/*
    * $Id: CharsetToolkit.java 4112 2006-10-13 13:21:25Z blackdrag $
    *
    * Copyright 2003 (C) Guillaume Laforge. All Rights Reserved.
    *
    * Redistribution and use of this software and associated documentation
    * ("Software"), with or without modification, are permitted provided that the
    * following conditions are met:
    *  1. Redistributions of source code must retain copyright statements and
   * notices. Redistributions must also contain a copy of this document.
   *  2. Redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution.
   *  3. The name "groovy" must not be used to endorse or promote products
   * derived from this Software without prior written permission of The Codehaus.
   * For written permission, please contact info@codehaus.org.
   *  4. Products derived from this Software may not be called "groovy" nor may
   * "groovy" appear in their names without prior written permission of The
   * Codehaus. "groovy" is a registered trademark of The Codehaus.
   *  5. Due credit should be given to The Codehaus - http://groovy.codehaus.org/
   *
   * THIS SOFTWARE IS PROVIDED BY THE CODEHAUS AND CONTRIBUTORS ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE CODEHAUS OR ITS CONTRIBUTORS BE LIABLE FOR
   * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
   * DAMAGE.
   *
   */
  
  package groovy.util;
  
  import java.io.*;
  import java.nio.charset.Charset;
  import java.util.*;
  
  /***
   * <p>Utility class to guess the encoding of a given text file.</p>
   *
   * <p>Unicode files encoded in UTF-16 (low or big endian) or UTF-8 files
   * with a Byte Order Marker are correctly discovered. For UTF-8 files with no BOM, if the buffer
   * is wide enough, the charset should also be discovered.</p>
   *
   * <p>A byte buffer of 4KB is usually sufficient to be able to guess the encoding.</p>
   *
   * <p>Usage:</p>
   * <pre>
   * // guess the encoding
   * Charset guessedCharset = CharsetToolkit.guessEncoding(file, 4096);
   *
   * // create a reader with the correct charset
   * CharsetToolkit toolkit = new CharsetToolkit(file);
   * BufferedReader reader = toolkit.getReader();
   *
   * // read the file content
   * String line;
   * while ((line = br.readLine())!= null)
   * {
   *     System.out.println(line);
   * }
   * </pre>
   *
   * @author Guillaume Laforge
   */
  public class CharsetToolkit {
      private byte[] buffer;
      private Charset defaultCharset;
      private Charset charset;
      private boolean enforce8Bit = true;
      private File file;
  
      /***
       * Constructor of the <code>CharsetToolkit</code> utility class.
       *
       * @param file of which we want to know the encoding.
       */
      public CharsetToolkit(File file) throws IOException {
          this.file = file;
          this.defaultCharset = getDefaultSystemCharset();
          this.charset = null;
          InputStream input = new FileInputStream(file);
          try {
              byte[] bytes = new byte[4096];
              int bytesRead = input.read(bytes);
              if (bytesRead == -1) {
                  this.buffer = new byte[0];
              }
              else if (bytesRead < 4096) {
                  byte[] bytesToGuess = new byte[bytesRead];
                  System.arraycopy(bytes, 0, bytesToGuess, 0, bytesRead);
                  this.buffer = bytesToGuess;
              }
              else {
                  this.buffer = bytes;
             }
         } finally {
             try {input.close();} catch (IOException e){}
         }
     }
 
     /***
      * Defines the default <code>Charset</code> used in case the buffer represents
      * an 8-bit <code>Charset</code>.
      *
      * @param defaultCharset the default <code>Charset</code> to be returned by <code>guessEncoding()</code>
      * if an 8-bit <code>Charset</code> is encountered.
      */
     public void setDefaultCharset(Charset defaultCharset) {
         if (defaultCharset != null)
             this.defaultCharset = defaultCharset;
         else
             this.defaultCharset = getDefaultSystemCharset();
     }
 
     public Charset getCharset() {
         if (this.charset == null)
             this.charset = guessEncoding();
         return charset;
     }
 
     /***
      * If US-ASCII is recognized, enforce to return the default encoding, rather than US-ASCII.
      * It might be a file without any special character in the range 128-255, but that may be or become
      * a file encoded with the default <code>charset</code> rather than US-ASCII.
      *
      * @param enforce a boolean specifying the use or not of US-ASCII.
      */
     public void setEnforce8Bit(boolean enforce) {
         this.enforce8Bit = enforce;
     }
 
     /***
      * Gets the enforce8Bit flag, in case we do not want to ever get a US-ASCII encoding.
      *
      * @return a boolean representing the flag of use of US-ASCII.
      */
     public boolean getEnforce8Bit() {
         return this.enforce8Bit;
     }
 
     /***
      * Retrieves the default Charset
      */
     public Charset getDefaultCharset() {
         return defaultCharset;
     }
 
     /***
      * <p>Guess the encoding of the provided buffer.</p>
      * If Byte Order Markers are encountered at the beginning of the buffer, we immidiately
      * return the charset implied by this BOM. Otherwise, the file would not be a human
      * readable text file.</p>
      *
      * <p>If there is no BOM, this method tries to discern whether the file is UTF-8 or not.
      * If it is not UTF-8, we assume the encoding is the default system encoding
      * (of course, it might be any 8-bit charset, but usually, an 8-bit charset is the default one).</p>
      *
      * <p>It is possible to discern UTF-8 thanks to the pattern of characters with a multi-byte sequence.</p>
      * <pre>
      * UCS-4 range (hex.)        UTF-8 octet sequence (binary)
      * 0000 0000-0000 007F       0xxxxxxx
      * 0000 0080-0000 07FF       110xxxxx 10xxxxxx
      * 0000 0800-0000 FFFF       1110xxxx 10xxxxxx 10xxxxxx
      * 0001 0000-001F FFFF       11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
      * 0020 0000-03FF FFFF       111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
      * 0400 0000-7FFF FFFF       1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
      * </pre>
      * <p>With UTF-8, 0xFE and 0xFF never appear.</p>
      *
      * @return the Charset recognized.
      */
     private Charset guessEncoding() {
         // if the file has a Byte Order Marker, we can assume the file is in UTF-xx
         // otherwise, the file would not be human readable
         if (hasUTF8Bom())
             return Charset.forName("UTF-8");
         if (hasUTF16LEBom())
             return Charset.forName("UTF-16LE");
         if (hasUTF16BEBom())
             return Charset.forName("UTF-16BE");
 
         // if a byte has its most significant bit set, the file is in UTF-8 or in the default encoding
         // otherwise, the file is in US-ASCII
         boolean highOrderBit = false;
 
         // if the file is in UTF-8, high order bytes must have a certain value, in order to be valid
         // if it's not the case, we can assume the encoding is the default encoding of the system
         boolean validU8Char = true;
 
         // TODO the buffer is not read up to the end, but up to length - 6
 
         int length = buffer.length;
         int i = 0;
         while (i < length - 6) {
             byte b0 = buffer[i];
             byte b1 = buffer[i + 1];
             byte b2 = buffer[i + 2];
             byte b3 = buffer[i + 3];
             byte b4 = buffer[i + 4];
             byte b5 = buffer[i + 5];
             if (b0 < 0) {
                 // a high order bit was encountered, thus the encoding is not US-ASCII
                 // it may be either an 8-bit encoding or UTF-8
                 highOrderBit = true;
                 // a two-bytes sequence was encoutered
                 if (isTwoBytesSequence(b0)) {
                     // there must be one continuation byte of the form 10xxxxxx,
                     // otherwise the following characteris is not a valid UTF-8 construct
                     if (!isContinuationChar(b1))
                         validU8Char = false;
                     else
                         i++;
                 }
                 // a three-bytes sequence was encoutered
                 else if (isThreeBytesSequence(b0)) {
                     // there must be two continuation bytes of the form 10xxxxxx,
                     // otherwise the following characteris is not a valid UTF-8 construct
                     if (!(isContinuationChar(b1) && isContinuationChar(b2)))
                         validU8Char = false;
                     else
                         i += 2;
                 }
                 // a four-bytes sequence was encoutered
                 else if (isFourBytesSequence(b0)) {
                     // there must be three continuation bytes of the form 10xxxxxx,
                     // otherwise the following characteris is not a valid UTF-8 construct
                     if (!(isContinuationChar(b1) && isContinuationChar(b2) && isContinuationChar(b3)))
                         validU8Char = false;
                     else
                         i += 3;
                 }
                 // a five-bytes sequence was encoutered
                 else if (isFiveBytesSequence(b0)) {
                     // there must be four continuation bytes of the form 10xxxxxx,
                     // otherwise the following characteris is not a valid UTF-8 construct
                     if (!(isContinuationChar(b1)
                         && isContinuationChar(b2)
                         && isContinuationChar(b3)
                         && isContinuationChar(b4)))
                         validU8Char = false;
                     else
                         i += 4;
                 }
                 // a six-bytes sequence was encoutered
                 else if (isSixBytesSequence(b0)) {
                     // there must be five continuation bytes of the form 10xxxxxx,
                     // otherwise the following characteris is not a valid UTF-8 construct
                     if (!(isContinuationChar(b1)
                         && isContinuationChar(b2)
                         && isContinuationChar(b3)
                         && isContinuationChar(b4)
                         && isContinuationChar(b5)))
                         validU8Char = false;
                     else
                         i += 5;
                 }
                 else
                     validU8Char = false;
             }
             if (!validU8Char)
                 break;
             i++;
         }
         // if no byte with an high order bit set, the encoding is US-ASCII
         // (it might have been UTF-7, but this encoding is usually internally used only by mail systems)
         if (!highOrderBit) {
             // returns the default charset rather than US-ASCII if the enforce8Bit flag is set.
             if (this.enforce8Bit)
                 return this.defaultCharset;
             else
                 return Charset.forName("US-ASCII");
         }
         // if no invalid UTF-8 were encountered, we can assume the encoding is UTF-8,
         // otherwise the file would not be human readable
         if (validU8Char)
             return Charset.forName("UTF-8");
         // finally, if it's not UTF-8 nor US-ASCII, let's assume the encoding is the default encoding
         return this.defaultCharset;
     }
 
     /***
      * If the byte has the form 10xxxxx, then it's a continuation byte of a multiple byte character;
      *
      * @param b a byte.
      * @return true if it's a continuation char.
      */
     private static boolean isContinuationChar(byte b) {
         return -128 <= b && b <= -65;
     }
 
     /***
      * If the byte has the form 110xxxx, then it's the first byte of a two-bytes sequence character.
      *
      * @param b a byte.
      * @return true if it's the first byte of a two-bytes sequence.
      */
     private static boolean isTwoBytesSequence(byte b) {
         return -64 <= b && b <= -33;
     }
 
     /***
      * If the byte has the form 1110xxx, then it's the first byte of a three-bytes sequence character.
      *
      * @param b a byte.
      * @return true if it's the first byte of a three-bytes sequence.
      */
     private static boolean isThreeBytesSequence(byte b) {
         return -32 <= b && b <= -17;
     }
 
     /***
      * If the byte has the form 11110xx, then it's the first byte of a four-bytes sequence character.
      *
      * @param b a byte.
      * @return true if it's the first byte of a four-bytes sequence.
      */
     private static boolean isFourBytesSequence(byte b) {
         return -16 <= b && b <= -9;
     }
 
     /***
      * If the byte has the form 11110xx, then it's the first byte of a five-bytes sequence character.
      *
      * @param b a byte.
      * @return true if it's the first byte of a five-bytes sequence.
      */
     private static boolean isFiveBytesSequence(byte b) {
         return -8 <= b && b <= -5;
     }
 
     /***
      * If the byte has the form 1110xxx, then it's the first byte of a six-bytes sequence character.
      *
      * @param b a byte.
      * @return true if it's the first byte of a six-bytes sequence.
      */
     private static boolean isSixBytesSequence(byte b) {
         return -4 <= b && b <= -3;
     }
 
     /***
      * Retrieve the default charset of the system.
      *
      * @return the default <code>Charset</code>.
      */
     public static Charset getDefaultSystemCharset() {
         return Charset.forName(System.getProperty("file.encoding"));
     }
 
     /***
      * Has a Byte Order Marker for UTF-8 (Used by Microsoft's Notepad and other editors).
      *
      * @return true if the buffer has a BOM for UTF8.
      */
     public boolean hasUTF8Bom() {
         if (buffer.length >= 3)
             return (buffer[0] == -17 && buffer[1] == -69 && buffer[2] == -65);
         else
             return false;
     }
 
     /***
      * Has a Byte Order Marker for UTF-16 Low Endian
      * (ucs-2le, ucs-4le, and ucs-16le).
      *
      * @return true if the buffer has a BOM for UTF-16 Low Endian.
      */
     public boolean hasUTF16LEBom() {
         if (buffer.length >= 2)
             return (buffer[0] == -1 && buffer[1] == -2);
         else
             return false;
     }
 
     /***
      * Has a Byte Order Marker for UTF-16 Big Endian
      * (utf-16 and ucs-2).
      *
      * @return true if the buffer has a BOM for UTF-16 Big Endian.
      */
     public boolean hasUTF16BEBom() {
         if (buffer.length >= 2)
             return (buffer[0] == -2 && buffer[1] == -1);
         else
             return false;
     }
 
     /***
      * Gets a <code>BufferedReader</code> (indeed a <code>LineNumberReader</code>) from the <code>File</code>
      * specified in the constructor of <code>CharsetToolkit</code> using the charset discovered by the
      * method <code>guessEncoding()</code>.
      *
      * @return a <code>BufferedReader</code>
      * @throws FileNotFoundException if the file is not found.
      */
     public BufferedReader getReader() throws FileNotFoundException {
         LineNumberReader reader = new LineNumberReader(new InputStreamReader(new FileInputStream(file), getCharset()));
         if (hasUTF8Bom() || hasUTF16LEBom() || hasUTF16BEBom()) {
             try {
                 reader.read();
             }
             catch (IOException e) {
                 // should never happen, as a file with no content
                 // but with a BOM has at least one char
             }
         }
         return reader;
     }
 
     /***
      * Retrieves all the available <code>Charset</code>s on the platform,
      * among which the default <code>charset</code>.
      *
      * @return an array of <code>Charset</code>s.
      */
     public static Charset[] getAvailableCharsets() {
         Collection collection = Charset.availableCharsets().values();
         return (Charset[]) collection.toArray(new Charset[collection.size()]);
     }
 }