/*
 * Copyright 2006 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package com.sun.xml.internal.messaging.saaj.packaging.mime.util;

import java.io.*;

/**
 * This class implements a UUDecoder. It is implemented as
 * a FilterInputStream, so one can just wrap this class around
 * any input stream and read bytes from this filter. The decoding
 * is done as the bytes are read out.
 *
 * @author John Mani
 * @author Bill Shannon
 */

public class UUDecoderStream extends FilterInputStream {
    private String name;
    private int mode;

    private byte[] buffer;      // cache of decoded bytes
    private int bufsize = 0;    // size of the cache
    private int index = 0;      // index into the cache
    private boolean gotPrefix = false;
    private boolean gotEnd = false;
    private LineInputStream lin;

    /**
     * Create a UUdecoder that decodes the specified input stream
     * @param in        the input stream
     */
    public UUDecoderStream(InputStream in) {
        super(in);
        lin = new LineInputStream(in);
        buffer = new byte[45]; // max decoded chars in a line = 45
    }

    /**
     * Read the next decoded byte from this input stream. The byte
     * is returned as an <code>int</code> in the range <code>0</code>
     * to <code>255</code>. If no byte is available because the end of
     * the stream has been reached, the value <code>-1</code> is returned.
     * This method blocks until input data is available, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     next byte of data, or <code>-1</code> if the end of
     *             stream is reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */

    public int read() throws IOException {
        if (index >= bufsize) {
            readPrefix();
            if (!decode())
                return -1;
            index = 0; // reset index into buffer
        }
        return buffer[index++] & 0xff; // return lower byte
    }

    public int read(byte[] buf, int off, int len) throws IOException {
        int i, c;
        for (i = 0; i < len; i++) {
            if ((c = read()) == -1) {
                if (i == 0) // At end of stream, so we should
                    i = -1; // return -1, NOT 0.
                break;
            }
            buf[off+i] = (byte)c;
        }
        return i;
    }

    public boolean markSupported() {
        return false;
    }

    public int available() throws IOException {
         // This is only an estimate, since in.available()
         // might include CRLFs too ..
         return ((in.available() * 3)/4 + (bufsize-index));
    }

    /**
     * Get the "name" field from the prefix. This is meant to
     * be the pathname of the decoded file
     *
     * @return     name of decoded file
     * @exception  IOException  if an I/O error occurs.
     */
    public String getName() throws IOException {
        readPrefix();
        return name;
    }

    /**
     * Get the "mode" field from the prefix. This is the permission
     * mode of the source file.
     *
     * @return     permission mode of source file
     * @exception  IOException  if an I/O error occurs.
     */
    public int getMode() throws IOException {
        readPrefix();
        return mode;
    }

    /**
     * UUencoded streams start off with the line:
     *  "begin <mode> <filename>"
     * Search for this prefix and gobble it up.
     */
    private void readPrefix() throws IOException {
        if (gotPrefix) // got the prefix
            return;

        String s;
        for (;;) {
            // read till we get the prefix: "begin MODE FILENAME"
            s = lin.readLine(); // NOTE: readLine consumes CRLF pairs too
            if (s == null)
                throw new IOException("UUDecoder error: No Begin");
            if (s.regionMatches(true, 0, "begin", 0, 5)) {
                try {
                    mode = Integer.parseInt(s.substring(6,9));
                } catch (NumberFormatException ex) {
                    throw new IOException("UUDecoder error: " + ex.toString());
                }
                name = s.substring(10);
                gotPrefix = true;
                return;
            }
        }
    }

    private boolean decode() throws IOException {

        if (gotEnd)
            return false;
        bufsize = 0;
        String line;
        do {
            line = lin.readLine();

            /*
             * Improperly encoded data sometimes omits the zero length
             * line that starts with a space character, we detect the
             * following "end" line here.
             */
            if (line == null)
                throw new IOException("Missing End");
            if (line.regionMatches(true, 0, "end", 0, 3)) {
                gotEnd = true;
                return false;
            }
        } while (line.length() == 0);
        int count = line.charAt(0);
        if (count < ' ')
            throw new IOException("Buffer format error");

        /*
         * The first character in a line is the number of original (not
         *  the encoded atoms) characters in the line. Note that all the
         *  code below has to handle the <SPACE> character that indicates
         *  end of encoded stream.
         */
        count = (count - ' ') & 0x3f;

        if (count == 0) {
            line = lin.readLine();
            if (line == null || !line.regionMatches(true, 0, "end", 0, 3))
                throw new IOException("Missing End");
            gotEnd = true;
            return false;
        }

        int need = ((count * 8)+5)/6;
//System.out.println("count " + count + ", need " + need + ", len " + line.length());
        if (line.length() < need + 1)
            throw new IOException("Short buffer error");

        int i = 1;
        byte a, b;
        /*
         * A correct uuencoder always encodes 3 characters at a time, even
         * if there aren't 3 characters left.  But since some people out
         * there have broken uuencoders we handle the case where they
         * don't include these "unnecessary" characters.
         */
        while (bufsize < count) {
            // continue decoding until we get 'count' decoded chars
            a = (byte)((line.charAt(i++) - ' ') & 0x3f);
            b = (byte)((line.charAt(i++) - ' ') & 0x3f);
            buffer[bufsize++] = (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3));

            if (bufsize < count) {
                a = b;
                b = (byte)((line.charAt(i++) - ' ') & 0x3f);
                buffer[bufsize++] =
                                (byte)(((a << 4) & 0xf0) | ((b >>> 2) & 0xf));
            }

            if (bufsize < count) {
                a = b;
                b = (byte)((line.charAt(i++) - ' ') & 0x3f);
                buffer[bufsize++] = (byte)(((a << 6) & 0xc0) | (b & 0x3f));
            }
        }
        return true;
    }

    /*** begin TEST program *****
    public static void main(String argv[]) throws Exception {
        FileInputStream infile = new FileInputStream(argv[0]);
        UUDecoderStream decoder = new UUDecoderStream(infile);
        int c;

        try {
            while ((c = decoder.read()) != -1)
                System.out.write(c);
            System.out.flush();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    **** end TEST program ****/
}
