package net.sf.saxon.expr;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.NodeInfo;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.trace.Location;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.*;
/**
* A FilterIterator filters an input sequence using a filter expression. Note that a FilterIterator
* is not used where the filter is a constant number (PositionFilter is used for this purpose instead),
* so this class does no optimizations for numeric predicates.
*/
public class FilterIterator implements SequenceIterator {
protected SequenceIterator base;
protected Expression filter;
private int position = 0;
private Item current = null;
protected XPathContext filterContext;
/**
* Constructor
* @param base An iteration of the items to be filtered
* @param filter The expression defining the filter predicate
* @param context The context in which the expression is being evaluated
*/
public FilterIterator(SequenceIterator base, Expression filter,
XPathContext context) {
this.base = base;
this.filter = filter;
filterContext = context.newMinorContext();
filterContext.setCurrentIterator(base);
filterContext.setOriginatingConstructType(Location.FILTER_EXPRESSION);
}
/**
* Get the next item if there is one
*/
public Item next() throws XPathException {
current = getNextMatchingItem();
if (current == null) {
position = -1;
} else {
position++;
}
return current;
}
/**
* Get the next item in the base sequence that matches the filter predicate
* if there is such an item, or null if not.
* @return the next item that matches the predicate
*/
protected Item getNextMatchingItem() throws XPathException {
while (true) {
Item next = base.next();
if (next == null) {
return null;
}
if (matches()) {
return next;
}
}
}
/**
* Determine whether the context item matches the filter predicate
* @return true if the context item matches
*/
protected boolean matches() throws XPathException {
// This code is carefully designed to avoid reading more items from the
// iteration of the filter expression than are absolutely essential.
// The code is almost identical to the code in ExpressionTool#effectiveBooleanValue
// except for the handling of a numeric result
SequenceIterator iterator = filter.iterate(filterContext);
Item first = iterator.next();
if (first == null) {
return false;
}
if (first instanceof NodeInfo) {
return true;
} else {
if (first instanceof BooleanValue) {
if (iterator.next() != null) {
ExpressionTool.ebvError("sequence of two or more items starting with a boolean");
}
return ((BooleanValue)first).getBooleanValue();
} else if (first instanceof StringValue) {
if (iterator.next() != null) {
ExpressionTool.ebvError("sequence of two or more items starting with a string");
}
return (first.getStringValueCS().length()!=0);
} else if (first instanceof Int64Value) {
if (iterator.next() != null) {
ExpressionTool.ebvError("sequence of two or more items starting with a numeric value");
}
return ((Int64Value)first).longValue() == base.position();
} else if (first instanceof NumericValue) {
if (iterator.next() != null) {
ExpressionTool.ebvError("sequence of two or more items starting with a numeric value");
}
return ((NumericValue)first).compareTo(base.position()) == 0;
} else {
ExpressionTool.ebvError("sequence starting with an atomic value other than a boolean, number, or string");
return false;
}
}
}
public Item current() {
return current;
}
public int position() {
return position;
}
public void close() {
base.close();
}
/**
* Get another iterator to return the same nodes
*/
public SequenceIterator getAnother() throws XPathException {
return new FilterIterator(base.getAnother(), filter,
filterContext);
}
/**
* 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;
}
/**
* Subclass to handle the common special case where it is statically known
* that the filter cannot return a numeric value
*/
public static final class NonNumeric extends FilterIterator {
/**
* Create a FilterIterator for the situation where it is known that the filter
* expression will never evaluate to a number value. For this case we can simply
* use the effective boolean value of the predicate
* @param base iterator over the sequence to be filtered
* @param filter the filter expression
* @param context the current context (for evaluating the filter expression as a whole).
* A new context will be created to evaluate the predicate.
*/
public NonNumeric(SequenceIterator base, Expression filter,
XPathContext context) {
super(base, filter, context);
}
/**
* Determine whether the context item matches the filter predicate
*/
protected boolean matches() throws XPathException {
return filter.effectiveBooleanValue(filterContext);
}
/**
* Get another iterator to return the same nodes
*/
public SequenceIterator getAnother() throws XPathException {
return new FilterIterator.NonNumeric(base.getAnother(), filter, filterContext);
}
}
}
//
// 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 H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//