package org.opentrafficsim.road.gtu.generator;
   
   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.perception.object.PerceivedGtu;
  import org.opentrafficsim.road.gtu.tactical.util.SpeedLimitUtil;
  import org.opentrafficsim.road.network.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) 2013-2026 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 Alexander Verbraeck
   * @author Peter Knoppers
   * @author Wouter Schakel
   */
  public class TtcRoomChecker implements RoomChecker
  {
  
      /** Time to collision. */
      private final Duration ttc;
  
      /**
       * Constructor.
       * @param ttc time to collision
       */
      public TtcRoomChecker(final Duration ttc)
      {
          this.ttc = ttc;
      }
  
      @Override
      public final Placement canPlace(final SortedSet<PerceivedGtu> leaders, final LaneBasedGtuCharacteristics characteristics,
              final Duration since, final LanePosition initialPosition) throws NetworkException, GtuException
      {
          Speed desiredSpeedProxy = SpeedLimitUtil.getDesiredSpeedProxy(
                  initialPosition.lane().getSpeedLimits(characteristics.getGtuType()), characteristics.getMaximumSpeed());
          if (leaders.isEmpty())
          {
              return new Placement(desiredSpeedProxy, initialPosition);
          }
          PerceivedGtu leader = leaders.first();
          Speed speed = Speed.min(leader.getSpeed(), desiredSpeedProxy);
          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 TTC value
       */
      public final Duration getTtc()
      {
          return this.ttc;
      }
  
      @Override
      public final String toString()
      {
          return "TTCRoomChecker [ttc=" + this.ttc + "]";
      }
  
  }