package net.sf.saxon.expr;
import net.sf.saxon.om.GroundedIterator;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.om.ValueRepresentation;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.SequenceExtent;
import net.sf.saxon.value.Value;
import java.util.Iterator;
/**
* A TailExpression represents a FilterExpression of the form EXPR[position() > n]
* Here n is usually 2, but we allow other values
*/
public class TailExpression extends Expression {
Expression base;
int start; // 1-based offset of first item from base expression
// to be included
/**
* Construct a TailExpression, representing a filter expression of the form
* $base[position() >= $start]
* @param base the expression to be filtered
* @param start the position (1-based) of the first item to be included
*/
public TailExpression(Expression base, int start) {
this.base = base;
this.start = start;
adoptChildExpression(base);
}
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
base = visitor.typeCheck(base, contextItemType);
return this;
}
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
base = visitor.optimize(base, contextItemType);
if (base instanceof Literal) {
ValueRepresentation value =
SequenceExtent.makeSequenceExtent(iterate(visitor.getStaticContext().makeEarlyEvaluationContext()));
return Literal.makeLiteral(Value.asValue(value));
}
return this;
}
public Expression promote(PromotionOffer offer, Expression parent) throws XPathException {
Expression exp = offer.accept(parent, this);
if (exp != null) {
return exp;
} else {
if (offer.action != PromotionOffer.UNORDERED) {
base = doPromotion(this, base, offer);
}
return this;
}
}
public int computeSpecialProperties() {
return base.getSpecialProperties();
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
public Expression copy() {
return new TailExpression(base.copy(), start);
}
public ItemType getItemType(TypeHierarchy th) {
return base.getItemType(th);
}
public int computeCardinality() {
return base.getCardinality() | StaticProperty.ALLOWS_ZERO;
}
public Iterator<Expression> iterateSubExpressions() {
return new MonoIterator(base);
}
/**
* Replace one subexpression by a replacement subexpression
* @param original the original subexpression
* @param replacement the replacement subexpression
* @return true if the original subexpression is found
*/
public boolean replaceSubExpression(Expression original, Expression replacement) {
boolean found = false;
if (base == original) {
base = replacement;
found = true;
}
return found;
}
/**
* Get the base expression (of which this expression returns the tail part of the value)
* @return the base expression
*/
public Expression getBaseExpression() {
return base;
}
/**
* Get the start offset
* @return the one-based start offset (returns 2 if all but the first item is being selected)
*/
public int getStart() {
return start;
}
/**
* Compare two expressions to see if they are equal
* @param other the other expression
* @return true if the expressions are equivalent
*/
public boolean equals(Object other) {
return other instanceof TailExpression &&
base.equals(((TailExpression)other).base) &&
start == ((TailExpression)other).start;
}
public int hashCode() {
return base.hashCode();
}
public SequenceIterator iterate(XPathContext context) throws XPathException {
SequenceIterator baseIter = base.iterate(context);
if ((baseIter.getProperties() & SequenceIterator.GROUNDED) != 0) {
return new ValueTailIterator(((GroundedIterator)baseIter).materialize(), start - 1);
} else {
return TailIterator.make(baseIter, start);
}
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter destination) {
destination.startElement("tail");
destination.emitAttribute("start", start+"");
base.explain(destination);
destination.endElement();
}
}
//
// 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.
//