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/*
 * Copyright (c) 2014-2018 Enrico M. Crisostomo
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice, this
 *     list of conditions and the following disclaimer.
 *
 *   * Redistributions in binary form must reproduce the above copyright notice,
 *     this list of conditions and the following disclaimer in the documentation
 *     and/or other materials provided with the distribution.
 *
 *   * Neither the name of the author nor the names of its
 *     contributors may be used to endorse or promote products derived from
 *     this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package io.github.sinri.keel.helper.authenticator.googleauth;

import io.github.sinri.keel.helper.authenticator.googleauth.sync.GoogleAuthenticator;

import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.util.concurrent.atomic.AtomicInteger;

public class ReseedingSecureRandom {
    private static final int MAX_OPERATIONS = 1_000_000;
    private final String provider;
    private final String algorithm;
    private final AtomicInteger count = new AtomicInteger(0);
    private volatile SecureRandom secureRandom;

    public ReseedingSecureRandom() {
        this.algorithm = null;
        this.provider = null;

        buildSecureRandom();
    }

    public ReseedingSecureRandom(String algorithm) {
        if (algorithm == null) {
            throw new IllegalArgumentException("Algorithm cannot be null.");
        }

        this.algorithm = algorithm;
        this.provider = null;

        buildSecureRandom();
    }

    public ReseedingSecureRandom(String algorithm, String provider) {
        if (algorithm == null) {
            throw new IllegalArgumentException("Algorithm cannot be null.");
        }

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

        this.algorithm = algorithm;
        this.provider = provider;

        buildSecureRandom();
    }

    private void buildSecureRandom() {
        try {
            if (this.algorithm == null && this.provider == null) {
                this.secureRandom = new SecureRandom();
            } else if (this.provider == null) {
                this.secureRandom = SecureRandom.getInstance(this.algorithm);
            } else {
                this.secureRandom = SecureRandom.getInstance(this.algorithm, this.provider);
            }
        } catch (NoSuchAlgorithmException e) {
            throw new GoogleAuthenticatorException(
                    String.format(
                            "Could not initialise SecureRandom with the specified algorithm: %s. " +
                                    "Another provider can be chosen setting the %s system property.",
                            this.algorithm,
                            GoogleAuthenticator.RNG_ALGORITHM
                    ), e
            );
        } catch (NoSuchProviderException e) {
            throw new GoogleAuthenticatorException(
                    String.format(
                            "Could not initialise SecureRandom with the specified provider: %s. " +
                                    "Another provider can be chosen setting the %s system property.",
                            this.provider,
                            GoogleAuthenticator.RNG_ALGORITHM_PROVIDER
                    ), e
            );
        }
    }

    public void nextBytes(byte[] bytes) {
        if (count.incrementAndGet() > MAX_OPERATIONS) {
            synchronized (this) {
                if (count.get() > MAX_OPERATIONS) {
                    buildSecureRandom();
                    count.set(0);
                }
            }
        }

        this.secureRandom.nextBytes(bytes);
    }
}