package org.opentrafficsim.road.gtu.lane.tactical.following;
   
   import org.djunits.unit.AccelerationUnit;
   import org.djunits.unit.LengthUnit;
   import org.djunits.unit.SpeedUnit;
   import org.djunits.unit.TimeUnit;
   import org.djunits.value.vdouble.scalar.Acceleration;
   import org.djunits.value.vdouble.scalar.Length;
   import org.djunits.value.vdouble.scalar.Speed;
  import org.djunits.value.vdouble.scalar.Time;
  
  /**
   * The Intelligent Driver Model by Treiber, Hennecke and Helbing.
   * <p>
   * Copyright (c) 2013-2015 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/license.html">OpenTrafficSim License</a>.
   * <p>
   * @version $Revision: 1408 $, $LastChangedDate: 2015-09-24 15:17:25 +0200 (Thu, 24 Sep 2015) $, by $Author: pknoppers $,
   *          initial version 19 nov. 2014 <br>
   * @author <a href="http://www.tudelft.nl/pknoppers">Peter Knoppers</a>
   */
  public class IDMOld extends AbstractGTUFollowingModelMobil
  {
      /** Preferred net longitudinal distance when stopped [m]. */
      private final Length.Rel s0;
  
      /** Maximum longitudinal acceleration [m/s^2]. */
      private final 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 final Time.Rel tSafe;
  
      /**
       * Time slot size used by IDM (not defined in the paper, but 0.5s is a reasonable trade-off between computational speed and
       * accuracy).
       */
      private final Time.Rel stepSize = new Time.Rel(0.5, TimeUnit.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 final 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.Rel(3, LengthUnit.METER);
          this.tSafe = new Time.Rel(1.2, TimeUnit.SECOND);
          this.delta = 1d;
      }
  
      /**
       * Construct a new IDM car following model.
       * @param a Acceleration; the maximum acceleration of a stationary vehicle (normal value is 1 m/s/s)
       * @param b Acceleration; the maximum deemed-safe deceleration (this is a positive value). Normal value is 1.5 m/s/s.
       * @param s0 Length.Rel; the minimum stationary headway (normal value is 2 m)
       * @param tSafe Time.Rel; the minimum time-headway (normal value is 1s)
       * @param delta double; 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.Rel s0, final Time.Rel 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 DoubleScalarAbs&lt;SpeedUnit&gt;; the speed limit
       * @param followerMaximumSpeed Speed; the maximum speed that the follower can drive
       * @return DoubleScalarRel&lt;SpeedUnit&gt;; 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);
      }
  
      /** {@inheritDoc} */
      public final Acceleration computeAcceleration(final Speed followerSpeed, final Speed followerMaximumSpeed,
          final Speed leaderSpeed, final Length.Rel headway, final Speed speedLimit)
      {
          return computeAcceleration(followerSpeed, followerMaximumSpeed, leaderSpeed, headway, speedLimit, this.stepSize);
      }
      
      /** {@inheritDoc} */
      public final Acceleration computeAcceleration(final Speed followerSpeed, final Speed followerMaximumSpeed,
          final Speed leaderSpeed, final Length.Rel headway, final Speed speedLimit, final Time.Rel 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;
     }
 
     /** {@inheritDoc} */
     @Override
     public final Time.Rel getStepSize()
     {
         return this.stepSize;
     }
 
     /** {@inheritDoc} */
     @Override
     public final Acceleration getMaximumSafeDeceleration()
     {
         return this.b;
     }
 
     /** {@inheritDoc} */
     @Override
     public final String getName()
     {
         return "IDM";
     }
 
     /** {@inheritDoc} */
     @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);
     }
 
 }