package org.opentrafficsim.road.gtu.lane;
   
   import java.util.function.Supplier;
   
   import org.djunits.value.vdouble.scalar.Length;
   import org.djutils.exceptions.Throw;
   import org.opentrafficsim.road.gtu.lane.perception.PerceptionCollectable.Intermediate;
   import org.opentrafficsim.road.gtu.lane.perception.PerceptionCollectable.PerceptionAccumulator;
   import org.opentrafficsim.road.gtu.lane.perception.PerceptionCollectable.PerceptionCollector;
  import org.opentrafficsim.road.gtu.lane.perception.PerceptionCollectable.PerceptionFinalizer;
  
  /**
   * Collision detector that detects a negative headway when used on a {@code PerceptionCollectable<HeadwayGTU, LaneBasedGTU>}.
   * This is done by {@code AbstractLaneBasedGTU.getCarFollowingAcceleration()}.
   * <p>
   * Copyright (c) 2013-2019 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="http://opentrafficsim.org/node/13">OpenTrafficSim License</a>.
   * <p>
   * @version $Revision$, $LastChangedDate$, by $Author$, initial version 19 feb. 2019 <br>
   * @author <a href="http://www.tbm.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="http://www.tudelft.nl/pknoppers">Peter Knoppers</a>
   * @author <a href="http://www.transport.citg.tudelft.nl">Wouter Schakel</a>
   */
  public class CollisionDetector implements PerceptionCollector<Void, LaneBasedGTU, Void>
  {
  
      /** GTU id. */
      private final String id;
  
      /**
       * Constructor.
       * @param id String; GTU id
       */
      public CollisionDetector(final String id)
      {
          this.id = id;
      }
  
      /** {@inheritDoc} */
      @Override
      public Supplier<Void> getIdentity()
      {
          return new Supplier<Void>()
          {
              /** {@inheritDoc} */
              @Override
              public Void get()
              {
                  return null;
              }
          };
      }
  
      /** {@inheritDoc} */
      @Override
      public PerceptionAccumulator<LaneBasedGTU, Void> getAccumulator()
      {
          return new PerceptionAccumulator<LaneBasedGTU, Void>()
          {
              /** {@inheritDoc} */
              @SuppressWarnings("synthetic-access")
              @Override
              public Intermediate<Void> accumulate(final Intermediate<Void> intermediate, final LaneBasedGTU object,
                      final Length distance)
              {
                  Throw.when(distance.lt0(), CollisionException.class, "GTU %s collided with GTU %s", CollisionDetector.this.id,
                          object.getId());
                  intermediate.stop();
                  return intermediate;
              }
          };
      }
  
      /** {@inheritDoc} */
      @Override
      public PerceptionFinalizer<Void, Void> getFinalizer()
      {
          return new PerceptionFinalizer<Void, Void>()
          {
              @Override
              public Void collect(final Void intermediate)
              {
                  return null;
              }
          };
      }
  
  }