/**
 * @(#)TranscodeUtil.java	1.0 2001/09/25
 *
 * Copyleft 2001 by Steve Excellent Lee,
 */
package org.bulbul.webmail.util;

import java.io.UnsupportedEncodingException;
import java.util.Locale;
import javax.mail.internet.MimeUtility;


/**
 * TranscodeUtil.
 *
 * Provides transcoding utilities.
 *
 * @author		Steve Excellent Lee.
 * @version		1.0 2000
 */
public class TranscodeUtil {
    /**
     * Why we need 
     * org.bulbul.util.TranscodeUtil.transcodeThenEncodeByLocale()?
     *
   	 * Because we specify client browser's encoding to UTF-8, IE seems
     * to send all data encoded in UTF-8. That means the byte sequences 
     * we received are all UTF-8 bytes. However, strings read from HTTP
     * is ISO8859_1 encoded, that's we need to transcode them (usually
     * from ISO8859_1 to UTF-8.
     * Next we encode those strings using MimeUtility.encodeText() depending
     * on user's locale. Since MimeUtility.encodeText() is used to convert 
     * the strings into its transmission format, finally we can use the 
     * strings in the outgoing e-mail, then receiver's email agent is 
     * responsible for decoding the strings.
     *
     * As described in JavaMail document, MimeUtility.encodeText() conforms
     * to RFC2047 and as a result, we'll get strings like "=?Big5?B......".
     * @param	sourceString			String to be encoded
     * @param	sourceStringEncoding	The encoding to decode `sourceString' 
     *									string. If `sourceStringEncoding'
     *									is null, use JVM's default enconding.
     * @param	Locale					prefered locale
     *
     * @return	empty string(prevent NullPointerException) if sourceString 
     *			is null or empty(""); 
     *			otherwise RFC2047 conformed string, eg, "=?Iso8859-1?Q....."
     */
    public static String transcodeThenEncodeByLocale(
						     String sourceString, 
						     String sourceStringEncoding,
						     Locale locale) 
	throws java.io.UnsupportedEncodingException {
	String str;
	
	if ((sourceString == null) || (sourceString.equals("")))
	    return "";
	
	// Transcode to UTF-8
	if ((sourceStringEncoding == null) || 
	    (sourceStringEncoding.equals("")))
	    str = new String(sourceString.getBytes(), "UTF-8");
	else
	    str = new String(sourceString.getBytes(sourceStringEncoding),"UTF-8");
	
	// Encode text
	if (locale.getLanguage().equals("zh") && locale.getCountry().equals("TW")) {
	    return MimeUtility.encodeText(str, "Big5", null);
	} else {
	    return MimeUtility.encodeText(str);
	}
    }
}