(function () {
  'use strict';

  var stage = document.querySelector('[data-btp581-stage]');
  if (!stage) return;

  var windows = Array.prototype.slice.call(stage.querySelectorAll('[data-btp581-domain]'));
  if (!windows.length) return;

  var reducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)');
  var desktopLayout = window.matchMedia('(min-width: 861px)');
  var activeIndex = 0;
  var timer = 0;
  var stageVisible = true;
  var userHolding = false;

  function setActive(index) {
    activeIndex = (index + windows.length) % windows.length;
    windows.forEach(function (item, itemIndex) {
      item.classList.toggle('is-active', itemIndex === activeIndex);
    });
    stage.setAttribute('data-active-domain', windows[activeIndex].getAttribute('data-btp581-domain'));
  }

  function stopCycle() {
    if (!timer) return;
    window.clearInterval(timer);
    timer = 0;
  }

  function canCycle() {
    return !reducedMotion.matches && desktopLayout.matches && !document.hidden && stageVisible && !userHolding;
  }

  function startCycle() {
    stopCycle();
    if (!canCycle()) return;
    timer = window.setInterval(function () {
      setActive(activeIndex + 1);
    }, 4800);
  }

  windows.forEach(function (item, index) {
    item.addEventListener('pointerenter', function () {
      userHolding = true;
      stopCycle();
      setActive(index);
    }, { passive: true });

    item.addEventListener('focus', function () {
      userHolding = true;
      stopCycle();
      setActive(index);
    });
  });

  stage.addEventListener('pointerleave', function () {
    userHolding = false;
    startCycle();
  }, { passive: true });

  stage.addEventListener('focusout', function (event) {
    if (stage.contains(event.relatedTarget)) return;
    userHolding = false;
    startCycle();
  });

  function handleEnvironmentChange() {
    if (!desktopLayout.matches) {
      stopCycle();
      setActive(0);
      return;
    }
    startCycle();
  }

  if (typeof reducedMotion.addEventListener === 'function') {
    reducedMotion.addEventListener('change', handleEnvironmentChange);
    desktopLayout.addEventListener('change', handleEnvironmentChange);
  } else {
    reducedMotion.addListener(handleEnvironmentChange);
    desktopLayout.addListener(handleEnvironmentChange);
  }

  document.addEventListener('visibilitychange', startCycle);

  if ('IntersectionObserver' in window) {
    var visibilityObserver = new IntersectionObserver(function (entries) {
      stageVisible = Boolean(entries[0] && entries[0].isIntersecting);
      startCycle();
    }, { threshold: 0.16 });
    visibilityObserver.observe(stage);
  }

  window.addEventListener('pagehide', stopCycle, { once: true });
  setActive(0);
  startCycle();
}());