let particles = [];
const numParticles = 25;
let cylinderRadius = 200;
let cylinderHeight = 400;
let sphereRadius = 300;
let rotationAngle = 0;
let zoom = 1;
let zoomDirection = 1;

function setup() {
  createCanvas(800, 800, WEBGL);
  colorMode(HSB, 360, 100, 100);
  
  for (let i = 0; i < numParticles; i++) {
    particles.push(new Particle(
      random(-cylinderRadius, cylinderRadius),
      random(-cylinderHeight/2, cylinderHeight/2),
      random(-cylinderRadius, cylinderRadius),
      i * (360/numParticles)
    ));
  }
}

function draw() {
  background(0);
  scale(zoom);
  
  zoom += 0.002 * zoomDirection;
  if (zoom > 1.5) zoomDirection = -1;
  if (zoom < 0.8) zoomDirection = 1;
  
  rotateY(rotationAngle);
  rotationAngle += 0.005;
  
  push();
  noFill();
  stroke(200, 50, 50, 50);
  sphere(sphereRadius);
  pop();
  
  push();
  noFill();
  stroke(100, 50, 50, 50);
  cylinder(cylinderRadius, cylinderHeight);
  pop();
  
  for (let particle of particles) {
    particle.update();
    particle.checkCollisions();
    particle.display();
  }
}

class Particle {
  constructor(x, y, z, hue) {
    this.pos = createVector(x, y, z);
    this.vel = p5.Vector.random3D().mult(random(2, 5));
    this.radius = 8;
    this.hue = hue;
    this.trail = [];
    this.maxTrailLength = 20;
  }
  
  update() {
    this.pos.add(this.vel);
    this.trail.push(this.pos.copy());
    if (this.trail.length > this.maxTrailLength) {
      this.trail.splice(0, 1);
    }
  }
  
  checkCollisions() {
    let radialDist = sqrt(this.pos.x * this.pos.x + this.pos.z * this.pos.z);
    if (radialDist + this.radius > cylinderRadius) {
      let normal = createVector(this.pos.x, 0, this.pos.z).normalize();
      let dotProduct = this.vel.dot(normal);
      this.vel.sub(normal.mult(2 * dotProduct));
      this.pos.set(
        this.pos.x * (cylinderRadius - this.radius) / radialDist,
        this.pos.y,
        this.pos.z * (cylinderRadius - this.radius) / radialDist
      );
    }
    
    if (this.pos.y + this.radius > cylinderHeight/2) {
      this.vel.y = -abs(this.vel.y);
      this.pos.y = cylinderHeight/2 - this.radius;
    }
    if (this.pos.y - this.radius < -cylinderHeight/2) {
      this.vel.y = abs(this.vel.y);
      this.pos.y = -cylinderHeight/2 + this.radius;
    }
    
    let distFromCenter = this.pos.mag();
    if (distFromCenter + this.radius > sphereRadius) {
      let normal = this.pos.copy().normalize();
      let dotProduct = this.vel.dot(normal);
      this.vel.sub(normal.mult(2 * dotProduct));
      this.pos.setMag(sphereRadius - this.radius);
    }
  }
  
  display() {
    push();
    noFill();
    strokeWeight(2);
    beginShape();
    for (let i = 0; i < this.trail.length; i++) {
      let alpha = map(i, 0, this.trail.length, 0, 100);
      stroke(this.hue, 80, 100, alpha);
      vertex(this.trail[i].x, this.trail[i].y, this.trail[i].z);
    }
    endShape();
    
    fill(this.hue, 80, 100);
    noStroke();
    translate(this.pos.x, this.pos.y, this.pos.z);
    sphere(this.radius);
    pop();
  }
}