/*
* Copyright 2003-2014 JetBrains s.r.o.
*
* Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.jetbrains.mps.util;
import org.jetbrains.annotations.NotNull;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
/**
* Ensures elements coming from iterator are unique. Doesn't support element removal.
* Iterator elements are required for fulfil the contract of <code>hashCode()</code> and <code>equals()</code> methods
* @author Artem Tikhomirov
*/
public class UniqueIterator<T> implements Iterable<T>, Iterator<T> {
private final Set<T> myReportedElements;
private final Iterable<T> myDelegate;
private Iterator<T> myIterator;
private T myNextElement;
public UniqueIterator(@NotNull Iterable<T> delegate) {
myDelegate = delegate;
myReportedElements = new HashSet<T>();
}
@Override
public Iterator<T> iterator() {
myReportedElements.clear();
myIterator = myDelegate.iterator();
myNextElement = filterNext();
return this;
}
@Override
public boolean hasNext() {
return myNextElement != null;
}
@Override
public T next() {
assert hasNext();
final T rv = myNextElement;
myReportedElements.add(rv);
myNextElement = filterNext();
return rv;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
// find first unreported element
private T filterNext() {
while (myIterator.hasNext()) {
final T next = myIterator.next();
if (!myReportedElements.contains(next)) {
return next;
}
}
return null;
}
}