/*
    * The contents of this file are subject to the terms of the Common Development and
    * Distribution License (the License). You may not use this file except in compliance with the
    * License.
    *
    * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
    * specific language governing permission and limitations under the License.
    *
    * When distributing Covered Software, include this CDDL Header Notice in each file and include
   * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
   * Header, with the fields enclosed by brackets [] replaced by your own identifying
   * information: "Portions copyright [year] [name of copyright owner]".
   *
   * Copyright 2016 ForgeRock AS.
   */
  
  package org.forgerock.json.jose.jwe.handlers.encryption;
  
  import java.security.Key;
  import java.security.NoSuchAlgorithmException;
  import java.security.SecureRandom;
  
  import org.forgerock.json.jose.exceptions.JweEncryptionException;
  import org.forgerock.json.jose.jwe.EncryptionMethod;
  import org.forgerock.json.jose.jwe.JweEncryption;
  import org.forgerock.util.Reject;
  
  /**
   * Handles the underlying {@link EncryptionMethod}.
   */
  abstract class ContentEncryptionHandler {
      private static final String INITIALISATION_VECTOR_ALGORITHM = "SHA1PRNG";
  
      /**
       * Returns an appropriate content encryption handler for the given encryption method.
       *
       * @param method the encryption method.
       * @return an appropriate handler for the given encryption method.
       */
      static ContentEncryptionHandler getInstance(EncryptionMethod method) {
          Reject.ifNull(method, "EncryptionMethod cannot be null");
          switch (method) {
          case A128CBC_HS256:
          case A192CBC_HS384:
          case A256CBC_HS512:
              return new AESCBCHMACSHA2ContentEncryptionHandler(method);
          case A128GCM:
          case A192GCM:
          case A256GCM:
              return new AESGCMContentEncryptionHandler(method);
          default:
              throw new UnsupportedOperationException("Unsupported encryption method: " + method);
          }
      }
  
      abstract JweEncryption encrypt(Key key, byte[] iv, byte[] plainText, byte[] additionalData);
  
      abstract byte[] decrypt(Key key, byte[] iv, JweEncryption cipherText, byte[] additionalData);
  
      abstract Key generateEncryptionKey();
  
      byte[] generateInitialisationVector() {
          try {
              final int ivByteLength = getIVByteLength();
              SecureRandom randomGen = SecureRandom.getInstance(INITIALISATION_VECTOR_ALGORITHM);
  
              byte[] bytes = new byte[ivByteLength];
              randomGen.nextBytes(bytes);
              return bytes;
          } catch (NoSuchAlgorithmException e) {
              throw new JweEncryptionException("Unsupported Algorithm, " + INITIALISATION_VECTOR_ALGORITHM, e);
          }
      }
  
      int getIVByteLength() {
          return 128 / 8;
      }
  }