// Forked from "Continuous line drawing" by markknol
// https://turtletoy.net/turtle/7d37b38d32

const turtle = new Turtle();

const seed = -1; // min=-1, max=1234, step=1
const grid = 200; // min=4, max=300, step=4
const size = 80;  // min=50, max=100, step=5
const distortionX = 1; // min=0, max=20, step=0.1
const distortionY = 8; // min=0, max=20, step=0.1
const radial = 2.5;
const steps = 6 // min=2, max=20, step=1

const aseed = seed === -1 ? Math.random()*12345678|0 : seed;
console.log({aseed})
const noise = new SimplexNoise(aseed);

function rnd(amount = 1.0, rnd = Math.random()) {
   return Math.floor((-0.5 + Math.abs(smoothstep(rnd)%1)) * steps) / steps * amount;
}

function walk(i) {
    let x = i % grid
    let y = i / grid | 0;
    if (y % 2) x = grid - x;
    
    let tx = x/grid;
    let ty = y/grid;
    
    const pos = [-size+tx*size*2,-size+ty*size*2];
    
    r = (radial * 0.5) - Math.abs(((0.5-tx)**2 + (0.5-ty)**2)) * radial;
    
    const f = 0.05; // min=0.001, max=0.02, step=0.0001
    const fs = 2; // min=0, max=3, step=0.0001
    const n1 = rnd(noise.noise2D([pos[0] * f*fs, pos[1] * f*fs]));
    const n2 = rnd(noise.noise2D([pos[1] * f, pos[0] * f]));
    const n3 = noise.noise2D([(pos[1]) * f * n1, (pos[0]) * f * n2]);
    
    pos[0] += rnd(distortionX * r, n3);
    pos[1] += rnd(distortionY * r, n3); 
    
    if (i === 0) turtle.jump(pos);
    else turtle.goto(pos);
    
    return i < (grid ** 2) + grid - 1;
}

function smoothstep(t) {
    return t * t * (3 - 2 * t);
}

////////////////////////////////////////////////////////////////
// Simplex Noise utility code. Created by Reinder Nijhoff 2020
// https://turtletoy.net/turtle/6e4e06d42e
// Based on: http://webstaff.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf
////////////////////////////////////////////////////////////////
function SimplexNoise(seed = 1) {
	const grad = [  [1, 1, 0], [-1, 1, 0], [1, -1, 0], [-1, -1, 0],
	            	[1, 0, 1], [-1, 0, 1], [1, 0, -1], [-1, 0, -1],
            		[0, 1, 1], [0, -1, 1], [0, 1, -1], [0, -1, -1] ];
	const perm = new Uint8Array(512);
            		
	const F2 = (Math.sqrt(3) - 1) / 2, F3 = 1/3;
	const G2 = (3 - Math.sqrt(3)) / 6, G3 = 1/6;

	const dot2 = (a, b) => a[0] * b[0] + a[1] * b[1];
	const sub2 = (a, b) => [a[0] - b[0], a[1] - b[1]];
	const dot3 = (a, b) => a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
	const sub3 = (a, b) => [a[0] - b[0], a[1] - b[1], a[2] - b[2]];

	class SimplexNoise {
		constructor(seed = 1) {
			for (let i = 0; i < 512; i++) {
				perm[i] = i & 255;
			}
			for (let i = 0; i < 255; i++) {
				const r = (seed = this.hash(i+seed)) % (256 - i)  + i;
				const swp = perm[i];
				perm[i + 256] = perm[i] = perm[r];
				perm[r + 256] = perm[r] = swp;
			}
		}
		noise2D(p) {
			const s = dot2(p, [F2, F2]);
			const c = [Math.floor(p[0] + s), Math.floor(p[1] + s)];
			const i = c[0] & 255, j = c[1] & 255;
			const t = dot2(c, [G2, G2]);

			const p0 = sub2(p, sub2(c, [t, t]));
			const o  = p0[0] > p0[1] ? [1, 0] : [0, 1];
			const p1 = sub2(sub2(p0, o), [-G2, -G2]);
			const p2 = sub2(p0, [1-2*G2, 1-2*G2]);
			
			let n =  Math.max(0, 0.5-dot2(p0, p0))**4 * dot2(grad[perm[i+perm[j]] % 12], p0);
			    n += Math.max(0, 0.5-dot2(p1, p1))**4 * dot2(grad[perm[i+o[0]+perm[j+o[1]]] % 12], p1);
		    	n += Math.max(0, 0.5-dot2(p2, p2))**4 * dot2(grad[perm[i+1+perm[j+1]] % 12], p2);
			
			return 70 * n;
		}
		hash(i) {
            i = 1103515245 * ((i >> 1) ^ i);
            const h32 = 1103515245 * (i ^ (i>>3));
            return h32 ^ (h32 >> 16);
		}
	}
	return new SimplexNoise(seed);
}