CS480-Personal-Navigation-Systems/PA5/src/graph/LabelCorrectingAlgorithm.java

package graph;

import java.util.Collections;
import java.util.Map;

import feature.Intersection;
import feature.StreetSegment;

/**
 * Label-correcting shortest-path algorithm.
 */
public class LabelCorrectingAlgorithm extends AbstractShortestPathAlgorithm
{
  private CandidateLabelManager labels;

  /**
   * Explicit value constructor.
   *
   * @param labels candidate label manager
   */
  public LabelCorrectingAlgorithm(final CandidateLabelManager labels)
  {
    this.labels = labels;
  }

  @Override
  public Map<String, StreetSegment> findPath(final int origin, final int destination,
      final StreetNetwork net)
  {
    if (labels == null || net == null)
    {
      return Collections.emptyMap();
    }

    Label originLabel = labels.getLabel(origin);
    if (originLabel == null)
    {
      return Collections.emptyMap();
    }
    originLabel.setValue(0.0);

    Intersection originIntersection = net.getIntersection(origin);
    if (originIntersection != null)
    {
      for (StreetSegment segment : originIntersection.getOutbound())
      {
        labels.adjustHeadValue(segment);
        notifyStreetSegmentObservers(segment.getID());
      }
    }

    Label current = labels.getCandidateLabel();
    while (current != null)
    {
      Intersection intersection = net.getIntersection(current.getID());
      if (intersection != null)
      {
        for (StreetSegment segment : intersection.getOutbound())
        {
          labels.adjustHeadValue(segment);
          notifyStreetSegmentObservers(segment.getID());
        }
      }

      current = labels.getCandidateLabel();
    }

    return buildPath(labels, origin, destination);
  }
}