package com.icl.saxon.expr;
import com.icl.saxon.Controller;
import com.icl.saxon.om.NodeInfo;
import com.icl.saxon.om.NodeEnumeration;


import java.util.*;

/**
* An enumeration representing a nodeset that is an intersection of two other NodeSets.
* There is currently no operator in XPath to create such an expression, but it is used
* by the extension function intersection(). The code is derived from the analagous UnionEnumeration,
* an inner class of UnionExpression.
*/


public class IntersectionEnumeration implements NodeEnumeration {

    private NodeEnumeration p1;
    private NodeEnumeration p2;
    private NodeEnumeration e1;
    private NodeEnumeration e2;
    private NodeInfo nextNode1 = null;
    private NodeInfo nextNode2 = null;

    private NodeInfo nextNode = null;
    private Controller controller;

    /**
    * Form an enumeration of the intersection of the nodes in two nodesets
    * @param p1 the first operand
    * @param p2 the second operand
    * @param controller Comparer to be used for putting nodes in document order
    */

    public IntersectionEnumeration(NodeEnumeration p1, NodeEnumeration p2,
                                    Controller controller) throws XPathException {
        this.p1 = p1;
        this.p2 = p2;
        this.controller = controller;
        e1 = p1;
        e2 = p2;
        if (!e1.isSorted()) {
            e1 = (new NodeSetExtent(e1, controller)).sort().enumerate();
        }
        if (!e2.isSorted()) {
            e2 = (new NodeSetExtent(e2, controller)).sort().enumerate();
        }

        // move to the first node in each input nodeset

        if (e1.hasMoreElements()) {
            nextNode1 = e1.nextElement();
        }
        if (e2.hasMoreElements()) {
            nextNode2 = e2.nextElement();
        }            

        // move to the first node that matches in  both
        
        advance();
        
    }

    public boolean hasMoreElements() {
        return nextNode!=null;
    }

    public NodeInfo nextElement() throws XPathException {
        NodeInfo current = nextNode;
        advance();
        return current;
    }
 
    private void advance() throws XPathException {

        // main merge loop: iterate whichever set has the lower value, returning when a pair
        // is found that match.

        while (nextNode1 != null && nextNode2 !=null) {
            int c = controller.compare(nextNode1, nextNode2);
            if (c<0) {
                NodeInfo next = nextNode1;
                if (e1.hasMoreElements()) {
                    nextNode1 = e1.nextElement();
                } else {
                    nextNode1 = null;
                    nextNode = null;
                }
            
            } else if (c>0) {
                NodeInfo next = nextNode2;
                if (e2.hasMoreElements()) {
                    nextNode2 = e2.nextElement();
                } else {
                    nextNode2 = null;
                    nextNode = null;
                }
            
            } else {            // keys are equal
                
                nextNode = nextNode2;           // which is the same as nextNode1
                if (e2.hasMoreElements()) {
                    nextNode2 = e2.nextElement();
                } else {
                    nextNode2 = null;
                }
                if (e1.hasMoreElements()) {
                    nextNode1 = e1.nextElement();
                } else {
                    nextNode1 = null;
                }

                return;
            }
        }
        nextNode = null;
    }

    public boolean isSorted() {
        return true;
    }

    public boolean isReverseSorted()  {
        return false;
    }

    public boolean isPeer() {
        return false;
    }


}

//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (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.mozilla.org/MPL/ 
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License. 
//
// The Original Code is: all this file. 
//
// The Initial Developer of the Original Code is
// Michael Kay of International Computers Limited (mhkay@iclway.co.uk).
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved. 
//
// Contributor(s): none. 
//