/**
 * Copyright (c) 2017 The JNanoID Authors
 * Copyright (c) 2017 Aventrix LLC
 * Copyright (c) 2017 Andrey Sitnik
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package net.gepafin.tendermanagement.model.util;

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


public final class NanoIdUtils {

    /**
     * <code>NanoIdUtils</code> instances should NOT be constructed in standard programming.
     * Instead, the class should be used as <code>NanoIdUtils.randomNanoId();</code>.
     */
    private NanoIdUtils() {
        //Do Nothing
    }

    /**
     * The default random number generator used by this class.
     * Creates cryptographically strong NanoId Strings.
     */
    public static final SecureRandom DEFAULT_NUMBER_GENERATOR = new SecureRandom();

    /**
     * The default alphabet used by this class.
     * Creates url-friendly NanoId Strings using 64 unique symbols.
     */
    public static final char[] DEFAULT_ALPHABET =
            "_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();

    /**
     * The default size used by this class.
     * Creates NanoId Strings with slightly more unique values than UUID v4.
     */
    public static final int DEFAULT_SIZE = 21;

    /**
     * Static factory to retrieve a url-friendly, pseudo randomly generated, NanoId String.
     *
     * The generated NanoId String will have 21 symbols.
     *
     * The NanoId String is generated using a cryptographically strong pseudo random number
     * generator.
     *
     * @return A randomly generated NanoId String.
     */
    public static String randomNanoId() {
        return randomNanoId(DEFAULT_NUMBER_GENERATOR, DEFAULT_ALPHABET, DEFAULT_SIZE);
    }

    /**
     * Static factory to retrieve a NanoId String.
     *
     * The string is generated using the given random number generator.
     *
     * @param random   The random number generator.
     * @param alphabet The symbols used in the NanoId String.
     * @param size     The number of symbols in the NanoId String.
     * @return A randomly generated NanoId String.
     */
    public static String randomNanoId(final Random random, final char[] alphabet, final int size) {

        if (random == null) {
            throw new IllegalArgumentException("random cannot be null.");
        }

        if (alphabet == null) {
            throw new IllegalArgumentException("alphabet cannot be null.");
        }

        if (alphabet.length == 0 || alphabet.length >= 256) {
            throw new IllegalArgumentException("alphabet must contain between 1 and 255 symbols.");
        }

        if (size <= 0) {
            throw new IllegalArgumentException("size must be greater than zero.");
        }
        
        double value = (double) (alphabet.length - 1);

        final int mask = (2 << (int) Math.floor(Math.log(value) / Math.log(2))) - 1;
        final int step = (int) Math.ceil(1.6 * mask * size / alphabet.length);

        final StringBuilder idBuilder = new StringBuilder();

        while (true) {

            final byte[] bytes = new byte[step];
            random.nextBytes(bytes);

            for (int i = 0; i < step; i++) {

                final int alphabetIndex = bytes[i] & mask;

                if (alphabetIndex < alphabet.length) {
                    idBuilder.append(alphabet[alphabetIndex]);
                    if (idBuilder.length() == size) {
                        return idBuilder.toString();
                    }
                }

            }

        }

    }
}