/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.shardingsphere.db.protocol.mysql.packet.handshake;

import lombok.AccessLevel;
import lombok.Getter;
import lombok.NoArgsConstructor;

import java.security.SecureRandom;
import java.util.Random;

/**
 * Random generator for MySQL.
 */
@NoArgsConstructor(access = AccessLevel.NONE)
public final class MySQLRandomGenerator {
    
    @Getter
    private static final MySQLRandomGenerator INSTANCE = new MySQLRandomGenerator();
    
    private static final byte[] SEED = {
            'a', 'b', 'e', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
    
    private final Random random = new SecureRandom();
    
    /**
     * Generate random bytes.
     *
     * @param length length for generated bytes
     * @return generated bytes
     */
    public byte[] generateRandomBytes(final int length) {
        byte[] result = new byte[length];
        for (int i = 0; i < length; i++) {
            result[i] = SEED[random.nextInt(SEED.length)];
        }
        return result;
    }
}
