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Add H2 read/write support for file formats such as ESRI shape file
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/**
 * H2GIS is a library that brings spatial support to the H2 Database Engine
 * .
 *
 * H2GIS is distributed under GPL 3 license. It is produced by CNRS
 * .
 *
 * H2GIS is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 *
 * H2GIS 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * H2GIS. If not, see .
 *
 * For more information, please consult: 
 * or contact directly: info_at_h2gis.org
 */
package org.h2gis.drivers.utility;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.FileChannel;

/**
 * Class to write files using nio.
 *
 * @author Fernando Gonzalez Cortes
 */
public final class WriteBufferManager {

	private static final int BUFFER_SIZE = 1024 * 128;

	private FileChannel channel;

	private ByteBuffer buffer;

	/**
	 * Creates a new WriteBufferManager that writes to the specified file
	 * channel
	 *
	 * @param channel
	 * @throws java.io.IOException
	 */
	public WriteBufferManager(FileChannel channel) throws IOException {
		this.channel = channel;
		buffer = ByteBuffer.allocate(BUFFER_SIZE);
	}

	/**
	 * Puts the specified byte at the current position
	 *
	 * @param b
	 * @throws java.io.IOException
	 */
	public void put(byte b) throws IOException {
		prepareToAddBytes(1);
		buffer.put(b);
	}

	/**
	 * Moves the window
	 *
	 * @param numBytes
	 * @throws java.io.IOException
	 */
	private void prepareToAddBytes(int numBytes) throws IOException {
		if (buffer.remaining() < numBytes) {
			buffer.flip();
			channel.write(buffer);

			int bufferCapacity = Math.max(BUFFER_SIZE, numBytes);
			if (bufferCapacity != buffer.capacity()) {
				ByteOrder order = buffer.order();
				buffer = ByteBuffer.allocate(bufferCapacity);
				buffer.order(order);
			} else {
				buffer.clear();
			}
		}
	}

	/**
	 * Puts the specified bytes at the current position
	 *
	 * @param bs
	 * @throws java.io.IOException
	 */
	public void put(byte[] bs) throws IOException {
		prepareToAddBytes(bs.length);
		buffer.put(bs);
	}

	/**
	 * flushes the cached contents into the channel. It is mandatory to call
	 * this method to finish the writing of the channel
	 *
	 * @throws java.io.IOException
	 */
	public void flush() throws IOException {
		buffer.flip();
		channel.write(buffer);
	}

	/**
	 * Specifies the byte order. One of the constants in {@link java.nio.ByteBuffer}
	 *
	 * @param order
	 */
	public void order(ByteOrder order) {
		this.buffer.order(order);
	}

	/**
	 * Puts the specified int at the current position
	 *
	 * @param value
	 * @throws java.io.IOException
	 */
	public void putInt(int value) throws IOException {
		prepareToAddBytes(4);
		buffer.putInt(value);
	}

	/**
	 * Puts the specified double at the current position
	 *
	 * @param d
	 * @throws java.io.IOException
	 */
	public void putDouble(double d) throws IOException {
		prepareToAddBytes(8);
		buffer.putDouble(d);
	}

}