src/doc/book/ferris.js

// @ts-check

/**
 * @typedef {{ attr: string, title: string }} FerrisType
 */

/** @type {Array<FerrisType>} */
const FERRIS_TYPES = [
  {
    attr: 'does_not_compile',
    title: 'This code does not compile!'
  },
  {
    attr: 'panics',
    title: 'This code panics!'
  },
  {
    attr: 'not_desired_behavior',
    title: 'This code does not produce the desired behavior.'
  }
]

document.addEventListener('DOMContentLoaded', () => {
  for (let ferrisType of FERRIS_TYPES) {
    attachFerrises(ferrisType)
  }
})

/**
 * @param {FerrisType} type
 */
function attachFerrises(type) {
  let elements = document.getElementsByClassName(type.attr)

  for (let codeBlock of elements) {
    // Skip SVG etc.: in principle, these should never be attached to those, but
    // this means if someone happens to have a browser extension which *is*
    // attaching them, it will not break the code.
    if (!(codeBlock instanceof HTMLElement)) {
      continue
    }

    let lines = codeBlock.innerText.replace(/\n$/, '').split(/\n/).length

    /** @type {'small' | 'large'} */
    let size = lines < 4 ? 'small' : 'large'

    let container = prepareFerrisContainer(codeBlock, size == 'small')
    if (!container) {
      continue
    }

    container.appendChild(createFerris(type, size))
  }
}

/**
 * @param {HTMLElement} element - Code block element to attach a Ferris to.
 * @param {boolean} useButtons - Whether to attach to existing buttons.
 * @returns {Element | null} - The container element to use.
 */
function prepareFerrisContainer(element, useButtons) {
  let foundButtons = element.parentElement?.querySelector('.buttons')
  if (useButtons && foundButtons) {
    return foundButtons
  }

  let div = document.createElement('div')
  div.classList.add('ferris-container')

  if (!element.parentElement) {
    console.error(`Could not install Ferris on ${element}, which is missing a parent`);
    return null;
  }

  element.parentElement.insertBefore(div, element)

  return div
}

/**
 * @param {FerrisType} type
 * @param {'small' | 'large'} size
 * @returns {HTMLAnchorElement} - The generated anchor element.
 */
function createFerris(type, size) {
  let a = document.createElement('a')
  a.setAttribute('href', 'ch00-00-introduction.html#ferris')
  a.setAttribute('target', '_blank')

  let img = document.createElement('img')
  img.setAttribute('src', 'img/ferris/' + type.attr + '.svg')
  img.setAttribute('title', type.title)
  img.classList.add('ferris')
  img.classList.add('ferris-' + size)

  a.appendChild(img)

  return a
}