// You can find the Turtle API reference here: https://turtletoy.net/syntax
Canvas.setpenopacity(0.85);

// Global code will be evaluated once.
const turtle = new Turtle();
turtle.penup();
////////////////////////////////////////////////////////////////////////////
turtle.quadraticCurveTo = (cx, cy, x1, y1, steps = 20) => {
    const s = 1 / steps;
    const p = turtle.pos();
    const x0 = p[0];
    const y0 = p[1];
    for (let t = 0; t < 1; t += s) {
        turtle.goto(
            (1 - t) * (1 - t) * x0 + 2 * (1 - t) * t * cx + t * t * x1,
            (1 - t) * (1 - t) * y0 + 2 * (1 - t) * t * cy + t * t * y1
        );
    }
    turtle.goto(x1, y1);
};
////////////////////////////////////////////////////////////////////////////
// quadratic curve maths adapted from: http://wa.zozuar.org/code.php?c=9os2
// LOVE MATRIX by nutsu, a study for drawing curl curve.
class Mat2 {
	constructor() {
		this.a = 1.0;
		this.b = 0.0;
		this.c = 0.0;
		this.d = 1.0;
		this.tx = 0.0;
		this.ty = 0.0;
	}
	static create() {
		return new Mat2();
	}
	multiply(b) {
		const aa = this.a, ab = this.b, ac = this.c, ad = this.d;
		this.a = aa * b.a + ac * b.b;
		this.b = ab * b.a + ad * b.b;
		this.c = aa * b.c + ac * b.d;
		this.d = ab * b.c + ad * b.d;
		this.tx += aa * b.tx + ac * b.ty;
		this.ty += ab * b.tx + ad * b.ty;
		return this;
	}
	rotate(rad) {
		const aa = this.a, ab = this.b, ac = this.c, ad = this.d;
		const s = Math.sin(rad);
		const c = Math.cos(rad);
		this.a = aa * c + ac * s;
		this.b = ab * c + ad * s;
		this.c = aa * -s + ac * c;
		this.d = ab * -s + ad * c;
		return this;
	}
	translate(x, y) {
		this.tx += this.a * x + this.c * y;
		this.ty += this.b * x + this.d * y;
		return this;
	}
	scale(x, y) {
		this.a *= x;
		this.b *= x;
		this.c *= y;
		this.d *= y;
		return this;
	}
}
class WormObject {
	constructor(x, y, vx, vy, len) {
		this.vmt = Mat2.create().translate(x, y).rotate(Math.atan2(vy, vx));
		const angle = (Math.random() * Math.PI / 2) - (Math.PI / 4);
		this.tmt = Mat2.create().scale(0.92, 0.92).translate(len, 0).rotate(angle);
		this.c1x = this.p1x = -0.5 * this.vmt.c + this.vmt.tx;
		this.c1y = this.p1y = -0.5 * this.vmt.d + this.vmt.ty;
		this.c2x = this.p2x =  0.5 * this.vmt.c + this.vmt.tx;
		this.c2y = this.p2y =  0.5 * this.vmt.d + this.vmt.ty;
		this.r = angle;
		this.w = len * 0.4;
	}
	draw() {
		if (Math.random() > 0.9) {
			this.tmt.rotate(-this.r * 2);
			this.r *= -1;
		}
		this.vmt.multiply(this.tmt);
		const cc1x = -this.w * this.vmt.c + this.vmt.tx;
		const cc1y = -this.w * this.vmt.d + this.vmt.ty;
		const pp1x = (this.c1x + cc1x) / 2;
		const pp1y = (this.c1y + cc1y) / 2;
		const cc2x = this.w * this.vmt.c + this.vmt.tx;
		const cc2y = this.w * this.vmt.d + this.vmt.ty;
		const pp2x = (this.c2x + cc2x) / 2;
		const pp2y = (this.c2y + cc2y) / 2;
		turtle.goto(this.p1x, this.p1y);
		turtle.down();
		turtle.quadraticCurveTo(this.c1x, this.c1y, pp1x, pp1y);
		turtle.goto(pp2x, pp2y);
		turtle.quadraticCurveTo(this.c2x, this.c2y, this.p2x, this.p2y);
		turtle.up();
		this.c1x = cc1x;
		this.c1y = cc1y;
		this.p1x = pp1x;
		this.p1y = pp1y;
		this.c2x = cc2x;
		this.c2y = cc2y;
		this.p2x = pp2x;
		this.p2y = pp2y;
	}
}
// The walk function will be called until it returns false.
let px = 0, py = -20;
function walk(i) {
	const t = i / 20;
	const x = 4 * (16 * Math.pow(Math.sin(t), 3));
	const y = -4 * (13 * Math.cos(t) - 5 * Math.cos(2 * t) - 2 * Math.cos(3 * t) - Math.cos(4 * t));
	const vx = x - px;
	const vy = y - py;
	px = x;
	py = y;
	let len = 1.3 * Math.sqrt(vx * vx + vy * vy);
	if (Math.random() > 0.95) len *= 2;
	const o = new WormObject(x, y, -vx, -vy, len);
	for (let j = 0; j < 50; j++) {
        const x = o.vmt.a * o.vmt.a + o.vmt.b * o.vmt.b;
        if (x * o.w < 0.02) break;
	    o.draw();
	}
    return i < 120;
}