/* ============================================================
   Global Presence — fullpage screen controller
   One screen per wheel gesture / swipe / arrow; dot nav jumps.
   Footer (after the last screen) remains freely reachable.
   ============================================================ */
(function () {
  var screens = Array.prototype.slice.call(document.querySelectorAll('.gp-screen'));
  var links = Array.prototype.slice.call(document.querySelectorAll('.gp-nav-list a'));
  var n = screens.length;
  if (!n) return;

  var current = 0;
  var animating = false;

  function topOf(i) { return screens[i].offsetTop; }
  function clamp(i) { return Math.max(0, Math.min(n - 1, i)); }

  function setActive(i) {
    current = i;
    links.forEach(function (a) {
      a.classList.toggle('active', parseInt(a.getAttribute('data-i'), 10) === i);
    });
  }

  function go(i) {
    i = clamp(i);
    if (animating || i === current) return;
    animating = true;
    window.scrollTo({ top: topOf(i), behavior: 'smooth' });
    setTimeout(function () { animating = false; }, 650);
  }

  function syncActive() {
    var y = window.scrollY + window.innerHeight * 0.4;
    var i = 0;
    for (var k = 0; k < n; k++) { if (y >= topOf(k)) i = k; }
    if (i !== current) setActive(i);
  }

  function inFooterZone() { return window.scrollY > topOf(n - 1) + 20; }

  // ---- wheel: one screen per gesture; release to footer at the last screen ----
  window.addEventListener('wheel', function (e) {
    if (animating) { e.preventDefault(); return; }
    var d = e.deltaY;
    if (inFooterZone()) {
      // free scroll inside footer; snap back up when crossing the boundary
      if (d < 0 && window.scrollY <= topOf(n - 1) + 80) { e.preventDefault(); go(n - 1); }
      return;
    }
    if (current === n - 1 && d > 0) return;   // allow scrolling down into the footer
    e.preventDefault();
    if (Math.abs(d) < 5) return;
    go(current + (d > 0 ? 1 : -1));
  }, { passive: false });

  // ---- keyboard ----
  window.addEventListener('keydown', function (e) {
    var k = e.key;
    if (k === 'ArrowDown' || k === 'PageDown') { e.preventDefault(); go(current + 1); }
    else if (k === 'ArrowUp' || k === 'PageUp') { e.preventDefault(); go(current - 1); }
    else if (k === 'Home') { e.preventDefault(); go(0); }
    else if (k === 'End') { e.preventDefault(); go(n - 1); }
  });

  // ---- touch swipe ----
  var ty = null;
  window.addEventListener('touchstart', function (e) { ty = e.touches[0].clientY; }, { passive: true });
  window.addEventListener('touchend', function (e) {
    if (ty === null) return;
    var dy = ty - e.changedTouches[0].clientY;
    if (Math.abs(dy) > 50) go(current + (dy > 0 ? 1 : -1));
    ty = null;
  }, { passive: true });

  // ---- region nav links (overview screen) ----
  links.forEach(function (a) {
    a.addEventListener('click', function (e) {
      e.preventDefault();
      var i = parseInt(a.getAttribute('data-i'), 10);
      if (!isNaN(i)) go(i);
    });
  });

  // ---- sync + resize ----
  window.addEventListener('scroll', syncActive, { passive: true });
  window.addEventListener('resize', function () { window.scrollTo({ top: topOf(current), behavior: 'auto' }); });

  syncActive();
})();