Canvas.setpenopacity(-0.05);

const size = 200;

let turtles = [];
let nt, sync, iter = 0;

Turtle.prototype.withinBounds = function() {
    return this.x() >= this.bounds[0] && this.y() >= this.bounds[1] && this.x() < this.bounds[2] && this.y() < this.bounds[3];
}

Turtle.prototype.setBounds = function(...args) {
    this.bounds = [...args];
}

const spawnTurtle = (x = 0, y = 0, angle = 15) => {
    const turtle = new Turtle();
    turtle.penup();
    turtle.goto(x, y);
    turtle.seth(angle);
    turtle.root = true;
    turtle.pendown();
    turtle.health = 1000;
    return turtle;
}

function walk(i) {
    if (turtles.length) {
        turtles.map((turtle, idx) => {
            sync = Math.sin(0.25*iter+0.03*i+0.5*Math.cos(100+turtle.y()*(idx+1))*(idx+1))
            turtle.angle = 30*sync;
            iter%2==0 ? turtle.left(turtle.angle) : turtle.right(turtle.angle);
            turtle.forward(0.5);
            if (turtle.root && Math.abs(turtle.angle) > 2) {
                nt = turtle.clone();
                nt.angle = turtle.angle*10*sync;
                nt.setBounds(
                    Math.max(-100, turtle.x()-turtle.health),
                    Math.max(-100, turtle.y()-turtle.health),
                    Math.min(100, turtle.x()+turtle.health),
                    Math.min(100, turtle.y()+turtle.health)
                );
                turtles.push(nt);
            }
            turtle.health -= 0.02;
        });
        turtles = turtles.filter(turtle => {
            if (!turtle.withinBounds() || (Math.abs(turtle.x()) < 10 && (turtle.y() > -55 && turtle.y() < 55))) {
                iter++;
                return false;
            }
            return true;
        });
    }
    else {
        for (let n = 5; n > 0; n--) {
            nt = spawnTurtle(-50, -160+40*n, 360*Math.random());
            nt.setBounds(-size/2, -size/2, size/2, size/2);
            turtles.push(nt);    
        }
    }
    return i < 40000;
}