<canvas id="canvas" title="Click to generate a new pattern"></canvas>

body, html {
  margin: 0;
  overflow: hidden;
}

canvas {
  display: block;
  cursor: pointer;
}

/*
  Johan Karlsson 2020
  https://twitter.com/DonKarlssonSan
  MIT License, see Details View
*/

let canvas;
let ctx;
let w, h;
let colors;
let colorSchemeIndex;

function setup() {
  setupColors();
  canvas = document.querySelector("#canvas");
  ctx = canvas.getContext("2d");
  reset();
  canvas.addEventListener("click", draw); 
  window.addEventListener("resize", reset);
}

function setupColors() {
  colors = [
    [
      "#ffffff",
      "#84dcc6",
      "#a5ffd6",
      "#ffa69e",
      "#ff686b"
    ],
    [
      "#ef476f",
      "#ffd166",
      "#06d6a0",
      "#118ab2",
      "#073b4c"
    ],
    [
      "#f2d7ee",
      "#d3bcc0",
      "#a5668b",
      "#69306d",
      "#0e103d"
    ],
    [
      "#ffbe0b",
      "#fb5607",
      "#ff006e",
      "#8338ec",
      "#3a86ff"
    ],
    [
      "#ffac81",
      "#ff928b",
      "#fec3a6",
      "#efe9ae",
      "#cdeac0"
    ],
    [
      "#011627",
      "#fdfffc",
      "#2ec4b6",
      "#e71d36",
      "#ff9f1c"
    ],
    [
      "#03256c",
      "#2541b2",
      "#1768ac",
      "#06bee1",
      "#ffffff"
    ],
    [
      "#f7b267",
      "#f79d65",
      "#f4845f",
      "#f27059",
      "#f25c54"
    ],
    [
      "#4b6e70",
      "#97b5ac",
      "#718f86",
      "#d4ded4",
      "#a9b0cb"
    ],
    [
      "#a7c6da",
      "#c3957d",
      "#bd5f70",
      "#dcd9f8",
      "#cbb38c"
    ],
    [
      "#ffbe0b",
      "#fb5607",
      "#ff006e",
      "#8338ec",
      "#3a86ff"
    ],
    [
      "#283d3b",
      "#197278",
      "#edddd4",
      "#c44536",
      "#772e25"
    ],
    [
      "#ffe74c",
      "#ff5964",
      "#ffffff",
      "#6bf178",
      "#35a7ff"
    ]    
  ];
}

function getRandomColor() {
  let len = colors[colorSchemeIndex].length;
  let randomIndex = random(len);
  return colors[colorSchemeIndex][randomIndex];
}

function reset() {
  w = canvas.width = window.innerWidth;
  h = canvas.height = window.innerHeight;
  draw();
}

function draw() {
  let nrOfColorSchemes = colors.length;
  colorSchemeIndex = random(nrOfColorSchemes);
  ctx.fillStyle = getRandomColor();
  ctx.fillRect(0, 0, w, h);
  let size = 50;
  let lineWidth = size / 6;
  for(let x = 0; x < w + size; x += size) {
    for(let y = 0; y < h + size; y += size) {
      drawSquares(x, y, size * 0.85, lineWidth);
    }
  }
}

function drawSquares(x, y, size, lineWidth) {
  ctx.lineWidth = lineWidth;
  ctx.strokeStyle = getRandomColor();
  ctx.strokeRect(x - size / 2, y - size / 2, size, size);
  ctx.strokeStyle = getRandomColor();
  ctx.strokeRect(x - size / 3, y - size / 3, size / 1.5, size / 1.5);
  ctx.strokeStyle = getRandomColor();
  ctx.strokeRect(x - size / 6, y - size / 6, size / 3, size / 3);
  ctx.fillStyle = getRandomColor();
  ctx.fillRect(x - size / 12, y - size / 12, size / 6, size / 6);
}

function random(max) {
  return Math.floor(Math.random() * max);
}
  
setup();