package edu.stanford.peer.rbtm.engine;

import java.util.*;

/**
 * SimpleProofQueue maintains two queues of nodes that have not been visited, 
 * one for forward, and one for backward.
 */
public class SimpleProofQueue implements ProofQueue
{
	//HashSet 	forwardNodes = new HashSet();
	//HashSet     backwardNodes = new HashSet();
	LinkedList  forwardQueue = new LinkedList();
	LinkedList  backwardQueue = new LinkedList();

    public boolean hasUnexploredForwardNodes() { 
    	return !forwardQueue.isEmpty(); 
    }

    public boolean hasUnexploredBackwardNodes() { 
    	return !backwardQueue.isEmpty(); 
    }

    public ProofNode nextUnexploredForwardNode() { 
        return (ProofNode)forwardQueue.removeFirst(); 
    }

    public ProofNode nextUnexploredBackwardNode() { 
        return (ProofNode)backwardQueue.removeFirst(); 
    }

    public void addForwardNode(ProofNode node) {
		//if (! forwardNodes.contains(node)) {
			forwardQueue.add(node);
		//	forwardNodes.add(node);
		//}
    }

    public void addBackwardNode(ProofNode node) {
		//if (! backwardNodes.contains(node)) {
			backwardQueue.add(node);
		//	backwardNodes.add(node);
		//}
    }
}