using UnityEngine;

namespace AibisDream.Kit
{
    public class SpriteLooper : MonoBehaviour
    {
        private SpriteRenderer _fadeOutRenderer;
        private SpriteRenderer _fadeInRenderer;

        public Sprite[] sprites;
        [Range(0, 1)]public float fadeRadio;

        public float CurProgress { get; private set; }

        private void Awake()
        {
            InitRefs();
        }

        private void InitRefs()
        {
            _fadeOutRenderer = transform.Find("Sprite1").GetComponent<SpriteRenderer>();
            _fadeInRenderer = transform.Find("Sprite2").GetComponent<SpriteRenderer>();
        }

        public void Init()
        {
            CurProgress = 0;
            // 激活初始状态
            _fadeOutRenderer.sprite = sprites[0];
            _fadeOutRenderer.color = Color.white;
            _fadeInRenderer.sprite = sprites[1];
            _fadeInRenderer.color = Color.clear;
        }

        public void SetLoopProgress(float progress)
        {
            CurProgress = progress;

            // 将进度条转为图片序号和淡出进度
            var calculator = new LoopDataCalculator(progress, sprites.Length, fadeRadio);

            _fadeOutRenderer.sprite = sprites[calculator.CurIdx];
            _fadeOutRenderer.color = calculator.FadeOutColor;
            _fadeInRenderer.sprite = sprites[calculator.NextIdx];
            _fadeInRenderer.color = calculator.FadeInColor;
        }
    }

    public readonly struct LoopDataCalculator
    {
        private readonly float _progress;
        private readonly float _localProgress;
        private readonly float _fadeRadio;
        public int CurIdx { get; }
        public int NextIdx { get; }

        public LoopDataCalculator(float progress, int spriteCount, float fadeRadio)
        {
            _progress = progress;
            _localProgress = 1 / (float)spriteCount;
            _fadeRadio = fadeRadio;
            CurIdx = Mathf.FloorToInt(progress / _localProgress);
            NextIdx = CurIdx + 1 >= spriteCount ? 0 : CurIdx + 1;
        }

        private float LeftProgress =>
            Mathf.Clamp01((_progress - (CurIdx + 1 - _fadeRadio) * _localProgress) / (_localProgress * _fadeRadio));

        public Color FadeOutColor => new(1f, 1f, 1f, 1 - LeftProgress);

        public Color FadeInColor => new(1f, 1f, 1f, LeftProgress);
    }
}