script.js

(function() {
  if (localStorage.getItem('th') === 'dark') { document.body.classList.add('dark'); }

  var themeToggle = document.getElementById('theme-toggle');
  if (themeToggle) {
    themeToggle.addEventListener('click', function() {
      document.body.classList.toggle('dark');
      localStorage.setItem('th', document.body.classList.contains('dark') ? 'dark' : '');
    });
  }

  var nav = document.getElementById('main-nav');
  if (nav) {
    window.addEventListener('scroll', function() {
      var currentScroll = window.scrollY || 0;
      if (currentScroll < 100) {
        nav.style.transform = 'translate(-50%, 0)';
        nav.style.opacity = '1';
        nav.style.pointerEvents = '';
      } else {
        nav.style.transform = 'translate(-50%, -120px)';
        nav.style.opacity = '0';
        nav.style.pointerEvents = 'none';
      }
    }, { passive: true });
  }

  var backToTop = document.getElementById('back-to-top');
  if (backToTop) {
    function updateBackToTop() {
      if (window.scrollY > 200) {
        backToTop.classList.add('visible');
      } else {
        backToTop.classList.remove('visible');
      }
    }
    window.addEventListener('scroll', updateBackToTop, { passive: true });
    updateBackToTop();

    backToTop.addEventListener('click', function() {
      window.scrollTo({ top: 0, behavior: 'smooth' });
    });
  }

  document.querySelectorAll('.nav-link').forEach(function(link) {
    e.preventDefault();
    var target = document.querySelector(link.getAttribute('href'));
    if (!target) return;
    var start = window.scrollY || 0;
    var end = target.getBoundingClientRect().top + start - 100;
    var dist = end - start;
    var dur = 600;
    var startTime = null;
    function step(now) {
      if (!startTime) startTime = now;
      var t = Math.min((now - startTime) / dur, 1);
      var ease = t < .5 ? 2*t*t : -1+(4-2*t)*t;
      window.scrollTo(0, start + dist*ease);
      if (t < 1) requestAnimationFrame(step);
    }
    requestAnimationFrame(step);
  });

  var footer = document.querySelector('.contact-footer');
  if (footer) {
    var lastScroll = window.scrollY || 0;

    window.addEventListener('scroll', function() {
      var currentScroll = window.scrollY || 0;
      var scrollDirection = currentScroll > lastScroll ? 'down' : 'up';

      if (scrollDirection === 'up' && currentScroll > 0) {
        footer.classList.add('visible');
      } else {
        footer.classList.remove('visible');
      }

      lastScroll = currentScroll;
    }, { passive: true });
  }
})();