const g = 10 + 5 * Math.random();
const bx = 2 * Math.random();
const by = -10 - 130 * Math.random();
const dt = 0.0001 + 0.0009 * Math.random();

console.log('g', g, 'bx', bx, 'by', by, 'dt', dt);

class Vector {
    constructor(x, y) {
        this.x = x;
        this.y = y;
    }

    mul(a) {
        return new Vector(this.x * a, this.y * a);
    }

    sub(v) {
        return new Vector(this.x - v.x, this.y - v.y);
    }

    add(v) {
        return new Vector(this.x + v.x, this.y + v.y);
    }

    len() {
        return Math.sqrt(this.x * this.x + this.y * this.y);
    }

    lenSqr() {
        return this.x * this.x + this.y * this.y;
    }

    norm() {
        return this.mul(1 / this.len());
    }
}

class Body {
    constructor(position, speed, mass) {
        this.position = position;
        this.speed = speed;
        this.mass = mass;
    }
}

function simulate(dt, staticBody, body) {

    let bbV = staticBody.position.sub(body.position);
    let fAbs = g * body.mass * staticBody.mass / bbV.len();
    let f = bbV.norm().mul(fAbs);
    let a = f.mul(1 / body.mass);
    let dv = a.mul(dt);

    let dr = body.speed.mul(dt);
    body.position = body.position.add(dr);
    body.speed = body.speed.add(dv);
}

let body = new Body(new Vector(50, 50), new Vector(bx, by), 10);
let staticBody = new Body(new Vector(0, 0), new Vector(0, 0), 1000);


Canvas.setpenopacity(0.8);


const turtle = new Turtle();
turtle.penup();
turtle.goto(body.position.x, body.position.y);
turtle.pendown();


function walk(i) {
    staticBody.position = new Vector(0, 0).add(new Vector(20*Math.cos(i/150000), 20*Math.sin(i/150000)));
    for (let j=0; j<10; j++) {
        simulate(dt, staticBody, body);    
    }
    turtle.goto(body.position.x, body.position.y);
    return i < 4000000;
}