const { getPlatformFromUserAgent } = require('platform-utils')
const supportedPlatforms = ['mac', 'windows', 'linux']
const detectedPlatforms = new Set()

// Emphasize content for the visitor's OS (inferred from user agent string)

export default function displayPlatformSpecificContent () {
  let platform = getPlatformFromUserAgent()

  // adjust platform names to fit existing mac/windows/linux scheme
  if (!platform) platform = 'mac' // default to 'mac' on mobile
  if (platform === 'darwin') platform = 'mac'
  if (platform.startsWith('win')) platform = 'windows'

  const platformsInContent = findPlatformSpecificContent(platform)

  hideSwitcherLinks(platformsInContent)

  showContentForPlatform(platform)

  // configure links for switching platform content
  switcherLinks().forEach(link => {
    link.addEventListener('click', (event) => {
      event.preventDefault()
      showContentForPlatform(event.target.dataset.platform)
      findPlatformSpecificContent(event.target.dataset.platform)
    })
  })
}

function showContentForPlatform (platform) {
  // (de)activate switcher link appearances
  switcherLinks().forEach(link => {
    (link.dataset.platform === platform)
      ? link.classList.add('selected')
      : link.classList.remove('selected')
  })
}

function findPlatformSpecificContent (platform) {
  // find all platform-specific *block* elements and hide or show as appropriate
  // example: {{ #mac }} block content {{/mac}}
  Array.from(document.querySelectorAll('.extended-markdown'))
    .filter(el => supportedPlatforms.some(platform => el.classList.contains(platform)))
    .forEach(el => {
      detectPlatforms(el)
      el.style.display = el.classList.contains(platform)
        ? ''
        : 'none'
    })

  // find all platform-specific *inline* elements and hide or show as appropriate
  // example: <span class="platform-mac">inline content</span>
  Array.from(document.querySelectorAll('.platform-mac, .platform-windows, .platform-linux'))
    .forEach(el => {
      detectPlatforms(el)
      el.style.display = el.classList.contains('platform-' + platform)
        ? ''
        : 'none'
    })

  return Array.from(detectedPlatforms)
}

// hide links for any platform-specific sections that are not present
function hideSwitcherLinks (platformsInContent) {
  Array.from(document.querySelectorAll('a.platform-switcher'))
    .forEach(link => {
      if (platformsInContent.includes(link.dataset.platform)) return
      link.style.display = 'none'
    })
}

function detectPlatforms (el) {
  el.classList.forEach(elClass => {
    const value = elClass.replace(/platform-/, '')
    if (supportedPlatforms.includes(value)) detectedPlatforms.add(value)
  })
}

function switcherLinks () {
  return Array.from(document.querySelectorAll('a.platform-switcher'))
}