package client.net.sf.saxon.ce.expr;
import client.net.sf.saxon.ce.om.Item;
import client.net.sf.saxon.ce.om.NodeInfo;
import client.net.sf.saxon.ce.om.SequenceIterator;
import client.net.sf.saxon.ce.expr.sort.NodeOrderComparer;
import client.net.sf.saxon.ce.trans.XPathException;
/**
* An enumeration representing a nodeset that is teh difference of two other NodeSets.
* There is an "except" operator in XPath 2.0 to create such an expression.
*/
public class DifferenceEnumeration implements SequenceIterator {
private SequenceIterator p1;
private SequenceIterator p2;
private NodeInfo nextNode1 = null;
private NodeInfo nextNode2 = null;
private NodeOrderComparer comparer;
//private NodeInfo nextNode = null;
private NodeInfo current = null;
private int position = 0;
/**
* Form an enumeration of the difference of two nodesets, that is, the nodes
* that are in p1 and that are not in p2.
* @param p1 the first operand, with nodes delivered in document order
* @param p2 the second operand, with nodes delivered in document order
* @param comparer the comparer
*/
public DifferenceEnumeration(SequenceIterator p1, SequenceIterator p2,
NodeOrderComparer comparer) throws XPathException {
this.p1 = p1;
this.p2 = p2;
this.comparer = comparer;
// move to the first node in each input nodeset
nextNode1 = next(p1);
nextNode2 = next(p2);
}
/**
* Get the next item from one of the input sequences,
* checking that it is a node.
* @param iter the iterator from which the next node is to be read
* @return the node that was read, or null if the stream is exhausted
*/
private NodeInfo next(SequenceIterator iter) throws XPathException {
return (NodeInfo)iter.next();
// rely on type-checking to prevent a ClassCastException
}
public Item next() throws XPathException {
// main merge loop: if the node in p1 has a lower key value that that in p2, return it;
// if they are equal, advance both nodesets; if p1 is higher, advance p2.
while (true) {
if (nextNode1 == null) {
current = null;
position = -1;
return null;
}
if (nextNode2 == null) {
// second node-set is exhausted; return the next node from the first node-set
return deliver();
}
int c = comparer.compare(nextNode1, nextNode2);
if (c<0) { // p1 is lower
return deliver();
} else if (c>0) { // p1 is higher
nextNode2 = next(p2);
if (nextNode2 == null) {
return deliver();
}
} else { // keys are equal
nextNode2 = next(p2);
nextNode1 = next(p1);
}
}
}
/**
* Deliver the next node from the first node-set, advancing the iterator to
* look-ahead for the next item, and setting the current and position variables.
* @return the next node from the first node-set
* @throws XPathException
*/
private NodeInfo deliver() throws XPathException {
current = nextNode1;
nextNode1 = next(p1);
position++;
return current;
}
public Item current() {
return current;
}
public int position() {
return position;
}
public SequenceIterator getAnother() throws XPathException {
return new DifferenceEnumeration(p1.getAnother(), p2.getAnother(), comparer);
}
/**
* Get properties of this iterator, as a bit-significant integer.
*
* @return the properties of this iterator. This will be some combination of
* properties such as {@link SequenceIterator#GROUNDED}, {@link SequenceIterator#LAST_POSITION_FINDER},
* and {@link SequenceIterator#LOOKAHEAD}. It is always
* acceptable to return the value zero, indicating that there are no known special properties.
* It is acceptable for the properties of the iterator to change depending on its state.
*/
public int getProperties() {
return 0;
}
}
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is “Incompatible With Secondary Licenses”, as defined by the Mozilla Public License, v. 2.0.