package org.apache.lucene.util;
/**
 * Copyright 2005 Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


/**
 * Skips along two docNrSkipper sets which have common entries
 * @author maharwood
 */
public class AndDocNrSkipper implements DocNrSkipper
{
    DocNrSkipper listA,listB;
    int aDoc=Integer.MIN_VALUE;
    int bDoc=Integer.MIN_VALUE;
    int lastDocNrLookup=Integer.MIN_VALUE;
    
    public AndDocNrSkipper(DocNrSkipper listA,DocNrSkipper listB)
    {
        this.listA=listA;
        this.listB=listB;
    }
    
    public int nextDocNr(int docNr)
    {
        if(lastDocNrLookup>docNr)
        {
            //user has rewinded position - need to reset position on both lists
            aDoc=listA.nextDocNr(docNr); //reset A           
            bDoc=listB.nextDocNr(docNr); //reset B           
        }
        lastDocNrLookup=docNr;
        
        int jumpTo=docNr;
        while(true)
        {
	        //jump forward
	        if(aDoc<jumpTo)
	        {
	            aDoc=listA.nextDocNr(jumpTo); //advance A           
	        }
	        if(aDoc==-1)
	        {
	            return -1; //reached end of A
	        }
	        if(bDoc<jumpTo)
	        {
	            bDoc=listB.nextDocNr(jumpTo);//advance B
	        }
	        if(bDoc==-1)
	        {
	            return -1; //reached end of B
	        }
	        //assess position
	        if(aDoc==bDoc)
	        {
	            return aDoc; //found match
	        }
	        //set jumpTo to larger of the two current positions
	        if(aDoc>bDoc)
	        {
	            jumpTo=aDoc;
	            bDoc=listB.nextDocNr(aDoc); //advance B to A's current position
	        }
	        else
	        {
	            jumpTo=bDoc;
	            aDoc=listA.nextDocNr(bDoc); //advance A to B's current position
	        }
        }
        
    }
}