package Sequenic.T2ext.Selection;

import java.util.Map;
import java.util.WeakHashMap;

/**
 * This will return a new Object with the given hashCode.
 * The equals method is overridden so that it will return true 
 * when compared to any Object with the same hashCode.
 * 
 * Note that the contract of equals will only be satisfied if the other object
 * also overrides equals in the same manner.
 * 
 * I.e. a.equals(b) if and only if b.equals(a), thus the other object must have a 
 * similarly defined equals method.
 * 
 * @author Jeiel Schalkwijk
 *
 */
class HashEqualsEdge {

	/** This int is returned by hashCode. 
	 * It is interpreted by toString as an edge where the most-significant 16 bits
	 * encode the source node id as an unsigned short (i.e. in range [0,65535]) and the least-significant 16 bits
	 * encode the destination node id in the same manner.
	 */
	protected int edge;
		
	protected HashEqualsEdge(){};
	private HashEqualsEdge(final int edge){ this.edge = edge;}
	
	public int fst() { return edge >>> 16; }
	public int snd() { return edge & 65535; }
	
	@Override public int hashCode()
	{ 					
		return edge;				
	}
	
	@Override public boolean equals(Object obj)
	{		
		return edge==obj.hashCode();
	}	
	
	@Override public String toString()
	{				
		return "("+fst()+","+snd()+")"; 
	}
	
	/**
	 * A factory to create HashEqualsEdge objects.
	 * It uses a WeakHashMap to maintain a cache of canonical instances in order to avoid
	 * creating duplicate instances of existing edges.
	 * 
	 * @author Jeiel Schalkwijk
	 *
	 */
	static final class CanonicalMappings extends HashEqualsEdge
	{
		private final Map<HashEqualsEdge, HashEqualsEdge> canonMappings = new WeakHashMap<HashEqualsEdge, HashEqualsEdge>();

		final synchronized HashEqualsEdge make(final int edge) 
		{
			this.edge = edge;
			HashEqualsEdge res = canonMappings.get(this);
			if(res==null) 
			{
				res = new HashEqualsEdge(edge);
				canonMappings.put(res, res);
			}
			return res;
		}
		
		final HashEqualsEdge make(int srcId, int dstId)
		{
			return make((srcId << 16 ) | dstId);
		}	
	}
	
	/** Because the make method is synchronized, a single global weakCache can be shared.
	 */
	static final CanonicalMappings weakCache = new CanonicalMappings();
}