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Provides common utility functions
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/*
 * Copyright (c) CQSE GmbH
 *
 * 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 org.conqat.lib.commons.digest;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import org.conqat.lib.commons.error.EnvironmentError;
import org.conqat.lib.commons.string.StringUtils;

/**
 * Utility functions for creation of digests.
 *
 * @deprecated this class uses MD5, which is cryptographically weak and relatively slow to
 *             calculate. Please only use this for legacy code, where migrating to a new hash
 *             function is hard (e.g. contained in backups, etc.) and use the faster XXhash (see
 *             class XXHashUtils) instead.
 */
@Deprecated
public class Digester {

	/** Number of bytes in an MD5 sum. */
	public static final int MD5_BYTES = 16;

	/**
	 * MD5 Digesters used organized by thread. This is used to avoid recreation of digesters, while
	 * keeping the code thread safe (i.e. each thread has its own instance).
	 */
	private static final ThreadLocal MD5_DIGESTERS = new ThreadLocal() {

		@Override
		protected MessageDigest initialValue() {
			return getMD5();
		}
	};

	/**
	 * Computes an MD5 hash for a string. The hash is always 32 characters long and only uses characters
	 * from [0-9A-F].
	 *
	 * @deprecated this method uses MD5, which is cryptographically weak and relatively slow to
	 *             calculate. Please only use this for legacy code, where migrating to a new hash
	 *             function is hard (e.g. contained in backups, etc.) and use the faster XXhash (see
	 *             class XXHashUtils) instead.
	 */
	@Deprecated
	public static String createMD5Digest(String base) {
		return createMD5Digest(base.getBytes());
	}

	/**
	 * Computes an MD5 hash for a byte array. The hash is always 32 characters long and only uses
	 * characters from [0-9A-F].
	 * 
	 * @deprecated this method uses MD5, which is cryptographically weak and relatively slow to
	 *             calculate. Please only use this for legacy code, where migrating to a new hash
	 *             function is hard (e.g. contained in backups, etc.) and use the faster XXhash (see
	 *             class XXHashUtils) instead.
	 */
	@Deprecated
	public static String createMD5Digest(byte[] data) {
		MessageDigest digester = MD5_DIGESTERS.get();
		digester.reset();
		return StringUtils.encodeAsHex(digester.digest(data));
	}

	/**
	 * Computes an MD5 hash for a byte array and returns the binary hash (i.e. no string conversion).
	 * 
	 * @deprecated this method uses MD5, which is cryptographically weak and relatively slow to
	 *             calculate. Please only use this for legacy code, where migrating to a new hash
	 *             function is hard (e.g. contained in backups, etc.) and use the faster XXhash (see
	 *             class XXHashUtils) instead.
	 */
	@Deprecated
	public static byte[] createBinaryMD5Digest(byte[] data) {
		MessageDigest digester = MD5_DIGESTERS.get();
		digester.reset();
		return digester.digest(data);
	}

	/**
	 * Returns MD5 digester or throws an AssertionError if the digester could not be located.
	 * 
	 * @deprecated this method uses MD5, which is cryptographically weak and relatively slow to
	 *             calculate. Please only use this for legacy code, where migrating to a new hash
	 *             function is hard (e.g. contained in backups, etc.) and use the faster XXhash (see
	 *             class XXHashUtils) instead.
	 */
	@Deprecated
	public static MessageDigest getMD5() {
		try {
			return MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			throw new EnvironmentError("No MD5 algorithm found. Please check your JRE installation", e);
		}
	}
}