var vec = p5.Vector;

class Segment {
  constructor(x, y, size) {
    this.size = size;
    this.pos = new vec(x, y);
    this.forward = new vec(0, 0);
  }

  get_rel(angleOffset, dist) {
    let dir = vec.rotate(this.forward, angleOffset);
    dir.setMag(dist);
    return vec.add(this.pos, dir)
  }
  
  follow(targetX, targetY, parentForward = null) {
    let target = new vec(targetX, targetY);
    
    let targetForward = vec.sub(target, this.pos);
    let targetAngle = targetForward.heading();

    if (parentForward) {
      let parentAngle = parentForward.heading();
      let diff = targetAngle - parentAngle;

      while (diff < -PI) diff += TWO_PI;
      while (diff > PI) diff -= TWO_PI;

      let maxAngle = PI / 10; 
      diff = constrain(diff, -maxAngle, maxAngle);

      targetAngle = parentAngle + diff;
    }

    this.forward = p5.Vector.fromAngle(targetAngle);

    let segmentLength = 20;
    let dir = p5.Vector.mult(this.forward, -segmentLength);
    this.pos = vec.add(target, dir);
  }
}

var n = 0;
var sizes = [60, 55, 50, 40, 45, 47, 50, 45, 42, 39, 35, 30, 25, 22, 17, 13, ]
var segments = [];
function setup() {
  createCanvas(800, 800);
  n = sizes.length;
  for (let i = 0; i < n; i++) {
    let seg = new Segment(400, 400, sizes[i]);
    segments.push(seg);
  }
  
}

function draw() {
background(150);
  
  // fisica
  segments[0].follow(mouseX, mouseY);
  for (let i = 1; i < n; i++) {
    let prev_seg = segments[i - 1];
    segments[i].follow(prev_seg.pos.x, prev_seg.pos.y, prev_seg.forward);
  }

  // dibujar
  fill(249, 182, 249);
  stroke(0);
  strokeWeight(2);
  
  beginShape();

  let head = segments[0];
  let tail = segments[n - 1];

  for (let a = -HALF_PI; a <= HALF_PI; a += PI / 10) {
    let p = head.get_rel(a, head.size);
    vertex(p.x, p.y);
  }

  for (let i = 1; i < n - 1; i++) {
    let p = segments[i].get_rel(HALF_PI, segments[i].size);
    vertex(p.x, p.y);
  }

  for (let a = HALF_PI; a <= HALF_PI + PI; a += PI / 10) {
    let p = tail.get_rel(a, tail.size);
    vertex(p.x, p.y);
  }

  for (let i = n - 2; i >= 1; i--) {
    let p = segments[i].get_rel(-HALF_PI, segments[i].size);
    vertex(p.x, p.y);
  }


  endShape(CLOSE);

  let eye1 = head.get_rel(HALF_PI / 2, 45);
  let eye2 = head.get_rel(-HALF_PI / 2, 45);
  fill(0);
  circle(eye1.x, eye1.y, 12);
  circle(eye2.x, eye2.y, 12);
}