/*
 * Copyright [2020] [MaxKey of copyright http://www.maxkey.top]
 * 
 * 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.maxkey.authz.cas.endpoint.ticket.generator;

import java.security.SecureRandom;

/**
 * Implementation of the RandomStringGenerator that allows you to define the
 * length of the random part.
 *
 * @author Scott Battaglia

 * @since 3.0.0
 */
public class DefaultRandomStringGenerator implements RandomStringGenerator {

    /** The default maximum length. */
    public static final int DEFAULT_MAX_RANDOM_LENGTH = 35;

    /** The array of printable characters to be used in our random string. */
    private static final char[] PRINTABLE_CHARACTERS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ012345679".toCharArray();

    /** An instance of secure random to ensure randomness is secure. */
    private SecureRandom randomizer = new SecureRandom();

    /** The maximum length the random string can be. */
    private int maximumRandomLength;

    /**
     * Instantiates a new default random string generator
     * with length set to {@link #DEFAULT_MAX_RANDOM_LENGTH}.
     */
    public DefaultRandomStringGenerator() {
        this.maximumRandomLength = DEFAULT_MAX_RANDOM_LENGTH;
    }

    /**
     * Instantiates a new default random string generator.
     *
     * @param maxRandomLength the max random length
     */
    public DefaultRandomStringGenerator(final int maxRandomLength) {
        this.maximumRandomLength = maxRandomLength;
    }

    @Override
    public int getMinLength() {
        return this.maximumRandomLength;
    }

    @Override
    public int getMaxLength() {
        return this.maximumRandomLength;
    }

    @Override
    public String getNewString() {
        final byte[] random = getNewStringAsBytes();

        return convertBytesToString(random);
    }

    @Override
    public byte[] getNewStringAsBytes() {
        final byte[] random = new byte[this.maximumRandomLength];
        this.randomizer.nextBytes(random);
        return random;
    }

    /**
     * Convert bytes to string, taking into account {@link #PRINTABLE_CHARACTERS}.
     *
     * @param random the random
     * @return the string
     */
    private String convertBytesToString(final byte[] random) {
        final char[] output = new char[random.length];
        for (int i = 0; i < random.length; i++) {
            final int index = Math.abs(random[i] % PRINTABLE_CHARACTERS.length);
            output[i] = PRINTABLE_CHARACTERS[index];
        }

        return new String(output);
    }
}
