/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file 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, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.vfs2.util;
  
  import java.nio.charset.StandardCharsets;
  
  import javax.crypto.Cipher;
  import javax.crypto.spec.SecretKeySpec;
  
  /**
   * Allows passwords to be encrypted and decrypted.
   * <p>
   * Warning: This uses AES128 with a fixed encryption key. This is only an obfuscation no cryptographic secure
   * protection.
   * </p>
   *
   * @since 2.0
   */
  public class DefaultCryptor implements Cryptor {
      private static final char[] HEX_CHARS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
  
      private static final byte[] KEY_BYTES = {0x41, 0x70, 0x61, 0x63, 0x68, 0x65, 0x43, 0x6F, 0x6D, 0x6D, 0x6F, 0x6E, 0x73, 0x56, 0x46, 0x53};
  
      private static final int INDEX_NOT_FOUND = -1;
  
      private static final int BITS_IN_HALF_BYTE = 4;
  
      private static final char MASK = 0x0f;
  
      /**
       * Constructs a new instance.
       */
      public DefaultCryptor() {
          // empty
      }
  
      /** Decodes Hex-Bytes. */
      private byte[] decode(final String str) {
          final char[] chars = str.toCharArray();
          final int length = chars.length / 2;
          final byte[] decoded = new byte[length];
          if (length * 2 != chars.length) {
              throw new IllegalArgumentException("The given string must have even number of hex chars.");
          }
          int index = 0;
          for (int i = 0; i < length; i++) {
              final int id1 = indexOf(HEX_CHARS, chars[index++]);
              if (id1 == INDEX_NOT_FOUND) {
                  throw new IllegalArgumentException("Character " + chars[index - 1] + " at position " + (index - 1) + " is not a valid hexadecimal character");
              }
              final int id2 = indexOf(HEX_CHARS, chars[index++]);
              if (id2 == INDEX_NOT_FOUND) {
                  throw new IllegalArgumentException("Character " + chars[index - 1] + " at position " + (index - 1) + " is not a valid hexadecimal character");
              }
              decoded[i] = (byte) (id1 << BITS_IN_HALF_BYTE | id2);
          }
          return decoded;
      }
  
      /**
       * Decrypts the password.
       *
       * @param encryptedKey the encrypted password.
       * @return The plain text password.
       * @throws Exception If an error occurs.
       */
      @Override
      public String decrypt(final String encryptedKey) throws Exception {
          final SecretKeySpec key = new SecretKeySpec(KEY_BYTES, "AES");
          final Cipher cipher = Cipher.getInstance("AES");
          cipher.init(Cipher.DECRYPT_MODE, key);
          final byte[] decoded = decode(encryptedKey);
          final byte[] plainText = new byte[cipher.getOutputSize(decoded.length)];
          int ptLength = cipher.update(decoded, 0, decoded.length, plainText, 0);
          ptLength += cipher.doFinal(plainText, ptLength);
          return new String(plainText, StandardCharsets.UTF_8).substring(0, ptLength);
      }
  
      /** Hex-encode bytes. */
      private String encode(final byte[] bytes) {
          final StringBuilder builder = new StringBuilder();
  
          for (final byte b : bytes) {
              builder.append(HEX_CHARS[b >> BITS_IN_HALF_BYTE & MASK]);
              builder.append(HEX_CHARS[b & MASK]);
         }
         return builder.toString();
     }
 
     /**
      * Encrypt the plain text password.
      * <p>
      * Warning: This uses AES128 with a fixed encryption key. This is only an obfuscation no cryptographic secure
      * protection.
      *
      * @param plainKey The password.
      * @return The encrypted password String.
      * @throws Exception If an error occurs.
      */
     @Override
     public String encrypt(final String plainKey) throws Exception {
         final byte[] input = plainKey.getBytes(StandardCharsets.UTF_8);
         final SecretKeySpec key = new SecretKeySpec(KEY_BYTES, "AES");
 
         final Cipher cipher = Cipher.getInstance("AES");
 
         // encryption pass
         cipher.init(Cipher.ENCRYPT_MODE, key);
 
         final byte[] cipherText = new byte[cipher.getOutputSize(input.length)];
         int ctLength = cipher.update(input, 0, input.length, cipherText, 0);
         ctLength += cipher.doFinal(cipherText, ctLength);
         return encode(cipherText);
     }
 
     private int indexOf(final char[] array, final char valueToFind) {
         if (array == null) {
             return INDEX_NOT_FOUND;
         }
         for (int i = 0; i < array.length; i++) {
             if (valueToFind == array[i]) {
                 return i;
             }
         }
         return INDEX_NOT_FOUND;
     }
 }