(function () {
  'use strict';

  if (window.__kspMissionGalleryRuntimeV1) { return; }
  window.__kspMissionGalleryRuntimeV1 = true;

  var selector = '.wiki-article .gallery-grid img[data-wiki-asset]';
  var overlay = document.createElement('div');
  overlay.className = 'wiki-image-lightbox';
  overlay.hidden = true;
  overlay.innerHTML = '<figure class="wiki-image-lightbox-panel" role="dialog" aria-modal="true" aria-label="Mission gallery image preview">' +
    '<button class="wiki-image-lightbox-close" type="button" aria-label="Close image preview">&times;</button>' +
    '<button class="wiki-image-lightbox-nav wiki-image-lightbox-prev" type="button" aria-label="Previous image">&lsaquo;</button>' +
    '<img alt="">' +
    '<button class="wiki-image-lightbox-nav wiki-image-lightbox-next" type="button" aria-label="Next image">&rsaquo;</button>' +
    '<span class="wiki-image-lightbox-counter" aria-live="polite"></span>' +
    '<figcaption class="thumbcaption"></figcaption></figure>';

  var previewImage = overlay.querySelector('img');
  var previewCaption = overlay.querySelector('figcaption');
  var counter = overlay.querySelector('.wiki-image-lightbox-counter');
  var closeButton = overlay.querySelector('.wiki-image-lightbox-close');
  var previousButton = overlay.querySelector('.wiki-image-lightbox-prev');
  var nextButton = overlay.querySelector('.wiki-image-lightbox-next');
  var images = [];
  var activeIndex = 0;
  var lastTrigger = null;

  function captionFor(image) {
    var container = image.closest('.gallery-item, figure, td, tr, .infobox-image');
    var caption = container && container.querySelector('.thumbcaption');
    return caption ? caption.textContent.trim() : (image.alt || '');
  }

  function enhanceImages(root) {
    var scope = root && root.querySelectorAll ? root : document;
    Array.prototype.forEach.call(scope.querySelectorAll(selector), function (image) {
      image.tabIndex = 0;
      image.setAttribute('role', 'button');
      image.setAttribute('aria-label', 'Open image preview: ' + (image.alt || 'mission image'));
      var article = image.closest('.wiki-article');
      if (article) { article.dataset.galleryLightboxReady = '1'; }
    });
  }

  function render(index) {
    activeIndex = (index + images.length) % images.length;
    var image = images[activeIndex];
    previewImage.src = image.dataset.wikiAsset || image.currentSrc || image.src;
    previewImage.alt = image.alt || '';
    previewCaption.textContent = captionFor(image);
    counter.textContent = (activeIndex + 1) + ' / ' + images.length;
    previousButton.hidden = images.length < 2;
    nextButton.hidden = images.length < 2;
  }

  function openPreview(image, event) {
    var article = image.closest('.wiki-article');
    images = Array.prototype.slice.call(article.querySelectorAll('.gallery-grid img[data-wiki-asset]'));
    if (!images.length) { return; }
    if (event) { event.preventDefault(); event.stopPropagation(); }
    lastTrigger = image;
    render(images.indexOf(image));
    overlay.hidden = false;
    document.body.classList.add('wiki-image-lightbox-open');
    closeButton.focus();
  }

  function closePreview() {
    overlay.hidden = true;
    previewImage.removeAttribute('src');
    document.body.classList.remove('wiki-image-lightbox-open');
    if (lastTrigger && lastTrigger.isConnected) { lastTrigger.focus(); }
  }

  document.body.appendChild(overlay);
  enhanceImages(document);

  document.addEventListener('click', function (event) {
    var image = event.target.closest && event.target.closest(selector);
    if (image) { openPreview(image, event); }
  });
  document.addEventListener('keydown', function (event) {
    if (!overlay.hidden) {
      if (event.key === 'Escape') { closePreview(); }
      if (event.key === 'ArrowLeft') { render(activeIndex - 1); }
      if (event.key === 'ArrowRight') { render(activeIndex + 1); }
      return;
    }
    if ((event.key === 'Enter' || event.key === ' ') && document.activeElement.matches(selector)) {
      openPreview(document.activeElement, event);
    }
  });
  previousButton.addEventListener('click', function () { render(activeIndex - 1); });
  nextButton.addEventListener('click', function () { render(activeIndex + 1); });
  closeButton.addEventListener('click', closePreview);
  overlay.addEventListener('click', function (event) {
    if (event.target === overlay) { closePreview(); }
  });

  new MutationObserver(function (mutations) {
    mutations.forEach(function (mutation) {
      Array.prototype.forEach.call(mutation.addedNodes, function (node) {
        if (node.nodeType === 1) { enhanceImages(node); }
      });
    });
  }).observe(document.body, { childList: true, subtree: true });
}());