/*******************************************************************************
 * Copyright (c) 2001-2005 Sasa Markovic and Ciaran Treanor.
 * Copyright (c) 2011 The OpenNMS Group, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *******************************************************************************/

package org.jrobin.core;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * JRobin backend which is used to store RRD data to ordinary disk files
 * by using fast java.nio.* package. This is the default backend engine since JRobin 1.4.0.
 */
public class RrdNioByteBufferBackend extends RrdFileBackend {

	private ByteBuffer m_byteBuffer;

	private FileChannel m_ch;

	private static final ReadWriteLock m_readWritelock = new ReentrantReadWriteLock();
	private static final Lock m_readLock = m_readWritelock.readLock();
	private static final Lock m_writeLock = m_readWritelock.writeLock();

	/**
	 * Creates RrdFileBackend object for the given file path, backed by java.nio.* classes.
	 *
	 * @param path	   Path to a file
	 * @param readOnly   True, if file should be open in a read-only mode. False otherwise
	 * @throws IOException Thrown in case of I/O error
	 */
	protected RrdNioByteBufferBackend(final String path, final boolean readOnly) throws IOException, IllegalStateException {
		super(path, readOnly);

		if (file != null) {
			m_ch = file.getChannel();
			m_byteBuffer = ByteBuffer.allocate((int) m_ch.size());
			m_ch.read(m_byteBuffer, 0);
		} else {
			throw new IllegalStateException("File in base class is null.");
		}
	}

	/**
	 * Sets length of the underlying RRD file. This method is called only once, immediately
	 * after a new RRD file gets created.
	 *
	 * @param newLength Length of the RRD file
	 * @throws IOException Thrown in case of I/O error.
	 */
	@Override
	protected void setLength(final long newLength) throws IOException {
	    m_writeLock.lock();
	    try {
			super.setLength(newLength);
			m_ch = file.getChannel();
			m_byteBuffer = ByteBuffer.allocate((int) newLength);
			m_ch.read(m_byteBuffer, 0);
			m_byteBuffer.position(0);
		} finally {
		    m_writeLock.unlock();
		}
	}

	/**
	 * Writes bytes to the underlying RRD file on the disk
	 *
	 * @param offset Starting file offset
	 * @param b	  Bytes to be written.
	 */
	@Override
	protected void write(final long offset, final byte[] b) {
	    m_writeLock.lock();
	    try {
            m_byteBuffer.position((int) offset);
            m_byteBuffer.put(b);
	    } finally {
	        m_writeLock.unlock();
	    }
	}

	/**
	 * Reads a number of bytes from the RRD file on the disk
	 *
	 * @param offset Starting file offset
	 * @param b	  Buffer which receives bytes read from the file.
	 */
	@Override
	protected void read(final long offset, final byte[] b) {
	    m_readLock.lock();
	    try {
            m_byteBuffer.position((int) offset);
            m_byteBuffer.get(b);
	    } finally {
	        m_readLock.unlock();
	    }
	}

	/**
	 * Closes the underlying RRD file.
	 *
	 * @throws IOException Thrown in case of I/O error
	 */
	public void close() throws IOException {
	    m_writeLock.lock();
	    try {
			m_byteBuffer.position(0);

			if (!isReadOnly()) m_ch.write(m_byteBuffer, 0);
			//just calling close here because the super calls close
			//on the File object and Java calls close on the channel
			super.close();
		} finally {
		    m_writeLock.unlock();
		}
	}

}