<svg
  xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  width="200"
  height="200"
  viewBox="0 0 1000 1000"
  style="background: #000;"
  role="img"
  aria-labelledby="solarSystemTitle"
  aria-describedby="solarSystemDescription"
>
  <title id="solarSystemTitle">A procedurally generated solar system</title>
  <desc id="solarSystemDescription">A 2D rendering of a solar system, with planets orbiting a central star.</desc>

  <!-- This element will store our graphics -->
  <g class="js-svg-wrapper"></g>
  
  <!-- This stores any global CSS styles -->
  <style></style>  
</svg>

<button class="js-refresh-button">Refresh</button>

/**
 * Code related to setting up the codepen, not the solar systems
 */

* {
  margin: 0;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
}

svg {
  width: min(100vw, calc(100vh - 4.5em));
  height: auto;
}

button {
  margin-top: 1em;
  appearance: none;
}

:root {
  --hue: 200;
}

button {
  /* Text Colors */
  --text-saturation: 90%;
  --text-lightness: 40%;
  
  --text-saturation-hover: calc(var(--text-saturation) + 10%);
  --text-lightness-hover: calc(var(--text-lightness) - 5%); ;
  
  --text-saturation-active: var(--text-saturation-hover);
  --text-lightness-active: calc(var(--text-lightness) - 10%); ;
  
  --text-saturation-disabled: calc(var(--text-saturation) - 60%);
  --text-lightness-disabled: calc(var(--text-lightness) + 10%);
  
  /* Background Colors */
  --background-saturation: 0%;
  --background-lightness: 100%;
  
  --background-saturation-hover: calc(var(--background-saturation) + 80%);
  --background-lightness-hover: calc(var(--background-lightness) - 5%);
  
  --background-saturation-active: var(--background-saturation-hover);
  --background-lightness-active: calc(var(--background-lightness) - 10%);
  
  --background-saturation-disabled: calc(var(--background-saturation) + 30%);
  --background-lightness-disabled: calc(var(--background-lightness) - 10%);
  
  /* Border Colors */
  --border-saturation: 90%;
  --border-lightness: 60%;
  
  --border-saturation-hover: calc(var(--border-saturation) + 10%);
  --border-lightness-hover: calc(var(--border-lightness) - 10%);
  
  --border-saturation-active: var(--border-saturation-hover);
  --border-lightness-active: calc(var(--border-lightness) - 20%);
  
  --border-saturation-disabled: calc(var(--border-saturation) - 60%);
  --border-lightness-disabled: calc(var(--border-lightness) + 20%);
  
  /* Focus shadow styles */
  --shadow-saturation-focus: 100%;
  --shadow-lightness-focus: 85%;
  
  /* Color Styles */
  color: hsl(var(--hue), var(--text-saturation), var(--text-lightness));
  background-color: hsl(var(--hue), var(--background-saturation), var(--background-lightness)); 
  border:0.1em solid hsl(var(--hue), var(--border-saturation), var(--border-lightness)); 
  
  /* Misc. Styles */
  border-radius: 0.25em;
  cursor: pointer;
  display: inline-block;
  font-size: 1em;
  padding: 0.5em 1em;
  transition-property: box-shadow, background-color, border-color, color;
  transition-timing-function: ease-out;
  transition-duration: 0.2s;
}

button:hover {
  color: hsl(
    var(--hue), 
    var(--text-saturation-hover), 
    var(--text-lightness-hover)
  );
  
  background-color: hsl(
    var(--hue), 
    var(--background-saturation-hover), 
    var(--background-lightness-hover)
  );
  
  border-color: hsl(
    var(--hue), 
    var(--border-saturation-hover), 
    var(--border-lightness-hover)
  );
}

button:active {
  color: hsl(
    var(--hue), 
    var(--text-saturation-active), 
    var(--text-lightness-active)
  );
  
  background-color: hsl(
    var(--hue), 
    var(--background-saturation-active), 
    var(--background-lightness-active)
  );
  
  border-color: hsl(
    var(--hue), 
    var(--border-saturation-active), 
    var(--border-lightness-active)
  );
}

button:focus {
  outline: none;
  box-shadow: 0 0 0 0.25em hsl(
    var(--hue), 
    var(--shadow-saturation-focus),
    var(--shadow-lightness-focus)
  );
}

body {
  font-family: -apple-system, BlinkMacSystemFont, avenir next, avenir, helvetica neue, helvetica, Ubuntu, roboto, noto, segoe ui, arial, sans-serif; 
}

// Define a couple variables about our SVG grid
const width = 1000;
const height = 1000;

// Define some helper functions to randomize plant size and orbit distance
let randomPlanetSize = () => randomInt(10, 50);
let randomOrbitDistance = () => randomInt(100, 120);

function draw() {
  let starSize = randomInt(70, 120);
  let markup = drawStar(starSize) + addPlanets(starSize);
  
  document.querySelector(".js-svg-wrapper").innerHTML = markup;
}

function addPlanets(starSize) {
  let markup = '';

  // Set up our first planet
  let planetSize = randomPlanetSize();
  let orbitDistance = starSize + randomOrbitDistance();

  // Keep adding planets until a planet's orbital distance and size would lead
  // to it extending past our canvas
  while (orbitDistance + planetSize < 500) {
    // Add our new planet and its orbit path to our markup
    markup += drawOrbit(orbitDistance) + drawPlanet(planetSize, orbitDistance);

    // Prep our next planet so the while loop can check whether it's in bounds
    planetSize = randomPlanetSize();
    orbitDistance += randomOrbitDistance();
  }

  return markup;
}

// We create a separate drawStar function to make it easier to change later
function drawStar(size) {
  // `cx` and `cy` represent the x and y coordinates for the center of our circle.
  // `r` sets the radius of the circle. We'll use our star size.
  // For now we'll make our star white (`#fff`). We'll change the color soon.
  return `
    <circle 
      cx="${width / 2}" 
      cy="${height / 2}" 
      r="${size}" 
      fill="#fff"
    />
  `;
}

function drawPlanet(size, distance) {
  // We center the planet vertically, but we adjust the x position
  // by our orbit distance.
  return `
    <circle 
      cx="${width/2 + distance}" 
      cy="${height/2}" 
      r="${size}" 
      fill="#fff"
    />
  `;
}

function drawOrbit(distance) {
  // The orbit is centered and has a radius equal to our current distance
  return `
    <circle 
      cx="${width/2}" 
      cy="${height/2}" 
      r="${distance}" 
      stroke="#ccc"
      fill="none"
    />
  `;
}


/**
 * Initialize our art piece
 */
draw();

document.querySelector(".js-refresh-button").addEventListener("click", draw);

//
// Randomization Functions
//

// Return a number between two values.
function random(min, max) {
  const difference = max - min;
  return min + difference * Math.random();
}

// Returns a random integer between two values
function randomInt(min, max) {
  return Math.round(random(min, max));
}

// Returns true or false. By default the chance is 50/50 but you can pass in
// a custom probability between 0 and 1. (Higher values are more likely to
// return true.)
function randomBool(probability = 0.5) {
  return Math.random() > probability;
}