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

/**
* An enumeration representing a nodeset that is a union of two other NodeSets.
*/

public class UnionEnumeration implements NodeEnumeration {

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

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

    public boolean hasMoreElements() {
        return nextNode1!=null || nextNode2!=null;
    }

    public NodeInfo nextElement() throws XPathException {

        // main merge loop: take a value from whichever set has the lower value

        if (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;
                }
                return next;
            
            } else if (c>0) {
                NodeInfo next = nextNode2;
                if (e2.hasMoreElements()) {
                    nextNode2 = e2.nextElement();
                } else {
                    nextNode2 = null;
                }
                return next;
            
            } else {
                NodeInfo next = nextNode2;
                if (e2.hasMoreElements()) {
                    nextNode2 = e2.nextElement();
                } else {
                    nextNode2 = null;
                }
                if (e1.hasMoreElements()) {
                    nextNode1 = e1.nextElement();
                } else {
                    nextNode1 = null;
                }
                return next;
            }
        } 

        // collect the remaining nodes from whichever set has a residue
    
        if (nextNode1!=null) {
            NodeInfo next = nextNode1;
            if (e1.hasMoreElements()) {
                nextNode1 = e1.nextElement();
            } else {
                nextNode1 = null;
            }
            return next;
        }
        if (nextNode2!=null) {
            NodeInfo next = nextNode2;
            if (e2.hasMoreElements()) {
                nextNode2 = e2.nextElement();
            } else {
                nextNode2 = null;
            }
            return next;
        }
        return 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. 
//