package cz.cuni.amis.utils.maps;
   
   import java.util.Collections;
   import java.util.HashMap;
   import java.util.Map;
   import java.util.WeakHashMap;
   
   /**
    * Two-level hashMap where the first-level keys are weakly referenced!
   * This means that if the key is not strongly referenced elsewhere, the maps can be garbage collected.
   * @author srlok
   *
   * @param <PRIMARY_KEY>
   * @param <SECONDARY_KEY>
   * @param <ITEM>
   */
  public class WeakHashMapMap<PRIMARY_KEY,SECONDARY_KEY,ITEM>
  	extends WeakHashMap<PRIMARY_KEY, Map<SECONDARY_KEY, ITEM>> {
  	
  	@SuppressWarnings("unchecked")
  	@Override
  	public Map<SECONDARY_KEY,ITEM> get(Object primaryKey)
  	{
  		Map<SECONDARY_KEY,ITEM> result = super.get( primaryKey );
  		if (result != null) return result;
  		result = Collections.synchronizedMap( new HashMap<SECONDARY_KEY,ITEM>() );
  		super.put( (PRIMARY_KEY)primaryKey, result);
  		return result;
  	}
  	
  	/**
  	 * Returns the requested item under primary and secondary key.
  	 * @param primaryKey weakly-referenced
  	 * @param secondaryKey
  	 * @return if no such item exists returns  NULL
  	 */
  	public ITEM get(PRIMARY_KEY primaryKey, SECONDARY_KEY secondaryKey)
  	{
  		return get(primaryKey).get(secondaryKey);
  	}
  	
  	/**
  	 * Inserts item under primary and secondary_key.
  	 * @param primaryKey weakly-referenced
  	 * @param secondaryKey
  	 * @param item
  	 * @return inserted item
  	 */
  	public ITEM put(PRIMARY_KEY primaryKey, SECONDARY_KEY secondaryKey, ITEM item)
  	{
  		return get(primaryKey).put(secondaryKey, item);
  	}
  	
  	/**
  	 * removes the item under primary and secondary key.
  	 * @param primaryKey
  	 * @param secondaryKey
  	 * @return removed item
  	 */
  	public ITEM remove(PRIMARY_KEY primaryKey, SECONDARY_KEY secondaryKey)
  	{
  		return get(primaryKey).remove( secondaryKey);
  	}
  	
  	/**
  	 * removes all items under primaryKey
  	 * @param primaryKey
  	 * @return map of all removed items
  	 */
  	@Override
  	public Map<SECONDARY_KEY,ITEM> remove(Object primaryKey)
  	{
  		Map<SECONDARY_KEY,ITEM> result = super.remove(primaryKey);
  		if (result != null) { return result ; }
  		result = Collections.synchronizedMap( new HashMap<SECONDARY_KEY,ITEM>() );
  		return result;
  	}
  	
  	
  }