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/***********************************************************************************************************************
 * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
 *
 * Licensed 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 eu.stratosphere.nephele.services.iomanager;

import java.io.File;
import java.util.Random;

import eu.stratosphere.util.StringUtils;

/**
 * A Channel represents a collection of files that belong logically to the same resource. An example is a collection of
 * files that contain sorted runs of data from the same stream, that will later on be merged together.
 * 
 */
public final class Channel
{
	private static final int RANDOM_BYTES_LENGTH = 16;

	/**
	 * An ID identifying an underlying fileChannel.
	 * 
	 */
	public static class ID
	{
		private final String path;
		
		private final int threadNum;

		protected ID(final String path, final int threadNum) {
			this.path = path;
			this.threadNum = threadNum;
		}

		protected ID(final String basePath, final int threadNum, final Random random)
		{
			this.path = basePath + File.separator + randomString(random) + ".channel";
			this.threadNum = threadNum;
		}

		/**
		 * Returns the path to the underlying temporary file.
		 * 
		 * @return
		 */
		public String getPath() {
			return path;
		}
		
		int getThreadNum() {
			return this.threadNum;
		}

		public String toString() {
			return path;
		}
	}

	public static final class Enumerator
	{
		private static final String FORMAT = "%s%s%s.%06d.channel";

		private final String[] paths;
		
		private final String namePrefix;

		private int counter;

		protected Enumerator(final String[] basePaths, final Random random)
		{
			this.paths = basePaths;
			this.namePrefix = randomString(random);
			this.counter = 0;
		}

		public ID next()
		{
			final int threadNum = counter % paths.length;
			return new ID(String.format(FORMAT, this.paths[threadNum], File.separator, namePrefix, (counter++)), threadNum);
		}
	}

	/**
	 * Creates a random byte sequence using the provided {@code random} generator and returns its hex representation.
	 * 
	 * @param random
	 *        The random number generator to be used.
	 * @return A hex representation of the generated byte sequence
	 */
	private static final String randomString(final Random random) {
		final byte[] bytes = new byte[RANDOM_BYTES_LENGTH];
		random.nextBytes(bytes);
		return StringUtils.byteToHexString(bytes);
	}
}