/******************************************************************************
 * Copyright (c) 2002 - 2011 IBM Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *****************************************************************************/
package com.ibm.wala.cast.js.html;

/**
 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
 FE FF          = UTF-16, big-endian
 FF FE          = UTF-16, little-endian
 EF BB BF       = UTF-8

 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.
 */
public class UnicodeReader extends Reader {
  PushbackInputStream internalIn;

  InputStreamReader internalIn2 = null;

  String defaultEnc;

  private static final int BOM_SIZE = 6;

  /*
   * Default encoding is used only if BOM is not found. If defaultEncoding is NULL then systemdefault is used.
   */
  public UnicodeReader(InputStream in, String defaultEnc) {
    internalIn = new PushbackInputStream(in, BOM_SIZE);
    this.defaultEnc = defaultEnc;
  }

  public String getDefaultEncoding() {
    return defaultEnc;
  }

  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) 0xEF) && (bom[1] == (byte) 0xBB) && (bom[2] == (byte) 0xBF) && (bom[3] == (byte) 0xEF) && (bom[4] == (byte) 0xBB) && (bom[5] == (byte) 0xBF)) {
      encoding = "UTF-8";
      unread = n - 6;
    } 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 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 {
      // 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);
    else if (unread < -1)
      internalIn.unread(bom, 0, 0);

    // 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);
  }

}