// 法律/信息页左侧目录滚动高亮
(function () {
  var toc = document.getElementById('legalToc');
  if (!toc) return;
  var links = Array.prototype.slice.call(toc.querySelectorAll('a'));
  var sections = links
    .map(function (a) { return document.getElementById(a.getAttribute('href').slice(1)); })
    .filter(Boolean);
  if (!sections.length || !window.IntersectionObserver) return;

  var active = null;
  function setActive(id) {
    if (id === active) return;
    active = id;
    links.forEach(function (a) {
      a.classList.toggle('active', a.getAttribute('href') === '#' + id);
    });
  }

  var observer = new IntersectionObserver(function (entries) {
    entries.forEach(function (e) {
      if (e.isIntersecting) setActive(e.target.id);
    });
  }, { rootMargin: '-15% 0px -75% 0px', threshold: 0 });

  sections.forEach(function (s) { observer.observe(s); });
  setActive(sections[0].id);
})();