapsed  += Time.unscaledDeltaTime;
                yield return null;
            }
            _cg.alpha = target;
        }
    }
}