using UnityEngine;
using UnityEngine.UI;

[RequireComponent(typeof(Image))]
public class UiAnimation : MonoBehaviour
{
    private Image _image;
    private int _index;
    private float _nextTime;
    public float frameRate = 20f;
    public float delayBetweenCycle;
    public bool loop = true;
    public Sprite[] sprites;

    private void Awake()
    {
        _image = GetComponent<Image>();
    }

    private void OnEnable()
    {
        SetIndex(0);
    }

    private void Update()
    {
        if (Time.time > _nextTime)
        {
            _index++;
            if (_index >= sprites.Length)
            {
                if (loop)
                {
                    _index = 0;
                    SetImage();
                    _nextTime += GetFrameTime();
                }
                else
                {
                    _nextTime = float.PositiveInfinity;
                }
            }
            else
            {
                SetImage();
                if (_index < sprites.Length - 1)
                    _nextTime += GetFrameTime();
                else
                    _nextTime += Mathf.Max(GetFrameTime(), delayBetweenCycle);
            }
            // 防止一次渲染帧越过太多动画帧，然后导致动画快速播放
            _nextTime = Mathf.Max(_nextTime, Time.time);
        }
    }

    private float GetFrameTime()
    {
        return 1f / Mathf.Max(1, frameRate);
    }

    private void SetImage()
    {
        if (_index < sprites.Length)
            _image.sprite = sprites[_index];
    }

    public void SetIndex(int index)
    {
        _index = Mathf.Min(index, sprites.Length - 1);
        SetImage();
        _nextTime = Time.time + GetFrameTime();
    }
}