package org.opentrafficsim.road.gtu.lane.perception;
   
   import org.djunits.value.vdouble.scalar.Length;
   import org.opentrafficsim.base.parameters.ParameterException;
   import org.opentrafficsim.core.gtu.GtuException;
   import org.opentrafficsim.core.gtu.RelativePosition;
   import org.opentrafficsim.road.gtu.lane.LaneBasedGtu;
   import org.opentrafficsim.road.gtu.lane.perception.categories.neighbors.HeadwayGtuType;
   import org.opentrafficsim.road.gtu.lane.perception.headway.HeadwayGtu;
  import org.opentrafficsim.road.gtu.lane.perception.structure.LaneRecordInterface;
  
  /**
   * Iterable to find upstream GTU's.
   * <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/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://tudelft.nl/staff/p.knoppers-1">Peter Knoppers</a>
   * @author <a href="https://github.com/wjschakel">Wouter Schakel</a>
   */
  public class UpstreamNeighborsIterable extends AbstractPerceptionIterable<HeadwayGtu, LaneBasedGtu, Integer>
  {
  
      /** Margin in case of a left lane. */
      private static final Length LEFT = Length.instantiateSI(0.000001);
  
      /** Margin in case of a right lane. */
      private static final Length RIGHT = Length.instantiateSI(-0.000001);
  
      /** Headway GTU type that should be used. */
      private final HeadwayGtuType headwayGtuType;
  
      /**
       * Margin used for neighbor search in some cases to prevent possible deadlock. This does not affect calculated distances to
       * neighbors, but only whether they are considered a leader or follower.
       */
      private final Length margin;
  
      /**
       * Constructor.
       * @param perceivingGtu LaneBasedGtu; perceiving GTU
       * @param root LaneRecord&lt;?&gt;; root record
       * @param initialPosition Length; position on the root record
       * @param maxDistance Length; maximum distance to search
       * @param relativePosition RelativePosition; position to which distance are calculated by subclasses
       * @param headwayGtuType HeadwayGtuType; type of HeadwayGtu to return
       * @param lane RelativeLane; relative lane (used for a left/right distinction to prevent dead-locks)
       */
      public UpstreamNeighborsIterable(final LaneBasedGtu perceivingGtu, final LaneRecordInterface<?> root,
              final Length initialPosition, final Length maxDistance, final RelativePosition relativePosition,
              final HeadwayGtuType headwayGtuType, final RelativeLane lane)
      {
          super(perceivingGtu, root, initialPosition, false, maxDistance, relativePosition, null);
          this.headwayGtuType = headwayGtuType;
          this.margin = lane.getLateralDirectionality().isLeft() ? LEFT : RIGHT;
      }
  
      /** {@inheritDoc} */
      @Override
      protected Entry getNext(final LaneRecordInterface<?> record, final Length position, final Integer counter)
              throws GtuException
      {
          int n;
          LaneBasedGtu next;
          Length pos;
          if (counter == null)
          {
              if (position.ge(record.getLane().getLength()))
              {
                  next = record.getLane().getLastGtu();
              }
              else
              {
                  Length searchPos = position.plus(this.margin);
                  next = record.getLane().getGtuBehind(searchPos, RelativePosition.FRONT,
                          record.getLane().getLink().getSimulator().getSimulatorAbsTime());
              }
              if (next == null)
              {
                  return null;
              }
              n = record.getLane().indexOfGtu(next);
              pos = next.position(record.getLane(), next.getFront());
  
              if (this.getGtu() != null && next.getId().equals(this.getGtu().getId()))
              {
                  // ignore self
                  pos = pos.minus(next.getLength());
                  return getNext(record, pos, n);
              }
          }
          else
          {
              n = counter - 1;
              if (n < 0 || n >= record.getLane().numberOfGtus())
              {
                  return null;
              }
             next = record.getLane().getGtu(n);
             pos = next.position(record.getLane(), next.getFront());
         }
         return new Entry(next, n, pos);
     }
 
     /** {@inheritDoc} */
     @Override
     protected Length getDistance(final LaneBasedGtu object, final LaneRecordInterface<?> record, final Length position)
     {
         return record.getDistanceToPosition(position).neg().plus(getDx());
     }
 
     /** {@inheritDoc} */
     @Override
     public HeadwayGtu perceive(final LaneBasedGtu perceivingGtu, final LaneBasedGtu object, final Length distance)
             throws GtuException, ParameterException
     {
         return this.headwayGtuType.createUpstreamGtu(perceivingGtu, object, distance);
     }
 
 }