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/**
*  This file is part of FNLP (formerly FudanNLP).
*  
*  FNLP is free software: you can redistribute it and/or modify
*  it under the terms of the GNU Lesser General Public License as published by
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*  
*  FNLP 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 Lesser General Public License for more details.
*  
*  You should have received a copy of the GNU General Public License
*  along with FudanNLP.  If not, see .
*  
*  Copyright 2009-2014 www.fnlp.org. All rights reserved. 
*/

package org.fnlp.util;

/**
 version: 1.1 / 2007-01-25
 - changed BOM recognition ordering (longer boms first)

 Original pseudocode   : Thomas Weidenfeller
 Implementation tweaked: Aki Nieminen

 http://www.unicode.org/unicode/faq/utf_bom.html
 BOMs:
   00 00 FE FF    = UTF-32, big-endian
   FF FE 00 00    = UTF-32, little-endian
   EF BB BF       = UTF-8,
   FE FF          = UTF-16, big-endian
   FF FE          = UTF-16, little-endian

 Win2k Notepad:
   Unicode format = UTF-16LE
***/

import java.io.*;

/**
 * Generic unicode textreader, which will use BOM mark
 * to identify the encoding to be used. If BOM is not found
 * then use a given default or system encoding.
 */
public class UnicodeReader extends Reader {
   PushbackInputStream internalIn;
   InputStreamReader   internalIn2 = null;
   String              defaultEnc;

   private static final int BOM_SIZE = 4;

   /**
    *
    * @param in  inputstream to be read
    * @param defaultEnc default encoding if stream does not have 
    *                   BOM marker. Give NULL to use system-level default.
    */
   public UnicodeReader(InputStream in, String defaultEnc) {
      internalIn = new PushbackInputStream(in, BOM_SIZE);
      this.defaultEnc = defaultEnc;
   }

   public String getDefaultEncoding() {
      return defaultEnc;
   }

   /**
    * Get stream encoding or NULL if stream is uninitialized.
    * Call init() or read() method to initialize it.
    */
   public String getEncoding() {
      if (internalIn2 == null) return null;
      return internalIn2.getEncoding();
   }

   /**
    * Read-ahead four bytes and check for BOM marks. Extra bytes are
    * unread back to the stream, only BOM bytes are skipped.
    */
   protected void init() throws IOException {
      if (internalIn2 != null) return;

      String encoding;
      byte bom[] = new byte[BOM_SIZE];
      int n, unread;
      n = internalIn.read(bom, 0, bom.length);

      if ( (bom[0] == (byte)0x00) && (bom[1] == (byte)0x00) &&
                  (bom[2] == (byte)0xFE) && (bom[3] == (byte)0xFF) ) {
         encoding = "UTF-32BE";
         unread = n - 4;
      } else if ( (bom[0] == (byte)0xFF) && (bom[1] == (byte)0xFE) &&
                  (bom[2] == (byte)0x00) && (bom[3] == (byte)0x00) ) {
         encoding = "UTF-32LE";
         unread = n - 4;
      } else if (  (bom[0] == (byte)0xEF) && (bom[1] == (byte)0xBB) &&
            (bom[2] == (byte)0xBF) ) {
         encoding = "UTF-8";
         unread = n - 3;
      } else if ( (bom[0] == (byte)0xFE) && (bom[1] == (byte)0xFF) ) {
         encoding = "UTF-16BE";
         unread = n - 2;
      } else if ( (bom[0] == (byte)0xFF) && (bom[1] == (byte)0xFE) ) {
         encoding = "UTF-16LE";
         unread = n - 2;
      } else {
         // Unicode BOM mark not found, unread all bytes
         encoding = defaultEnc;
         unread = n;
      }    
      //System.out.println("read=" + n + ", unread=" + unread);

      if (unread > 0) internalIn.unread(bom, (n - unread), unread);

      // Use given encoding
      if (encoding == null) {
         internalIn2 = new InputStreamReader(internalIn);
      } else {
         internalIn2 = new InputStreamReader(internalIn, encoding);
      }
   }

   public void close() throws IOException {
      init();
      internalIn2.close();
   }

   public int read(char[] cbuf, int off, int len) throws IOException {
      init();
      return internalIn2.read(cbuf, off, len);
   }

}