discourse/app/assets/javascripts/discourse/lib/theme-selector.js.es6

import { ajax } from 'discourse/lib/ajax';
const keySelector = 'meta[name=discourse_theme_key]';

export function currentThemeKey() {
  let themeKey = null;
  let elem = _.first($(keySelector));
  if (elem) {
    themeKey = elem.content;
    if (_.isEmpty(themeKey)) {
      themeKey = null;
    }
  }
  return themeKey;
}

export function setLocalTheme(key, themeSeq) {
  if (key) {
    $.cookie('theme_key', `${key},${themeSeq}`, {path: '/', expires: 9999});
  } else {
    $.cookie('theme_key', null, {path: '/', expires: 1});
  }
}

export function refreshCSS(node, hash, newHref, options) {

  let $orig = $(node);

  if ($orig.data('reloading')) {

    if (options && options.force) {
      clearTimeout($orig.data('timeout'));
      $orig.data("copy").remove();
    } else {
      return;
    }
  }

  if (!$orig.data('orig')) {
    $orig.data('orig', node.href);
  }

  $orig.data('reloading', true);

  const orig = $(node).data('orig');

  let reloaded = $orig.clone(true);
  if (hash) {
    reloaded[0].href = orig + (orig.indexOf('?') >= 0 ? "&hash=" : "?hash=") + hash;
  } else {
    reloaded[0].href = newHref;
  }

  $orig.after(reloaded);

  let timeout = setTimeout(()=>{
    $orig.remove();
    reloaded.data('reloading', false);
  }, 2000);

  $orig.data("timeout", timeout);
  $orig.data("copy", reloaded);
}

export function previewTheme(key) {
  if (currentThemeKey() !== key) {

    Discourse.set("assetVersion", "forceRefresh");

    ajax(`/themes/assets/${key ? key : 'default'}`).then(results => {
      let elem = _.first($(keySelector));
      if (elem) {
        elem.content = key;
      }

      results.themes.forEach(theme => {
        let node = $(`link[rel=stylesheet][data-target=${theme.target}]`)[0];
        if (node) {
          refreshCSS(node, null, theme.url, {force: true});
        }
      });
    });
  }
}

export function listThemes(site) {
  let themes = site.get('user_themes');

  if (!themes) {
    return null;
  }

  let hasDefault = !!themes.findBy('default', true);

  let results = [];
  if (!hasDefault) {
    results.push({name: I18n.t('themes.default_description'), id: null});
  }

  themes.forEach(t=>{
    results.push({name: t.name, id: t.theme_key});
  });

  return results.length === 0 ? null : results;
}