package org.opentrafficsim.road.gtu.perception.mental.channel;
   
   import java.util.Iterator;
   import java.util.NoSuchElementException;
   import java.util.Set;
   import java.util.function.Function;
   
   import org.djunits.value.vdouble.scalar.Duration;
   import org.opentrafficsim.base.DistancedObject;
  import org.opentrafficsim.base.OtsRuntimeException;
  import org.opentrafficsim.base.parameters.ParameterTypeDuration;
  import org.opentrafficsim.core.gtu.perception.EgoPerception;
  import org.opentrafficsim.road.gtu.LaneBasedGtu;
  import org.opentrafficsim.road.gtu.perception.LanePerception;
  import org.opentrafficsim.road.gtu.perception.RelativeLane;
  import org.opentrafficsim.road.gtu.perception.categories.neighbors.NeighborsPerception;
  import org.opentrafficsim.road.gtu.perception.mental.AbstractTask;
  import org.opentrafficsim.road.gtu.perception.mental.ar.ArTaskCarFollowingExp;
  
  /**
   * Task demand for car-following. This is defined as {@code exp(-T/h)} where {@code T} is the time headway to the leader and
   * {@code h} is the car-following task parameter that scales it.
   * <p>
   * Copyright (c) 2024-2026 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 Wouter Schakel
   */
  public class ChannelTaskCarFollowing extends AbstractTask implements ChannelTask
  {
  
      /** Car-following task parameter. */
      public static final ParameterTypeDuration HEXP = ArTaskCarFollowingExp.HEXP;
  
      /** Singleton instance. */
      private static final ChannelTaskCarFollowing DEFAULT = new ChannelTaskCarFollowing();
  
      /** Default set that is returned by the supplier. */
      private static final Set<ChannelTask> SET = Set.of(DEFAULT);
  
      /** Standard supplier that supplies a single instance of the car-following task. */
      public static final Function<LanePerception, Set<ChannelTask>> SUPPLIER = (p) -> SET;
  
      /** Leader supplier. */
      private final Function<LanePerception, DistancedObject<LaneBasedGtu>> leaderSupplier;
  
      /**
       * Constructor that will use the first leader from NeighborsPerception in the current lane.
       */
      public ChannelTaskCarFollowing()
      {
          this((perception) ->
          {
              NeighborsPerception neighbors = perception.getPerceptionCategoryOptional(NeighborsPerception.class)
                      .orElseThrow(() -> new NoSuchElementException("NeighborsPerception not present."));
              Iterator<DistancedObject<LaneBasedGtu>> leader =
                      neighbors.getLeaders(RelativeLane.CURRENT).underlyingWithDistance();
              if (!leader.hasNext())
              {
                  return null;
              }
              return leader.next();
          });
      }
  
      /**
       * Constructor that provides a supplier for a leader that follows a non-default logic.
       * @param leaderSupplier leader supplier
       */
      public ChannelTaskCarFollowing(final Function<LanePerception, DistancedObject<LaneBasedGtu>> leaderSupplier)
      {
          super("car-following (front)");
          this.leaderSupplier = leaderSupplier;
      }
  
      @Override
      public String getId()
      {
          return "car-following (front)";
      }
  
      @Override
      public Object getChannel()
      {
          return FRONT;
      }
  
      @Override
      public double calculateTaskDemand(final LanePerception perception)
      {
          DistancedObject<LaneBasedGtu> leader = this.leaderSupplier.apply(perception);
          if (leader == null)
          {
              return 0.0;
          }
          EgoPerception<?, ?> ego = perception.getPerceptionCategoryOptional(EgoPerception.class)
                  .orElseThrow(() -> new NoSuchElementException("EgoPerception not present."));
          Duration headway = leader.distance().divide(ego.getSpeed());
          Duration h = perception.getGtu().getParameters().getOptionalParameter(HEXP)
                 .orElseThrow(() -> new OtsRuntimeException("Parameter h_exp not present."));
         return headway.si <= 0.0 ? 0.999 : Math.exp(-headway.si / h.si);
     }
 
 }