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

[ExecuteInEditMode] // 让脚本在编辑器模式下也能执行
public class ParticleAttractionPoint : MonoBehaviour
{
    [Header("吸附参数")]
    [Tooltip("粒子吸附目标点")]
    public Transform attractionPoint; // 吸附目标点
    [Tooltip("粒子生成多久后开始进行吸附")]
    [Range(0.0f, 100.0f)]
    public float delayTime = 0.0f; // 延迟时间
    [Tooltip("粒子开始进行吸附计算后的大小变化曲线")]
    public AnimationCurve SizeCurve = new AnimationCurve(); // 控制移动的曲线
    [Tooltip("是否使用距离比例计算")]
    public bool UseDistance = false;

    [Header("逐帧计算")]
    public float attractionSpeed=50.0f;

    [Header("距离比例计算")]
    [Range(0.001f, 2.0f)] // 限制时间缩放的最大值和最小值
    public float timeScale = 1.0f; // 时间缩放

    private ParticleSystem particleSystemComponent;
    private ParticleSystem.Particle[] particles;

    void OnEnable()  // 改用OnEnable替代Start,这样在编辑器中也能初始化
    {
        particleSystemComponent = GetComponent<ParticleSystem>();
        particles = new ParticleSystem.Particle[particleSystemComponent.main.maxParticles];
    }

    void LateUpdate()
    {
        if(!particleSystemComponent) return; // 添加空检查

        int particleCount = particleSystemComponent.GetParticles(particles);

        if(attractionPoint == null) return; // 添加目标点空检查

        for (int i = 0; i < particleCount; i++)
        {
            float lifePercent = 1.0f - (particles[i].remainingLifetime / particles[i].startLifetime);
            
            // 只有当粒子存在时间超过延迟时间才开始移动
            if(particles[i].startLifetime - particles[i].remainingLifetime >= delayTime)
            {
                //暂存粒子位置
                Vector3 startPos=particles[i].position;

                if (UseDistance)
                {
                // 位置计算方法1 重新计算剩余的距离比例
                float adjustedLifePercent = (particles[i].startLifetime - particles[i].remainingLifetime - delayTime) / 
                                          (particles[i].startLifetime - delayTime);
                // 根据距离比例计算位置
                particles[i].position = Vector3.Lerp(particles[i].position, attractionPoint.position, adjustedLifePercent*timeScale);
                } else
                {
                // 位置计算方法2 朝向吸附点移动
                Vector3 direction = (attractionPoint.position - particles[i].position).normalized;
                particles[i].position += direction * attractionSpeed * Time.deltaTime;
                }
                
                // 修正粒子size
                float distancePercent=Vector3.Distance(startPos, particles[i].position) / Vector3.Distance(startPos, attractionPoint.position);
                particles[i].startSize = particles[i].startSize * SizeCurve.Evaluate(distancePercent);

                // 当粒子到达目标点时立即消失,可能会有大量粒子，引起优化问题
                // if(Vector3.Distance(particles[i].position, attractionPoint.position) <= 0.9f) 
                // {
                //     particles[i].remainingLifetime = 0.0f;
                // }   

                // // 优化方法1 通过使用SqrMagnitude，可以避免开方运算
                // if (Vector3.SqrMagnitude(particles[i].position - attractionPoint.position) <= 0.9f * 0.9f)
                // {
                //     particles[i].remainingLifetime = 0.0f;
                // }

                // 优化方法2 使用Mathf.Approximately进行比较
                if (Mathf.Approximately(Vector3.Distance(particles[i].position, attractionPoint.position), 0.0f) || 
                    Vector3.Distance(particles[i].position, attractionPoint.position) <= 0.9f)
                {
                    particles[i].remainingLifetime = 0.0f;
                }
            }

            
        }

        particleSystemComponent.SetParticles(particles, particleCount);
    }
}