/***********************************************************************************************************************
 *
 * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
 *
 * 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 eu.stratosphere.api.java.operators.translation;

import java.util.Iterator;

import eu.stratosphere.api.java.tuple.Tuple2;

/**
 * An iterator that reads 2-tuples (key value pairs) and returns only the values (second field).
 * The iterator also tracks the keys, as the pairs flow though it.
 */
public class TupleUnwrappingIterator<T, K> implements Iterator<T>, java.io.Serializable {

	private static final long serialVersionUID = 1L;
	
	private K lastKey; 
	private Iterator<Tuple2<K, T>> iterator;
	
	public void set(Iterator<Tuple2<K, T>> iterator) {
		this.iterator = iterator;
	}
	
	public K getLastKey() {
		return lastKey;
	}

	@Override
	public boolean hasNext() {
		return iterator.hasNext();
	}

	@Override
	public T next() {
		Tuple2<K, T> t = iterator.next(); 
		this.lastKey = t.f0;
		return t.f1;
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException();
	}
}