discourse/app/assets/javascripts/pretty-text/image-short-url.js.es6

let _cache = {};

export function lookupCachedUploadUrl(shortUrl) {
  return _cache[shortUrl];
}

export function lookupUncachedUploadUrls(urls, ajax) {
  return ajax('/uploads/lookup-urls', { method: 'POST', data: { short_urls: urls } })
    .then(uploads => {
      uploads.forEach(upload => _cache[upload.short_url] = upload.url);
      urls.forEach(url => _cache[url] = _cache[url] || "missing");
      return uploads;
    });
}

export function cacheShortUploadUrl(shortUrl, url) {
  _cache[shortUrl] = url;
}

function _loadCachedShortUrls($images) {
  $images.each((idx, image) => {
    let $image = $(image);
    let url = lookupCachedUploadUrl($image.data('orig-src'));
    if (url) {
      $image.removeAttr('data-orig-src');
      if (url !== "missing") {
        $image.attr('src', url);
      }
    }
  });
}

function _loadShortUrls($images, ajax) {
  const urls = _.map($images, img => $(img).data('orig-src'));
  lookupUncachedUploadUrls(urls, ajax).then(() => _loadCachedShortUrls($images));
}

export function resolveAllShortUrls(ajax) {
  let $shortUploadUrls = $('img[data-orig-src]');

  if ($shortUploadUrls.length > 0) {
    _loadCachedShortUrls($shortUploadUrls);

    $shortUploadUrls = $('img[data-orig-src]');
    if ($shortUploadUrls.length > 0) {
      // this is carefully batched so we can do a leading debounce (trigger right away)
      Ember.run.debounce(null, () => { _loadShortUrls($shortUploadUrls, ajax); }, 450, true);
    }
  }
}