package org.opentrafficsim.road.gtu.lane.perception.categories.neighbors;
   
   import java.util.function.Supplier;
   
   import org.djunits.value.vdouble.scalar.Duration;
   import org.djunits.value.vdouble.scalar.Length;
   import org.djunits.value.vdouble.scalar.Speed;
   import org.opentrafficsim.road.gtu.lane.LaneBasedGTU;
   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;
  
  /**
   * Simple collector implementation to obtain time headway.
   * <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 3 apr. 2018 <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 TaskHeadwayCollector implements PerceptionCollector<Duration, LaneBasedGTU, Duration>
  {
  
      /** Own speed. */
      private final Speed speed;
  
      /**
       * Constructor.
       * @param speed Speed; speed
       */
      public TaskHeadwayCollector(final Speed speed)
      {
          this.speed = speed;
      }
  
      /** {@inheritDoc} */
      @Override
      public Supplier<Duration> getIdentity()
      {
          return new Supplier<Duration>()
          {
              @Override
              public Duration get()
              {
                  return null; // if no leader
              }
          };
      }
  
      /** {@inheritDoc} */
      @Override
      public PerceptionAccumulator<LaneBasedGTU, Duration> getAccumulator()
      {
          return new PerceptionAccumulator<LaneBasedGTU, Duration>()
          {
              @SuppressWarnings("synthetic-access")
              @Override
              public Intermediate<Duration> accumulate(final Intermediate<Duration> intermediate, final LaneBasedGTU object,
                      final Length distance)
              {
                  intermediate.setObject(distance.divideBy(TaskHeadwayCollector.this.speed));
                  intermediate.stop(); // need only 1 leader
                  return intermediate;
              }
          };
      }
  
      /** {@inheritDoc} */
      @Override
      public PerceptionFinalizer<Duration, Duration> getFinalizer()
      {
          return new PerceptionFinalizer<Duration, Duration>()
          {
              @Override
              public Duration collect(final Duration intermediate)
              {
                  return intermediate == null ? intermediate : (intermediate.gt0() ? intermediate : Duration.ZERO);
              }
          };
      }
  
  }