package org.opentrafficsim.road.gtu.tactical.following;
   
   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.opentrafficsim.base.parameters.ParameterException;
   import org.opentrafficsim.base.parameters.ParameterTypeAcceleration;
   import org.opentrafficsim.base.parameters.ParameterTypeDouble;
  import org.opentrafficsim.base.parameters.ParameterTypeDuration;
  import org.opentrafficsim.base.parameters.ParameterTypeLength;
  import org.opentrafficsim.base.parameters.ParameterTypes;
  import org.opentrafficsim.base.parameters.Parameters;
  import org.opentrafficsim.base.parameters.constraint.ConstraintInterface;
  import org.opentrafficsim.core.gtu.Stateless;
  import org.opentrafficsim.road.gtu.perception.PerceptionIterable;
  import org.opentrafficsim.road.gtu.perception.object.PerceivedObject;
  import org.opentrafficsim.road.network.speed.SpeedLimits;
  
  /**
   * Implementation of the IDM. See <a
   * href=https://en.wikipedia.org/wiki/Intelligent_driver_model>https://en.wikipedia.org/wiki/Intelligent_driver_model</a>
   * <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
   */
  // @docs/06-behavior/parameters.md
  public abstract class AbstractIdm extends AbstractCarFollowingModel
  {
  
      /** Acceleration parameter type. */
      // @docs/06-behavior/parameters.md
      protected static final ParameterTypeAcceleration A = ParameterTypes.A;
  
      /** Comfortable deceleration parameter type. */
      protected static final ParameterTypeAcceleration B = ParameterTypes.B;
  
      /** Desired headway parameter type. */
      protected static final ParameterTypeDuration T = ParameterTypes.T;
  
      /** Stopping distance parameter type. */
      protected static final ParameterTypeLength S0 = ParameterTypes.S0;
  
      /** Adjustment deceleration parameter type. */
      protected static final ParameterTypeAcceleration B0 = ParameterTypes.B0;
  
      /** Lane speed limit adherence factor parameter type. */
      protected static final ParameterTypeDouble FSPEED = ParameterTypes.FSPEED;
  
      /** GTU type speed limit adherence factor parameter type. */
      protected static final ParameterTypeDouble FSPEED_GTU = ParameterTypes.FSPEED_GTU;
  
      /** Speed to which FSPEED is applied if there is no speed limit. */
      private static final Speed NO_SPEED_LIMIT_SPEED = new Speed(130.0, SpeedUnit.KM_PER_HOUR);
  
      /** Acceleration flattening. */
      // @docs/06-behavior/parameters.md
      public static final ParameterTypeDouble DELTA = new ParameterTypeDouble("delta",
              "Acceleration flattening exponent towards desired speed", 4.0, ConstraintInterface.POSITIVE);
  
      /** Default IDM desired headway model. */
      public static final IdmDesiredHeadwayModel HEADWAY = IdmDesiredHeadwayModel.SINGLETON;
  
      /** Default IDM desired speed model. */
      public static final IdmDesiredSpeedModel DESIRED_SPEED = IdmDesiredSpeedModel.SINGLETON;
  
      /**
       * Constructor with modular models for desired headway and desired speed.
       * @param desiredHeadwayModel desired headway model
       * @param desiredSpeedModel desired speed model
       */
      public AbstractIdm(final DesiredHeadwayModel desiredHeadwayModel, final DesiredSpeedModel desiredSpeedModel)
      {
          super(desiredHeadwayModel, desiredSpeedModel);
      }
  
      /**
       * Determination of car-following acceleration, possibly based on multiple leaders. This implementation calculates the IDM
       * free term, which is returned if there are no leaders. If there are leaders <code>combineInteractionTerm()</code> is
       * invoked to combine the free term with some implementation specific interaction term. The IDM free term is limited by a
       * deceleration of <code>B0</code> for cases where the current speed is above the desired speed. This method can be
       * overridden if the free term needs to be redefined.
       * @param parameters Parameters.
       * @param speed Current speed.
       * @param desiredSpeed Desired speed.
       * @param desiredHeadway Desired headway.
       * @param leaders Set of leader headways (guaranteed positive) and speeds, ordered by headway (closest first).
       * @throws ParameterException If parameter exception occurs.
       * @return Car-following acceleration.
       */
      @Override
      @SuppressWarnings("checkstyle:designforextension")
      protected Acceleration followingAcceleration(final Parameters parameters, final Speed speed, final Speed desiredSpeed,
              final Length desiredHeadway, final PerceptionIterable<? extends PerceivedObject> leaders) throws ParameterException
      {
         Acceleration a = parameters.getParameter(A);
         Acceleration b0 = parameters.getParameter(B0);
         double delta = parameters.getParameter(DELTA);
         double aFree = a.si * (1 - Math.pow(speed.si / desiredSpeed.si, delta));
         // limit deceleration in free term (occurs if speed > desired speed)
         aFree = aFree > -b0.si ? aFree : -b0.si;
         // return free term if there are no leaders
         if (leaders.isEmpty())
         {
             return Acceleration.ofSI(aFree);
         }
         // return combined acceleration
         return combineInteractionTerm(Acceleration.ofSI(aFree), parameters, speed, desiredSpeed, desiredHeadway, leaders);
     }
 
     /**
      * Combines an interaction term with the free term. There should be at least 1 leader for this method.
      * @param aFree Free term of acceleration.
      * @param parameters Parameters.
      * @param speed Current speed.
      * @param desiredSpeed Desired speed.
      * @param desiredHeadway Desired headway.
      * @param leaders Set of leader headways (guaranteed positive) and speeds, ordered by headway (closest first).
      * @return Combination of terms into a single acceleration.
      * @throws ParameterException In case of parameter exception.
      */
     protected abstract Acceleration combineInteractionTerm(Acceleration aFree, Parameters parameters, Speed speed,
             Speed desiredSpeed, Length desiredHeadway, PerceptionIterable<? extends PerceivedObject> leaders)
             throws ParameterException;
 
     /**
      * Determines the dynamic desired headway, which is non-negative.
      * @param parameters Parameters.
      * @param speed Current speed.
      * @param desiredHeadway Desired headway.
      * @param leaderSpeed Speed of the leading vehicle.
      * @return Dynamic desired headway.
      * @throws ParameterException In case of parameter exception.
      */
     protected final Length dynamicDesiredHeadway(final Parameters parameters, final Speed speed, final Length desiredHeadway,
             final Speed leaderSpeed) throws ParameterException
     {
         double sStar = desiredHeadway.si + dynamicHeadwayTerm(parameters, speed, leaderSpeed).si;
         /*
          * Due to a power of 2 in the IDM, negative values of sStar are not allowed. A negative sStar means that the leader is
          * faster to such an extent, that the equilibrium headway (s0+vT) is completely compensated by the dynamic part in
          * sStar. This might occur if a much faster leader changes lane closely in front. The compensation is limited to the
          * equilibrium headway minus the stopping distance (i.e. sStar > s0), which means the driver wants to follow with
          * acceleration. Note that usually the free term determines acceleration in such cases.
          */
         Length s0 = parameters.getParameter(S0);
         /*
          * Limit used to be 0, but the IDM is very sensitive there. With a decelerating leader, an ok acceleration in one time
          * step, may results in acceleration < -10 in the next.
          */
         return Length.ofSI(sStar >= s0.si ? sStar : s0.si);
     }
 
     /**
      * Determines the dynamic headway term. May be used on individual leaders for multi-anticipative following.
      * @param parameters Parameters.
      * @param speed Current speed.
      * @param leaderSpeed Speed of the leading vehicle.
      * @return Dynamic headway term.
      * @throws ParameterException In case of parameter exception.
      */
     protected final Length dynamicHeadwayTerm(final Parameters parameters, final Speed speed, final Speed leaderSpeed)
             throws ParameterException
     {
         Acceleration a = parameters.getParameter(A);
         Acceleration b = parameters.getParameter(B);
         return Length.ofSI(speed.si * (speed.si - leaderSpeed.si) / (2 * Math.sqrt(a.si * b.si)));
     }
 
     /**
      * IDM desired headway model.
      */
     public static class IdmDesiredHeadwayModel implements DesiredHeadwayModel, Stateless<IdmDesiredHeadwayModel>
     {
         /** Singleton instance. */
         public static final IdmDesiredHeadwayModel SINGLETON = new IdmDesiredHeadwayModel();
 
         /**
          * Constructor.
          */
         public IdmDesiredHeadwayModel()
         {
             //
         }
 
         @Override
         public IdmDesiredHeadwayModel get()
         {
             return SINGLETON;
         }
 
         @Override
         public Length desiredHeadway(final Parameters parameters, final Speed speed) throws ParameterException
         {
             return Length.ofSI(parameters.getParameter(S0).si + speed.si * parameters.getParameter(T).si);
         }
     }
 
     /**
      * IDM desired speed model. This model returns the minimum of fSpeed'*laneSpeedLimit and fSpeedGtu'*gtuTypeSpeedLimit if
      * both exist, or one of them if one exists. If both do not exist this model returns fSpeed*130km/h. For both fSpeed' and
      * fSpeedGtu', if the speed limit is enforced the value is the minimum of fSpeed/fSpeedGtu (respectively) and 1.0.
      */
     public static class IdmDesiredSpeedModel implements DesiredSpeedModel, Stateless<IdmDesiredSpeedModel>
     {
         /** Singleton instance. */
         public static final IdmDesiredSpeedModel SINGLETON = new IdmDesiredSpeedModel();
 
         /**
          * Constructor.
          */
         public IdmDesiredSpeedModel()
         {
             //
         }
 
         @Override
         public IdmDesiredSpeedModel get()
         {
             return SINGLETON;
         }
 
         @Override
         public Speed desiredSpeed(final Parameters parameters, final SpeedLimits speedLimits, final Speed maxVehicleSpeed)
                 throws ParameterException
         {
             Speed speed = null;
             if (speedLimits.laneSpeedLimit() != null)
             {
                 double laneFactor = parameters.getParameter(FSPEED);
                 if (speedLimits.laneSpeedLimit().enforced() && laneFactor > 1.0)
                 {
                     laneFactor = 1.0;
                 }
                 speed = speedLimits.laneSpeedLimit().speed().times(laneFactor);
             }
             if (speedLimits.gtuTypeSpeedLimit() != null)
             {
                 double gtuTypeFactor = parameters.getParameter(FSPEED_GTU);
                 if (speedLimits.gtuTypeSpeedLimit().enforced() && gtuTypeFactor > 1.0)
                 {
                     gtuTypeFactor = 1.0;
                 }
                 if (speed == null)
                 {
                     speed = speedLimits.gtuTypeSpeedLimit().speed().times(gtuTypeFactor);
                 }
                 else
                 {
                     speed = Speed.min(speed, speedLimits.gtuTypeSpeedLimit().speed().times(gtuTypeFactor));
                 }
             }
             else if (speed != null)
             {
                 return Speed.min(maxVehicleSpeed, speed);
             }
             return Speed.min(maxVehicleSpeed, NO_SPEED_LIMIT_SPEED.times(parameters.getParameter(FSPEED)));
         }
     }
 
 }