// TODO we can avoid node level if we store this into a temporary array and
  // disconnect all edges which goes from higher to lower level
  // uninitialized nodes have a level of 0
  // TODO we could avoid the second storage for skippedEdge as we could store that info into linkB
  // or A if it is disconnected
  boolean prepareNodes() {
    int len = g.getNodes();

    for (int node = 0; node < len; node++) {
      int priority = oldPriorities[node] = calculatePriority(node);
      sortedNodes.insert(node, priority);
    }

    if (sortedNodes.isEmpty()) return false;

    return true;
  }
  void contractNodes() {
    meanDegree = g.getAllEdges().getMaxId() / g.getNodes();
    int level = 1;
    counter = 0;
    int initSize = sortedNodes.getSize();
    int logSize =
        (int) Math.round(Math.max(10, sortedNodes.getSize() / 100 * logMessagesPercentage));
    if (logMessagesPercentage == 0) logSize = Integer.MAX_VALUE;

    // preparation takes longer but queries are slightly faster with preparation
    // => enable it but call not so often
    boolean periodicUpdate = true;
    StopWatch periodSW = new StopWatch();
    int updateCounter = 0;
    int periodicUpdatesCount =
        Math.max(10, sortedNodes.getSize() / 100 * periodicUpdatesPercentage);
    if (periodicUpdatesPercentage == 0) periodicUpdate = false;

    // disable as preparation is slower and query time does not benefit
    int lastNodesLazyUpdates =
        lastNodesLazyUpdatePercentage == 0
            ? 0
            : sortedNodes.getSize() / 100 * lastNodesLazyUpdatePercentage;
    StopWatch lazySW = new StopWatch();

    // Recompute priority of uncontracted neighbors.
    // Without neighborupdates preparation is faster but we need them
    // to slightly improve query time. Also if not applied too often it decreases the shortcut
    // number.
    boolean neighborUpdate = true;
    if (neighborUpdatePercentage == 0) neighborUpdate = false;

    StopWatch neighborSW = new StopWatch();
    LevelGraphStorage lg = ((LevelGraphStorage) g);
    while (!sortedNodes.isEmpty()) {
      // periodically update priorities of ALL nodes
      if (periodicUpdate && counter > 0 && counter % periodicUpdatesCount == 0) {
        periodSW.start();
        sortedNodes.clear();
        int len = g.getNodes();
        for (int node = 0; node < len; node++) {
          if (g.getLevel(node) != 0) continue;

          int priority = oldPriorities[node] = calculatePriority(node);
          sortedNodes.insert(node, priority);
        }
        periodSW.stop();
        updateCounter++;
      }

      if (counter % logSize == 0) {
        // TODO necessary?
        System.gc();
        logger.info(
            Helper.nf(counter)
                + ", updates:"
                + updateCounter
                + ", nodes: "
                + Helper.nf(sortedNodes.getSize())
                + ", shortcuts:"
                + Helper.nf(newShortcuts)
                + ", dijkstras:"
                + Helper.nf(dijkstraCount)
                + ", t(dijk):"
                + (int) dijkstraSW.getSeconds()
                + ", t(period):"
                + (int) periodSW.getSeconds()
                + ", t(lazy):"
                + (int) lazySW.getSeconds()
                + ", t(neighbor):"
                + (int) neighborSW.getSeconds()
                + ", meanDegree:"
                + (long) meanDegree
                + ", algo:"
                + algo.getMemoryUsageAsString()
                + ", "
                + Helper.getMemInfo());
        dijkstraSW = new StopWatch();
        periodSW = new StopWatch();
        lazySW = new StopWatch();
        neighborSW = new StopWatch();
      }

      counter++;
      int polledNode = sortedNodes.pollKey();
      if (sortedNodes.getSize() < lastNodesLazyUpdates) {
        lazySW.start();
        int priority = oldPriorities[polledNode] = calculatePriority(polledNode);
        if (!sortedNodes.isEmpty() && priority > sortedNodes.peekValue()) {
          // current node got more important => insert as new value and contract it later
          sortedNodes.insert(polledNode, priority);
          lazySW.stop();
          continue;
        }
        lazySW.stop();
      }

      // contract!
      newShortcuts += addShortcuts(polledNode);
      g.setLevel(polledNode, level);
      level++;

      EdgeSkipIterator iter = vehicleAllExplorer.setBaseNode(polledNode);
      while (iter.next()) {
        int nn = iter.getAdjNode();
        if (g.getLevel(nn) != 0)
          // already contracted no update necessary
          continue;

        if (neighborUpdate && rand.nextInt(100) < neighborUpdatePercentage) {
          neighborSW.start();
          int oldPrio = oldPriorities[nn];
          int priority = oldPriorities[nn] = calculatePriority(nn);
          if (priority != oldPrio) sortedNodes.update(nn, oldPrio, priority);

          neighborSW.stop();
        }

        if (removesHigher2LowerEdges) lg.disconnect(vehicleAllTmpExplorer, iter);
      }
    }

    // Preparation works only once so we can release temporary data.
    // The preparation object itself has to be intact to create the algorithm.
    close();
    logger.info(
        "took:"
            + (int) allSW.stop().getSeconds()
            + ", new shortcuts: "
            + newShortcuts
            + ", "
            + prepareWeighting
            + ", "
            + prepareEncoder
            + ", removeHigher2LowerEdges:"
            + removesHigher2LowerEdges
            + ", dijkstras:"
            + dijkstraCount
            + ", t(dijk):"
            + (int) dijkstraSW.getSeconds()
            + ", t(period):"
            + (int) periodSW.getSeconds()
            + ", t(lazy):"
            + (int) lazySW.getSeconds()
            + ", t(neighbor):"
            + (int) neighborSW.getSeconds()
            + ", meanDegree:"
            + (long) meanDegree
            + ", initSize:"
            + initSize
            + ", periodic:"
            + periodicUpdatesPercentage
            + ", lazy:"
            + lastNodesLazyUpdatePercentage
            + ", neighbor:"
            + neighborUpdatePercentage);
  }