package org.opentrafficsim.road.gtu.generator;
   
   import java.util.Set;
   import java.util.SortedSet;
   
   import org.djunits.unit.DurationUnit;
   import org.djunits.unit.LengthUnit;
   import org.djunits.value.vdouble.scalar.Duration;
   import org.djunits.value.vdouble.scalar.Length;
  import org.djunits.value.vdouble.scalar.Speed;
  import org.opentrafficsim.core.gtu.GtuException;
  import org.opentrafficsim.core.network.NetworkException;
  import org.opentrafficsim.road.gtu.generator.LaneBasedGtuGenerator.Placement;
  import org.opentrafficsim.road.gtu.generator.LaneBasedGtuGenerator.RoomChecker;
  import org.opentrafficsim.road.gtu.generator.characteristics.LaneBasedGtuCharacteristics;
  import org.opentrafficsim.road.gtu.lane.perception.headway.HeadwayGtu;
  import org.opentrafficsim.road.network.lane.LanePosition;
  
  /**
   * Room checker based on time-to-collision. The room is considered ok if:
   * <ol>
   * <li>The headway is larger than speed*1.0s + 3m</li>
   * <li>time-to-collision &lt; value
   * </ol>
   * where 'value' is a given value in the constructor.
   * <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 TtcRoomChecker implements RoomChecker
  {
  
      /** Time to collision. */
      private final Duration ttc;
  
      /**
       * Constructor.
       * @param ttc Duration; time to collision
       */
      public TtcRoomChecker(final Duration ttc)
      {
          this.ttc = ttc;
      }
  
      /** {@inheritDoc} */
      @Override
      public final Placement canPlace(final SortedSet<HeadwayGtu> leaders, final LaneBasedGtuCharacteristics characteristics,
              final Duration since, final Set<LanePosition> initialPosition) throws NetworkException, GtuException
      {
          Speed speedLimit = initialPosition.iterator().next().getLane().getSpeedLimit(characteristics.getGtuType());
          Speed desiredSpeedProxy = Speed.min(characteristics.getMaximumSpeed(), speedLimit);
          if (leaders.isEmpty())
          {
              return new Placement(desiredSpeedProxy, initialPosition);
          }
          HeadwayGtu leader = leaders.first();
          Speed speed = Speed.min(leader.getSpeed(), desiredSpeedProxy);
          for (LanePosition dlp : initialPosition)
          {
              if (dlp.getLane().getType().isCompatible(characteristics.getGtuType()))
              {
                  speed = Speed.min(speed, dlp.getLane().getSpeedLimit(characteristics.getGtuType()));
              }
          }
          if ((speed.le(leader.getSpeed()) || leader.getDistance().divide(speed.minus(leader.getSpeed())).gt(this.ttc)) && leader
                  .getDistance().gt(speed.times(new Duration(1.0, DurationUnit.SI)).plus(new Length(3.0, LengthUnit.SI))))
          {
              return new Placement(speed, initialPosition);
          }
          return Placement.NO;
      }
  
      /**
       * Returns the TTC value.
       * @return Duration; TTC value
       */
      public final Duration getTtc()
      {
          return this.ttc;
      }
  
      /** {@inheritDoc} */
      @Override
      public final String toString()
      {
          return "TTCRoomChecker [ttc=" + this.ttc + "]";
      }
  
  }