/*
 * 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.resettable;

import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
import org.apache.flink.runtime.memory.MemoryAllocationException;
import org.apache.flink.runtime.memory.MemoryManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

/**
 * Implementation of an iterator that fetches a block of data into main memory and offers resettable
 * access to the data in that block.
 * 
 */
public class ReusingBlockResettableIterator<T> extends NonReusingBlockResettableIterator<T> {

	public static final Logger LOG = LoggerFactory.getLogger(ReusingBlockResettableIterator.class);

	private final T reuseElement;

	// ------------------------------------------------------------------------

	public ReusingBlockResettableIterator(MemoryManager memoryManager, Iterator<T> input,
			TypeSerializer<T> serializer, int numPages,
			AbstractInvokable ownerTask)
	throws MemoryAllocationException
	{
		this(memoryManager, serializer, numPages, ownerTask);
		this.input = input;
	}

	public ReusingBlockResettableIterator(MemoryManager memoryManager, TypeSerializer<T>
			serializer, int numPages, AbstractInvokable ownerTask)
	throws MemoryAllocationException
	{
		super(memoryManager, serializer, numPages, ownerTask);
		
		this.reuseElement = serializer.createInstance();
	}
	
	// ------------------------------------------------------------------------
	
	@Override
	public boolean hasNext() {
		try {
			if (this.nextElement == null) {
				if (this.readPhase) {
					// read phase, get next element from buffer
					T tmp = getNextRecord(this.reuseElement);
					if (tmp != null) {
						this.nextElement = tmp;
						return true;
					} else {
						return false;
					}
				} else {
					if (this.input.hasNext()) {
						final T next = this.input.next();
						if (writeNextRecord(next)) {
							this.nextElement = next;
							return true;
						} else {
							this.leftOverElement = next;
							return false;
						}
					} else {
						this.noMoreBlocks = true;
						return false;
					}
				}
			} else {
				return true;
			}
		} catch (IOException ioex) {
			throw new RuntimeException("Error (de)serializing record in block resettable iterator.", ioex);
		}
	}
}