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 *  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,
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 *  KIND, either express or implied.  See the License for the
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package org.apache.cayenne.crypto.transformer.bytes;

import java.security.Key;
import java.security.SecureRandom;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

import javax.crypto.Cipher;

import org.apache.cayenne.crypto.cipher.CipherFactory;
import org.apache.cayenne.crypto.key.KeySource;

/**
 * @since 4.0
 */
class CbcBytesTransformerFactory implements BytesTransformerFactory {

    private CipherFactory cipherFactory;
    private Key key;
    private Header encryptionHeader;
    private int blockSize;
    private KeySource keySource;
    private Queue<SecureRandom> randoms;

    CbcBytesTransformerFactory(CipherFactory cipherFactory, KeySource keySource, Header encryptionHeader) {

        this.randoms = new ConcurrentLinkedQueue<>();
        this.keySource = keySource;

        this.cipherFactory = cipherFactory;
        this.blockSize = cipherFactory.blockSize();
        this.encryptionHeader = encryptionHeader;

        String keyName = keySource.getDefaultKeyAlias();
        this.key = keySource.getKey(keyName);
    }

    protected byte[] generateSeedIv() {

        byte[] iv = new byte[blockSize];

        // the idea of a queue of SecureRandoms for concurrency is taken from
        // Tomcat's SessionIdGenerator. Also some code...

        SecureRandom random = randoms.poll();
        if (random == null) {
            random = createSecureRandom();
        }

        random.nextBytes(iv);
        randoms.add(random);

        return iv;
    }

    /**
     * Create a new random number generator instance we should use for
     * generating session identifiers.
     */
    private SecureRandom createSecureRandom() {

        // TODO: allow to customize provider?
        SecureRandom result = new SecureRandom();

        // Force seeding to take place
        result.nextInt();
        return result;
    }

    @Override
    public BytesEncryptor encryptor() {
        Cipher cipher = cipherFactory.cipher();
        BytesEncryptor delegate = new CbcEncryptor(cipher, key, generateSeedIv());

        if (encryptionHeader.isCompressed()) {
            delegate = new GzipEncryptor(delegate);
        }
        if (encryptionHeader.haveHMAC()) {
            delegate = new HmacEncryptor(delegate, encryptionHeader, key);
        }

        return new HeaderEncryptor(delegate, encryptionHeader);
    }

    @Override
    public BytesDecryptor decryptor() {
        Cipher cipher = cipherFactory.cipher();
        BytesDecryptor cbcDecryptor = new CbcDecryptor(cipher);
        BytesDecryptor gzipDecryptor = new GzipDecryptor(cbcDecryptor);
        return new HeaderDecryptor(cbcDecryptor, gzipDecryptor, keySource);
    }

}