/*
  Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FLOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program 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; version 2
  of the License.

  This program 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 this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA

 */

package com.mysql.fabric;

import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

/**
 * A shard mapping with ranges defined by hashing key values. Lookups work essentially
 * the same as in {@link RangeShardMapping} but strings are compared as opposed to ints.
 */
public class HashShardMapping extends ShardMapping {
	private static class ReverseShardIndexSorter implements Comparator<ShardIndex> {
		public int compare(ShardIndex i1, ShardIndex i2) {
			return i2.getBound().compareTo(i1.getBound());
		}
		// singleton instance
		public static final ReverseShardIndexSorter instance  = new ReverseShardIndexSorter();
	}

	private static final MessageDigest md5Hasher;
	static {
		try {
			md5Hasher = MessageDigest.getInstance("MD5");
		} catch(java.security.NoSuchAlgorithmException ex) {
			throw new ExceptionInInitializerError(ex);
		}
	}

	public HashShardMapping(String mappingId, ShardingType shardingType, String globalGroupName,
							 Set<ShardTable> shardTables, Set<ShardIndex> shardIndices) {
		super(mappingId, shardingType, globalGroupName, shardTables,
			  new TreeSet<ShardIndex>(ReverseShardIndexSorter.instance));
		this.shardIndices.addAll(shardIndices);
	}

	protected ShardIndex getShardIndexForKey(String stringKey) {
		String hashedKey = new BigInteger(/* unsigned/positive */1,
										  md5Hasher.digest(stringKey.getBytes()))
			.toString(16).toUpperCase();

		// pad out to 32 digits
		for (int i = 0; i < (32 - hashedKey.length()); ++i) {
			hashedKey = "0" + hashedKey;
		}

		for (ShardIndex i : this.shardIndices) {
			if (i.getBound().compareTo(hashedKey) <= 0)
				return i;
		}

		// default to the first (highest) bound,
		// implementing wrapping
		return this.shardIndices.iterator().next();
	}
}