/* 
 * This file is part of the HyperGraphDB source distribution. This is copyrighted 
 * software. For permitted uses, licensing options and redistribution, please see  
 * the LicensingInformation file at the root level of the distribution.  
 * 
 * Copyright (c) 2005-2010 Kobrix Software, Inc.  All rights reserved. 
 */
package org.hypergraphdb.query;

import java.util.List;

import org.hypergraphdb.HGHandle;
import org.hypergraphdb.HGLink;
import org.hypergraphdb.HGPersistentHandle;
import org.hypergraphdb.HyperGraph;
import org.hypergraphdb.HGException;
import org.hypergraphdb.HGQuery.hg;
import org.hypergraphdb.util.HGUtils;
import org.hypergraphdb.util.Ref;

/**
 * <p>
 * A <code>OrderedLinkCondition</code> constraints the query result set to ordered links
 * pointing to a target set of atoms. The target set is specified when
 * the condition is constructed through an array of <code>HGHandle</code>s. This array
 * must have the targets in the desired order. Note that the <code>targetSet</code> parameter
 * of this condition need only be a subset of the examined links' target sets. Thus a link
 * with an ordered target set of (a,b,c,d) would be satisfied by an <code>OrderedLinkCondition</code>
 * constructed with the target set (b,d) for example. If same arity is desired, the <code>ArityCondition</code>
 * should be used in conjunction with this one.
 * </p>
 *  
 * @author Borislav Iordanov
 */
public class OrderedLinkCondition implements HGQueryCondition, HGAtomPredicate
{
	@SuppressWarnings("unchecked")
	static Ref<HGHandle> [] EMPTY_TUPLE = new Ref[0];
	private Ref<HGHandle> [] targetSet = EMPTY_TUPLE;
	
	public OrderedLinkCondition()
	{
		
	}
	
	@SuppressWarnings("unchecked")
	public OrderedLinkCondition(HGHandle...targetSet)
	{
		if (targetSet == null)
			throw new HGException("OrderedLinkCondition instantiated with a null target set.");
        this.targetSet = new Ref[targetSet.length];
        for (int i = 0; i < targetSet.length; i++)
        	this.targetSet[i] = hg.constant(targetSet[i]);
	}

	public OrderedLinkCondition(Ref<HGHandle>...targetSet)
	{
		this.targetSet = targetSet;
	}
	
    @SuppressWarnings("unchecked")
	public OrderedLinkCondition(List<HGHandle> targetSet)
    {
        if (targetSet == null)
            throw new HGException("OrderedLinkCondition instantiated with a null target set.");
        this.targetSet = new Ref[targetSet.size()];
        int i = 0;
        for (HGHandle h : targetSet)
            this.targetSet[i++] = hg.constant(h); 
    }
	
	public Ref<HGHandle> [] targets()
	{
		return targetSet;
	}
	
	public Ref<HGHandle> [] getTargets()
	{
		return targetSet;
	}

	public void setTargets(Ref<HGHandle>[] targetSet)
	{
		this.targetSet = targetSet;
	}

	public void setTarget(int pos, HGHandle newTarget)
	{
		targetSet[pos] = hg.constant(newTarget);
	}
	
	public boolean satisfies(HyperGraph hg, HGHandle handle) 
	{
		// If the atom corresponding to 'handle' is already in the cache, there
		// is no point fetching it from permanent storage. Otherwise, there's no point
		// caching the actual atom...
		if (hg.isLoaded(handle))
		{
			Object atom = hg.get(handle);
			if (! (atom instanceof HGLink))
				return false;
			HGLink link = (HGLink)atom;
			int i = 0, j = 0;
			while (i < link.getArity() && j < targetSet.length)
			{
				if (targetSet[j].get().equals(link.getTargetAt(i))
				    || targetSet[j].get().equals(hg.getHandleFactory().anyHandle())) 
					j++;
				i++;
			}
			return j == targetSet.length;
		}
		else
		{
 			HGPersistentHandle [] A = hg.getStore().getLink(hg.getPersistentHandle(handle));			
			int i = 2, j = 0;
			while (i < A.length && j < targetSet.length)
			{
				if (targetSet[j].get().equals(A[i]) || targetSet[j].get().equals(hg.getHandleFactory().anyHandle()))
					j++;
				i++;
			}
			return j == targetSet.length; 			
		}
	}

	public String toString()
	{
		StringBuffer result = new StringBuffer("orderedLinks(");
		for (int i = 0; i < targetSet.length; i++)
		{
			result.append(targetSet[i].get());
			if (i < targetSet.length - 1)
				result.append(",");
		}
		result.append(")");
		return result.toString();
	}
	
	public int hashCode() 
	{ 
		int x = 0;
		for (Ref<HGHandle> h : targetSet) x += h.get().hashCode();
		return x;
	}
	
	public boolean equals(Object x)
	{
		if (! (x instanceof OrderedLinkCondition))
			return false;
		else
			return HGUtils.eq(targetSet, ((OrderedLinkCondition)x).targetSet);
	}	
}