/****************************************************************
 * Licensed to the Apache Software Foundation (ASF) under one   *
 * or more contributor license agreements.  See the NOTICE file *
 * distributed with this work for additional information        *
 * regarding copyright ownership.  The ASF licenses this file   *
 * to you 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 org.apache.james.mime4j.codec;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.james.mime4j.util.CharsetUtil;

/**
 * Static methods for decoding strings, byte arrays and encoded words.
 */
public class DecoderUtil {
    private static Log log = LogFactory.getLog(DecoderUtil.class);
    
    /**
     * Decodes a string containing quoted-printable encoded data. 
     * 
     * @param s the string to decode.
     * @return the decoded bytes.
     */
    public static byte[] decodeBaseQuotedPrintable(String s) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        
        try {
            byte[] bytes = s.getBytes("US-ASCII");
            
            QuotedPrintableInputStream is = new QuotedPrintableInputStream(
                                               new ByteArrayInputStream(bytes));
            
            int b = 0;
            while ((b = is.read()) != -1) {
                baos.write(b);
            }
        } catch (IOException e) {
            /*
             * This should never happen!
             */
            log.error(e);
        }
        
        return baos.toByteArray();
    }
    
    /**
     * Decodes a string containing base64 encoded data. 
     * 
     * @param s the string to decode.
     * @return the decoded bytes.
     */
    public static byte[] decodeBase64(String s) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        
        try {
            byte[] bytes = s.getBytes("US-ASCII");
            
            Base64InputStream is = new Base64InputStream(
                                        new ByteArrayInputStream(bytes));
            
            int b = 0;
            while ((b = is.read()) != -1) {
                baos.write(b);
            }
        } catch (IOException e) {
            /*
             * This should never happen!
             */
            log.error(e);
        }
        
        return baos.toByteArray();
    }
    
    /**
     * Decodes an encoded word encoded with the 'B' encoding (described in 
     * RFC 2047) found in a header field body.
     * 
     * @param encodedWord the encoded word to decode.
     * @param charset the Java charset to use.
     * @return the decoded string.
     * @throws UnsupportedEncodingException if the given Java charset isn't 
     *         supported.
     */
    public static String decodeB(String encodedWord, String charset) 
            throws UnsupportedEncodingException {
        
        return new String(decodeBase64(encodedWord), charset);
    }
    
    /**
     * Decodes an encoded word encoded with the 'Q' encoding (described in 
     * RFC 2047) found in a header field body.
     * 
     * @param encodedWord the encoded word to decode.
     * @param charset the Java charset to use.
     * @return the decoded string.
     * @throws UnsupportedEncodingException if the given Java charset isn't 
     *         supported.
     */
    public static String decodeQ(String encodedWord, String charset)
            throws UnsupportedEncodingException {
           
        /*
         * Replace _ with =20
         */
        StringBuilder sb = new StringBuilder(128);
        for (int i = 0; i < encodedWord.length(); i++) {
            char c = encodedWord.charAt(i);
            if (c == '_') {
                sb.append("=20");
            } else {
                sb.append(c);
            }
        }
        
        return new String(decodeBaseQuotedPrintable(sb.toString()), charset);
    }
    
    /**
     * Decodes a string containing encoded words as defined by RFC 2047.
     * Encoded words in have the form 
     * =?charset?enc?Encoded word?= where enc is either 'Q' or 'q' for 
     * quoted-printable and 'B' or 'b' for Base64.
     * 
     * @param body the string to decode.
     * @return the decoded string.
     */
    public static String decodeEncodedWords(String body) {
        int previousEnd = 0;
        boolean previousWasEncoded = false;

        StringBuilder sb = new StringBuilder();

        while (true) {
            int begin = body.indexOf("=?", previousEnd);
            int end = begin == -1 ? -1 : body.indexOf("?=", begin + 2);
            if (end == -1) {
                if (previousEnd == 0)
                    return body;

                sb.append(body.substring(previousEnd));
                return sb.toString();
            }
            end += 2;

            String sep = body.substring(previousEnd, begin);

            String decoded = decodeEncodedWord(body, begin, end);
            if (decoded == null) {
                sb.append(sep);
                sb.append(body.substring(begin, end));
            } else {
                if (!previousWasEncoded || !CharsetUtil.isWhitespace(sep)) {
                    sb.append(sep);
                }
                sb.append(decoded);
            }

            previousEnd = end;
            previousWasEncoded = decoded != null;
        }
    }

    // return null on error
    private static String decodeEncodedWord(String body, int begin, int end) {
        int qm1 = body.indexOf('?', begin + 2);
        if (qm1 == end - 2)
            return null;

        int qm2 = body.indexOf('?', qm1 + 1);
        if (qm2 == end - 2)
            return null;

        String mimeCharset = body.substring(begin + 2, qm1);
        String encoding = body.substring(qm1 + 1, qm2);
        String encodedText = body.substring(qm2 + 1, end - 2);

        String charset = CharsetUtil.toJavaCharset(mimeCharset);
        if (charset == null) {
            if (log.isWarnEnabled()) {
                log.warn("MIME charset '" + mimeCharset + "' in encoded word '"
                        + body.substring(begin, end) + "' doesn't have a "
                        + "corresponding Java charset");
            }
            return null;
        } else if (!CharsetUtil.isDecodingSupported(charset)) {
            if (log.isWarnEnabled()) {
                log.warn("Current JDK doesn't support decoding of charset '"
                        + charset + "' (MIME charset '" + mimeCharset
                        + "' in encoded word '" + body.substring(begin, end)
                        + "')");
            }
            return null;
        }

        if (encodedText.length() == 0) {
            if (log.isWarnEnabled()) {
                log.warn("Missing encoded text in encoded word: '"
                        + body.substring(begin, end) + "'");
            }
            return null;
        }

        try {
            if (encoding.equalsIgnoreCase("Q")) {
                return DecoderUtil.decodeQ(encodedText, charset);
            } else if (encoding.equalsIgnoreCase("B")) {
                return DecoderUtil.decodeB(encodedText, charset);
            } else {
                if (log.isWarnEnabled()) {
                    log.warn("Warning: Unknown encoding in encoded word '"
                            + body.substring(begin, end) + "'");
                }
                return null;
            }
        } catch (UnsupportedEncodingException e) {
            // should not happen because of isDecodingSupported check above
            if (log.isWarnEnabled()) {
                log.warn("Unsupported encoding in encoded word '"
                        + body.substring(begin, end) + "'", e);
            }
            return null;
        } catch (RuntimeException e) {
            if (log.isWarnEnabled()) {
                log.warn("Could not decode encoded word '"
                        + body.substring(begin, end) + "'", e);
            }
            return null;
        }
    }
}