/*
 * 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 java.io.EOFException;
import java.io.IOException;
import java.util.ArrayList;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.core.memory.MemorySegment;
import org.apache.flink.runtime.io.disk.RandomAccessInputView;
import org.apache.flink.runtime.io.disk.SimpleCollectingOutputView;
import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
import org.apache.flink.runtime.memory.ListMemorySegmentSource;
import org.apache.flink.runtime.memory.MemoryAllocationException;
import org.apache.flink.runtime.memory.MemoryManager;
import org.apache.flink.runtime.util.MemoryBlockIterator;

/**
 * Base class for iterators that fetch a block of data into main memory and offer resettable
 * access to the data in that block.
 */
abstract class AbstractBlockResettableIterator<T> implements MemoryBlockIterator {
	
	protected static final Logger LOG = LoggerFactory.getLogger(AbstractBlockResettableIterator.class);
	
	// ------------------------------------------------------------------------
	
	protected final RandomAccessInputView readView;
	
	protected final SimpleCollectingOutputView collectingView;
	
	protected final TypeSerializer<T> serializer;
	
	protected int numRecordsInBuffer;
	
	protected int numRecordsReturned;
	
	protected final ArrayList<MemorySegment> emptySegments;
	
	protected final ArrayList<MemorySegment> fullSegments;
	
	private final MemoryManager memoryManager;
	
	protected volatile boolean closed;		// volatile since it may be asynchronously set to abort after current block
	
	// ------------------------------------------------------------------------
	
	protected AbstractBlockResettableIterator(TypeSerializer<T> serializer, MemoryManager memoryManager,
			int numPages, AbstractInvokable ownerTask)
	throws MemoryAllocationException
	{
		if (numPages < 1) {
			throw new IllegalArgumentException("Block Resettable iterator requires at leat one page of memory");
		}
		
		this.memoryManager = memoryManager;
		this.serializer = serializer;
		
		this.emptySegments = new ArrayList<MemorySegment>(numPages);
		this.fullSegments = new ArrayList<MemorySegment>(numPages);
		memoryManager.allocatePages(ownerTask, emptySegments, numPages);
		
		this.collectingView = new SimpleCollectingOutputView(this.fullSegments, 
						new ListMemorySegmentSource(this.emptySegments), memoryManager.getPageSize());
		this.readView = new RandomAccessInputView(this.fullSegments, memoryManager.getPageSize());
		
		if (LOG.isDebugEnabled()) {
			LOG.debug("Iterator initialized using " + numPages + " memory buffers.");
		}
	}
	
	// --------------------------------------------------------------------------------------------

	public void open() {
		if (LOG.isDebugEnabled()) {
			LOG.debug("Block Resettable Iterator opened.");
		}
	}
	

	public void reset() {
		if (this.closed) {
			throw new IllegalStateException("Iterator was closed.");
		}
		
		this.readView.setReadPosition(0);
		this.numRecordsReturned = 0;
	}
	

	@Override
	public boolean nextBlock() throws IOException {
		this.numRecordsInBuffer = 0;
		
		// add the full segments to the empty ones
		for (int i = this.fullSegments.size() - 1; i >= 0; i--) {
			this.emptySegments.add(this.fullSegments.remove(i));
		}
		
		// reset the views
		this.collectingView.reset();
		this.readView.setReadPosition(0);
		return true;
	}
	
	/**
	 * This method closes the iterator and releases all resources. This method works both as a regular
	 * shutdown and as a canceling method. The method may be called multiple times and will not produce
	 * an error.
	 */
	public void close() {
		synchronized (this) {
			if (this.closed) {
				return;
			}
			this.closed = true;
		}
		
		this.numRecordsInBuffer = 0;
		this.numRecordsReturned = 0;
		
		// add the full segments to the empty ones
		for (int i = this.fullSegments.size() - 1; i >= 0; i--) {
			this.emptySegments.add(this.fullSegments.remove(i));
		}
		
		// release the memory segment
		this.memoryManager.release(this.emptySegments);
		this.emptySegments.clear();
		
		if (LOG.isDebugEnabled()) {
			LOG.debug("Block Resettable Iterator closed.");
		}
	}
	
	// --------------------------------------------------------------------------------------------
	
	protected boolean writeNextRecord(T record) throws IOException {
		try {
			this.serializer.serialize(record, this.collectingView);
			this.numRecordsInBuffer++;
			return true;
		} catch (EOFException eofex) {
			return false;
		}
	}
	
	protected T getNextRecord(T reuse) throws IOException {
		if (this.numRecordsReturned < this.numRecordsInBuffer) {
			this.numRecordsReturned++;
			return this.serializer.deserialize(reuse, this.readView);
		} else {
			return null;
		}
	}

	protected T getNextRecord() throws IOException {
		if (this.numRecordsReturned < this.numRecordsInBuffer) {
			this.numRecordsReturned++;
			return this.serializer.deserialize(this.readView);
		} else {
			return null;
		}
	}

}