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/*******************************************************************************
* Copyright (c) 2009, 2010 Cloudsmith Inc. and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Cloudsmith Inc. - initial API and implementation
*******************************************************************************/
package org.eclipse.equinox.internal.p2.metadata.expression;
import java.util.*;
import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
/**
* A collection filter that limits the number of entries in the collection
*/
final class Limit extends Binary {
/**
* An iterator that stops iterating after a given number of iterations.
*/
static final class CountingIterator<T> implements Iterator<T> {
private final Iterator<? extends T> innerIterator;
private int counter;
public CountingIterator(Iterator<? extends T> iterator, int count) {
this.innerIterator = iterator;
this.counter = count;
}
public boolean hasNext() {
return counter > 0 && innerIterator.hasNext();
}
public T next() {
if (counter > 0) {
--counter;
return innerIterator.next();
}
throw new NoSuchElementException();
}
public void remove() {
innerIterator.remove();
}
}
Limit(Expression operand, Expression param) {
super(operand, param);
}
Limit(Expression operand, int limit) {
this(operand, (Expression) ExpressionFactory.INSTANCE.constant(new Integer(limit)));
}
public Object evaluate(IEvaluationContext context) {
return evaluateAsIterator(context);
}
public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
Object rval = rhs.evaluate(context);
int limit = -1;
if (rval instanceof Integer)
limit = ((Integer) rval).intValue();
if (limit < 0)
throw new IllegalArgumentException("limit expression did not evalutate to a positive integer"); //$NON-NLS-1$
return limit == 0 ? Collections.emptySet().iterator() : new CountingIterator<Object>(lhs.evaluateAsIterator(context), limit);
}
public int getExpressionType() {
return TYPE_LIMIT;
}
public void toString(StringBuffer bld, Variable rootVariable) {
CollectionFilter.appendProlog(bld, rootVariable, lhs, getOperator());
appendOperand(bld, rootVariable, rhs, IExpressionConstants.PRIORITY_COMMA);
bld.append(')');
}
public String getOperator() {
return KEYWORD_LIMIT;
}
public int getPriority() {
return PRIORITY_COLLECTION;
}
}
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