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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.functions;
import net.sf.saxon.expr.Expression;
import net.sf.saxon.expr.LastPositionFinder;
import net.sf.saxon.expr.StaticProperty;
import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.expr.parser.ContextItemStaticInfo;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.om.SequenceTool;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.transpile.CSharpReplaceBody;
import net.sf.saxon.tree.iter.ListIterator;
import net.sf.saxon.tree.iter.ReversibleIterator;
import net.sf.saxon.value.SequenceExtent;
import java.util.List;
/**
* Implement XPath function fn:reverse()
*/
public class Reverse extends SystemFunction {
@Override
public int getSpecialProperties(Expression[] arguments) {
int baseProps = arguments[0].getSpecialProperties();
if ((baseProps & StaticProperty.REVERSE_DOCUMENT_ORDER) != 0) {
return (baseProps &
~StaticProperty.REVERSE_DOCUMENT_ORDER) |
StaticProperty.ORDERED_NODESET;
} else if ((baseProps & StaticProperty.ORDERED_NODESET) != 0) {
return (baseProps &
~StaticProperty.ORDERED_NODESET) |
StaticProperty.REVERSE_DOCUMENT_ORDER;
} else {
return baseProps;
}
}
// /**
// * Perform optimisation of an expression and its subexpressions.
// * This method is called after all references to functions and variables have been resolved
// * to the declaration of the function or variable, and after all type checking has been done.
// *
// * @param visitor an expression visitor
// * @param contextItemType the static type of "." at the point where this expression is invoked.
// * The parameter is set to null if it is known statically that the context item will be undefined.
// * If the type of the context item is not known statically, the argument is set to
// * {@link net.sf.saxon.type.Type#ITEM_TYPE}
// * @return the original expression, rewritten if appropriate to optimize execution
// * @throws net.sf.saxon.trans.XPathException
// * if an error is discovered during this phase
// * (typically a type error)
// */
// @Override
// public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException {
// Expression e2 = super.optimize(visitor, contextItemType);
// if (e2 != this) {
// ExpressionTool.copyLocationInfo(this, e2);
// return e2;
// }
// if (!Cardinality.allowsMany(getArg(0).getCardinality())) {
// return getArg(0);
// }
// return this;
// }
public static SequenceIterator getReverseIterator(SequenceIterator forwards) {
if (forwards instanceof ReversibleIterator) {
return ((ReversibleIterator) forwards).getReverseIterator();
} else {
return SequenceExtent.from(forwards).reverseIterate();
}
}
@Override
public Sequence call(XPathContext context, Sequence[] arguments) throws XPathException {
SequenceExtent input;
if (arguments[0] instanceof SequenceExtent) {
input = (SequenceExtent)arguments[0];
} else {
input = SequenceExtent.from(arguments[0].iterate());
}
return SequenceTool.toLazySequence(input.reverseIterate());
}
/**
* Allow the function to create an optimized call based on the values of the actual arguments
*
* @param visitor the expression visitor
* @param contextInfo information about the context item
* @param arguments the supplied arguments to the function call. Note: modifying the contents
* of this array should not be attempted, it is likely to have no effect.
* @return either a function call on this function, or an expression that delivers
* the same result, or null indicating that no optimization has taken place
* @throws XPathException if an error is detected
*/
@Override
public Expression makeOptimizedFunctionCall(
ExpressionVisitor visitor, ContextItemStaticInfo contextInfo, Expression... arguments)
throws XPathException {
// When reverse() has only a zero-or-one argument, there is no need to reverse
// This often occurs in reverse-axis steps
if (arguments[0].getCardinality() == StaticProperty.ALLOWS_ZERO_OR_ONE) {
return arguments[0];
}
return super.makeOptimizedFunctionCall(visitor, contextInfo, arguments);
}
@CSharpReplaceBody(code="return new Saxon.Impl.Helpers.ReverseListIterator(list);")
public static SequenceIterator reverseIterator(List list) {
return new ReverseListIterator(list);
}
@Override
public String getStreamerName() {
return "Reverse";
}
public static class ReverseListIterator implements SequenceIterator, LastPositionFinder, ReversibleIterator {
private final java.util.ListIterator listIter;
private final List list;
public ReverseListIterator(List list) {
this.list = list;
this.listIter = list.listIterator(list.size());
}
@Override
public boolean supportsGetLength() {
return true;
}
/**
* Get the last position (that is, the number of items in the sequence).
* @return the number of items in the sequence
*/
@Override
public int getLength() {
return list.size();
}
/**
* Get the next item in the sequence.
*
* @return the next Item. If there are no more items, return null.
*/
@Override
public Item next() {
return listIter.hasPrevious() ? listIter.previous() : null;
}
/**
* Get a new SequenceIterator that returns the same items in reverse order.
* If this SequenceIterator is an AxisIterator, then the returned SequenceIterator
* must also be an AxisIterator.
*
* @return an iterator over the items in reverse order
*/
@Override
public SequenceIterator getReverseIterator() {
return new ListIterator.Of<>(list);
}
}
}