package org.opentrafficsim.road.gtu.lane.tactical.following;
   
   import java.io.Serializable;
   
   import org.djunits.unit.AccelerationUnit;
   import org.djunits.unit.DurationUnit;
   import org.djunits.unit.LengthUnit;
   import org.djunits.unit.SpeedUnit;
   import org.djunits.value.vdouble.scalar.Acceleration;
  import org.djunits.value.vdouble.scalar.Duration;
  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.Parameters;
  import org.opentrafficsim.road.gtu.lane.perception.PerceptionIterable;
  import org.opentrafficsim.road.gtu.lane.perception.headway.Headway;
  import org.opentrafficsim.road.network.speed.SpeedLimitInfo;
  import org.opentrafficsim.road.network.speed.SpeedLimitTypes;
  
  /**
   * The Intelligent Driver Model by Treiber, Hennecke and Helbing.
   * <p>
   * Copyright (c) 2013-2024 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/peter-knoppers">Peter Knoppers</a>
   */
  public class IdmOld extends AbstractGtuFollowingModelMobil implements Serializable
  {
      /** */
      private static final long serialVersionUID = 20141119L;
  
      /** Preferred net longitudinal distance when stopped [m]. */
      private final Length s0;
  
      /** Maximum longitudinal acceleration [m/s^2]. */
      private Acceleration a;
  
      /** Longitudinal deceleration [m/s^2]. (Should be a positive value even though it is a <b>de</b>celeration.) */
      private final Acceleration b;
  
      /** Safe time headway. */
      private Duration tSafe;
  
      /**
       * Default step size used by IDM (not defined in the paper, but 0.5s is a reasonable trade-off between computational speed
       * and accuracy).
       */
      private static final Duration DEFAULT_STEP_SIZE = new Duration(0.5, DurationUnit.SECOND);
  
      /**
       * Mean speed limit adherence (1.0: mean free speed equals the speed limit; 1.1: mean speed limit equals 110% of the speed
       * limit, etc.).
       */
      private double delta;
  
      /**
       * Construct a new IDM car following model with reasonable values (reasonable for passenger cars).
       */
      public IdmOld()
      {
          this.a = new Acceleration(1.56, AccelerationUnit.METER_PER_SECOND_2);
          this.b = new Acceleration(2.09, AccelerationUnit.METER_PER_SECOND_2);
          this.s0 = new Length(3, LengthUnit.METER);
          this.tSafe = new Duration(1.2, DurationUnit.SECOND);
          this.delta = 1.0;
      }
  
      /**
       * Construct a new IDM car following model.
       * @param a the maximum acceleration of a stationary vehicle (normal value is 1.56 m/s/s)
       * @param b the maximum deemed-safe deceleration (this is a positive value). Normal value is 2.09 m/s/s.
       * @param s0 the minimum stationary headway (normal value is 3 m)
       * @param tSafe the minimum time-headway (normal value is 1.2 s)
       * @param delta the speed limit adherence (1.0; mean free speed equals the speed limit; 1.1: mean free speed equals 110% of
       *            the speed limit; etc.)
       */
      public IdmOld(final Acceleration a, final Acceleration b, final Length s0, final Duration tSafe, final double delta)
      {
          this.a = a;
          this.b = b;
          this.s0 = s0;
          this.tSafe = tSafe;
          this.delta = delta;
      }
  
      /**
       * Desired speed (taking into account the urge to drive a little faster or slower than the posted speed limit).
       * @param speedLimit the speed limit
       * @param followerMaximumSpeed the maximum speed that the follower can drive
       * @return the desired speed
       */
      private Speed vDes(final Speed speedLimit, final Speed followerMaximumSpeed)
      {
          return new Speed(Math.min(this.delta * speedLimit.getSI(), followerMaximumSpeed.getSI()), SpeedUnit.SI);
      }
  
      @Override
      public final Acceleration computeAcceleration(final Speed followerSpeed, final Speed followerMaximumSpeed,
             final Speed leaderSpeed, final Length headway, final Speed speedLimit)
     {
         return computeAcceleration(followerSpeed, followerMaximumSpeed, leaderSpeed, headway, speedLimit, DEFAULT_STEP_SIZE);
     }
 
     @Override
     public final Acceleration computeAcceleration(final Speed followerSpeed, final Speed followerMaximumSpeed,
             final Speed leaderSpeed, final Length headway, final Speed speedLimit, final Duration stepSize)
     {
         // TODO maxDistance
         // dV is the approach speed
         Speed dV = followerSpeed.minus(leaderSpeed);
         double sStar = this.s0.si + followerSpeed.si * this.tSafe.si
                 + dV.si * followerSpeed.si / (2.0 * Math.sqrt(this.a.si * this.b.si));
         if (sStar < 0.0 && headway.si < 0.0)
         {
             return new Acceleration(Double.NEGATIVE_INFINITY, AccelerationUnit.SI);
         }
         sStar = sStar >= 0.0 ? sStar : 0.0;
         double s = headway.si > 0.0 ? headway.si : 1E-99;
         Acceleration aInteraction = new Acceleration(this.a.si * (sStar / s) * (sStar / s), AccelerationUnit.SI);
         Acceleration aFree =
                 new Acceleration(this.a.si * (1.0 - Math.pow(followerSpeed.si / vDes(speedLimit, followerMaximumSpeed).si, 4)),
                         AccelerationUnit.SI);
         // limit deceleration for free term (= aFree)
         if (aFree.si < -0.5)
         {
             aFree = new Acceleration(-0.5, AccelerationUnit.SI);
         }
         Acceleration newAcceleration = aFree.minus(aInteraction);
         if (newAcceleration.si * stepSize.si + followerSpeed.si < 0)
         {
             newAcceleration = new Acceleration(-followerSpeed.si / stepSize.si, AccelerationUnit.SI);
         }
         return newAcceleration;
     }
 
     @Override
     public final Duration getStepSize()
     {
         return DEFAULT_STEP_SIZE;
     }
 
     @Override
     public final Acceleration getMaximumSafeDeceleration()
     {
         return this.b;
     }
 
     @Override
     public final String getName()
     {
         return "IDM";
     }
 
     @Override
     public final String getLongName()
     {
         return String.format("%s (a=%.1fm/s\u00b2, b=%.1fm/s\u00b2, s0=%.1fm, tSafe=%.1fs, delta=%.2f)", getName(),
                 this.a.getSI(), this.b.getSI(), this.s0.getSI(), this.tSafe.getSI(), this.delta);
     }
 
     @Override
     public final void setA(final Acceleration a)
     {
         this.a = a;
     }
 
     @Override
     public final void setT(final Duration t)
     {
         this.tSafe = t;
     }
 
     @Override
     public final void setFspeed(final double fSpeed)
     {
         this.delta = fSpeed;
     }
 
     // The following is inherited from CarFollowingModel
 
     @Override
     public final Speed desiredSpeed(final Parameters parameters, final SpeedLimitInfo speedInfo) throws ParameterException
     {
         throw new UnsupportedOperationException("Old car-following model does not support desired speed.");
     }
 
     @Override
     public final Length desiredHeadway(final Parameters parameters, final Speed speed) throws ParameterException
     {
         throw new UnsupportedOperationException("Old car-following model does not support desired headway.");
     }
 
     @Override
     public final Acceleration followingAcceleration(final Parameters parameters, final Speed speed,
             final SpeedLimitInfo speedInfo, final PerceptionIterable<? extends Headway> leaders) throws ParameterException
     {
         Length headway;
         Speed leaderSpeed;
         if (leaders.isEmpty())
         {
             headway = new Length(Double.MAX_VALUE, LengthUnit.SI);
             leaderSpeed = speed;
         }
         else
         {
             Headway leader = leaders.first();
             headway = leader.getDistance();
             leaderSpeed = leader.getSpeed();
         }
         return this.computeAcceleration(speed, speedInfo.getSpeedInfo(SpeedLimitTypes.MAX_VEHICLE_SPEED), leaderSpeed, headway,
                 speedInfo.getSpeedInfo(SpeedLimitTypes.FIXED_SIGN));
     }
 
     @Override
     public final String toString()
     {
         return "IDMOld [s0=" + this.s0 + ", a=" + this.a + ", b=" + this.b + ", tSafe=" + this.tSafe + ", stepSize="
                 + DEFAULT_STEP_SIZE + ", delta=" + this.delta + "]";
     }
 
 }