package client.net.sf.saxon.ce.functions;
import client.net.sf.saxon.ce.expr.*;
import client.net.sf.saxon.ce.om.Item;
import client.net.sf.saxon.ce.om.SequenceIterator;
import client.net.sf.saxon.ce.trans.XPathException;
import client.net.sf.saxon.ce.type.ItemType;
import client.net.sf.saxon.ce.type.TypeHierarchy;
import client.net.sf.saxon.ce.value.AtomicValue;
import client.net.sf.saxon.ce.value.NumericValue;
import client.net.sf.saxon.ce.value.IntegerValue;
/**
* The XPath 2.0 remove() function
*/
public class Remove extends SystemFunction {
public Remove newInstance() {
return new Remove();
}
/**
* Simplify. Recognize remove(seq, 1) as a TailExpression.
* @param visitor an expression visitor
*/
public Expression simplify(ExpressionVisitor visitor) throws XPathException {
Expression exp = super.simplify(visitor);
if (exp instanceof Remove) {
return ((Remove)exp).simplifyAsTailExpression();
} else {
return exp;
}
}
/**
* Simplify. Recognize remove(seq, 1) as a TailExpression. This
* is worth doing because tail expressions used in a recursive call
* are handled specially.
*/
private Expression simplifyAsTailExpression() {
if (Literal.isAtomic(argument[1])) {
try {
long value = ((IntegerValue)((Literal)argument[1]).getValue()).intValue();
if (value <= 0) {
return argument[0];
} else if (value == 1) {
Expression t = SystemFunction.makeSystemFunction("subsequence",
new Expression[]{argument[0], new Literal(IntegerValue.TWO)});
ExpressionTool.copyLocationInfo(this, t);
return t;
}
} catch (XPathException err) {
return this;
}
}
return this;
}
/**
* Perform optimisation of an expression and its subexpressions.
* <p/>
* <p>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.</p>
*
* @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 client.net.sf.saxon.ce.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws client.net.sf.saxon.ce.trans.XPathException
* if an error is discovered during this phase
* (typically a type error)
*/
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
Expression e = super.optimize(visitor, contextItemType);
if (e == this) {
return simplifyAsTailExpression();
}
return e;
}
/**
* Determine the data type of the items in the sequence
* @return the type of the input sequence
* @param th the type hierarchy cache
*/
public ItemType getItemType(TypeHierarchy th) {
return argument[0].getItemType(th);
}
/**
* Evaluate the function to return an iteration of selected nodes.
*/
public SequenceIterator iterate(XPathContext context) throws XPathException {
SequenceIterator seq = argument[0].iterate(context);
AtomicValue n0 = (AtomicValue)argument[1].evaluateItem(context);
NumericValue n = (NumericValue)n0;
int pos = (int)n.intValue();
if (pos < 1) {
return seq;
}
return new RemoveIterator(seq, pos);
}
/**
* An implementation of SequenceIterator that returns all items except the one
* at a specified position.
*/
public static class RemoveIterator implements SequenceIterator, LastPositionFinder {
SequenceIterator base;
int removePosition;
int position = 0;
Item current = null;
public RemoveIterator(SequenceIterator base, int removePosition) {
this.base = base;
this.removePosition = removePosition;
}
public Item next() throws XPathException {
current = base.next();
if (current != null && base.position() == removePosition) {
current = base.next();
}
if (current == null) {
position = -1;
} else {
position++;
}
return current;
}
public Item current() {
return current;
}
public int position() {
return position;
}
/**
* Get the last position (that is, the number of items in the sequence). This method is
* non-destructive: it does not change the state of the iterator.
* The result is undefined if the next() method of the iterator has already returned null.
*/
public int getLastPosition() throws XPathException {
if (base instanceof LastPositionFinder) {
int x = ((LastPositionFinder)base).getLastPosition();
if (removePosition >= 1 && removePosition <= x) {
return x - 1;
} else {
return x;
}
} else {
// This shouldn't happen, because this iterator only has the LAST_POSITION_FINDER property
// if the base iterator has the LAST_POSITION_FINDER property
throw new AssertionError("base of removeIterator is not a LastPositionFinder");
}
}
public SequenceIterator getAnother() throws XPathException {
return new RemoveIterator( base.getAnother(),
removePosition);
}
/**
* 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 base.getProperties() & LAST_POSITION_FINDER;
}
}
}
// 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.