/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.flink.runtime.operators.util;

import java.io.IOException;

import org.apache.flink.runtime.memory.MemoryAllocationException;

/**
 * Interface describing the methods that have to be implemented by local strategies for the CoGroup Pact.
 * 
 * @param <T1> The generic type of the first input's data type.
 * @param <T2> The generic type of the second input's data type.
 */
public interface CoGroupTaskIterator<T1, T2> {
	
	/**
	 * General-purpose open method.
	 * 
	 * @throws IOException
	 * @throws MemoryAllocationException
	 * @throws InterruptedException 
	 */
	void open() throws IOException, MemoryAllocationException, InterruptedException;

	/**
	 * General-purpose close method.
	 */
	void close();

	/**
	 * Moves the internal pointer to the next key (if present). Returns true if the operation was
	 * successful or false if no more keys are present.
	 * <p>
	 * The key is not necessarily shared by both inputs. In that case an empty iterator is 
	 * returned by getValues1() or getValues2().
	 * 
	 * @return true on success, false if no more keys are present
	 * @throws IOException
	 */
	boolean next() throws IOException;

	/**
	 * Returns an iterable over the left input values for the current key.
	 * 
	 * @return an iterable over the left input values for the current key.
	 */
	Iterable<T1> getValues1();

	/**
	 * Returns an iterable over the left input values for the current key.
	 * 
	 * @return an iterable over the left input values for the current key.
	 */
	Iterable<T2> getValues2();
}