package org.opentrafficsim.road.gtu.lane.tactical.util;
   
   import org.djunits.unit.AccelerationUnit;
   import org.djunits.unit.SpeedUnit;
   import org.djunits.value.vdouble.scalar.Acceleration;
   import org.djunits.value.vdouble.scalar.Length;
   import org.djunits.value.vdouble.scalar.Speed;
   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.gtu.GTUException;
  import org.opentrafficsim.road.gtu.lane.perception.PerceptionIterable;
  import org.opentrafficsim.road.gtu.lane.perception.PerceptionIterableSet;
  import org.opentrafficsim.road.gtu.lane.perception.headway.AbstractHeadway;
  import org.opentrafficsim.road.gtu.lane.perception.headway.Headway;
  import org.opentrafficsim.road.gtu.lane.perception.headway.HeadwayGTU;
  import org.opentrafficsim.road.gtu.lane.tactical.following.CarFollowingModel;
  import org.opentrafficsim.road.network.speed.SpeedLimitInfo;
  
  /**
   * Static methods regarding car-following for composition in tactical planners.
   * <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/docs/current/license.html">OpenTrafficSim License</a>.
   * <p>
   * @version $Revision$, $LastChangedDate$, by $Author$, initial version May 23, 2016 <br>
   * @author <a href="http://www.tbm.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="http://www.transport.citg.tudelft.nl">Wouter Schakel</a>
   */
  public final class CarFollowingUtil
  {
  
      /**
       * Do not instantiate.
       */
      private CarFollowingUtil()
      {
          //
      }
  
      /**
       * Follow a set of headway GTUs.
       * @param carFollowingModel CarFollowingModel; car-following model
       * @param parameters Parameters; parameters
       * @param speed Speed; current speed
       * @param speedLimitInfo SpeedLimitInfo; speed limit info
       * @param distance Length; distance
       * @param leaderSpeed Speed; speed of the leader
       * @return acceleration for following the leader
       * @throws ParameterException if a parameter is not given or out of bounds
       */
      public static Acceleration followSingleLeader(final CarFollowingModel carFollowingModel, final Parameters parameters,
              final Speed speed, final SpeedLimitInfo speedLimitInfo, final Length distance, final Speed leaderSpeed)
              throws ParameterException
      {
          return carFollowingModel.followingAcceleration(parameters, speed, speedLimitInfo, createLeader(distance, leaderSpeed));
      }
  
      /**
       * Follow a set of headway GTUs.
       * @param carFollowingModel CarFollowingModel; car-following model
       * @param parameters Parameters; parameters
       * @param speed Speed; current speed
       * @param speedLimitInfo SpeedLimitInfo; speed limit info
       * @param leader HeadwayGTU; leader
       * @return acceleration for following the leader
       * @throws ParameterException if a parameter is not given or out of bounds
       */
      public static Acceleration followSingleLeader(final CarFollowingModel carFollowingModel, final Parameters parameters,
              final Speed speed, final SpeedLimitInfo speedLimitInfo, final HeadwayGTU leader) throws ParameterException
      {
          return carFollowingModel.followingAcceleration(parameters, speed, speedLimitInfo, new PerceptionIterableSet<>(leader));
      }
  
      /**
       * Stop within given distance.
       * @param carFollowingModel CarFollowingModel; car-following model
       * @param parameters Parameters; parameters
       * @param speed Speed; current speed
       * @param speedLimitInfo SpeedLimitInfo; speed limit info
       * @param distance Length; distance to stop over
       * @return acceleration to stop over distance
       * @throws ParameterException if a parameter is not given or out of bounds
       */
      public static Acceleration stop(final CarFollowingModel carFollowingModel, final Parameters parameters, final Speed speed,
              final SpeedLimitInfo speedLimitInfo, final Length distance) throws ParameterException
      {
          return carFollowingModel.followingAcceleration(parameters, speed, speedLimitInfo, createLeader(distance, Speed.ZERO));
      }
  
      /**
       * Return constant acceleration in order to stop in specified distance. The car-following model is used to determine the
       * stopping distance (i.e. distance remaining at stand still, e.g. 1-3m).
       * @param carFollowingModel CarFollowingModel; car-following model
       * @param parameters Parameters; parameters
       * @param speed Speed; current speed
       * @param distance Length; distance to stop over
       * @return constant acceleration in order to stop in specified distance
      * @throws ParameterException on missing parameter
      */
     public static Acceleration constantAccelerationStop(final CarFollowingModel carFollowingModel, final Parameters parameters,
             final Speed speed, final Length distance) throws ParameterException
     {
         Length s0 = carFollowingModel.desiredHeadway(parameters, Speed.ZERO);
         return new Acceleration(-0.5 * speed.si * speed.si / (distance.si - s0.si), AccelerationUnit.SI);
     }
 
     /**
      * Calculate free acceleration.
      * @param carFollowingModel CarFollowingModel; car-following model
      * @param parameters Parameters; parameters
      * @param speed Speed; current speed
      * @param speedLimitInfo SpeedLimitInfo; speed limit info
      * @return acceleration free acceleration
      * @throws ParameterException if a parameter is not given or out of bounds
      */
     public static Acceleration freeAcceleration(final CarFollowingModel carFollowingModel, final Parameters parameters,
             final Speed speed, final SpeedLimitInfo speedLimitInfo) throws ParameterException
     {
         PerceptionIterableSet<Headway> leaders = new PerceptionIterableSet<>();
         return carFollowingModel.followingAcceleration(parameters, speed, speedLimitInfo, leaders);
     }
 
     /**
      * Returns an acceleration based on the car-following model in order to adjust the speed to a given value at some location
      * ahead. This is done by placing a virtual vehicle somewhere near the location. Both the location and speed of this virtual
      * vehicle are dynamically adjusted to resemble a car-following situation. To explain, first consider the situation where a
      * virtual vehicle is placed at the target speed and such that the equilibrium headway is in line with the location:
      * 
      * <pre>
      * 
      *  ___    location of target speed --)|        ___
      * |___|(--------------s--------------) (--h--)|___| ))) vTar
      * </pre>
      * 
      * Here, {@code s} is the distance to the target speed, and {@code h} is the desired headway if the vehicle would drive at
      * the target speed {@code vTar}.<br>
      * <br>
      * In this way car-following models will first underestimate the required deceleration, as the virtual vehicle is actually
      * stationary and does not move with {@code vTar} at all. Because of this underestimation, strong deceleration is required
      * later. This behavior is not in line with the sensitivity parameters of the car-following model.<br>
      * <br>
      * To correct for the fact that the virtual vehicle is actually not moving, the speed difference should be larger, i.e. the
      * speed of the virtual vehicle {@code vTar'} should be lower. We require:
      * <ul>
      * <li>if {@code v = vTar} then {@code vTar' = vTar}, otherwise there is an incentive to accelerate or decelerate for no
      * good reason</li>
      * <li>if {@code vTar ~ 0} then {@code vTar' ~ 0}, as car-following models are suitable for stopping and need no additional
      * incentive to decelerate in such cases</li>
      * <li>if {@code 0 < vTar < v} then {@code vTar' < vTar}, introducing additional deceleration to compensate for the fact
      * that the virtual vehicle does not move
      * </ul>
      * These requirements are met by {@code vTar' = vTar * (vTar/v) = vTar^2/v}.<br>
      * <br>
      * Furthermore, if {@code v < vTar} we get {@code vTar' > vTar} leading to additional acceleration. Acceleration is then
      * appropriate, and possibly limited by a free term in the car-following model.<br>
      * <br>
      * The virtual vehicle is thus placed with speed {@code vTar'} at a distance {@code s + h'} where {@code h'} is the desired
      * headway if the vehicle would drive at speed {@code vTar'}. Both {@code vTar'} and {@code h'} depend on the current speed
      * of the vehicle, so the virtual vehicle in this case actually moves, but not with {@code vTar}.<br>
      * <br>
      * This approach has been tested with the IDM+ to deliver decelerations in line with the parameters. On a plane with initial
      * speed ranging from 0 to 33.33m/s and a target speed in 300m also ranging from 0 to 33.33m/s, strongest deceleration is
      * equal to the car-following model stopping from 33.33m/s to a stand-still vehicle in 300m (+ stopping distance of 3m).
      * Throughout the plane the maximum deceleration of each scenario is close to this value, unless the initial speed is so
      * low, and the target speed is so high, that such levels of deceleration are never required.<br>
      * <br>
      * @param carFollowingModel CarFollowingModel; car-following model to use
      * @param parameters Parameters; parameters
      * @param speed Speed; current speed
      * @param speedLimitInfo SpeedLimitInfo; info regarding the desired speed for car-following
      * @param distance Length; distance to the location of the target speed
      * @param targetSpeed Speed; target speed
      * @return acceleration acceleration based on the car-following model in order to adjust the speed
      * @throws ParameterException if parameter exception occurs
      * @throws NullPointerException if any input is null
      * @throws IllegalArgumentException if the distance or target speed is not at least 0
      */
     public static Acceleration approachTargetSpeed(final CarFollowingModel carFollowingModel, final Parameters parameters,
             final Speed speed, final SpeedLimitInfo speedLimitInfo, final Length distance, final Speed targetSpeed)
             throws ParameterException
     {
         Throw.whenNull(parameters, "Parameters may not be null.");
         Throw.whenNull(speed, "Speed may not be null.");
         Throw.whenNull(speedLimitInfo, "Speed limit info may not be null.");
         Throw.whenNull(distance, "Distance may not be null");
         Throw.whenNull(targetSpeed, "Target speed may not be null");
         Throw.when(distance.si < 0, IllegalArgumentException.class, "Distance must be at least 0.");
         Throw.when(targetSpeed.si < 0, IllegalArgumentException.class, "Target speed must be at least 0.");
         // adjust speed of virtual vehicle to add deceleration incentive as the virtual vehicle does not move
         Speed virtualSpeed;
         if (speed.si > 0)
         {
             virtualSpeed = new Speed(targetSpeed.si * targetSpeed.si / speed.si, SpeedUnit.SI);
         }
         else
         {
             virtualSpeed = new Speed(Double.MAX_VALUE, SpeedUnit.SI);
         }
         // set distance in line with equilibrium headway at virtual speed
         Length virtualDistance = distance.plus(carFollowingModel.desiredHeadway(parameters, virtualSpeed));
         // calculate acceleration towards virtual vehicle with car-following model
         return carFollowingModel.followingAcceleration(parameters, speed, speedLimitInfo,
                 createLeader(virtualDistance, virtualSpeed));
     }
 
     /**
      * Create a single leader set.
      * @param headway Length; distance to the leader
      * @param speed Speed; leader speed
      * @return Set; set with a single leader
      */
     private static PerceptionIterable<Headway> createLeader(final Length headway, final Speed speed)
     {
         PerceptionIterable<Headway> leaders =
                 Try.assign(() -> new PerceptionIterableSet<>(new CarFollowingHeadway(headway, speed)),
                         "Exception during headway creation.");
         return leaders;
     }
 
     /**
      * Simple headway implementation for minimum car-following information.
      * <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 26 feb. 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 static class CarFollowingHeadway extends AbstractHeadway
     {
         /** */
         private static final long serialVersionUID = 20180226L;
 
         /** Speed of the leader. */
         private final Speed speed;
 
         /**
          * Constructor.
          * @param headway Length; distance to the leader
          * @param speed Speed; leader speed
          * @throws GTUException on exception
          */
         public CarFollowingHeadway(final Length headway, final Speed speed) throws GTUException
         {
             super(headway);
             this.speed = speed;
         }
 
         /** {@inheritDoc} */
         @Override
         public String getId()
         {
             return null;
         }
 
         /** {@inheritDoc} */
         @Override
         public Length getLength()
         {
             return null;
         }
 
         /** {@inheritDoc} */
         @Override
         public Speed getSpeed()
         {
             return this.speed;
         }
 
         /** {@inheritDoc} */
         @Override
         public ObjectType getObjectType()
         {
             return null;
         }
 
         /** {@inheritDoc} */
         @Override
         public Acceleration getAcceleration()
         {
             return null;
         }
     }
 
 }