/*
 * Copyright 2006-2013 the original author or authors.
 *
 * 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.springframework.batch.core;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

/**
 * Default implementation of the {@link JobKeyGenerator} interface.
 * This implementation provides a single hash value based on the JobParameters
 * passed in.  Only identifying parameters (per {@link JobParameter#isIdentifying()})
 * are used in the calculation of the key.
 *
 * @author Michael Minella
 * @since 2.2
 */
public class DefaultJobKeyGenerator implements JobKeyGenerator<JobParameters> {

	/**
	 * Generates the job key to be used based on the {@link JobParameters} instance
	 * provided.
	 */
	@Override
	public String generateKey(JobParameters source) {

		Map<String, JobParameter> props = source.getParameters();
		StringBuilder stringBuffer = new StringBuilder();
		List<String> keys = new ArrayList<String>(props.keySet());
		Collections.sort(keys);
		for (String key : keys) {
			JobParameter jobParameter = props.get(key);
			if(jobParameter.isIdentifying()) {
				String value = jobParameter.getValue()==null ? "" : jobParameter.toString();
				stringBuffer.append(key).append("=").append(value).append(";");
			}
		}

		MessageDigest digest;
		try {
			digest = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalStateException(
					"MD5 algorithm not available.  Fatal (should be in the JDK).");
		}

		try {
			byte[] bytes = digest.digest(stringBuffer.toString().getBytes(
					"UTF-8"));
			return String.format("%032x", new BigInteger(1, bytes));
		} catch (UnsupportedEncodingException e) {
			throw new IllegalStateException(
					"UTF-8 encoding not available.  Fatal (should be in the JDK).");
		}
	}
}