let heading = null;

let endHeading = null;

​

function setup() {

  createCanvas(600, 600);

  trail.push(createVector(0, 0));

  heading = createVector(1, 0);

  endHeading = heading;

}

​

function draw() {

  trail.unshift(

    trail[0].copy().add(

      createVector(mouseX, mouseY).sub(trail[0]).mult(0.4)

    )

  );

  if (trail.length > 50) {

    trail.pop();

  }

  if (trail.length > 1) {

    const diff = trail[0].copy().sub(trail[Math.min(5, trail.length-1)]);

    if (diff.mag() > 0) {

      heading = diff.normalize();

    }

    const rearDiff = trail[trail.length-Math.min(5, trail.length-1)].copy().sub(trail[trail.length-1]);

    if (rearDiff.mag() > 0) {

      endHeading = rearDiff.normalize();

    }

  }

  trail.forEach((pt, i) => {

    const distFromHead = pt.copy().sub(trail[0]).mag();

    const alpha = 1/Math.pow(distFromHead + 3, 2);

    const pos = pt.copy().mult(1 - alpha).add(

      trail[0].copy().add(heading.copy().mult(-20*i)).mult(alpha)

    );

    trail[i] = pos;

  });

  let totalLength = 0;

  for (let i = 1; i < trail.length; i++) {

    totalLength += trail[i].copy().sub(trail[i-1]).mag();

  }

  background(220);

  noFill();

  stroke(0);

  strokeJoin(ROUND);

  strokeCap(ROUND);

  const thickness = 20 + 100/(totalLength/40 + 1);

  strokeWeight(thickness);

  beginShape();

  trail.forEach(pt => vertex(pt.x, pt.y));

  endShape();

  const stretch = Math.min(totalLength/40, 1.35);

  push();

  translate(trail[0].x, trail[0].y);

  rotate(heading.heading());

  translate(-120/thickness, 0);

  scale(1 * stretch, 1 / stretch);

  strokeWeight(10);

  line(0, 0, 15, -50);

  line(-15, 0, 0, -50);

  noStroke();

  fill(0);

  circle(0, -15, 30);

  [-1, 1].forEach(side => {

    push();

    scale(side, 1);

    fill(0);

    beginShape();

    vertex(0, 5);

    vertex(10, 50);

    vertex(20, 5);

    endShape(CLOSE);

    circle(10, -10, 30);

​

    fill(255);

    circle(15, 0, 10);

    pop();

  });

  pop();

  push();

  translate(trail[trail.length-1].x, trail[trail.length-1].y);

  rotate(endHeading.heading());

  translate(-120/thickness, 0);

  scale(1 * stretch, 1 / stretch);

  stroke(0);

  noFill();

  strokeWeight(10);

  line(0, 0, -15, -50);

  line(15, 0, 0, -50);

  bezier(0, 0, 0, 100, -50, 100, -50, 50);

  pop();

}