package org.opentrafficsim.road.gtu.lane.tactical.util.lmrs;
   
   import org.djunits.value.vdouble.scalar.Duration;
   import org.djunits.value.vdouble.scalar.Length;
   import org.djunits.value.vdouble.scalar.Speed;
   import org.djutils.exceptions.Try;
   import org.opentrafficsim.base.parameters.ParameterException;
   import org.opentrafficsim.base.parameters.ParameterTypeDouble;
   import org.opentrafficsim.base.parameters.ParameterTypes;
  import org.opentrafficsim.base.parameters.Parameters;
  import org.opentrafficsim.base.parameters.constraint.ConstraintInterface;
  import org.opentrafficsim.core.gtu.perception.EgoPerception;
  import org.opentrafficsim.road.gtu.lane.LaneBasedGTU;
  import org.opentrafficsim.road.gtu.lane.perception.LanePerception;
  import org.opentrafficsim.road.gtu.lane.perception.PerceptionCollectable;
  import org.opentrafficsim.road.gtu.lane.perception.RelativeLane;
  import org.opentrafficsim.road.gtu.lane.perception.categories.neighbors.NeighborsPerception;
  import org.opentrafficsim.road.gtu.lane.perception.headway.HeadwayGTU;
  
  /**
   * Interface for LMRS tailgating behavior.
   * <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 7 mrt. 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 interface Tailgating
  {
  
      /** Social pressure applied to the leader. */
      ParameterTypeDouble RHO = new ParameterTypeDouble("rho", "Social pressure", 0.0, ConstraintInterface.UNITINTERVAL);
  
      /** No tailgating. */
      Tailgating NONE = new Tailgating()
      {
          /** {@inheritDoc} */
          @Override
          public void tailgate(final LanePerception perception, final Parameters parameters)
          {
              //
          }
      };
  
      /** No tailgating, but social pressure exists. */
      Tailgating RHO_ONLY = new Tailgating()
      {
          /** {@inheritDoc} */
          @Override
          public void tailgate(final LanePerception perception, final Parameters parameters)
          {
              PerceptionCollectable<HeadwayGTU, LaneBasedGTU> leaders =
                      perception.getPerceptionCategoryOrNull(NeighborsPerception.class).getLeaders(RelativeLane.CURRENT);
              if (leaders == null || leaders.isEmpty())
              {
                  return;
              }
              try
              {
                  Speed speed = perception.getPerceptionCategoryOrNull(EgoPerception.class).getSpeed();
                  Speed vCong = parameters.getParameter(ParameterTypes.VCONG);
                  Length x0 = parameters.getParameter(ParameterTypes.LOOKAHEAD);
                  Speed vGain = parameters.getParameter(LmrsParameters.VGAIN);
                  HeadwayGTU leader = leaders.first();
                  Speed desiredSpeed = Try.assign(() -> perception.getGtu().getDesiredSpeed(), "Could not obtain the GTU.");
                  double rho = socialPressure(speed, vCong, desiredSpeed, leader.getSpeed(), vGain, leader.getDistance(), x0);
                  parameters.setParameter(RHO, rho);
              }
              catch (ParameterException exception)
              {
                  throw new RuntimeException("Could not obtain or set parameter value.", exception);
              }
          }
      };
  
      /** Tailgating based on speed pressure. */
      Tailgating PRESSURE = new Tailgating()
      {
          /** {@inheritDoc} */
          @Override
          public void tailgate(final LanePerception perception, final Parameters parameters)
          {
              PerceptionCollectable<HeadwayGTU, LaneBasedGTU> leaders =
                      perception.getPerceptionCategoryOrNull(NeighborsPerception.class).getLeaders(RelativeLane.CURRENT);
              if (leaders == null || leaders.isEmpty())
              {
                  return;
              }
              try
              {
                  Speed speed = perception.getPerceptionCategoryOrNull(EgoPerception.class).getSpeed();
                  Speed vCong = parameters.getParameter(ParameterTypes.VCONG);
                  Duration t = parameters.getParameter(ParameterTypes.T);
                  Duration tMin = parameters.getParameter(ParameterTypes.TMIN);
                  Duration tMax = parameters.getParameter(ParameterTypes.TMAX);
                  Length x0 = parameters.getParameter(ParameterTypes.LOOKAHEAD);
                 Speed vGain = parameters.getParameter(LmrsParameters.VGAIN);
                 HeadwayGTU leader = leaders.first();
                 Speed desiredSpeed = Try.assign(() -> perception.getGtu().getDesiredSpeed(), "Could not obtain the GTU.");
                 double rho = socialPressure(speed, vCong, desiredSpeed, leader.getSpeed(), vGain, leader.getDistance(), x0);
                 parameters.setParameter(RHO, rho);
                 double tNew = rho * tMin.si + (1.0 - rho) * tMax.si;
                 if (tNew < t.si)
                 {
                     parameters.setParameter(ParameterTypes.T, Duration.createSI(tNew));
                 }
             }
             catch (ParameterException exception)
             {
                 throw new RuntimeException("Could not obtain or set parameter value.", exception);
             }
         }
     };
 
     /**
      * Returns a normalized social pressure, equal to (vDesired - vLead) / vGain.
      * @param speed Speed; speed
      * @param vCong Speed; speed indicating congestion
      * @param desiredSpeed Speed; desired speed
      * @param leaderSpeed Speed; leader speed
      * @param vGain Speed; vGain parameter
      * @param headway Length; headway to the leader
      * @param x0 Length; anticipation distance
      * @return normalized social pressure
      */
     static double socialPressure(final Speed speed, final Speed vCong, final Speed desiredSpeed, final Speed leaderSpeed,
             final Speed vGain, final Length headway, final Length x0)
     {
         double dv = desiredSpeed.si - leaderSpeed.si;
         if (dv < 0 || headway.gt(x0)) // larger headway may happen due to perception errors
         {
             return 0.0;
         }
         return 1.0 - Math.exp(-(dv / vGain.si) * (1.0 - (headway.si / x0.si)));
     }
 
     /**
      * Apply tailgating.
      * @param perception LanePerception; perception
      * @param parameters Parameters; parameters
      */
     void tailgate(LanePerception perception, Parameters parameters);
 
 }