(function () {
    var headings = document.querySelectorAll('.post-content h2, .post-content h3');
    var links    = document.querySelectorAll('.toc-list a');
    if (!headings.length || !links.length) return;

    var map = {};
    links.forEach(function (a) {
        map[decodeURIComponent(a.getAttribute('href').slice(1))] = a;
    });

    var active = null;
    var observer = new IntersectionObserver(function (entries) {
        entries.forEach(function (entry) {
            if (entry.isIntersecting) {
                if (active) active.classList.remove('toc-active');
                active = map[entry.target.id] || null;
                if (active) active.classList.add('toc-active');
            }
        });
    }, { rootMargin: '-8% 0px -82% 0px', threshold: 0 });

    headings.forEach(function (h) { observer.observe(h); });
})();