/* global window, document */

(function () {
  'use strict';

  var Luxtools = window.Luxtools || (window.Luxtools = {});

  // ============================================================
  // Gallery Thumbnails Module
  // ============================================================
  // Uses fetch() with AbortController to load thumbnails.
  // This allows true HTTP request cancellation on navigation,
  // unlike native loading="lazy" where queued requests block.
  Luxtools.GalleryThumbnails = (function () {
    var controller = null;
    var maxConcurrent = 4;
    var activeCount = 0;
    var queue = [];

    function abortAll() {
      if (controller) {
        controller.abort();
        controller = null;
      }
      queue = [];
      activeCount = 0;
    }

    function processQueue() {
      if (!controller) return;
      while (activeCount < maxConcurrent && queue.length > 0) {
        var img = queue.shift();
        loadThumb(img);
      }
    }

    function loadThumb(img) {
      if (!controller) return;

      var src = img.getAttribute('data-src');
      if (!src) {
        processQueue();
        return;
      }

      activeCount++;

      fetch(src, { signal: controller.signal })
        .then(function (response) {
          if (!response.ok) throw new Error('HTTP ' + response.status);
          return response.blob();
        })
        .then(function (blob) {
          img.src = URL.createObjectURL(blob);
          img.removeAttribute('data-src');
        })
        .catch(function (err) {
          // Aborted or failed - ignore
          if (err.name !== 'AbortError') {
            // Keep data-src for potential retry, just log
          }
        })
        .finally(function () {
          activeCount--;
          processQueue();
        });
    }

    function queueThumb(img) {
      if (!controller) return;
      if (!img.getAttribute('data-src')) return;
      if (img.getAttribute('data-queued') === '1') return;
      img.setAttribute('data-queued', '1');
      queue.push(img);
      processQueue();
    }

    function init() {
      var imgs = document.querySelectorAll(
        'div.luxtools-gallery img.luxtools-thumb[data-src], div.luxtools-imagebox img[data-src]'
      );
      if (!imgs || !imgs.length) return;

      // Create abort controller for all requests
      controller = new AbortController();

      // Abort all pending requests on navigation
      window.addEventListener('beforeunload', abortAll);
      window.addEventListener('pagehide', abortAll);

      // Use IntersectionObserver to trigger loading
      if ('IntersectionObserver' in window) {
        var io = new IntersectionObserver(function (entries) {
          entries.forEach(function (entry) {
            if (!entry.isIntersecting) return;
            queueThumb(entry.target);
            io.unobserve(entry.target);
          });
        }, { rootMargin: '200px' });

        imgs.forEach(function (img) { io.observe(img); });
      } else {
        // Fallback: queue all
        imgs.forEach(queueThumb);
      }
    }

    return {
      init: init
    };
  })();
})();