using System;
using System.Collections.Generic;
using UnityEngine;

[ExecuteInEditMode]
public class ParticleUVAnimation : MonoBehaviour
{
    public ParticleSystem particle;
    private ParticleSystemRenderer particleRender;

    private MaterialPropertyBlock materialProperty;
    private Action animFunc;

    [Header("[textST.xy : tile, textST.zw : offset]")]
    public Vector4 texST;

    public bool running = false;

    public float fps;
    private float fpsStep;

    private Func<float> calcuateTime;

    private bool init = false;

    private int frameCount;
    private int frameIndex;
    private int tilesX;
    private float wStart;

    void Init()
    {
        if (particle == null)
            particle = GetComponent<ParticleSystem>();
        particleRender = GetComponent<ParticleSystemRenderer>();
        materialProperty = new MaterialPropertyBlock();
        particleRender.GetPropertyBlock(materialProperty);
        var sheetAnim = particle.textureSheetAnimation;
        if (sheetAnim.animation == ParticleSystemAnimationType.SingleRow)
            animFunc = SingleRowUpdate;
        else
            animFunc = WholeSheetUpdate;

        switch (sheetAnim.timeMode)
        {
            case ParticleSystemAnimationTimeMode.FPS:
                fps = sheetAnim.fps;
                fpsStep = 1.0f / fps;
                break;
            case ParticleSystemAnimationTimeMode.Lifetime: //临时写一下
                fps = sheetAnim.fps;
                fpsStep = 1.0f / fps;
                break;
            case ParticleSystemAnimationTimeMode.Speed:
                fps = sheetAnim.fps;
                fpsStep = 1.0f / fps;
                break;

        }
        frameCount = sheetAnim.numTilesX * sheetAnim.numTilesY;
        frameIndex = 0;
        tilesX = sheetAnim.numTilesX;
        texST.x = 1.0f / sheetAnim.numTilesX;
        texST.y = 1.0f / sheetAnim.numTilesY;
        texST.z = 0;
        texST.w = wStart = 1 - texST.y;

        materialProperty.SetVector("_MainTex_ST", texST);
        particleRender.SetPropertyBlock(materialProperty);

        lastTime = 0f;
        init = true;

    }
    public void Play()
    {
        running = true;
        //lastTime = Time.time;
    }

    void Awake()
    {
        Init();
    }

    void Update()
    {
        if (!running)
            return;
        if (!init)
            Init();
        animFunc();
    }

    private void WholeSheetUpdate()
    {
        CalculateOffset();
        materialProperty.SetVector("_MainTex_ST", texST);
        particleRender.SetPropertyBlock(materialProperty);
    }

    float lastTime;
    private void SingleRowUpdate()
    {
        //texST.z = CalculateXOffset(texST.z);
    }

    private void CalculateOffset()
    {
        if (Time.time > lastTime)
        {
            if (lastTime == 0)
                lastTime = Time.time + fpsStep;
            else
                lastTime += fpsStep;
            ++frameIndex;
            if (frameIndex >= frameCount)
                frameIndex -= frameCount;
            texST.z = (frameIndex % tilesX) * texST.x;
            texST.w = wStart - (frameIndex / tilesX) * texST.y;
        }
    }
}