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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// 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.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr;
import net.sf.saxon.om.*;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.ArrayIterator;
import net.sf.saxon.tree.iter.GroundedIterator;
import net.sf.saxon.tree.iter.LookaheadIterator;
/**
* A SubsequenceIterator selects a subsequence of a sequence
*/
public class SubsequenceIterator implements SequenceIterator, LastPositionFinder, LookaheadIterator {
private final SequenceIterator base;
private int basePosition = 0;
private final int min;
private final int max;
/*@Nullable*/ private Item nextItem = null;
/**
* Private Constructor: use the factory method instead!
*
* @param base An iteration of the items to be filtered
* @param min The position of the first item to be included (1-based)
* @param max The position of the last item to be included (1-based)
* @throws XPathException if a dynamic error occurs
*/
private SubsequenceIterator(SequenceIterator base, int min, int max) throws XPathException {
this.base = base;
this.min = min;
if (min < 1) {
min = 1;
}
this.max = max;
if (max < min) {
nextItem = null;
return;
}
int i = 1;
while (i++ <= min) {
nextItem = base.next();
basePosition++;
if (nextItem == null) {
break;
}
}
}
/**
* Static factory method. Creates a SubsequenceIterator, unless for example the base Iterator is an
* ArrayIterator, in which case it optimizes by creating a new ArrayIterator directly over the
* underlying array. This optimization is important when doing recursion over a node-set using
* repeated calls of $nodes[position()>1]
*
* @param base An iteration of the items to be filtered
* @param min The position of the first item to be included (base 1)
* @param max The position of the last item to be included (base 1)
* @return an iterator over the requested subsequence
* @throws XPathException if a dynamic error occurs
*/
public static SequenceIterator make(SequenceIterator base, int min, int max) throws XPathException {
if (base instanceof ArrayIterator) {
return ((ArrayIterator) base).makeSliceIterator(min, max);
} else if (max == Integer.MAX_VALUE) {
return TailIterator.make(base, min);
} else if (base instanceof GroundedIterator && ((GroundedIterator)base).isActuallyGrounded() && min > 4) {
GroundedValue value = SequenceTool.toGroundedValue(base);
value = value.subsequence(min - 1, max - min + 1);
return value.iterate();
} else {
return new SubsequenceIterator(base, min, max);
}
}
@Override
public boolean supportsHasNext() {
return true;
}
/**
* Test whether there are any more items available in the sequence
*/
@Override
public boolean hasNext() {
return nextItem != null;
}
/**
* Get the next item if there is one
*/
@Override
public Item next() {
if (nextItem == null) {
return null;
}
Item current = nextItem;
if (basePosition < max) {
nextItem = base.next();
basePosition++;
} else {
nextItem = null;
base.close();
}
return current;
}
@Override
public void close() {
base.close();
}
@Override
public void discharge() {
base.discharge();
}
/**
* Ask whether this iterator supports use of the {@link #getLength()} method. This
* method should always be called before calling {@link #getLength()}, because an iterator
* that implements this interface may support use of {@link #getLength()} in some situations
* and not in others
*
* @return true if the {@link #getLength()} method can be called to determine the length
* of the underlying sequence.
*/
@Override
public boolean supportsGetLength() {
return SequenceTool.supportsGetLength(base);
}
/**
* Get the last position (that is, the number of items in the sequence).
*/
@Override
public int getLength() {
int lastBase = SequenceTool.getLength(base);
int z = Math.min(lastBase, max);
return Math.max(z - min + 1, 0);
}
}