document.getElementById('copyright-year').textContent = new Date().getFullYear();
const panels = [...document.querySelectorAll('.page-panel')];
const track = document.querySelector('.page-track');
const navLinks = [...document.querySelectorAll('.nav-link')];
const dots = [...document.querySelectorAll('.page-dots a')];
const reducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)');
let current = 0;
let lockedUntil = 0;
let transitionTimer;
const names = ['首页', '关于星年', '技术与服务', '联系我们', '公司信息与备案'];
const viewport = document.querySelector('.page-viewport');

function updatePosition() {
  const height = viewport.clientHeight;
  const last = panels.length - 1;
  const offset = current === last
    ? (last - 1) * height + panels[last].offsetHeight
    : current * height;
  track.style.transform = `translate3d(0, -${offset}px, 0)`;
}
window.addEventListener('resize', updatePosition);
if ('ResizeObserver' in window) {
  const sizeObserver = new ResizeObserver(updatePosition);
  sizeObserver.observe(viewport);
  sizeObserver.observe(panels[panels.length - 1]);
}

function goTo(index, updateHash = true) {
  index = Math.max(0, Math.min(panels.length - 1, index));
  const previous = panels[current];
  const restoreFocus = previous.contains(document.activeElement);
  current = index;
  // Main panels occupy one viewport; the final step reveals the shorter footer.
  updatePosition();
  document.body.dataset.page = String(index);
  panels.forEach((panel, i) => {
    panel.inert = i !== index;
    panel.setAttribute('aria-hidden', String(i !== index));
  });
  navLinks.forEach(link => {
    const active = link.hash === `#${panels[index].id}` || (panels[index].id === 'legal' && link.hash === '#contact');
    link.classList.toggle('active', active);
    if (active) link.setAttribute('aria-current', 'page');
    else link.removeAttribute('aria-current');
  });
  dots.forEach((dot, i) => {
    if (i === index) dot.setAttribute('aria-current', 'page');
    else dot.removeAttribute('aria-current');
  });
  document.getElementById('page-status').textContent = `第 ${index + 1} 页，共 ${panels.length} 页：${names[index]}`;
  if (updateHash && location.hash !== `#${panels[index].id}`) history.replaceState(null, '', `#${panels[index].id}`);
  lockedUntil = performance.now() + (reducedMotion.matches ? 180 : 850);
  clearTimeout(transitionTimer);
  transitionTimer = setTimeout(() => {
    if (restoreFocus) panels[current].focus({ preventScroll: true });
  }, reducedMotion.matches ? 0 : 780);
}

panels.forEach(panel => { panel.tabIndex = -1; });
function pageFromHash() {
  const index = panels.findIndex(panel => `#${panel.id}` === location.hash);
  goTo(index < 0 ? 0 : index, false);
}
pageFromHash();
window.addEventListener('hashchange', pageFromHash);

document.addEventListener('click', event => {
  const link = event.target.closest('a[href^="#"]');
  if (!link || event.metaKey || event.ctrlKey || event.shiftKey || event.altKey) return;
  const index = panels.findIndex(panel => `#${panel.id}` === link.hash);
  if (index >= 0) {
    event.preventDefault();
    goTo(index);
  } else if (link.hash === '#main') {
    event.preventDefault();
    panels[current].focus({ preventScroll: true });
  }
});

function scrollArea() { return panels[current].querySelector('.panel-scroll'); }
function canScroll(direction, area = scrollArea()) {
  if (!area) return false;
  return direction > 0
    ? area.scrollTop + area.clientHeight < area.scrollHeight - 2
    : area.scrollTop > 2;
}
let lastWheel = -Infinity;
let wheelTotal = 0;
let gestureUsed = false;
document.addEventListener('wheel', event => {
  if (event.ctrlKey || Math.abs(event.deltaX) > Math.abs(event.deltaY) || !event.deltaY) return;
  const now = performance.now();
  if (now - lastWheel > 220) { wheelTotal = 0; gestureUsed = false; }
  lastWheel = now;
  const direction = Math.sign(event.deltaY);
  if (canScroll(direction) && now >= lockedUntil) {
    // Long content remains readable; a new gesture at its boundary turns the page.
    gestureUsed = true;
    return;
  }
  event.preventDefault();
  if (gestureUsed || now < lockedUntil) return;
  const units = event.deltaMode === 1 ? 16 : event.deltaMode === 2 ? window.innerHeight : 1;
  wheelTotal += event.deltaY * units;
  if (Math.abs(wheelTotal) >= 32) {
    gestureUsed = true;
    goTo(current + Math.sign(wheelTotal));
  }
}, { passive: false });

let touch = null;
document.addEventListener('touchstart', event => {
  if (event.touches.length !== 1) { touch = null; return; }
  const area = scrollArea();
  touch = { x: event.touches[0].clientX, y: event.touches[0].clientY,
    top: area?.scrollTop ?? 0, max: area ? area.scrollHeight - area.clientHeight : 0 };
}, { passive: true });
function touchCanScroll(direction) {
  return direction > 0 ? touch.top < touch.max - 2 : touch.top > 2;
}
document.addEventListener('touchmove', event => {
  if (!touch || event.touches.length !== 1) return;
  const dy = touch.y - event.touches[0].clientY;
  const dx = touch.x - event.touches[0].clientX;
  if (Math.abs(dy) > Math.abs(dx) && !touchCanScroll(Math.sign(dy))) event.preventDefault();
}, { passive: false });
document.addEventListener('touchend', event => {
  if (!touch || !event.changedTouches.length) return;
  const dy = touch.y - event.changedTouches[0].clientY;
  const dx = touch.x - event.changedTouches[0].clientX;
  if (Math.abs(dy) > 55 && Math.abs(dy) > Math.abs(dx) && !touchCanScroll(Math.sign(dy)) && performance.now() >= lockedUntil) {
    goTo(current + Math.sign(dy));
  }
  touch = null;
}, { passive: true });
document.addEventListener('touchcancel', () => { touch = null; }, { passive: true });

document.addEventListener('keydown', event => {
  if (event.altKey || event.ctrlKey || event.metaKey || event.target.closest('input,textarea,select,button,[contenteditable="true"]')) return;
  const forward = ['ArrowDown', 'PageDown', ' '].includes(event.key);
  const backward = ['ArrowUp', 'PageUp'].includes(event.key);
  if (event.key === 'Home' || event.key === 'End') {
    event.preventDefault();
    goTo(event.key === 'Home' ? 0 : panels.length - 1);
  } else if (forward || backward) {
    const direction = event.key === ' ' && event.shiftKey ? -1 : forward ? 1 : -1;
    event.preventDefault();
    if (performance.now() < lockedUntil) return;
    const area = scrollArea();
    if (canScroll(direction, area)) {
      area.scrollBy({ top: direction * area.clientHeight * 0.8, behavior: reducedMotion.matches ? 'instant' : 'smooth' });
    } else goTo(current + direction);
  }
});