// Light/dark switch. The page follows the OS theme until the button is used;
// the choice is then remembered in localStorage. Loaded in <head> so a saved
// theme is applied before the page paints.
(function () {
  var root = document.documentElement;
  var media = window.matchMedia('(prefers-color-scheme: dark)');

  try {
    var saved = localStorage.getItem('theme');
    if (saved === 'light' || saved === 'dark') root.dataset.theme = saved;
  } catch (e) {}

  function current() {
    return root.dataset.theme || (media.matches ? 'dark' : 'light');
  }

  function label(btn) {
    var next = current() === 'dark' ? 'light' : 'dark';
    btn.textContent = next === 'dark' ? 'Dark mode' : 'Light mode';
    btn.setAttribute('aria-label', 'Switch to ' + next + ' mode');
  }

  document.addEventListener('DOMContentLoaded', function () {
    var btn = document.getElementById('theme-toggle');
    if (!btn) return;
    label(btn);
    btn.hidden = false;
    btn.addEventListener('click', function () {
      root.dataset.theme = current() === 'dark' ? 'light' : 'dark';
      try { localStorage.setItem('theme', root.dataset.theme); } catch (e) {}
      label(btn);
    });
    media.addEventListener('change', function () { label(btn); });
  });
})();