/**
 * AKSRT Instant Page
 *
 * Lightweight page prefetch on hover/focus.
 * Preloads pages when the user hovers over a link, so navigation feels instant.
 * No external dependencies — pure vanilla JS.
 *
 * Based on the instant.page concept (MIT license).
 *
 * @package AKSRT
 */

(function () {
  'use strict';

  // Only prefetch on desktop (no touch-only devices) with good connection
  if ('connection' in navigator) {
    var conn = navigator.connection;
    if (conn.saveData || (conn.effectiveType && conn.effectiveType.indexOf('2g') !== -1)) return;
  }

  // Don't run on touch-only devices (they don't benefit from hover prefetch)
  var hasHoverSupport = window.matchMedia('(hover: hover) and (pointer: fine)').matches;
  if (!hasHoverSupport) return;

  var prefetcher = document.createElement('link');
  var isPrefetched = {};
  var timer = null;
  var DELAY = 65; // ms to wait before prefetching
  var MAX_PREFETCH = 3; // max concurrent prefetches
  var prefetchedCount = 0;

  if (!prefetcher.relList || !prefetcher.relList.supports || !prefetcher.relList.supports('prefetch')) return;

  function prefetch(url) {
    if (isPrefetched[url] || prefetchedCount >= MAX_PREFETCH) return;

    // Don't prefetch URLs with hash (same page navigation)
    if (url.indexOf('#') !== -1) return;

    // Only prefetch same-origin URLs
    try {
      var link = new URL(url, window.location.origin);
      if (link.origin !== window.location.origin) return;
      // Don't prefetch the current page
      if (link.pathname === window.location.pathname && link.search === window.location.search) return;
    } catch (e) { return; }

    // Don't prefetch files/downloads
    if (/\.(pdf|zip|rar|7z|tar|gz|exe|dmg|apk|mp[34]|avi|mov|wmv|flv|webm|ogg|wav|bmp|gif|ico|svg|woff2?|ttf|eot)(\?|$)/i.test(url)) return;

    isPrefetched[url] = true;
    prefetchedCount++;

    var linkEl = document.createElement('link');
    linkEl.rel = 'prefetch';
    linkEl.href = url;
    linkEl.as = 'document';
    document.head.appendChild(linkEl);
  }

  function onHoverStart(e) {
    var link = e.target.closest('a');
    if (!link || !link.href) return;
    if (link.target === '_blank') return;
    if (link.hasAttribute('download')) return;
    if (link.getAttribute('rel') === 'nofollow') return;
    if (link.closest('.no-prefetch,[data-no-prefetch]')) return;

    clearTimeout(timer);
    timer = setTimeout(function () {
      prefetch(link.href);
    }, DELAY);
  }

  function onHoverEnd() {
    clearTimeout(timer);
  }

  document.addEventListener('mouseover', onHoverStart, { passive: true, capture: true });
  document.addEventListener('mouseout', onHoverEnd, { passive: true, capture: true });

  // Also prefetch on focus for keyboard navigation
  document.addEventListener('focusin', function (e) {
    var link = e.target.closest('a');
    if (link && link.href) {
      prefetch(link.href);
    }
  }, { passive: true, capture: true });

  // Cleanup after page hides (bfcache)
  window.addEventListener('pagehide', function () {
    isPrefetched = {};
    prefetchedCount = 0;
  });
})();