/*
 * JEF - Copyright 2009-2010 Jiyi (mr.jiyi@gmail.com)
 *
 * 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 jef.tools.io;

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

/**
* 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);
  }
}