function resolveTheme(root) {
  const preference = root.dataset.theme || 'auto';
  if (preference === 'light' || preference === 'dark') {
    return preference;
  }
  return window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark';
}

function applyThemeState(root) {
  const resolved = resolveTheme(root);
  root.dataset.themeResolved = resolved;

  const themeMeta = document.querySelector('meta[name="theme-color"]');
  if (themeMeta) {
    const background = getComputedStyle(root).getPropertyValue('--color-bg').trim();
    if (background) {
      themeMeta.setAttribute('content', background);
    }
  }
}

export function initTheme() {
  const root = document.documentElement;
  if (!root) {
    return;
  }

  applyThemeState(root);

  const media = window.matchMedia('(prefers-color-scheme: light)');
  const handleChange = () => {
    if ((root.dataset.theme || 'auto') === 'auto') {
      applyThemeState(root);
    }
  };

  if (typeof media.addEventListener === 'function') {
    media.addEventListener('change', handleChange);
  } else if (typeof media.addListener === 'function') {
    media.addListener(handleChange);
  }
}