/*
    * DavMail POP/IMAP/SMTP/CalDav/LDAP Exchange Gateway
    * Copyright (C) 2010  Mickael Guessant
    *
    * This program is free software; you can redistribute it and/or
    * modify it under the terms of the GNU General Public License
    * as published by the Free Software Foundation; either version 2
    * of the License, or (at your option) any later version.
    *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
   */
  
  package davmail.util;
  
  import davmail.Settings;
  
  import javax.crypto.Cipher;
  import javax.crypto.SecretKey;
  import javax.crypto.SecretKeyFactory;
  import javax.crypto.spec.IvParameterSpec;
  import javax.crypto.spec.PBEKeySpec;
  import javax.crypto.spec.PBEParameterSpec;
  import java.io.IOException;
  import java.nio.charset.StandardCharsets;
  import java.security.NoSuchAlgorithmException;
  import java.security.spec.InvalidKeySpecException;
  
  /**
   * Encrypt string using user password.
   * Simple implementation based on AES
   */
  public class StringEncryptor {
      static final String ALGO = "PBEWithHmacSHA256AndAES_128";
      static final String DEFAULT_FINGERPRINT = "davmailgateway!&";
  
      private final String password;
  
      public StringEncryptor(String password) {
          this.password = password;
      }
  
      public String encryptString(String value) throws IOException {
          try {
              byte[] plaintext = value.getBytes(StandardCharsets.UTF_8);
  
              // Encrypt
              Cipher enc = Cipher.getInstance(ALGO);
              enc.init(Cipher.ENCRYPT_MODE, getSecretKey(), getPBEParameterSpec());
              byte[] encrypted = enc.doFinal(plaintext);
              return "{AES}" + IOUtil.encodeBase64AsString(encrypted);
  
          } catch (Exception e) {
              throw new IOException(e);
          }
      }
  
      public String decryptString(String value) throws IOException {
          if (value != null && value.startsWith("{AES}")) {
              try {
                  byte[] encrypted = IOUtil.decodeBase64(value.substring(5));
  
                  Cipher dec = Cipher.getInstance(ALGO);
                  dec.init(Cipher.DECRYPT_MODE, getSecretKey(), getPBEParameterSpec());
                  byte[] decrypted = dec.doFinal(encrypted);
                  return new String(decrypted, StandardCharsets.UTF_8);
  
              } catch (Exception e) {
                  throw new IOException(e);
              }
          } else {
              return value;
          }
      }
  
      private SecretKey getSecretKey() throws InvalidKeySpecException, NoSuchAlgorithmException {
          PBEKeySpec keySpec = new PBEKeySpec(password.toCharArray());
  
          SecretKeyFactory kf = SecretKeyFactory.getInstance(ALGO);
          return kf.generateSecret(keySpec);
      }
  
      private PBEParameterSpec getPBEParameterSpec() {
          byte[] bytes = Settings.getProperty("davmail.oauth.fingerprint", DEFAULT_FINGERPRINT).getBytes(StandardCharsets.UTF_8);
          return new PBEParameterSpec(bytes, 10000, new IvParameterSpec(bytes));
      }
  }