static double ai_gc_scan_maxDistance_reached;

static S ai_gc_scan(S root) {

  ai_gc_clear();

  ai_startBuffering();

  Map<S, Double> distances;

  try {

    time "GC Scan" {

      ai_postTriple(root, "has GC distance", "0");

      distances = litcimap(root, 0.0);

      LinkedList<S> queue = litLinkedList(root);

      S word;

      while ping ((word = queue.poll()) != null) {

        double d = distances.get(word);

        for (WebNode node : indexedNodes(word)) {

          for (WebRelation r : web_forwardRelations(node)) {

            double dist = ai_gc_distanceFunction(web_text(r), true);

            if (!isNaN(dist))

              ai_gc_scan_update(distances, queue, r.b, d+dist);

          }

          for (WebRelation r : web_backwardRelations(node)) {

            double dist = ai_gc_distanceFunction(web_text(r), false);

            if (!isNaN(dist))

              ai_gc_scan_update(distances, queue, r.a, d+dist);

          }

        }

      }

      Collection<S> keys = keys(distances);

      if (ai_inTestMode())

        keys = keysSortedByValueDesc(distances);

      ai_gc_scan_maxDistance_reached = 0;

      for (S key : keys) {

        double d = distances.get(key);

        if (d > ai_gc_scan_maxDistance_reached) ai_gc_scan_maxDistance_reached = d;

        ai_postTriple(key, "has GC distance", formatDouble(d, 1));

      }

    }

  } finally {

    ai_stopBuffering();

  }

  ret print(l(distances) + "/" + l(indexedTerms()) + " terms were reached in " + toS(lastTiming(), 1) + " s GC scan from " + quote(root) + ". Max distance: " + formatDouble(ai_gc_scan_maxDistance_reached, 1));

}

static void ai_gc_scan_update(Map<S, Double> distances, L<S> queue, WebNode n, double d) {

  //S text = ai_shortenForIndex(web_text(n));

  S text = web_text(n);

  Double od = distances.get(text);

  if (od == null || d < od) {

    distances.put(text, d);

    queue.add(text);

  }

}