/* global document */

/**
 * Link Favicon Module
 *
 * Displays favicons for external links using DuckDuckGo's favicon service.
 * Based on the linkfavicon plugin by Shao Yanmin.
 *
 * Note: DDG returns a grey placeholder icon for domains without favicons.
 * Detecting this placeholder client-side is not reliably possible due to
 * CORS restrictions preventing canvas pixel inspection.
 */
(function () {
  'use strict';

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

  // Cache states for favicon URLs
  var ICON_NOT_FOUND = -1;
  var ICON_LOADING = 0;
  var ICON_LOADED = 1;
  var faviconCache = {};

  /**
   * Preload an image to verify it loads.
   * @param {string} src - Image URL to load
   * @returns {Promise} Resolves on load, rejects on error
   */
  function loadImage(src) {
    return new Promise(function (resolve, reject) {
      var image = new Image();
      image.addEventListener('load', resolve);
      image.addEventListener('error', reject);
      image.src = src;
    });
  }

  /**
   * Apply the favicon as background image to all matching links.
   * @param {string} faviconUrl - The favicon URL to apply
   */
  function applyFavicon(faviconUrl) {
    if (faviconCache[faviconUrl] !== ICON_LOADED) return;

    var links = document.querySelectorAll('[data-linkfavicon="' + faviconUrl + '"]');
    for (var i = 0; i < links.length; i++) {
      links[i].classList.add('linkfavicon');
      links[i].style.backgroundImage = 'url(' + faviconUrl + ')';
    }
  }

  /**
   * Get domain from URL.
   * @param {string} url - Full URL
   * @returns {string|null} Domain or null if invalid
   */
  function getDomain(url) {
    try {
      var parsed = new URL(url);
      return parsed.hostname;
    } catch (e) {
      return null;
    }
  }

  /**
   * Initialize favicons for all external links on the page.
   */
  function init() {
    // Find all external links (DokuWiki marks them with class 'urlextern')
    var links = document.querySelectorAll('a.urlextern');

    for (var i = 0; i < links.length; i++) {
      var link = links[i];
      var href = link.getAttribute('href');
      if (!href) continue;

      var domain = getDomain(href);
      if (!domain) continue;

      // DuckDuckGo favicon service URL
      var faviconUrl = 'https://icons.duckduckgo.com/ip3/' + domain + '.ico';

      // Mark the link with the favicon URL for later reference
      link.setAttribute('data-linkfavicon', faviconUrl);

      // Load and cache the favicon if not already processed
      if (faviconCache[faviconUrl] === undefined) {
        faviconCache[faviconUrl] = ICON_LOADING;

        (function (url) {
          loadImage(url)
            .then(function () {
              faviconCache[url] = ICON_LOADED;
              applyFavicon(url);
            })
            .catch(function () {
              faviconCache[url] = ICON_NOT_FOUND;
            });
        })(faviconUrl);
      } else if (faviconCache[faviconUrl] === ICON_LOADED) {
        // Already loaded, apply immediately
        link.classList.add('linkfavicon');
        link.style.backgroundImage = 'url(' + faviconUrl + ')';
      }
    }
  }

  // Export for potential external use
  Luxtools.LinkFavicon = {
    init: init
  };

  // Initialize when DOM is ready
  document.addEventListener('DOMContentLoaded', init, false);
})();