/*
 * 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.iterative.io;

import java.io.EOFException;
import java.io.IOException;
import java.util.Iterator;

import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.runtime.operators.hash.HashPartition;
import org.apache.flink.util.MutableObjectIterator;

/**
 * {@link Iterator} over the build side entries of a {@link HashPartition}
 * 
 * @param <BT>
 */
public class HashPartitionIterator<BT, PT> implements MutableObjectIterator<BT> {

	private final Iterator<HashPartition<BT, PT>> partitions;

	private final TypeSerializer<BT> serializer;

	private HashPartition<BT, PT> currentPartition;

	public HashPartitionIterator(Iterator<HashPartition<BT, PT>> partitions, TypeSerializer<BT> serializer) {
		this.partitions = partitions;
		this.serializer = serializer;
		currentPartition = null;
	}

	@Override
	public BT next(BT reuse) throws IOException {
		if (currentPartition == null) {
			if (!partitions.hasNext()) {
				return null;
			}
			currentPartition = partitions.next();
			currentPartition.setReadPosition(0);
		}

		try {
			reuse = serializer.deserialize(reuse, currentPartition);
		} catch (EOFException e) {
			reuse =  advanceAndRead(reuse);
		}

		return reuse;
	}

	@Override
	public BT next() throws IOException {
		if (currentPartition == null) {
			if (!partitions.hasNext()) {
				return null;
			}
			currentPartition = partitions.next();
			currentPartition.setReadPosition(0);
		}

		try {
			return serializer.deserialize(currentPartition);
		} catch (EOFException e) {
			return advanceAndRead();
		}

	}

	/* jump to the next partition and continue reading from that */
	private BT advanceAndRead(BT reuse) throws IOException {
		if (!partitions.hasNext()) {
			return null;
		}
		currentPartition = partitions.next();
		currentPartition.setReadPosition(0);

		try {
			reuse = serializer.deserialize(reuse, currentPartition);
		} catch (EOFException e) {
			reuse = advanceAndRead(reuse);
		}
		return reuse;
	}

	/* jump to the next partition and continue reading from that */
	private BT advanceAndRead() throws IOException {
		if (!partitions.hasNext()) {
			return null;
		}
		currentPartition = partitions.next();
		currentPartition.setReadPosition(0);

		try {
			return serializer.deserialize(currentPartition);
		} catch (EOFException e) {
			return advanceAndRead();
		}
	}

}