package nl.tudelft.goal.ut2004.floydwarshall;
   
   import java.lang.ref.WeakReference;
   import java.util.HashMap;
   import java.util.Map;
   import java.util.Set;
   import java.util.logging.Logger;
   
   import cz.cuni.amis.pogamut.unreal.communication.messages.UnrealId;
  import cz.cuni.amis.pogamut.ut2004.communication.messages.gbinfomessages.NavPoint;
  import cz.cuni.amis.pogamut.ut2004.communication.translator.shared.events.MapPointListObtained;
  
  /**
   * Cache for {@link FloydWarshallMap}s. Because FloydWarshallMaps consume a fair
   * amount of memory it is better to share this map between bots. As long as a
   * bot has a reference to a SharedFloydWarshallMap that map will remain in
   * memory.
   * 
   * A maps identity is based on the lexographically smallest unrealID and the
   * badEdgeflag. As such the FloydWarshallMapCache can handle different maps at
   * the same time.
   * 
   * @author mpkorstanje
   * 
   */
  public final class FloydWarshallMapCache {
  
  	/**
  	 * Singleton instance of this cache.
  	 */
  	private static FloydWarshallMapCache instance;
  
  	/**
  	 * Cache for {@link FloydWarshallMap}s.
  	 */
  	private final Map<MapKey, WeakReference<FloydWarshallMap>> cache = new HashMap<MapKey, WeakReference<FloydWarshallMap>>();
  
  	/**
  	 * A map can be uniquely identified by its badedge flag and a navpoint id
  	 * (which includes the map name). To make identification consistent we use
  	 * the smallest id.
  	 * 
  	 * @author mpkorstanje
  	 * 
  	 */
  	private static final class MapKey {
  
  		@Override
  		public String toString() {
  			return "MapKey [id=" + id + ", badEdgeFlag=" + badEdgeFlag + "]";
  		}
  
  		/**
  		 * The smallest navpoint id.
  		 */
  		private final String id;
  
  		/**
  		 * The prohibeted edges in this map.
  		 */
  		private final int badEdgeFlag;
  
  		public MapKey(Map<UnrealId, NavPoint> map, int badEdgeFlag) {
  			this.id = getSmallest(map.keySet());
  			this.badEdgeFlag = badEdgeFlag;
  		}
  
  		private String getSmallest(Set<UnrealId> set) {
  
  			if (set.isEmpty()) {
  				return null;
  			}
  
  			String smallestString = set.iterator().next().getStringId();
  			for (UnrealId candidate : set) {
  				String candidateString = candidate.getStringId();
  				if (candidateString.compareTo(smallestString) < 0) {
  					smallestString = candidateString;
  				}
  
  			}
  
  			return smallestString;
  		}
  
  		@Override
  		public int hashCode() {
  			final int prime = 31;
  			int result = 1;
  			result = prime * result + badEdgeFlag;
  			result = prime * result + ((id == null) ? 0 : id.hashCode());
  			return result;
  		}
  
  		@Override
  		public boolean equals(Object obj) {
  			if (this == obj)
  				return true;
  			if (obj == null)
 				return false;
 			if (!(obj instanceof MapKey))
 				return false;
 			MapKey other = (MapKey) obj;
 			if (badEdgeFlag != other.badEdgeFlag)
 				return false;
 			if (id == null) {
 				if (other.id != null)
 					return false;
 			} else if (!id.equals(other.id))
 				return false;
 			return true;
 		}
 
 	}
 
 	/**
 	 * Private constructor for singleton.
 	 */
 	private FloydWarshallMapCache() {
 
 	}
 
 	public synchronized FloydWarshallMap createMap(MapPointListObtained event, int badEdgeFlag, Logger log) {
 		MapKey key = new MapKey(event.getNavPoints(), badEdgeFlag);
 		FloydWarshallMap sharedMap = null;
 
 		// Check if map has been cached.
 		if (cache.containsKey(key)) {
 			sharedMap = cache.get(key).get();
 		}
 
 		// Even if entry exist, weak reference might still be null.
 		if (sharedMap != null) {
 			log.info("Map exists for " + key);	
 		} else {
 			log.info("Creating new map for " + key);
 			sharedMap = new FloydWarshallMap(badEdgeFlag, log);
 			sharedMap.performFloydWarshall(event);
 			cache.put(key, new WeakReference<FloydWarshallMap>(sharedMap));
 		} 
 		
 		return sharedMap;
 	}
 
 	public synchronized static FloydWarshallMapCache getInstance() {
 		if (instance == null) {
 			instance = new FloydWarshallMapCache();
 		}
 		return instance;
 	}
 
 }