const canvas = document.body.appendChild(document.createElement("canvas"));

const c = canvas.getContext("2d");

document.body.style.margin = 0;

function resize() {

  canvas.width = innerWidth * 2;

  canvas.height = innerHeight * 2;

  canvas.style.width = innerWidth + "px";

  canvas.style.height = innerHeight + "px";

}

addEventListener("resize", resize);

resize();

const PAD = 50;

const RAD = 2;

const SPEED = 40;

const TWO_PI = Math.PI * 2;

let mode = "draw";

let t = Math.random() * TWO_PI,

  x = innerWidth,

  y = innerHeight,

  vx = 0,

  vy = 0,

  ta = 0,

  w = 10,

  h = 1,

  hue = 20;

function loop() {

  c.globalAlpha = 1;

  if (Math.random() < 0.12) {

    let alpha = 0.02;

    if (Math.random() < 0.1) alpha = 0.1;

    c.fillStyle = `rgba(255, 255, 255, ${alpha})`;

    c.fillRect(0, 0, canvas.width, canvas.height);

  }

  for (var i = 0; i < SPEED; i++) {

    t = Math.sin(ta) * TWO_PI;

    vx = RAD * Math.cos(t);

    vy = RAD * Math.sin(t);

    ta += Math.random() * 0.1 - 0.05;

    x += vx;

    y += vy;

    if (Math.random() < 0.005) {

      mode = "no draw";

      hue = [200, 20, 10, 40][~~(Math.random() * 4)];

      if (Math.random() < 0.5) {

        w = Math.random() * 200;

        h = Math.random() * Math.random() * 10;

      } else {

        w = Math.random() * 20;

        h = Math.random() * Math.random() * 200;

      }

    } else if (Math.random() < 0.005) {

      mode = "draw";

    }

    if (mode === "draw") {

      c.shadowColor = "rgba(0, 205, 205, 0.2)";

      c.shadowBlur = 5;

      c.fillStyle = `hsl(${hue}, 100%, 50%)`;

      c.fillRect(x, y, w, h);

      c.shadowColor = null;

      c.shadowBlur = 0;

    }

    if (x < -PAD) {

      x = innerWidth + PAD;

    } else if (x > canvas.width + PAD) {

      x = -PAD;

    }

    if (y < -PAD) {

      y = innerHeight + PAD;

    } else if (y > canvas.height + PAD) {

      y = -PAD;

    }

  }

  c.globalAlpha = 0.9;

  c.drawImage(canvas, -2, -1, canvas.width + 3, canvas.height + 4);

  requestAnimationFrame(loop);

}

loop();