// js/ui.js
// Shared UI enhancements: Glass Header on scroll & Back-to-Top button.
document.addEventListener('DOMContentLoaded', () => {
  const header = document.querySelector('header.nav');
  // Don't run if there's no header on the page
  if (!header) return;

  // 1. Create and inject Back-to-Top button
  const btt = document.createElement('div');
  btt.className = 'back-to-top';
  btt.setAttribute('aria-label', 'Scroll to top');
  btt.innerHTML = `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 19V5M5 12l7-7 7 7"/></svg>`;
  document.body.appendChild(btt);

  // 2. Click listener to scroll to top
  btt.addEventListener('click', () => {
    window.scrollTo({ top: 0, behavior: 'smooth' });
  });

  // 3. Scroll listener to show/hide elements
  let isTicking = false;
  window.addEventListener('scroll', () => {
    if (!isTicking) {
      window.requestAnimationFrame(() => {
        const scrollY = window.scrollY;
        if (scrollY > 200) {
          btt.classList.add('visible');
        } else {
          btt.classList.remove('visible');
        }
        isTicking = false;
      });
      isTicking = true;
    }
  });
});