package org.opentrafficsim.road.gtu.generator;
   
   import java.io.Serializable;
   import java.rmi.RemoteException;
   import java.util.Collections;
   import java.util.LinkedHashMap;
   import java.util.LinkedHashSet;
   import java.util.LinkedList;
   import java.util.Map;
  import java.util.Queue;
  import java.util.Set;
  import java.util.SortedSet;
  import java.util.TreeSet;
  import java.util.UUID;
  import java.util.function.Supplier;
  
  import javax.naming.NamingException;
  
  import org.djunits.unit.DurationUnit;
  import org.djunits.value.vdouble.scalar.Duration;
  import org.djunits.value.vdouble.scalar.Length;
  import org.djunits.value.vdouble.scalar.Speed;
  import org.djunits.value.vdouble.scalar.Time;
  import org.djutils.draw.bounds.Bounds;
  import org.djutils.draw.bounds.Bounds2d;
  import org.djutils.draw.point.Point;
  import org.djutils.event.EventType;
  import org.djutils.event.LocalEventProducer;
  import org.djutils.exceptions.Throw;
  import org.djutils.metadata.MetaData;
  import org.djutils.metadata.ObjectDescriptor;
  import org.opentrafficsim.base.Identifiable;
  import org.opentrafficsim.base.TimeStampedObject;
  import org.opentrafficsim.base.parameters.ParameterException;
  import org.opentrafficsim.core.distributions.Generator;
  import org.opentrafficsim.core.distributions.ProbabilityException;
  import org.opentrafficsim.core.dsol.OtsSimulatorInterface;
  import org.opentrafficsim.core.geometry.DirectedPoint;
  import org.opentrafficsim.core.geometry.OtsGeometryException;
  import org.opentrafficsim.core.gtu.GtuErrorHandler;
  import org.opentrafficsim.core.gtu.GtuException;
  import org.opentrafficsim.core.gtu.GtuGenerator;
  import org.opentrafficsim.core.gtu.GtuType;
  import org.opentrafficsim.core.gtu.RelativePosition;
  import org.opentrafficsim.core.network.NetworkException;
  import org.opentrafficsim.road.gtu.generator.GeneratorPositions.GeneratorLanePosition;
  import org.opentrafficsim.road.gtu.generator.characteristics.LaneBasedGtuCharacteristics;
  import org.opentrafficsim.road.gtu.generator.characteristics.LaneBasedGtuCharacteristicsGenerator;
  import org.opentrafficsim.road.gtu.lane.LaneBasedGtu;
  import org.opentrafficsim.road.gtu.lane.perception.headway.HeadwayGtu;
  import org.opentrafficsim.road.gtu.lane.perception.headway.HeadwayGtuReal;
  import org.opentrafficsim.road.network.RoadNetwork;
  import org.opentrafficsim.road.network.lane.CrossSectionLink;
  import org.opentrafficsim.road.network.lane.Lane;
  import org.opentrafficsim.road.network.lane.LanePosition;
  
  import nl.tudelft.simulation.dsol.SimRuntimeException;
  
  /**
   * Lane based GTU generator. This generator generates lane based GTUs using a LaneBasedTemplateGTUType. The template is used to
   * generate a set of GTU characteristics at the times implied by the headway generator. These sets are queued until there is
   * sufficient room to construct a GTU at the specified lane locations. The speed of a construction GTU may be reduced to ensure
   * it does not run into its immediate leader GTU.
   * <p>
   * Copyright (c) 2013-2023 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author <a href="https://github.com/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://tudelft.nl/staff/p.knoppers-1">Peter Knoppers</a>
   * @author <a href="https://dittlab.tudelft.nl">Wouter Schakel</a>
   */
  public class LaneBasedGtuGenerator extends LocalEventProducer implements Serializable, Identifiable, GtuGenerator
  {
      /** */
      private static final long serialVersionUID = 20160000L;
  
      /**
       * Event of a generated GTU. Payload: LaneBasedGtu
       */
      public static final EventType GTU_GENERATED_EVENT = new EventType("GENERATOR.GTU_GENERATED", new MetaData("GTU generated",
              "GTU was generated", new ObjectDescriptor("GTU", "The GTU itself", LaneBasedGtu.class)));
  
      /** FIFO for templates that have not been generated yet due to insufficient room/headway, per position, and per link. */
      private final Map<CrossSectionLink,
              Map<GeneratorLanePosition, Queue<TimeStampedObject<LaneBasedGtuCharacteristics>>>> unplacedTemplates =
                      new LinkedHashMap<>();
  
      /** Name of the GTU generator. */
      private final String id;
  
      /** Unique id in the network. */
      private final String uniqueId;
  
      /** Time distribution that determines the interval times between GTUs. */
      private final Generator<Duration> interarrivelTimeGenerator;
  
      /** Generates most properties of the GTUs. */
      private final LaneBasedGtuCharacteristicsGenerator laneBasedGtuCharacteristicsGenerator;
  
     /** Total number of GTUs generated so far. */
     private long generatedGTUs = 0;
 
     /** Retry interval for checking if a GTU can be placed. */
     private Duration reTryInterval = new Duration(0.1, DurationUnit.SI);
 
     /** Location provider for all generated GTUs. */
     private final GeneratorPositions generatorPositions;
 
     /** Network. */
     private final RoadNetwork network;
 
     /** Simulator. */
     private final OtsSimulatorInterface simulator;
 
     /** The way that this generator checks if it is safe to construct and place the next lane based GTU. */
     private final RoomChecker roomChecker;
 
     /** ID generator. */
     private final Supplier<String> idGenerator;
 
     /** Initial distance over which lane changes shouldn't be performed. */
     private Length noLaneChangeDistance = null;
 
     /** Whether GTUs change lane instantaneously. */
     private boolean instantaneousLaneChange = false;
 
     /** GTU error handler. */
     private GtuErrorHandler errorHandler = GtuErrorHandler.THROW;
 
     /** Vehicle generation is ignored on these lanes. */
     private Set<Lane> disabled = new LinkedHashSet<>();
 
     /**
      * Construct a new lane base GTU generator.
      * @param id String; name of the new GTU generator
      * @param interarrivelTimeGenerator Generator&lt;Duration&gt;; generator for the interval times between GTUs
      * @param laneBasedGtuCharacteristicsGenerator LaneBasedGtuCharacteristicsGenerator; generator of the characteristics of
      *            each GTU
      * @param generatorPositions GeneratorPositions; location and initial direction provider for all generated GTUs
      * @param network RoadNetwork; the OTS network that owns the generated GTUs
      * @param simulator OtsSimulatorInterface; simulator
      * @param roomChecker RoomChecker; the way that this generator checks that there is sufficient room to place a new GTU
      * @param idGenerator Supplier&lt;String&gt;; id generator
      * @throws SimRuntimeException when <cite>startTime</cite> lies before the current simulation time
      * @throws ProbabilityException pe
      * @throws ParameterException if drawing from the interarrival generator fails
      * @throws NetworkException if the object could not be added to the network
      */
     @SuppressWarnings("parameternumber")
     public LaneBasedGtuGenerator(final String id, final Generator<Duration> interarrivelTimeGenerator,
             final LaneBasedGtuCharacteristicsGenerator laneBasedGtuCharacteristicsGenerator,
             final GeneratorPositions generatorPositions, final RoadNetwork network, final OtsSimulatorInterface simulator,
             final RoomChecker roomChecker, final Supplier<String> idGenerator)
             throws SimRuntimeException, ProbabilityException, ParameterException, NetworkException
     {
         this.id = id;
         this.uniqueId = UUID.randomUUID().toString() + "_" + id;
         this.interarrivelTimeGenerator = interarrivelTimeGenerator;
         this.laneBasedGtuCharacteristicsGenerator = laneBasedGtuCharacteristicsGenerator;
         this.generatorPositions = generatorPositions;
         this.network = network;
         this.simulator = simulator;
         this.roomChecker = roomChecker;
         this.idGenerator = idGenerator;
         Duration headway = this.interarrivelTimeGenerator.draw();
         if (headway != null) // otherwise no demand at all
         {
             simulator.scheduleEventRel(headway, this, "generateCharacteristics", new Object[] {});
         }
         this.network.addNonLocatedObject(this);
     }
 
     /**
      * Sets the initial distance over which lane changes shouldn't be performed.
      * @param noLaneChangeDistance Length; initial distance over which lane changes shouldn't be performed
      */
     public void setNoLaneChangeDistance(final Length noLaneChangeDistance)
     {
         this.noLaneChangeDistance = noLaneChangeDistance;
     }
 
     /**
      * Sets whether GTUs will change lane instantaneously.
      * @param instantaneous boolean; whether GTUs will change lane instantaneously
      */
     public void setInstantaneousLaneChange(final boolean instantaneous)
     {
         this.instantaneousLaneChange = instantaneous;
     }
 
     /**
      * Sets the GTU error handler.
      * @param gtuErrorHandler GTUErrorHandler; GTU error handler
      */
     public void setErrorHandler(final GtuErrorHandler gtuErrorHandler)
     {
         this.errorHandler = gtuErrorHandler;
     }
 
     /**
      * Generate the characteristics of the next GTU.
      * @throws ProbabilityException when something is wrongly defined in the LaneBasedTemplateGTUType
      * @throws SimRuntimeException when this method fails to re-schedule itself or the call to the method that tries to place a
      *             GTU on the road
      * @throws ParameterException in case of a parameter problem
      * @throws GtuException if strategical planner cannot generate a plan
      */
     @SuppressWarnings("unused")
     private void generateCharacteristics() throws ProbabilityException, SimRuntimeException, ParameterException, GtuException
     {
         synchronized (this.unplacedTemplates)
         {
             LaneBasedGtuCharacteristics characteristics = this.laneBasedGtuCharacteristicsGenerator.draw();
             GtuType gtuType = characteristics.getGtuType();
             // gather information on number of unplaced templates per lane, and per link, for the drawing of a new position
             Map<CrossSectionLink, Map<Integer, Integer>> unplaced = new LinkedHashMap<>();
             for (CrossSectionLink link : this.unplacedTemplates.keySet())
             {
                 Map<Integer, Integer> linkMap = new LinkedHashMap<>();
                 Map<GeneratorLanePosition, Queue<TimeStampedObject<LaneBasedGtuCharacteristics>>> linkTemplates =
                         this.unplacedTemplates.get(link);
                 for (GeneratorLanePosition lanePosition : linkTemplates.keySet())
                 {
                     linkMap.put(lanePosition.getLaneNumber(), linkTemplates.get(lanePosition).size());
                 }
                 unplaced.put(link, linkMap);
             }
             // position draw
             GeneratorLanePosition lanePosition = this.generatorPositions.draw(gtuType, characteristics, unplaced);
 
             // skip if disabled at this lane-direction
             Set<Lane> lanes = new LinkedHashSet<>();
             for (LanePosition pos : lanePosition.getPosition())
             {
                 lanes.add(pos.getLane());
             }
             if (Collections.disjoint(this.disabled, lanes))
             {
                 queueGtu(lanePosition, characteristics);
             }
 
         }
         // @docs/02-model-structure/dsol.md#event-based-simulation
         Duration headway = this.interarrivelTimeGenerator.draw();
         if (headway != null)
         {
             this.simulator.scheduleEventRel(headway, this, "generateCharacteristics", new Object[] {});
         }
         // @end
     }
 
     /**
      * Check if the queue is non-empty and, if it is, try to place the GTUs in the queue on the road.
      * @param position GeneratorLanePosition; position
      * @throws SimRuntimeException should never happen
      * @throws GtuException when something wrong in the definition of the GTU
      * @throws OtsGeometryException when something is wrong in the definition of the GTU
      * @throws NetworkException when something is wrong with the initial location of the GTU
      * @throws NamingException ???
      * @throws ProbabilityException pe
      */
     @SuppressWarnings("unused")
     private void tryToPlaceGTU(final GeneratorLanePosition position) throws SimRuntimeException, GtuException, NamingException,
             NetworkException, OtsGeometryException, ProbabilityException
     {
         TimeStampedObject<LaneBasedGtuCharacteristics> timedCharacteristics;
         Queue<TimeStampedObject<LaneBasedGtuCharacteristics>> queue =
                 this.unplacedTemplates.get(position.getLink()).get(position);
 
         synchronized (queue)
         {
             timedCharacteristics = queue.peek();
         }
         if (null == timedCharacteristics)
         {
             return; // Do not re-schedule this method
         }
 
         LaneBasedGtuCharacteristics characteristics = timedCharacteristics.getObject();
         SortedSet<HeadwayGtu> leaders = new TreeSet<>();
         for (LanePosition dirPos : position.getPosition())
         {
             getFirstLeaders(dirPos.getLane(), dirPos.getPosition().neg().minus(characteristics.getFront()),
                     dirPos.getPosition(), leaders);
         }
         Duration since = this.simulator.getSimulatorAbsTime().minus(timedCharacteristics.getTimestamp());
         Placement placement = this.roomChecker.canPlace(leaders, characteristics, since, position.getPosition());
         if (placement.canPlace())
         {
             // There is enough room; remove the template from the queue and construct the new GTU
             synchronized (queue)
             {
                 queue.remove();
             }
             placeGtu(characteristics, placement.getPosition(), placement.getSpeed());
             if (queue.size() > 0)
             {
                 this.simulator.scheduleEventNow(this, "tryToPlaceGTU", new Object[] {position});
             }
         }
         // @docs/02-model-structure/dsol.md#event-based-simulation (without the 'else')
         else if (queue.size() > 0)
         {
             this.simulator.scheduleEventRel(this.reTryInterval, this, "tryToPlaceGTU", new Object[] {position});
         }
         // @end
     }
 
     /**
      * Adds a GTU to the generation queue. This method ignores whether vehicle generation is enabled at the location. This
      * allows an external party to govern (over some time) what vehicles are generated.
      * @param characteristics LaneBasedGtuCharacteristics; characteristics of GTU to add to the queue
      * @param position Set&lt;Lane&gt;; position to generate the GTU at
      */
     public final void queueGtu(final LaneBasedGtuCharacteristics characteristics, final Set<Lane> position)
     {
         // first find the correct GeneratorLanePosition
         GeneratorLanePosition genPosition = null;
         Set<Lane> genSet = new LinkedHashSet<>();
         for (GeneratorLanePosition lanePosition : this.generatorPositions.getAllPositions())
         {
             for (LanePosition dirPos : lanePosition.getPosition())
             {
                 genSet.add(dirPos.getLane());
             }
             if (genSet.equals(position))
             {
                 genPosition = lanePosition;
                 break;
             }
             genSet.clear();
         }
         Throw.when(genPosition == null, IllegalStateException.class, "Position %s is not part of the generation.", position);
         try
         {
             queueGtu(genPosition, characteristics);
         }
         catch (SimRuntimeException exception)
         {
             throw new RuntimeException("Unexpected exception while scheduling tryToPlace event.", exception);
         }
     }
 
     /**
      * Places the characteristics in the queue pertaining to the position, and schedules a call to {@code tryToPlace} now if the
      * queue length is 1.
      * @param lanePosition GeneratorLanePosition; position to generate the GTU at
      * @param characteristics LaneBasedGtuCharacteristics; characteristics of GTU to add to the queue
      * @throws SimRuntimeException when an event is scheduled in the past
      */
     private void queueGtu(final GeneratorLanePosition lanePosition, final LaneBasedGtuCharacteristics characteristics)
             throws SimRuntimeException
     {
         if (!this.unplacedTemplates.containsKey(lanePosition.getLink()))
         {
             this.unplacedTemplates.put(lanePosition.getLink(), new LinkedHashMap<>());
         }
         Map<GeneratorLanePosition, Queue<TimeStampedObject<LaneBasedGtuCharacteristics>>> linkMap =
                 this.unplacedTemplates.get(lanePosition.getLink());
         if (!linkMap.containsKey(lanePosition))
         {
             linkMap.put(lanePosition, new LinkedList<>());
         }
         Queue<TimeStampedObject<LaneBasedGtuCharacteristics>> queue = linkMap.get(lanePosition);
         queue.add(new TimeStampedObject<>(characteristics, this.simulator.getSimulatorAbsTime()));
         // @docs/02-model-structure/dsol.md#event-based-simulation
         if (queue.size() == 1)
         {
             this.simulator.scheduleEventNow(this, "tryToPlaceGTU", new Object[] {lanePosition});
         }
         // @end
     }
 
     /**
      * Places a GTU, regardless of whether it has room. The user of this method should verify this is the case.
      * @param characteristics LaneBasedGtuCharacteristics; characteristics
      * @param position Set&lt;LanePosition&gt;; position
      * @param speed Speed; speed
      * @throws NamingException on exception
      * @throws GtuException on exception
      * @throws NetworkException on exception
      * @throws SimRuntimeException on exception
      * @throws OtsGeometryException on exception
      */
     public final void placeGtu(final LaneBasedGtuCharacteristics characteristics, final Set<LanePosition> position,
             final Speed speed) throws NamingException, GtuException, NetworkException, SimRuntimeException, OtsGeometryException
     {
         String gtuId = this.idGenerator.get();
         LaneBasedGtu gtu = new LaneBasedGtu(gtuId, characteristics.getGtuType(), characteristics.getLength(),
                 characteristics.getWidth(), characteristics.getMaximumSpeed(), characteristics.getFront(), this.network);
         gtu.setMaximumAcceleration(characteristics.getMaximumAcceleration());
         gtu.setMaximumDeceleration(characteristics.getMaximumDeceleration());
         gtu.setVehicleModel(characteristics.getVehicleModel());
         gtu.setNoLaneChangeDistance(this.noLaneChangeDistance);
         gtu.setInstantaneousLaneChange(this.instantaneousLaneChange);
         gtu.setErrorHandler(this.errorHandler);
         gtu.init(characteristics.getStrategicalPlannerFactory().create(gtu, characteristics.getRoute(),
                 characteristics.getOrigin(), characteristics.getDestination()), position, speed);
         this.generatedGTUs++;
         fireEvent(GTU_GENERATED_EVENT, gtu);
     }
 
     /**
      * Adds the first GTU on the lane to the set, or any number or leaders on downstream lane(s) if there is no GTU on the lane.
      * @param lane Lane; lane to search on
      * @param startDistance Length; distance from generator location (nose) to start of the lane
      * @param beyond Length; location to search downstream of which is the generator position, or the start for downstream lanes
      * @param set Set&lt;HeadwayGtu&gt;; set to add the GTU's to
      * @throws GtuException if a GTU is incorrectly positioned on a lane
      */
     private void getFirstLeaders(final Lane lane, final Length startDistance, final Length beyond, final Set<HeadwayGtu> set)
             throws GtuException
     {
         LaneBasedGtu next = lane.getGtuAhead(beyond, RelativePosition.FRONT, this.simulator.getSimulatorAbsTime());
         if (next != null)
         {
             Length headway = startDistance.plus(next.position(lane, next.getRear()));
             if (headway.si < 300)
             {
                 set.add(new HeadwayGtuReal(next, headway, true));
             }
             return;
         }
         Set<Lane> downstreamLanes = lane.nextLanes(null);
         for (Lane downstreamLane : downstreamLanes)
         {
             Length startDistanceDownstream = startDistance.plus(lane.getLength());
             if (startDistanceDownstream.si > 300)
             {
                 return;
             }
             Length beyondDownstream = Length.ZERO;
             getFirstLeaders(downstreamLane, startDistanceDownstream, beyondDownstream, set);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final String toString()
     {
         return "LaneBasedGtuGenerator " + this.id + " on " + this.generatorPositions.getAllPositions();
     }
 
     /**
      * @return generatedGTUs.
      */
     public final long getGeneratedGTUs()
     {
         return this.generatedGTUs;
     }
 
     /**
      * Retrieve the id of this LaneBasedGtuGenerator.
      * @return String; the id of this LaneBasedGtuGenerator
      */
     @Override
     public final String getId()
     {
         return this.id;
     }
 
     /**
      * Disable the vehicle generator during the specific time. Underlying processes such as drawing characteristics and headways
      * are continued, but simply will not result in the queuing of the GTU.
      * @param start Time; start time
      * @param end Time; end time
      * @param laneDirections Set&lt;Lane&gt;; lanes to disable generation on
      * @throws SimRuntimeException if time is incorrect
      */
     public void disable(final Time start, final Time end, final Set<Lane> laneDirections) throws SimRuntimeException
     {
         Throw.when(end.lt(start), SimRuntimeException.class, "End time %s is before start time %s.", end, start);
         this.simulator.scheduleEventAbsTime(start, this, "disable", new Object[] {laneDirections});
         this.simulator.scheduleEventAbsTime(end, this, "enable", new Object[0]);
     }
 
     /**
      * Disables the generator.
      * @param laneDirections Set&lt;Lane&gt;; lanes to disable generation on
      */
     @SuppressWarnings("unused")
     private void disable(final Set<Lane> laneDirections)
     {
         Throw.when(this.disabled != null && !this.disabled.isEmpty(), IllegalStateException.class,
                 "Disabling a generator that is already disabled is not allowed.");
         this.disabled = laneDirections;
     }
 
     /**
      * Enables the generator.
      */
     @SuppressWarnings("unused")
     private void enable()
     {
         this.disabled = new LinkedHashSet<>();
     }
 
     /** {@inheritDoc} */
     @Override
     public String getFullId()
     {
         return this.uniqueId;
     }
 
     /** {@inheritDoc} */
     @Override
     public Set<GtuGeneratorPosition> getPositions()
     {
         Set<GtuGeneratorPosition> set = new LinkedHashSet<>();
         for (GeneratorLanePosition lanePosition : this.generatorPositions.getAllPositions())
         {
             DirectedPoint p = lanePosition.getPosition().iterator().next().getLocation();
             set.add(new GtuGeneratorPosition()
             {
                 /** {@inheritDoc} */
                 @Override
                 public Point<?> getLocation() throws RemoteException
                 {
                     return p;
                 }
 
                 /** {@inheritDoc} */
                 @Override
                 public Bounds<?, ?, ?> getBounds() throws RemoteException
                 {
                     return new Bounds2d(-2.0, 2.0, -2.0, 2.0);
                 }
 
                 /** {@inheritDoc} */
                 @Override
                 public int getQueueCount()
                 {
                     return getQueueLength(lanePosition);
                 }
             });
         }
         return set;
     }
 
     /**
      * Returns the number of GTUs in queue at the position.
      * @param position GeneratorLanePosition; position.
      * @return int; number of GTUs in queue at the position.
      */
     private int getQueueLength(final GeneratorLanePosition position)
     {
         for (CrossSectionLink link : this.unplacedTemplates.keySet())
         {
             for (GeneratorLanePosition lanePosition : this.unplacedTemplates.get(link).keySet())
             {
                 if (lanePosition.equals(position))
                 {
                     return this.unplacedTemplates.get(link).get(lanePosition).size();
                 }
             }
         }
         return 0;
     }
 
     /**
      * Interface for class that checks that there is sufficient room for a proposed new GTU and returns the maximum safe speed
      * and position for the proposed new GTU.
      */
     public interface RoomChecker
     {
         /**
          * Return the maximum safe speed and position for a new GTU with the specified characteristics. Returns
          * {@code Placement.NO} if there is no safe speed and position. This method might be called with an empty leader set
          * such that the desired speed can be implemented.
          * @param leaders SortedSet&lt;HeadwayGtu&gt;; leaders, usually 1, possibly more after a branch
          * @param characteristics LaneBasedGtuCharacteristics; characteristics of the proposed new GTU
          * @param since Duration; time since the GTU wanted to arrive
          * @param initialPosition Set&lt;LanePosition&gt;; initial position
          * @return Speed; maximum safe speed, or null if a GTU with the specified characteristics cannot be placed at the
          *         current time
          * @throws NetworkException this method may throw a NetworkException if it encounters an error in the network structure
          * @throws GtuException on parameter exception
          */
         Placement canPlace(SortedSet<HeadwayGtu> leaders, LaneBasedGtuCharacteristics characteristics, Duration since,
                 Set<LanePosition> initialPosition) throws NetworkException, GtuException;
     }
 
     /**
      * Placement contains the information that a {@code RoomChecker} returns.
      * <p>
      * Copyright (c) 2013-2023 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved.
      * <br>
      * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
      * </p>
      * @author <a href="https://github.com/averbraeck">Alexander Verbraeck</a>
      * @author <a href="https://tudelft.nl/staff/p.knoppers-1">Peter Knoppers</a>
      * @author <a href="https://dittlab.tudelft.nl">Wouter Schakel</a>
      */
     public static final class Placement
     {
 
         /** Value if the GTU cannot be placed. */
         public static final Placement NO = new Placement();
 
         /** Speed. */
         private final Speed speed;
 
         /** Position. */
         private final Set<LanePosition> position;
 
         /**
          * Constructor for NO.
          */
         private Placement()
         {
             this.speed = null;
             this.position = null;
         }
 
         /**
          * Constructor.
          * @param speed Speed; speed
          * @param position Set&lt;LanePosition&gt;; position
          */
         public Placement(final Speed speed, final Set<LanePosition> position)
         {
             Throw.whenNull(speed, "Speed may not be null. Use Placement.NO if the GTU cannot be placed.");
             Throw.whenNull(position, "Position may not be null. Use Placement.NO if the GTU cannot be placed.");
             this.speed = speed;
             this.position = position;
         }
 
         /**
          * Returns whether the GTU can be placed.
          * @return whether the GTU can be placed
          */
         public boolean canPlace()
         {
             return this.speed != null && this.position != null;
         }
 
         /**
          * Returns the speed.
          * @return Speed; speed
          */
         public Speed getSpeed()
         {
             return this.speed;
         }
 
         /**
          * Returns the position.
          * @return Set&lt;LanePosition&gt;; position
          */
         public Set<LanePosition> getPosition()
         {
             return this.position;
         }
 
         /** {@inheritDoc} */
         @Override
         public String toString()
         {
             return "Placement [speed=" + this.speed + ", position=" + this.position + "]";
         }
 
     }
 
 }