content: /*
   * 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.libsodium.jni.encoders;
  
  /**
   * Converts hexadecimal Strings.
   * This class is thread-safe.
   *
   * @version $Id$
   * @since 1.1
   */
  public class Hex implements Encoder {
  
      /**
       * Used to build output as Hex
       */
      private static final char[] DIGITS_LOWER =
              {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
  
      /**
       * Used to build output as Hex
       */
      private static final char[] DIGITS_UPPER =
              {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
  
      /**
       * Converts an array of characters representing hexadecimal values into an array of bytes of those same values. The
       * returned array will be half the length of the passed array, as it takes two characters to represent any given
       * byte. An exception is thrown if the passed char array has an odd number of elements.
       *
       * @param data An array of characters containing hexadecimal digits
       * @return A byte array containing binary data decoded from the supplied char array.
       */
      private static byte[] decodeHex(final char[] data) {
  
          final int len = (data == null) ? 0 : data.length;
  
          if ((len & 0x01) != 0) {
              throw new RuntimeException("Odd number of characters.");
          }
  
          final byte[] out = new byte[len >> 1];
  
          // two characters form the hex value.
          for (int i = 0, j = 0; j < len; i++) {
              int f = toDigit(data[j], j) << 4;
              j++;
              f = f | toDigit(data[j], j);
              j++;
              out[i] = (byte) (f & 0xFF);
          }
  
          return out;
      }
  
      @Override
      public byte[] decode(final String value) {
  
          char[] data = value != null ? value.toCharArray() : new char[0];
          return decodeHex(data);
      }
  
      /**
       * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
       * The returned array will be double the length of the passed array, as it takes two characters to represent any
       * given byte.
       *
       * @param data a byte[] to convert to Hex characters
       * @return A char[] containing hexadecimal characters
       */
      private static char[] encodeHex(final byte[] data) {
          return encodeHex(data, true);
      }
  
      /**
       * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
       * The returned array will be double the length of the passed array, as it takes two characters to represent any
       * given byte.
       *
       * @param data        a byte[] to convert to Hex characters
       * @param toLowerCase {@code true} converts to lowercase, {@code false} to uppercase
       * @return A char[] containing hexadecimal characters
       * @since 1.4
       */
      private static char[] encodeHex(final byte[] data, final boolean toLowerCase) {
          return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
      }
  
      /**
       * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
       * The returned array will be double the length of the passed array, as it takes two characters to represent any
       * given byte.
       *
       * @param data     a byte[] to convert to Hex characters
       * @param toDigits the output alphabet
       * @return A char[] containing hexadecimal characters
       * @since 1.4
       */
      private static char[] encodeHex(final byte[] data, final char[] toDigits) {
          final int l = data.length;
          final char[] out = new char[l << 1];
          // two characters form the hex value.
          for (int i = 0, j = 0; i < l; i++) {
              out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
              out[j++] = toDigits[0x0F & data[i]];
          }
          return out;
      }
  
      /**
       * Converts an array of bytes into a String representing the hexadecimal values of each byte in order. The returned
       * String will be double the length of the passed array, as it takes two characters to represent any given byte.
       *
       * @param data a byte[] to convert to Hex characters
       * @return A String containing hexadecimal characters
       * @since 1.4
       */
      @Override
      public String encode(final byte[] data) {
          return new String(encodeHex(data));
      }
  
      /**
       * Converts a hexadecimal character to an integer.
       *
       * @param ch    A character to convert to an integer digit
       * @param index The index of the character in the source
       * @return An integer
       */
      private static int toDigit(final char ch, final int index) {
          final int digit = Character.digit(ch, 16);
          if (digit == -1) {
              throw new RuntimeException("Illegal hexadecimal character " + ch + " at index " + index);
          }
          return digit;
      }
  
      /**
       * Returns a string representation of the object, which includes the charset name.
       *
       * @return a string representation of the object.
       */
      @Override
      public String toString() {
          return super.toString() + "[charsetName=" + CHARSET + "]";
      }
  }
  