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 where either sets has an entry
 * @author maharwood
 */
public class OrDocNrSkipper implements DocNrSkipper
{
    DocNrSkipper listA,listB;
    int aDoc=Integer.MIN_VALUE;
    int bDoc=Integer.MIN_VALUE;
    int lastDocNrLookup=Integer.MIN_VALUE;
    
    public OrDocNrSkipper(DocNrSkipper listA,DocNrSkipper listB)
    {
        this.listA=listA;
        this.listB=listB;
    }
    
    public int nextDocNr(int docNr)
    {
        //Only call nextDocNr if necessary....
        if((docNr>lastDocNrLookup)&&(aDoc>=docNr))
        {
            //no need to advance listA - already positioned
        }        
        else
        {
            aDoc=listA.nextDocNr(docNr); //advance A
        }
        if((docNr>lastDocNrLookup)&&(bDoc>=docNr))
        {
            //no need to advance listB - already positioned
        }        
        else
        {
            bDoc=listB.nextDocNr(docNr); //advance B
        }
        
        lastDocNrLookup=docNr;//save the docNr
        
        if(aDoc==bDoc)
        {
            return aDoc; //both same -return
        }
        //a!=b so return smaller of two (but remember -1 indicates end of set) 
        if(aDoc>=0)
        {
            if(bDoc<0)
            {
                return aDoc; //B is at end - return A
            }
            if(aDoc<bDoc)
            {
                return aDoc; //aDoc is earlier than bDoc
            }           
        }
        return bDoc; //bDoc is earlier than aDoc or at end
    }
}