/* #267: jump to top / bottom controls for long content.
   Paste view scrolls the window; the /new editor scrolls its textarea.
   The active scroller is chosen via data-jump-scroll on the script tag. */
(function () {
  var nav = document.getElementById('jumpnav');
  if (!nav) return;
  var scroller = window;
  var sel = nav.dataset.jumpScroll;
  if (sel) scroller = document.querySelector(sel);

  function el() {
    return scroller === window ? document.scrollingElement : scroller;
  }
  function isLarge() {
    var e = el();
    if (!e) return false;
    var visible = scroller === window ? window.innerHeight : e.clientHeight;
    return e.scrollHeight > visible * 2;
  }
  function refresh() {
    nav.classList.toggle('hidden', !isLarge());
  }
  function jump(toTop) {
    var e = el();
    if (!e) return;
    if (scroller === window) {
      window.scrollTo({ top: toTop ? 0 : e.scrollHeight });
    } else {
      e.scrollTop = toTop ? 0 : e.scrollHeight;
    }
  }
  nav.addEventListener('click', function (ev) {
    var b = ev.target.closest('[data-jump]');
    if (!b) return;
    ev.preventDefault();
    jump(b.dataset.jump === 'top');
  });
  window.addEventListener('resize', refresh);
  if (scroller !== window && scroller) scroller.addEventListener('input', refresh);
  refresh();
  /* #282: the first evaluation can run before the layout settles (media
     queries, web fonts, async highlighting) and under-measure the content,
     leaving the nav hidden on long pages. Re-check once a real layout exists
     and after load; the ResizeObserver also catches late content growth. */
  requestAnimationFrame(function () { requestAnimationFrame(refresh); });
  window.addEventListener('load', refresh);
  window.setTimeout(refresh, 300);
  if (window.ResizeObserver && scroller === window && document.body) {
    new ResizeObserver(refresh).observe(document.body);
  }
})();