package org.opentrafficsim.road.gtu.lane.perception;
   
   import java.util.HashMap;
   import java.util.Iterator;
   import java.util.Map;
   import java.util.NoSuchElementException;
   import java.util.SortedMap;
   import java.util.TreeMap;
   
  import org.djunits.value.vdouble.scalar.Length;
  import org.opentrafficsim.base.parameters.ParameterException;
  import org.opentrafficsim.core.gtu.GTUException;
  import org.opentrafficsim.road.gtu.lane.LaneBasedGTU;
  import org.opentrafficsim.road.gtu.lane.perception.headway.Headway;
  
  /**
   * Iterable class to search over multiple lanes.
   * <p>
   * Copyright (c) 2013-2019 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 20 feb. 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>
   * @param <H> headway type
   * @param <U> underlying headway type
   */
  public class MultiLanePerceptionIterable<H extends Headway, U> extends AbstractPerceptionReiterable<H, U>
  {
  
      /** Set of iterators per lane. */
      final Map<RelativeLane, Iterator<PrimaryIteratorEntry>> iterators = new HashMap<>();
  
      /** Map of lane per object. */
      final Map<U, RelativeLane> laneMap = new HashMap<>();
  
      /** Map of iterable per lane. */
      final Map<RelativeLane, AbstractPerceptionReiterable<H, U>> iterables = new HashMap<>();
  
      /**
       * Constructor.
       * @param perceivingGtu LaneBasedGTU; perceiving GTU
       */
      public MultiLanePerceptionIterable(final LaneBasedGTU perceivingGtu)
      {
          super(perceivingGtu);
      }
  
      /**
       * Adds an iterable for a lane.
       * @param lane RelativeLane; lane
       * @param iterable AbstractPerceptionReiterable&lt;H, U&gt;; iterable
       */
      public void addIterable(final RelativeLane lane, final AbstractPerceptionReiterable<H, U> iterable)
      {
          this.iterators.put(lane, iterable.getPrimaryIterator());
          this.iterables.put(lane, iterable);
      }
  
      /** {@inheritDoc} */
      @Override
      public Iterator<PrimaryIteratorEntry> primaryIterator()
      {
          return new MultiLaneIterator();
      }
  
      /**
       * Iterator that returns the closest element from a set of lanes.
       * <p>
       * Copyright (c) 2013-2019 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 21 feb. 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>
       */
      private class MultiLaneIterator implements Iterator<PrimaryIteratorEntry>
      {
  
          /** Sorted elements per lane. */
          SortedMap<PrimaryIteratorEntry, RelativeLane> elements;
  
          /** Constructor. */
          MultiLaneIterator()
          {
              //
          }
  
          /** {@inheritDoc} */
          @Override
          public boolean hasNext()
          {
              assureNext();
              return !this.elements.isEmpty();
          }
  
         /** {@inheritDoc} */
         @Override
         public PrimaryIteratorEntry next()
         {
             assureNext();
             if (this.elements.isEmpty())
             {
                 throw new NoSuchElementException();
             }
 
             // get and remove next
             PrimaryIteratorEntry next = this.elements.firstKey();
             RelativeLane lane = this.elements.get(next);
             this.elements.remove(next);
 
             // prepare next
             Iterator<PrimaryIteratorEntry> laneIterator = MultiLanePerceptionIterable.this.iterators.get(lane);
             if (laneIterator != null)
             {
                 if (laneIterator.hasNext())
                 {
                     this.elements.put(laneIterator.next(), lane);
                 }
                 else
                 {
                     // remove it, it has no more elements to offer
                     MultiLanePerceptionIterable.this.iterators.remove(lane);
                 }
             }
 
             MultiLanePerceptionIterable.this.laneMap.put(next.object, lane);
             return next;
         }
 
         /**
          * Starts the process.
          */
         public void assureNext()
         {
             if (this.elements == null)
             {
                 this.elements = new TreeMap<>();
                 for (RelativeLane lane : MultiLanePerceptionIterable.this.iterators.keySet())
                 {
                     Iterator<PrimaryIteratorEntry> laneIterator = MultiLanePerceptionIterable.this.iterators.get(lane);
                     if (laneIterator.hasNext())
                     {
                         this.elements.put(laneIterator.next(), lane);
                     }
                 }
             }
         }
 
     }
 
     /** {@inheritDoc} */
     @Override
     public H perceive(final LaneBasedGTU perceivingGtu, final U object, final Length distance)
             throws GTUException, ParameterException
     {
         return this.iterables.get(this.laneMap.get(object)).perceive(perceivingGtu, object, distance);
     }
 }