// #267: jump to top / bottom for long content.
// Works on the paste view (page scroll) and the /new editor (textarea scroll).
// Buttons only appear when the content is tall enough to need them.
(function () {
  const nav = document.querySelector('.jump-nav');
  if (!nav) return;
  const topBtn = nav.querySelector('.jump-top');
  const botBtn = nav.querySelector('.jump-bottom');

  // Target: the editor textarea on /new, else the window (paste view).
  const editor = document.getElementById('content');
  const target = editor || window;

  function metrics() {
    if (editor) {
      return {
        top: editor.scrollTop,
        max: editor.scrollHeight - editor.clientHeight,
        view: editor.clientHeight
      };
    }
    const doc = document.documentElement;
    return {
      top: window.scrollY,
      max: doc.scrollHeight - window.innerHeight,
      view: window.innerHeight
    };
  }

  function refresh() {
    const m = metrics();
    const tall = m.max > m.view * 1.5;
    nav.classList.toggle('show', tall);
    if (!tall) return;
    // Hide the button for the edge you are already at.
    topBtn.classList.toggle('hidden', m.top < 8);
    botBtn.classList.toggle('hidden', m.max - m.top < 8);
  }

  function jump(toTop) {
    const y = toTop ? 0 : 99999999;
    if (editor) editor.scrollTo({ top: toTop ? 0 : editor.scrollHeight, behavior: 'smooth' });
    else window.scrollTo({ top: toTop ? 0 : document.documentElement.scrollHeight, behavior: 'smooth' });
  }

  topBtn.addEventListener('click', () => jump(true));
  botBtn.addEventListener('click', () => jump(false));

  target.addEventListener('scroll', refresh, { passive: true });
  if (editor) editor.addEventListener('input', refresh);
  window.addEventListener('resize', refresh);
  refresh();
})();