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

// Global code will be evaluated once.
const turtles = [];
let seed = 1000; // min=1, max=1000000, step=1
const bits = 20; 
const samples = 150000; 
const mod = 1<<bits;
const turtles_count = 351; // min = 1 max = 1000 step = 1
const steps = 2000 // min = 1 max = 3000 step = 1
const angle_perlin = 3; // min = 1 max = 10 step = 1
const angle_perlin_mag = 3.4; // min = .1 max = 5 step = .1
const length_perlin = 3; // min = 1 max = 10 step = 1
const length_perlin_mag = 1; // min = .1 max = 5 step = .1
const spawn_range = 9; // min = 0 max = 100 step = 1

function random() { // returns a number [0, 1[
    let r = 1103515245 * (((seed+=12345) >> 1) ^ seed);
    r = 1103515245 * (r ^ (r >> 3));
    r = r ^ (r >> 16);
    return (r % mod) / mod;
}


for(let i = turtles_count; i > 0; i--) {
    let turtle = new Turtle;
    turtle.penup();
    turtle.setheading(random() * 360);
    turtle.setx(random() * spawn_range * 2 - spawn_range);
    turtle.sety(random() * spawn_range * 2 - spawn_range);
    turtle.pendown();
    turtles.push(turtle);
}

class Perlin {
    constructor(size, gridSize) {
        this.size = size;
        this.gridSize = gridSize;
        this.grid = [];

        for (let i = 0; i <= gridSize; i++) {
            let table = [];
            for (let j = 0; j <= gridSize; j++) {
                let angle = random() * 2 * Math.PI;
                let x = Math.cos(angle);
                let y = Math.sin(angle);
                table.push([x, y]);
            }
            this.grid.push(table);
        }
    }

    get(x, y) {
        x = x / 2 + this.size / 2;
        y = y / 2 + this.size / 2;
        if (x < 0) x = 0;
        if (x >= this.size) x = this.size - 0.01;
        if (y < 0) y = 0;
        if (y >= this.size) y = this.size - 0.01;

        let posx = x * this.gridSize / this.size;
        let posy = y * this.gridSize / this.size;

        let x1 = Math.floor(posx);
        let x2 = x1 + 1;
        let y1 = Math.floor(posy);
        let y2 = y1 + 1;

        let scal = [];
        scal.push(this.scalar(posx, posy, x1, y1));
        scal.push(this.scalar(posx, posy, x2, y1));
        scal.push(this.scalar(posx, posy, x1, y2));
        scal.push(this.scalar(posx, posy, x2, y2));

        let int1 = this.interpolate(posx - x1, scal[0], scal[1]);
        let int2 = this.interpolate(posx - x1, scal[2], scal[3]);

        return this.interpolate(posy - y1, int1, int2);
    }

    scalar(x, y, vx, vy) {
        x -= vx;
        y -= vy;
        return x * this.grid[vx][vy][0] + y * this.grid[vx][vy][1];
    }

    smooth(v) {
        if (v < 0) v = 0;
        if (v > 1) v = 1;
        return v ** 2 * (3 - 2 * v);
    }

    interpolate(x, a, b) {
        return a + (b - a) * this.smooth(x);
    }
}

////////////////////////////////////////////////////////////////
// Pseudorandom number generator. Created by Reinder Nijhoff 2024
// https://turtletoy.net/turtle/a2274fd1fe
////////////////////////////////////////////////////////////////


let perlin_angle = new Perlin(100, angle_perlin);
let perlin_length = new Perlin(100, length_perlin);

// The walk function will be called until it returns false.
function walk(i) {
    for(let j = turtles_count-1; j > 0; j--) {
        let x = turtles[j].x();
        let y = turtles[j].y();
        turtles[j].forward(perlin_length.get(x,y) * length_perlin_mag);
        turtles[j].right(perlin_angle.get(x,y) * angle_perlin_mag);
    }
    return i < steps;
}