package org.opentrafficsim.road.gtu.lane.perception.categories;
   
   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;
   import org.opentrafficsim.base.parameters.ParameterException;
   import org.opentrafficsim.road.gtu.lane.LaneBasedGTU;
   import org.opentrafficsim.road.gtu.lane.perception.categories.Anticipation.NeighborTriplet;
  import org.opentrafficsim.road.gtu.lane.perception.mental.AdaptationSituationalAwareness;
  
  /**
   * Estimation of neighbor headway, speed and acceleration.
   * <p>
   * Copyright (c) 2013-2018 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 6 apr. 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 Estimation
  {
      /** No estimation errors. */
      public static final Estimation NONE = new Estimation()
      {
          @Override
          public NeighborTriplet estimate(final LaneBasedGTU perceivingGtu, final LaneBasedGTU perceivedGtu,
                  final Length distance, final boolean downstream, final Time when) throws ParameterException
          {
              return new NeighborTriplet(distance, perceivedGtu.getSpeed(), perceivedGtu.getAcceleration());
          }
      };
  
      /** Underestimation based on situational awareness. */
      public static final Estimation UNDERESTIMATION = new Estimation()
      {
          @Override
          public NeighborTriplet estimate(final LaneBasedGTU perceivingGtu, final LaneBasedGTU perceivedGtu,
                  final Length distance, final boolean downstream, final Time when) throws ParameterException
          {
              double factor = 1.0 - (perceivingGtu.getParameters().getParameter(AdaptationSituationalAwareness.SA_MAX)
                      - perceivingGtu.getParameters().getParameter(AdaptationSituationalAwareness.SA));
              double delta = (perceivedGtu.getOdometer().si - perceivedGtu.getOdometer(when).si)
                      - (perceivingGtu.getOdometer().si - perceivingGtu.getOdometer(when).si);
              if (!downstream)
              {
                  delta = -delta; // faster leader increases the headway, faster follower reduces the headway
              }
              Length headway = Length.createSI((distance.si + delta) * factor);
              double egoSpeed = perceivingGtu.getSpeed(when).si;
              Speed speed = Speed.createSI(egoSpeed + factor * (perceivedGtu.getSpeed(when).si - egoSpeed));
              Acceleration acceleration = perceivedGtu.getAcceleration(when);
              return new NeighborTriplet(headway, speed, acceleration);
          }
      };
  
      /**
       * Estimate headway, speed and acceleration.
       * @param perceivingGtu LaneBasedGTU; perceiving GTU
       * @param perceivedGtu LaneBasedGTU; perceived GTU
       * @param distance Length; actual headway at 'now' (i.e. not at 'when' if there is a reaction time)
       * @param downstream boolean; downstream (or upstream) neighbor
       * @param when Time; moment of perception, reaction time included
       * @return NeighborTriplet; perceived headway, speed and acceleration
       * @throws ParameterException on invalid parameter value or if parameter is not available
       */
      NeighborTriplet estimate(LaneBasedGTU perceivingGtu, LaneBasedGTU perceivedGtu, Length distance, boolean downstream,
              Time when) throws ParameterException;
  }