// Applies a theme's stylesheet. Texts are handled by i18n.js, mechanics are
// shared (public/data); a theme is only a skin: colours, vocabulary, images.

export function applyThemeStyles(themeId) {
  document.documentElement.dataset.theme = themeId;

  let link = document.getElementById('theme-css');
  if (!link) {
    link = document.createElement('link');
    link.id = 'theme-css';
    link.rel = 'stylesheet';
    document.head.append(link);
  }
  return new Promise((resolve) => {
    link.onload = link.onerror = () => resolve();
    link.href = `themes/${themeId}/theme.css`;
  });
}