// =============================================================================
// Empty Link Fixer — content script.
//
// On the website configured in config.js (loaded first, same isolated world),
// every anchor that has an href but NO visible content gets the href inserted
// as text, e.g.  <a href="/docs/api"></a>  becomes  <a href="/docs/api">/docs/api</a>
//
// This "always" works, including on dynamically rendered sites (SPAs, virtual
// DOM, infinite scroll, web components), because the extension:
//   1. fixes every empty anchor already present when the script starts,
//   2. observes ALL DOM changes (added/removed nodes, emptied text,
//      href attributes appearing) with a MutationObserver and fixes on the fly,
//   3. watches inside open shadow roots (web components), and
//   4. keeps a small periodic re-scan as a safety net.
// =============================================================================

(() => {
  'use strict';

  // -------------------------------------------------------------------------
  // Configuration (from config.js)
  // -------------------------------------------------------------------------
  const cfg = (globalThis && globalThis.LINK_FIX_CONFIG) || {};
  const hostList = Array.isArray(cfg.hosts) ? cfg.hosts : [];
  const includeSubdomains = cfg.includeSubdomains !== false;
  const wantAllSites = hostList.includes('*');
  const debug = cfg.debug === true;

  const currentHost = (location.hostname || '').toLowerCase();

  const normalizeHost = (input) =>
    String(input)
      .trim()
      .toLowerCase()
      .replace(/^[a-z][a-z0-9+.-]*:\/\//i, '') // scheme
      .replace(/^\/\//, '') // protocol-relative URLs
      .split('/')[0] // path
      .split(':')[0] // port
      .replace(/^www\./, '');

  const onTargetSite =
    wantAllSites ||
    hostList.some((entry) => {
      const configured = normalizeHost(entry);
      if (!configured) return false;
      return (
        currentHost === configured ||
        (includeSubdomains && currentHost.endsWith('.' + configured))
      );
    });

  if (!onTargetSite) return; // Not the configured website: do nothing.

  // -------------------------------------------------------------------------
  // What counts as an "empty" anchor
  // -------------------------------------------------------------------------

  // Elements that provide visible, non-text content inside an <a> (icons,
  // images, video, form controls, ...). Such links are NOT "empty".
  const MEDIA_SELECTOR = [
    'img', 'svg', 'picture', 'canvas', 'video', 'audio',
    'iframe', 'embed', 'object',
    'input', 'select', 'textarea', 'button', 'progress', 'meter',
  ].join(', ');

  // hrefs that are not real navigations: inserting them as text is pointless.
  const VOID_HREF_RE = /^(?:javascript|data|vbscript):/i;

  function isFixableAnchor(a) {
    if (!a || a.tagName !== 'A') return false;
    if (!a.hasAttribute('href')) return false;

    const href = a.getAttribute('href').trim();
    if (!href || href === '#' || VOID_HREF_RE.test(href)) return false;

    // Already has visible text?
    if (a.textContent.trim() !== '') return false;

    // Carries visible media content (icon, image, ...)?
    if (a.querySelector(MEDIA_SELECTOR) !== null) return false;

    // Leave WYSIWYG/editable regions alone.
    if (a.closest('[contenteditable]:not([contenteditable="false"])')) return false;

    return true;
  }

  function fixAnchor(a) {
    if (!isFixableAnchor(a)) return;
    const href = a.getAttribute('href').trim();

    // Remove whitespace-only text nodes so the result is tidy, then append the
    // href as real text (children that are merely empty are kept intact).
    a.normalize();
    const children = Array.from(a.childNodes);
    for (const node of children) {
      if (node.nodeType === Node.TEXT_NODE && !node.textContent.trim()) {
        node.remove();
      }
    }

    a.appendChild(a.ownerDocument.createTextNode(href));
    if (debug) console.debug('[linkfix] filled empty link ->', href, a);
  }

  // -------------------------------------------------------------------------
  // Watching the live document
  // -------------------------------------------------------------------------

  const OBSERVER_OPTIONS = {
    childList: true, // nodes added/removed anywhere
    characterData: true, // text emptied in place
    attributes: true, // href attribute appearing/changing
    attributeFilter: ['href'],
    subtree: true,
  };

  const observedRoots = new WeakSet();
  let lastMutationAt = Date.now();

  function fixAnchorsIn(root) {
    if (!root) return;
    if (
      root.nodeType === Node.ELEMENT_NODE &&
      root.matches &&
      root.matches('a[href]')
    ) {
      fixAnchor(root);
    }
    const anchors = root.querySelectorAll ? root.querySelectorAll('a[href]') : [];
    for (const a of anchors) fixAnchor(a);
  }

  function onMutations(mutations) {
    for (const mutation of mutations) {
      try {
        if (mutation.type === 'childList') {
          // Content removed from inside a link may have left it empty.
          if (
            mutation.target &&
            mutation.target.nodeType === Node.ELEMENT_NODE
          ) {
            const ownerAnchor = mutation.target.closest('a');
            if (ownerAnchor) fixAnchor(ownerAnchor);
          }
          // Newly added content: fix empty links inside it and look for
          // web components (open shadow roots) that came with it.
          for (const node of mutation.addedNodes) {
            if (node.nodeType !== Node.ELEMENT_NODE) continue;
            fixAnchorsIn(node);
            discoverShadowRoots(node);
          }
        } else {
          // characterData (text node emptied) or href attribute change:
          // the closest anchor may now be empty (or newly hrefless-empty).
          const el =
            mutation.target.nodeType === Node.ELEMENT_NODE
              ? mutation.target
              : mutation.target.parentElement;
          if (el && el.closest) {
            const ownerAnchor = el.closest('a');
            if (ownerAnchor) fixAnchor(ownerAnchor);
          }
        }
        lastMutationAt = Date.now();
      } catch (err) {
        console.warn('[linkfix] error while processing a mutation:', err);
      }
    }
  }

  function attachObserver(root) {
    if (!root || observedRoots.has(root)) return;
    observedRoots.add(root);
    const observer = new MutationObserver(onMutations);
    observer.observe(root, OBSERVER_OPTIONS);
    fixAnchorsIn(root); // fix what is already there
    discoverShadowRoots(root); // and what lives inside open shadow roots
  }

  // Find open shadow roots (web components) reachable from `scope` and watch
  // each one, recursively. Closed shadow roots cannot be touched — by design.
  function discoverShadowRoots(scope) {
    if (!scope) return;
    const stack = [
      scope.nodeType === Node.DOCUMENT_NODE ? scope.documentElement : scope,
    ];
    while (stack.length) {
      const node = stack.pop();
      if (!node || node.nodeType !== Node.ELEMENT_NODE) continue;
      if (node.shadowRoot) attachObserver(node.shadowRoot);
      for (const child of node.children) stack.push(child);
    }
  }

  function start() {
    if (document.readyState === 'loading') {
      document.addEventListener('DOMContentLoaded', start, { once: true });
      return;
    }
    try {
      attachObserver(document);
      if (debug) console.debug('[linkfix] active on', currentHost);

      // Safety net for content that changes without observable mutations
      // (e.g. a host element attaching its shadow root after connection).
      const rescanMs = Number(cfg.rescanIntervalMs) || 0;
      if (rescanMs > 0) {
        setInterval(() => {
          if (document.visibilityState === 'hidden') return;
          try {
            fixAnchorsIn(document);
            discoverShadowRoots(document);
          } catch (err) {
            console.warn('[linkfix] error during re-scan:', err);
          }
        }, rescanMs);
      }
    } catch (err) {
      console.warn('[linkfix] failed to initialise:', err);
    }
  }

  start();
})();