package org.opentrafficsim.core.gtu;
   
   import java.io.Serializable;
   import java.util.LinkedHashSet;
   import java.util.Set;
   
   import org.djunits.unit.DirectionUnit;
   import org.djunits.unit.DurationUnit;
   import org.djunits.unit.PositionUnit;
  import org.djunits.unit.TimeUnit;
  import org.djunits.value.vdouble.scalar.Acceleration;
  import org.djunits.value.vdouble.scalar.Direction;
  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.event.EventProducer;
  import org.djutils.exceptions.Throw;
  import org.djutils.exceptions.Try;
  import org.opentrafficsim.base.parameters.ParameterException;
  import org.opentrafficsim.base.parameters.Parameters;
  import org.opentrafficsim.core.dsol.OTSSimulatorInterface;
  import org.opentrafficsim.core.geometry.DirectedPoint;
  import org.opentrafficsim.core.geometry.OTSPoint3D;
  import org.opentrafficsim.core.gtu.plan.operational.OperationalPlan;
  import org.opentrafficsim.core.gtu.plan.operational.OperationalPlanException;
  import org.opentrafficsim.core.gtu.plan.strategical.StrategicalPlanner;
  import org.opentrafficsim.core.gtu.plan.tactical.TacticalPlanner;
  import org.opentrafficsim.core.idgenerator.IdGenerator;
  import org.opentrafficsim.core.network.NetworkException;
  import org.opentrafficsim.core.perception.Historical;
  import org.opentrafficsim.core.perception.HistoricalValue;
  import org.opentrafficsim.core.perception.HistoryManager;
  import org.opentrafficsim.core.perception.PerceivableContext;
  
  import nl.tudelft.simulation.dsol.SimRuntimeException;
  import nl.tudelft.simulation.dsol.formalisms.eventscheduling.SimEvent;
  
  /**
   * Implements the basic functionalities of any GTU: the ability to move on 3D-space according to a plan.
   * <p>
   * Copyright (c) 2013-2022 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/docs/license.html">OpenTrafficSim License</a>.
   * <p>
   * @version $Revision$, $LastChangedDate$, by $Author$, initial version Oct 22, 2014 <br>
   * @author <a href="http://www.tbm.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="http://www.tudelft.nl/pknoppers">Peter Knoppers</a>
   */
  public abstract class AbstractGTU extends EventProducer implements GTU
  {
      /** */
      private static final long serialVersionUID = 20140822L;
  
      /** The id of the GTU. */
      private final String id;
  
      /** unique number of the GTU. */
      private final int uniqueNumber;
  
      /** the unique number counter. */
      private static int staticUNIQUENUMBER = 0;
  
      /** The type of GTU, e.g. TruckType, CarType, BusType. */
      private final GTUType gtuType;
  
      /** The simulator to schedule activities on. */
      private final OTSSimulatorInterface simulator;
  
      /** Model parameters. */
      private Parameters parameters;
  
      /** The maximum acceleration. */
      private Acceleration maximumAcceleration;
  
      /** The maximum deceleration, stored as a negative number. */
      private Acceleration maximumDeceleration;
  
      /**
       * The odometer which measures how much distance have we covered between instantiation and the last completed operational
       * plan. In order to get a complete odometer reading, the progress of the current plan execution has to be added to this
       * value.
       */
      private Historical<Length> odometer;
  
      /** The strategical planner that can instantiate tactical planners to determine mid-term decisions. */
      private final Historical<StrategicalPlanner> strategicalPlanner;
  
      /** The tactical planner that can generate an operational plan. */
      private final Historical<TacticalPlanner<?, ?>> tacticalPlanner;
  
      /** The current operational plan, which provides a short-term movement over time. */
      protected final Historical<OperationalPlan> operationalPlan;
  
      /** The next move event as scheduled on the simulator, can be used for interrupting the current move. */
      private SimEvent<Duration> nextMoveEvent;
  
      /** The model in which this GTU is registered. */
      private PerceivableContext perceivableContext;
  
     /** Is this GTU destroyed? */
     private boolean destroyed = false;
 
     /** aligned or not. */
     // TODO: should be indicated with a Parameter
     public static boolean ALIGNED = true;
 
     /** aligned schedule count. */
     // TODO: can be removed after testing period
     public static int ALIGN_COUNT = 0;
 
     /** Cached speed time. */
     private double cachedSpeedTime = Double.NaN;
 
     /** Cached speed. */
     private Speed cachedSpeed = null;
 
     /** Cached acceleration time. */
     private double cachedAccelerationTime = Double.NaN;
 
     /** Cached acceleration. */
     private Acceleration cachedAcceleration = null;
 
     /** Parent GTU. */
     private GTU parent = null;
 
     /** Children GTU's. */
     private Set<GTU> children = new LinkedHashSet<>();
 
     /** Error handler. */
     private GTUErrorHandler errorHandler = GTUErrorHandler.THROW;
 
     /**
      * @param id String; the id of the GTU
      * @param gtuType GTUType; the type of GTU, e.g. TruckType, CarType, BusType
      * @param simulator OTSSimulatorInterface; the simulator to schedule plan changes on
      * @param perceivableContext PerceivableContext; the perceivable context in which this GTU will be registered
      * @throws GTUException when the preconditions of the constructor are not met
      */
     @SuppressWarnings("checkstyle:parameternumber")
     public AbstractGTU(final String id, final GTUType gtuType, final OTSSimulatorInterface simulator,
             final PerceivableContext perceivableContext) throws GTUException
     {
         Throw.when(id == null, GTUException.class, "id is null");
         Throw.when(gtuType == null, GTUException.class, "gtuType is null");
         Throw.when(perceivableContext == null, GTUException.class, "perceivableContext is null for GTU with id %s", id);
         Throw.when(perceivableContext.containsGtuId(id), GTUException.class,
                 "GTU with id %s already registered in perceivableContext %s", id, perceivableContext.getId());
         Throw.when(simulator == null, GTUException.class, "simulator is null for GTU with id %s", id);
 
         HistoryManager historyManager = simulator.getReplication().getHistoryManager(simulator);
         this.id = id;
         this.uniqueNumber = ++staticUNIQUENUMBER;
         this.gtuType = gtuType;
         this.simulator = simulator;
         this.odometer = new HistoricalValue<>(historyManager, Length.ZERO);
         this.perceivableContext = perceivableContext;
         this.perceivableContext.addGTU(this);
         this.strategicalPlanner = new HistoricalValue<>(historyManager);
         this.tacticalPlanner = new HistoricalValue<>(historyManager, null);
         this.operationalPlan = new HistoricalValue<>(historyManager, null);
     }
 
     /**
      * @param idGenerator IdGenerator; the generator that will produce a unique id of the GTU
      * @param gtuType GTUType; the type of GTU, e.g. TruckType, CarType, BusType
      * @param simulator OTSSimulatorInterface; the simulator to schedule plan changes on
      * @param perceivableContext PerceivableContext; the perceivable context in which this GTU will be registered
      * @throws GTUException when the preconditions of the constructor are not met
      */
     @SuppressWarnings("checkstyle:parameternumber")
     public AbstractGTU(final IdGenerator idGenerator, final GTUType gtuType, final OTSSimulatorInterface simulator,
             final PerceivableContext perceivableContext) throws GTUException
     {
         this(generateId(idGenerator), gtuType, simulator, perceivableContext);
     }
 
     /**
      * Initialize the GTU at a location and speed, and give it a mission to fulfill through the strategical planner.
      * @param strategicalPlanner StrategicalPlanner; the strategical planner responsible for the overall 'mission' of the GTU,
      *            usually indicating where it needs to go. It operates by instantiating tactical planners to do the work.
      * @param initialLocation DirectedPoint; the initial location (and direction) of the GTU
      * @param initialSpeed Speed; the initial speed of the GTU
      * @throws SimRuntimeException when scheduling after the first move fails
      * @throws GTUException when the preconditions of the parameters are not met or when the construction of the original
      *             waiting path fails
      */
     @SuppressWarnings({"checkstyle:hiddenfield", "hiding", "checkstyle:designforextension"})
     public void init(final StrategicalPlanner strategicalPlanner, final DirectedPoint initialLocation, final Speed initialSpeed)
             throws SimRuntimeException, GTUException
     {
         Throw.when(strategicalPlanner == null, GTUException.class, "strategicalPlanner is null for GTU with id %s", this.id);
         Throw.whenNull(initialLocation, "Initial location of GTU cannot be null");
         Throw.when(Double.isNaN(initialLocation.x) || Double.isNaN(initialLocation.y) || Double.isNaN(initialLocation.z),
                 GTUException.class, "initialLocation %s invalid for GTU with id %s", initialLocation, this.id);
         Throw.when(initialSpeed == null, GTUException.class, "initialSpeed is null for GTU with id %s", this.id);
         Throw.when(!getId().equals(strategicalPlanner.getGtu().getId()), GTUException.class,
                 "GTU %s is initialized with a strategical planner for GTU %s", getId(), strategicalPlanner.getGtu().getId());
 
         this.strategicalPlanner.set(strategicalPlanner);
         this.tacticalPlanner.set(strategicalPlanner.getTacticalPlanner());
         Time now = this.simulator.getSimulatorAbsTime();
 
         DirectedPoint location = getLocation();
         fireTimedEvent(GTU.INIT_EVENT, new Object[] {getId(), new OTSPoint3D(location).doubleVector(PositionUnit.METER),
                 new Direction(location.getZ(), DirectionUnit.EAST_RADIAN), getLength(), getWidth()}, now);
 
         try
         {
             move(initialLocation);
         }
         catch (OperationalPlanException | NetworkException | ParameterException exception)
         {
             throw new GTUException("Failed to create OperationalPlan for GTU " + this.id, exception);
         }
     }
 
     /**
      * Generate an id, but check first that we have a valid IdGenerator.
      * @param idGenerator IdGenerator; the generator that will produce a unique id of the GTU
      * @return a (hopefully unique) Id of the GTU
      * @throws GTUException when the idGenerator is null
      */
     private static String generateId(final IdGenerator idGenerator) throws GTUException
     {
         Throw.when(idGenerator == null, GTUException.class, "AbstractGTU.<init>: idGenerator is null");
         return idGenerator.nextId();
     }
 
     /**
      * Destructor. Don't forget to call with super.destroy() from any override to avoid memory leaks in the network.
      */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public void destroy()
     {
         DirectedPoint location = getLocation();
         fireTimedEvent(GTU.DESTROY_EVENT,
                 new Object[] {getId(), new OTSPoint3D(location).doubleVector(PositionUnit.METER),
                         new Direction(location.getZ(), DirectionUnit.EAST_RADIAN), getOdometer()},
                 this.simulator.getSimulatorTime());
 
         // cancel the next move
         if (this.nextMoveEvent != null)
         {
             this.simulator.cancelEvent(this.nextMoveEvent);
             this.nextMoveEvent = null;
         }
 
         this.perceivableContext.removeGTU(this);
         this.destroyed = true;
     }
 
     /**
      * Move from the current location according to an operational plan to a location that will bring us nearer to reaching the
      * location provided by the strategical planner. <br>
      * This method can be overridden to carry out specific behavior during the execution of the plan (e.g., scheduling of
      * triggers, entering or leaving lanes, etc.). Please bear in mind that the call to super.move() is essential, and that one
      * has to take care to handle the situation that the plan gets interrupted.
      * @param fromLocation DirectedPoint; the last known location (initial location, or end location of the previous operational
      *            plan)
      * @return boolean; whether an exception occurred
      * @throws SimRuntimeException when scheduling of the next move fails
      * @throws OperationalPlanException when there is a problem creating a good path for the GTU
      * @throws GTUException when there is a problem with the state of the GTU when planning a path
      * @throws NetworkException in case of a problem with the network, e.g., a dead end where it is not expected
      * @throws ParameterException in there is a parameter problem
      */
     @SuppressWarnings("checkstyle:designforextension")
     protected boolean move(final DirectedPoint fromLocation)
             throws SimRuntimeException, OperationalPlanException, GTUException, NetworkException, ParameterException
     {
         try
         {
             Time now = this.simulator.getSimulatorAbsTime();
 
             // Add the odometer distance from the currently running operational plan.
             // Because a plan can be interrupted, we explicitly calculate the covered distance till 'now'
             Length currentOdometer;
             if (this.operationalPlan.get() != null)
             {
                 currentOdometer = this.odometer.get().plus(this.operationalPlan.get().getTraveledDistance(now));
             }
             else
             {
                 currentOdometer = this.odometer.get();
             }
 
             // Do we have an operational plan?
             // TODO discuss when a new tactical planner may be needed
             TacticalPlanner<?, ?> tactPlanner = this.tacticalPlanner.get();
             if (tactPlanner == null)
             {
                 // Tell the strategical planner to provide a tactical planner
                 tactPlanner = this.strategicalPlanner.get().getTacticalPlanner();
                 this.tacticalPlanner.set(tactPlanner);
             }
             synchronized (this)
             {
                 tactPlanner.getPerception().perceive();
             }
             OperationalPlan newOperationalPlan = tactPlanner.generateOperationalPlan(now, fromLocation);
             synchronized (this)
             {
                 this.operationalPlan.set(newOperationalPlan);
                 this.cachedSpeedTime = Double.NaN;
                 this.cachedAccelerationTime = Double.NaN;
                 this.odometer.set(currentOdometer);
             }
 
             // TODO allow alignment at different intervals, also different between GTU's within a single simulation
             if (ALIGNED && newOperationalPlan.getTotalDuration().si == 0.5)
             {
                 // schedule the next move at exactly 0.5 seconds on the clock
                 // store the event, so it can be cancelled in case the plan has to be interrupted and changed halfway
                 double tNext = Math.floor(2.0 * now.si + 1.0) / 2.0;
                 DirectedPoint p = (tNext - now.si < 0.5) ? newOperationalPlan.getEndLocation()
                         : newOperationalPlan.getLocation(new Duration(tNext - now.si, DurationUnit.SI));
                 this.nextMoveEvent = new SimEvent<Duration>(
                         new Duration(tNext - getSimulator().getStartTimeAbs().si, DurationUnit.SI), this, this,
                         "move", new Object[] {p});
                 ALIGN_COUNT++;
             }
             else
             {
                 // schedule the next move at the end of the current operational plan
                 // store the event, so it can be cancelled in case the plan has to be interrupted and changed halfway
                 this.nextMoveEvent = new SimEvent<>(
                         now.plus(newOperationalPlan.getTotalDuration())
                                 .minus(getSimulator().getStartTimeAbs()),
                         this, this, "move", new Object[] {newOperationalPlan.getEndLocation()});
             }
             this.simulator.scheduleEvent(this.nextMoveEvent);
             fireTimedEvent(GTU.MOVE_EVENT,
                     new Object[] {getId(), new OTSPoint3D(fromLocation).doubleVector(PositionUnit.METER),
                             new Direction(fromLocation.getZ(), DirectionUnit.EAST_RADIAN), getSpeed(), getAcceleration(),
                             getOdometer()},
                     this.simulator.getSimulatorTime());
 
             return false;
         }
         catch (Exception ex)
         {
             try
             {
                 this.errorHandler.handle(this, ex);
             }
             catch (Exception exception)
             {
                 throw new GTUException(exception);
             }
             return true;
         }
     }
 
     /**
      * Interrupt the move and ask for a new plan. This method can be overridden to carry out the bookkeeping needed when the
      * current plan gets interrupted.
      * @throws OperationalPlanException when there was a problem retrieving the location from the running plan
      * @throws SimRuntimeException when scheduling of the next move fails
      * @throws OperationalPlanException when there is a problem creating a good path for the GTU
      * @throws GTUException when there is a problem with the state of the GTU when planning a path
      * @throws NetworkException in case of a problem with the network, e.g., unreachability of a certain point
      * @throws ParameterException when there is a problem with a parameter
      */
     @SuppressWarnings("checkstyle:designforextension")
     protected void interruptMove()
             throws SimRuntimeException, OperationalPlanException, GTUException, NetworkException, ParameterException
     {
         this.simulator.cancelEvent(this.nextMoveEvent);
         move(this.operationalPlan.get().getLocation(this.simulator.getSimulatorTime()));
     }
 
     /** {@inheritDoc} */
     @Override
     public final String getId()
     {
         return this.id;
     }
 
     /** {@inheritDoc} */
     @SuppressWarnings("checkstyle:designforextension")
     @Override
     public GTUType getGTUType()
     {
         return this.gtuType;
     }
 
     /** {@inheritDoc} */
     @Override
     public final RelativePosition getReference()
     {
         return RelativePosition.REFERENCE_POSITION;
     }
 
     /** {@inheritDoc} */
     @Override
     public final OTSSimulatorInterface getSimulator()
     {
         return this.simulator;
     }
 
     /** {@inheritDoc} */
     @Override
     public final Parameters getParameters()
     {
         return this.parameters;
     }
 
     /** {@inheritDoc} */
     @Override
     public final void setParameters(final Parameters parameters)
     {
         this.parameters = parameters;
     }
 
     /** {@inheritDoc} */
     @Override
     public StrategicalPlanner getStrategicalPlanner()
     {
         return this.strategicalPlanner.get();
     }
 
     /** {@inheritDoc} */
     @Override
     public StrategicalPlanner getStrategicalPlanner(final Time time)
     {
         return this.strategicalPlanner.get(time);
     }
 
     /** {@inheritDoc} */
     @Override
     public final OperationalPlan getOperationalPlan()
     {
         return this.operationalPlan.get();
     }
 
     /** {@inheritDoc} */
     @Override
     public final OperationalPlan getOperationalPlan(final Time time)
     {
         return this.operationalPlan.get(time);
     }
 
     /** {@inheritDoc} */
     @Override
     public final Length getOdometer()
     {
         return getOdometer(this.simulator.getSimulatorAbsTime());
     }
 
     /** {@inheritDoc} */
     @Override
     public final Length getOdometer(final Time time)
     {
         synchronized (this)
         {
             if (getOperationalPlan(time) == null)
             {
                 return this.odometer.get(time);
             }
             try
             {
                 return this.odometer.get(time).plus(getOperationalPlan(time).getTraveledDistance(time));
             }
             catch (OperationalPlanException ope)
             {
                 return this.odometer.get(time);
             }
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final Speed getSpeed()
     {
         synchronized (this)
         {
             return getSpeed(this.simulator.getSimulatorAbsTime());
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final Speed getSpeed(final Time time)
     {
         synchronized (this)
         {
             if (this.cachedSpeedTime != time.si)
             {
                 // Invalidate everything
                 this.cachedSpeedTime = Double.NaN;
                 this.cachedSpeed = null;
                 OperationalPlan plan = getOperationalPlan(time);
                 if (plan == null)
                 {
                     this.cachedSpeed = Speed.ZERO;
                 }
                 else if (time.si < plan.getStartTime().si)
                 {
                     this.cachedSpeed = plan.getStartSpeed();
                 }
                 else if (time.si > plan.getEndTime().si)
                 {
                     if (time.si - plan.getEndTime().si < 1e-6)
                     {
                         this.cachedSpeed = Try.assign(() -> plan.getSpeed(plan.getEndTime()),
                                 "getSpeed() could not derive a valid speed for the current operationalPlan");
                     }
                     else
                     {
                         throw new IllegalStateException("Requesting speed value beyond plan.");
                     }
                 }
                 else
                 {
                     this.cachedSpeed = Try.assign(() -> plan.getSpeed(time),
                             "getSpeed() could not derive a valid speed for the current operationalPlan");
                 }
                 this.cachedSpeedTime = time.si; // Do this last
             }
             return this.cachedSpeed;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final Acceleration getAcceleration()
     {
         synchronized (this)
         {
             return getAcceleration(this.simulator.getSimulatorAbsTime());
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final Acceleration getAcceleration(final Time time)
     {
         synchronized (this)
         {
             if (this.cachedAccelerationTime != time.si)
             {
                 // Invalidate everything
                 this.cachedAccelerationTime = Double.NaN;
                 this.cachedAcceleration = null;
                 OperationalPlan plan = getOperationalPlan(time);
                 if (plan == null)
                 {
                     this.cachedAcceleration = Acceleration.ZERO;
                 }
                 else if (time.si < plan.getStartTime().si)
                 {
                     this.cachedAcceleration =
                             Try.assign(() -> plan.getAcceleration(plan.getStartTime()), "Exception obtaining acceleration.");
                 }
                 else if (time.si > plan.getEndTime().si)
                 {
                     if (time.si - plan.getEndTime().si < 1e-6)
                     {
                         this.cachedAcceleration = Try.assign(() -> plan.getAcceleration(plan.getEndTime()),
                                 "getAcceleration() could not derive a valid acceleration for the current operationalPlan");
                     }
                     else
                     {
                         throw new IllegalStateException("Requesting acceleration value beyond plan.");
                     }
                 }
                 else
                 {
                     this.cachedAcceleration = Try.assign(() -> plan.getAcceleration(time),
                             "getAcceleration() could not derive a valid acceleration for the current operationalPlan");
                 }
                 this.cachedAccelerationTime = time.si;
             }
             return this.cachedAcceleration;
         }
     }
 
     /**
      * @return maximumAcceleration
      */
     @Override
     public final Acceleration getMaximumAcceleration()
     {
         return this.maximumAcceleration;
     }
 
     /**
      * @param maximumAcceleration Acceleration; set maximumAcceleration
      */
     public final void setMaximumAcceleration(final Acceleration maximumAcceleration)
     {
         if (maximumAcceleration.le(Acceleration.ZERO))
         {
             throw new RuntimeException("Maximum acceleration of GTU " + this.id + " set to value <= 0");
         }
         this.maximumAcceleration = maximumAcceleration;
     }
 
     /**
      * @return maximumDeceleration
      */
     @Override
     public final Acceleration getMaximumDeceleration()
     {
         return this.maximumDeceleration;
     }
 
     /**
      * Set the maximum deceleration.
      * @param maximumDeceleration Acceleration; set maximumDeceleration, must be a negative number
      */
     public final void setMaximumDeceleration(final Acceleration maximumDeceleration)
     {
         if (maximumDeceleration.ge(Acceleration.ZERO))
         {
             throw new RuntimeException("Cannot set maximum deceleration of GTU " + this.id + " to " + maximumDeceleration
                     + " (value must be negative)");
         }
         this.maximumDeceleration = maximumDeceleration;
     }
 
     /** Cache location time. */
     private Time cacheLocationTime = new Time(Double.NaN, TimeUnit.DEFAULT);
 
     /** Cached location at that time. */
     private DirectedPoint cacheLocation = null;
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public DirectedPoint getLocation()
     {
         synchronized (this)
         {
             if (this.operationalPlan.get() == null)
             {
                 this.simulator.getLogger().always()
                         .error("No operational plan for GTU " + this.id + " at t=" + this.getSimulator().getSimulatorTime());
                 return new DirectedPoint(0, 0, 0); // Do not cache it
             }
             try
             {
                 // cache
                 Time locationTime = this.simulator.getSimulatorAbsTime();
                 if (null == this.cacheLocationTime || this.cacheLocationTime.si != locationTime.si)
                 {
                     this.cacheLocationTime = null;
                     this.cacheLocation = this.operationalPlan.get().getLocation(locationTime);
                     this.cacheLocationTime = locationTime;
                 }
                 return this.cacheLocation;
             }
             catch (OperationalPlanException exception)
             {
                 return new DirectedPoint(0, 0, 0);
             }
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public final boolean isDestroyed()
     {
         return this.destroyed;
     }
 
     /** {@inheritDoc} */
     @Override
     public PerceivableContext getPerceivableContext()
     {
         return this.perceivableContext;
     }
 
     /** {@inheritDoc} */
     @Override
     public void addGtu(final GTU gtu) throws GTUException
     {
         this.children.add(gtu);
         gtu.setParent(this);
     }
 
     /** {@inheritDoc} */
     @Override
     public void removeGtu(final GTU gtu)
     {
         this.children.remove(gtu);
         try
         {
             gtu.setParent(null);
         }
         catch (GTUException exception)
         {
             // cannot happen, setting null is always ok
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public void setParent(final GTU gtu) throws GTUException
     {
         Throw.when(gtu != null && this.parent != null, GTUException.class, "GTU %s already has a parent.", this);
         this.parent = gtu;
     }
 
     /** {@inheritDoc} */
     @Override
     public GTU getParent()
     {
         return this.parent;
     }
 
     /** {@inheritDoc} */
     @Override
     public Set<GTU> getChildren()
     {
         return new LinkedHashSet<>(this.children); // safe copy
     }
 
     /**
      * @return errorHandler.
      */
     protected GTUErrorHandler getErrorHandler()
     {
         return this.errorHandler;
     }
 
     /** {@inheritDoc} */
     @Override
     public void setErrorHandler(final GTUErrorHandler errorHandler)
     {
         this.errorHandler = errorHandler;
     }
 
     /** {@inheritDoc} */
     @Override
     public final Serializable getSourceId()
     {
         return this; // TODO: see where the actual pointer to the GTU is needed
     }
 
     /**
      * Note that destroying the next move event of the GTU can be dangerous!
      * @return nextMoveEvent the next move event of the GTU, e.g. to cancel it from outside.
      */
     public final SimEvent<Duration> getNextMoveEvent()
     {
         return this.nextMoveEvent;
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("designforextension")
     public int hashCode()
     {
         final int prime = 31;
         int result = 1;
         result = prime * result + ((this.id == null) ? 0 : this.id.hashCode());
         result = prime * result + this.uniqueNumber;
         return result;
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings({"designforextension", "needbraces"})
     public boolean equals(final Object obj)
     {
         if (this == obj)
             return true;
         if (obj == null)
             return false;
         if (getClass() != obj.getClass())
             return false;
         AbstractGTU other = (AbstractGTU) obj;
         if (this.id == null)
         {
             if (other.id != null)
                 return false;
         }
         else if (!this.id.equals(other.id))
             return false;
         if (this.uniqueNumber != other.uniqueNumber)
             return false;
         return true;
     }
 
 }