// https://github.com/joeiddon/perlin/blob/master/perlin.js
let perlin = {
    rand_vect: function(){
        let theta = Math.random() * 2 * Math.PI;
        return {x: Math.cos(theta), y: Math.sin(theta)};
    },
    dot_prod_grid: function(x, y, vx, vy){
        let g_vect;
        let d_vect = {x: x - vx, y: y - vy};
        if (this.gradients[[vx,vy]]){
            g_vect = this.gradients[[vx,vy]];
        } else {
            g_vect = this.rand_vect();
            this.gradients[[vx, vy]] = g_vect;
        }
        return d_vect.x * g_vect.x + d_vect.y * g_vect.y;
    },
    smootherstep: function(x){
        return 6*x**5 - 15*x**4 + 10*x**3;
    },
    interp: function(x, a, b){
        return a + this.smootherstep(x) * (b-a);
    },
    seed: function(){
        this.gradients = {};
        this.memory = {};
    },
    get: function(x, y) {
        if (this.memory.hasOwnProperty([x,y]))
            return this.memory[[x,y]];
        let xf = Math.floor(x);
        let yf = Math.floor(y);
        //interpolate
        let tl = this.dot_prod_grid(x, y, xf,   yf);
        let tr = this.dot_prod_grid(x, y, xf+1, yf);
        let bl = this.dot_prod_grid(x, y, xf,   yf+1);
        let br = this.dot_prod_grid(x, y, xf+1, yf+1);
        let xt = this.interp(x-xf, tl, tr);
        let xb = this.interp(x-xf, bl, br);
        let v = this.interp(y-yf, xt, xb);
        this.memory[[x,y]] = v;
        return v;
    }
}
perlin.seed();

// http://davidbau.com/archives/2010/01/30/random_seeds_coded_hints_and_quintillions.html#more
!function(a,b,c,d,e,f,g,h,i){function j(a){var b,c=a.length,e=this,f=0,g=e.i=e.j=0,h=e.S=[];for(c||(a=[c++]);d>f;)h[f]=f++;for(f=0;d>f;f++)h[f]=h[g=s&g+a[f%c]+(b=h[f])],h[g]=b;(e.g=function(a){for(var b,c=0,f=e.i,g=e.j,h=e.S;a--;)b=h[f=s&f+1],c=c*d+h[s&(h[f]=h[g=s&g+b])+(h[g]=b)];return e.i=f,e.j=g,c})(d)}function k(a,b){var c,d=[],e=typeof a;if(b&&"object"==e)for(c in a)try{d.push(k(a[c],b-1))}catch(f){}return d.length?d:"string"==e?a:a+"\0"}function l(a,b){for(var c,d=a+"",e=0;e<d.length;)b[s&e]=s&(c^=19*b[s&e])+d.charCodeAt(e++);return n(b)}function m(c){try{return o?n(o.randomBytes(d)):(a.crypto.getRandomValues(c=new Uint8Array(d)),n(c))}catch(e){return[+new Date,a,(c=a.navigator)&&c.plugins,a.screen,n(b)]}}function n(a){return String.fromCharCode.apply(0,a)}var o,p=c.pow(d,e),q=c.pow(2,f),r=2*q,s=d-1,t=c["seed"+i]=function(a,f,g){var h=[];f=1==f?{entropy:!0}:f||{};var o=l(k(f.entropy?[a,n(b)]:null==a?m():a,3),h),s=new j(h);return l(n(s.S),b),(f.pass||g||function(a,b,d){return d?(c[i]=a,b):a})(function(){for(var a=s.g(e),b=p,c=0;q>a;)a=(a+c)*d,b*=d,c=s.g(1);for(;a>=r;)a/=2,b/=2,c>>>=1;return(a+c)/b},o,"global"in f?f.global:this==c)};if(l(c[i](),b),g&&g.exports){g.exports=t;try{o=require("crypto")}catch(u){}}else h&&h.amd&&h(function(){return t})}(this,[],Math,256,6,52,"object"==typeof module&&module,"function"==typeof define&&define,"random");
Math.seedrandom("aaa");

function iterTurtle(turtle, angle) {
    const p = perlin.get(turtle.x() / scale, turtle.y() / scale);
    // let p = perlin(turtle.x() / scale, turtle.y() / scale);
    turtle.seth(p * 45 + angle);
    turtle.forward(10);
}


const scale = 50.0;
let time;

// You can find the Turtle API reference here: https://turtletoy.net/syntax
Canvas.setpenopacity(1);

// Global code will be evaluated once.
const turtle = new Turtle();
turtle.penup();
turtle.goto(0, 0);
turtle.pendown();

const hTurtles = [];
for (let i = 0; i < 100; ++i) {
    const turtle = new Turtle();
    turtle.penup();
    turtle.goto(-100, (i - 50) * 5);
    turtle.pendown();
    hTurtles.push(turtle);
}

const vTurtles = [];
for (let i = 0; i < 100; ++i) {
    const turtle = new Turtle();
    turtle.penup();
    turtle.goto((i - 50) * 5, 100);
    turtle.pendown();
    vTurtles.push(turtle);
}

// The walk function will be called until it returns false.
function walk(i) {
    hTurtles.forEach((t) => iterTurtle(t, 0));
    vTurtles.forEach((t) => iterTurtle(t, -90));
    return hTurtles.some((turtle) => turtle.x() < 100)
        || vTurtles.some((turtle) => turtle.y() > -100);
}