content: /*
   * Copyright 2002-2019 Drew Noakes and contributors
   *
   *    Licensed 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
   *
   *        https://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.
   *
   * More information about this project is available at:
   *
   *    https://drewnoakes.com/code/exif/
   *    https://github.com/drewnoakes/metadata-extractor
   */
  package com.drew.metadata.iptc;
  
  import com.drew.lang.annotations.NotNull;
  import com.drew.lang.annotations.Nullable;
  
  import java.nio.ByteBuffer;
  import java.nio.charset.CharacterCodingException;
  import java.nio.charset.Charset;
  import java.nio.charset.CharsetDecoder;
  
  public final class Iso2022Converter
  {
      private static final String ISO_8859_1 = "ISO-8859-1";
      private static final String UTF_8 = "UTF-8";
  
      private static final byte LATIN_CAPITAL_A = 0x41;
      private static final int DOT = 0xe280a2;
      private static final byte LATIN_CAPITAL_G = 0x47;
      private static final byte PERCENT_SIGN = 0x25;
      private static final byte MINUS_SIGN = 0x2D;
      private static final byte DOT_SIGN = 0x2E;
      private static final byte ESC = 0x1B;
  
      /**
       * Converts the given ISO2022 char set to a Java charset name.
       * A reference of valid charsets can be found here: https://nozer0.github.io/en/technology/system/character-encoding/#ISO/IEC%202022
       *
       * @param bytes string data encoded using ISO2022
       * @return the Java charset name as a string, or <code>null</code> if the conversion was not possible
       */
      @Nullable
      public static String convertISO2022CharsetToJavaCharset(@NotNull final byte[] bytes)
      {
          if (bytes.length > 2 && bytes[0] == ESC && bytes[1] == PERCENT_SIGN && bytes[2] == LATIN_CAPITAL_G)
              return UTF_8;
  
          if (bytes.length > 2 && bytes[0] == ESC && bytes[1] == DOT_SIGN && bytes[2] == LATIN_CAPITAL_A)
              return ISO_8859_1;
  
          if (bytes.length > 3 && bytes[0] == ESC && (bytes[3] & 0xFF | ((bytes[2] & 0xFF) << 8) | ((bytes[1] & 0xFF) << 16)) == DOT && bytes[4] == LATIN_CAPITAL_A)
              return ISO_8859_1;
  
          if (bytes.length > 2 && bytes[0] == ESC && bytes[1] == MINUS_SIGN && bytes[2] == LATIN_CAPITAL_A)
              return ISO_8859_1;
  
          return null;
      }
  
      /**
       * Attempts to guess the {@link Charset} of a string provided as a byte array.
       * <p>
       * Charsets trialled are, in order:
       * <ul>
       *     <li>UTF-8</li>
       *     <li><code>System.getProperty("file.encoding")</code></li>
       *     <li>ISO-8859-1</li>
       * </ul>
       * <p>
       * Its only purpose is to guess the Charset if and only if IPTC tag coded character set is not set. If the
       * encoding is not UTF-8, the tag should be set. Otherwise it is bad practice. This method tries to
       * workaround this issue since some metadata manipulating tools do not prevent such bad practice.
       * <p>
       * About the reliability of this method: The check if some bytes are UTF-8 or not has a very high reliability.
       * The two other checks are less reliable.
       *
       * @param bytes some text as bytes
       * @return the name of the encoding or null if none could be guessed
       */
      @Nullable
      static Charset guessCharSet(@NotNull final byte[] bytes)
      {
          String[] encodings = { UTF_8, System.getProperty("file.encoding"), ISO_8859_1 };
  
          for (String encoding : encodings)
          {
              Charset charset = Charset.forName(encoding);
              CharsetDecoder cs = charset.newDecoder();
  
              try {
                  cs.decode(ByteBuffer.wrap(bytes));
                  return charset;
              } catch (CharacterCodingException e) {
                  // fall through...
              }
          }
  
          // No encodings succeeded. Return null.
          return null;
      }
  
      private Iso2022Converter()
      {}
  }
  