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);
  }
}