package org.opentrafficsim.road.gtu.strategical;
   
   import java.util.ArrayList;
   import java.util.LinkedHashMap;
   import java.util.List;
   import java.util.Map;
   
   import org.djutils.exceptions.Throw;
   import org.djutils.exceptions.Try;
  import org.djutils.multikeymap.MultiKeyMap;
  import org.opentrafficsim.core.gtu.GtuType;
  import org.opentrafficsim.core.math.Draw;
  import org.opentrafficsim.core.network.Connector;
  import org.opentrafficsim.core.network.Link;
  import org.opentrafficsim.core.network.LinkWeight;
  import org.opentrafficsim.core.network.NetworkException;
  import org.opentrafficsim.core.network.Node;
  import org.opentrafficsim.core.network.route.Route;
  
  import nl.tudelft.simulation.jstats.streams.StreamInterface;
  
  /**
   * Generates a route by determining one. This class is different from {@code Generator<Route>} in that it has the origin,
   * destination and GTU type as input.
   * <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://github.com/peter-knoppers">Peter Knoppers</a>
   * @author <a href="https://github.com/wjschakel">Wouter Schakel</a>
   */
  public interface RouteGenerator
  {
      /** No route route generator. */
      RouteGenerator NULL = new RouteGenerator()
      {
          @Override
          public Route getRoute(final Node origin, final Node destination, final GtuType gtuType)
          {
              return null;
          }
      };
  
      /** Cache of default route generators per stream and link-weight. */
      MultiKeyMap<RouteGenerator> DEFAULT_SUPPLIERS = new MultiKeyMap<>(StreamInterface.class, LinkWeight.class);
  
      /**
       * Returns a default route generator for shortest routes based on the given stream.
       * @param stream random number stream
       * @param linkWeight link weight.
       * @return default route generator for shortest routes based on the given stream
       */
      static RouteGenerator getDefaultRouteSupplier(final StreamInterface stream, final LinkWeight linkWeight)
      {
          RouteGenerator def = DEFAULT_SUPPLIERS.get(stream, linkWeight);
          if (def == null)
          {
              def = new DefaultRouteGenerator(stream, linkWeight);
              DEFAULT_SUPPLIERS.put(def, stream, linkWeight);
          }
          return def;
      }
  
      /** Shortest route route generator. */
      class DefaultRouteGenerator implements RouteGenerator
      {
          /** Shortest route cache. */
          private final MultiKeyMap<Route> shortestRouteCache =
                  new MultiKeyMap<>(GtuType.class, Node.class, Node.class, List.class);
  
          /** Link weight. */
          private final LinkWeight linkWeight;
  
          /** Stream of random numbers. */
          private final StreamInterface stream;
  
          /**
           * Constructor.
           * @param stream stream of random numbers
           * @param linkWeight link weight.
           */
          public DefaultRouteGenerator(final StreamInterface stream, final LinkWeight linkWeight)
          {
              Throw.whenNull(stream, "Stream may not be null.");
              Throw.whenNull(linkWeight, "Link weight may not be null.");
              this.stream = stream;
              this.linkWeight = linkWeight;
          }
  
          @Override
          public Route getRoute(final Node origin, final Node destination, final GtuType gtuType)
          {
              List<Node> viaNodes = new ArrayList<>();
              double cumulWeight = 0.0;
              Map<Link, Double> links = new LinkedHashMap<>();
              boolean directLinkExists = false;
              for (Link link : destination.getLinks())
              {
                 if (link.isConnector() && link instanceof Connector && ((Connector) link).getDemandWeight() > 0.0)
                 {
                     // Verify there is a route from origin to this link
                     List<Node> testViaNode = new ArrayList<>();
                     Node linkEntryNode = link.getStartNode();
                     testViaNode.add(linkEntryNode);
                     try
                     {
                         if (origin.getNetwork().getShortestRouteBetween(gtuType, origin, destination, viaNodes,
                                 this.linkWeight) != null)
                         {
                             Double weight = ((Connector) link).getDemandWeight();
                             links.put(link, weight);
                             cumulWeight += weight;
                         }
                     }
                     catch (NetworkException e)
                     {
                         // ignore this link
                     }
                 }
                 if (link.getStartNode().equals(origin) || link.getEndNode().equals(origin))
                 {
                     directLinkExists = true;
                 }
             }
             if (cumulWeight > 0.0 && links.size() > 1 && (!directLinkExists))
             {
                 Link via = Draw.drawWeighted(links, this.stream);
                 if (via.getEndNode().equals(destination))
                 {
                     viaNodes.add(via.getStartNode());
                 }
                 else if (via.getStartNode().equals(destination))
                 {
                     viaNodes.add(via.getEndNode());
                 }
                 else
                 {
                     viaNodes.add(via.getEndNode());
                 }
             }
             if (!this.linkWeight.isStatic())
             {
                 return Try.assign(
                         () -> origin.getNetwork().getShortestRouteBetween(gtuType, origin, destination, viaNodes,
                                 this.linkWeight),
                         "Could not determine the shortest route from %s to %s via %s.", origin, destination, viaNodes);
             }
             return this.shortestRouteCache.get(() -> Try.assign(
                     () -> origin.getNetwork().getShortestRouteBetween(gtuType, origin, destination, viaNodes, this.linkWeight),
                     "Could not determine the shortest route from %s to %s via %s.", origin, destination, viaNodes), gtuType,
                     origin, destination, viaNodes);
         }
 
         @Override
         public String toString()
         {
             return "DefaultRouteGenerator [linkWeight=" + this.linkWeight + "shortestRouteCache=" + this.shortestRouteCache
                     + "]";
         }
     };
 
     /**
      * Returns a route.
      * @param origin origin
      * @param destination destination
      * @param gtuType gtu type
      * @return route
      */
     Route getRoute(Node origin, Node destination, GtuType gtuType);
 }