/* Copyright (c) 2008 Google Inc.
 *
 * 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
 *
 *     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 nl.sogeti.android.gpstracker.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;

public class UnicodeReader extends Reader
{
   private static final int BOM_SIZE = 4;
   private final InputStreamReader reader;

   /**
    * Construct UnicodeReader
    * 
    * @param in Input stream.
    * @param defaultEncoding Default encoding to be used if BOM is not found, or <code>null</code> to use system default encoding.
    * @throws IOException If an I/O error occurs.
    */
   public UnicodeReader(InputStream in, String defaultEncoding) throws IOException
   {
      byte bom[] = new byte[BOM_SIZE];
      String encoding;
      int unread;
      PushbackInputStream pushbackStream = new PushbackInputStream( in, BOM_SIZE );
      int n = pushbackStream.read( bom, 0, bom.length );

      // Read ahead four bytes and check for BOM marks.
      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 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
      {
         encoding = defaultEncoding;
         unread = n;
      }

      // Unread bytes if necessary and skip BOM marks.
      if( unread > 0 )
      {
         pushbackStream.unread( bom, ( n - unread ), unread );
      }
      else if( unread < -1 )
      {
         pushbackStream.unread( bom, 0, 0 );
      }

      // Use given encoding.
      if( encoding == null )
      {
         reader = new InputStreamReader( pushbackStream );
      }
      else
      {
         reader = new InputStreamReader( pushbackStream, encoding );
      }
   }

   public String getEncoding()
   {
      return reader.getEncoding();
   }

   @Override
   public int read( char[] cbuf, int off, int len ) throws IOException
   {
      return reader.read( cbuf, off, len );
   }

   @Override
   public void close() throws IOException
   {
      reader.close();
   }
}