/**
    *
    * Copyright 2003-2006 The Apache Software Foundation
    *
    *  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 org.apache.geronimo.mail.util;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.FilterInputStream;
  
  /**
   * An implementation of a FilterInputStream that decodes the
   * stream data in BASE64 encoding format.  This version does the
   * decoding "on the fly" rather than decoding a single block of
   * data.  Since this version is intended for use by the MimeUtilty class,
   * it also handles line breaks in the encoded data.
   */
  public class Base64DecoderStream extends FilterInputStream {
  
      static protected final String MAIL_BASE64_IGNOREERRORS = "mail.mime.base64.ignoreerrors";
  
      // number of decodeable units we'll try to process at one time.  We'll attempt to read that much
      // data from the input stream and decode in blocks.
      static protected final int BUFFERED_UNITS = 2000;
  
      // our decoder for processing the data
      protected Base64Encoder decoder = new Base64Encoder();
  
      // can be overridden by a system property.
      protected boolean ignoreErrors = false;
  
      // buffer for reading in chars for decoding (which can support larger bulk reads)
      protected byte[] encodedChars = new byte[BUFFERED_UNITS * 4];
      // a buffer for one decoding unit's worth of data (3 bytes).  This is the minimum amount we
      // can read at one time.
      protected byte[] decodedChars = new byte[BUFFERED_UNITS * 3];
      // count of characters in the buffer
      protected int decodedCount = 0;
      // index of the next decoded character
      protected int decodedIndex = 0;
  
  
      public Base64DecoderStream(InputStream in) {
          super(in);
          // make sure we get the ignore errors flag
          ignoreErrors = SessionUtil.getBooleanProperty(MAIL_BASE64_IGNOREERRORS, false);
      }
  
      /**
       * Test for the existance of decoded characters in our buffer
       * of decoded data.
       *
       * @return True if we currently have buffered characters.
       */
      private boolean dataAvailable() {
          return decodedCount != 0;
      }
  
      /**
       * Get the next buffered decoded character.
       *
       * @return The next decoded character in the buffer.
       */
      private byte getBufferedChar() {
          decodedCount--;
          return decodedChars[decodedIndex++];
      }
  
      /**
       * Decode a requested number of bytes of data into a buffer.
       *
       * @return true if we were able to obtain more data, false otherwise.
       */
      private boolean decodeStreamData() throws IOException {
          decodedIndex = 0;
  
          // fill up a data buffer with input data
          int readCharacters = fillEncodedBuffer();
  
          if (readCharacters > 0) {
              decodedCount =  decoder.decode(encodedChars, 0, readCharacters, decodedChars);
              return true;
          }
          return false;
      }
  
 
     /**
      * Retrieve a single byte from the decoded characters buffer.
      *
      * @return The decoded character or -1 if there was an EOF condition.
      */
     private int getByte() throws IOException {
         if (!dataAvailable()) {
             if (!decodeStreamData()) {
                 return -1;
             }
         }
         decodedCount--;
         return decodedChars[decodedIndex++];
     }
 
     private int getBytes(byte[] data, int offset, int length) throws IOException {
 
         int readCharacters = 0;
         while (length > 0) {
             // need data?  Try to get some
             if (!dataAvailable()) {
                 // if we can't get this, return a count of how much we did get (which may be -1).
                 if (!decodeStreamData()) {
                     return readCharacters > 0 ? readCharacters : -1;
                 }
             }
 
             // now copy some of the data from the decoded buffer to the target buffer
             int copyCount = Math.min(decodedCount, length);
             System.arraycopy(decodedChars, decodedIndex, data, offset, copyCount);
             decodedIndex += copyCount;
             decodedCount -= copyCount;
             offset += copyCount;
             length -= copyCount;
             readCharacters += copyCount;
         }
         return readCharacters;
     }
 
 
     /**
      * Fill our buffer of input characters for decoding from the
      * stream.  This will attempt read a full buffer, but will
      * terminate on an EOF or read error.  This will filter out
      * non-Base64 encoding chars and will only return a valid
      * multiple of 4 number of bytes.
      *
      * @return The count of characters read.
      */
     private int fillEncodedBuffer() throws IOException
     {
         int readCharacters = 0;
 
         while (true) {
             // get the next character from the stream
             int ch = in.read();
             // did we hit an EOF condition?
             if (ch == -1) {
                 // now check to see if this is normal, or potentially an error
                 // if we didn't get characters as a multiple of 4, we may need to complain about this.
                 if ((readCharacters % 4) != 0) {
                     // the error checking can be turned off...normally it isn't
                     if (!ignoreErrors) {
                         throw new IOException("Base64 encoding error, data truncated");
                     }
                     // we're ignoring errors, so round down to a multiple and return that.
                     return (readCharacters / 4) * 4;
                 }
                 // return the count.
                 return readCharacters;
             }
             // if this character is valid in a Base64 stream, copy it to the buffer.
             else if (decoder.isValidBase64(ch)) {
                 encodedChars[readCharacters++] = (byte)ch;
                 // if we've filled up the buffer, time to quit.
                 if (readCharacters >= encodedChars.length) {
                     return readCharacters;
                 }
             }
 
             // we're filtering out whitespace and CRLF characters, so just ignore these
         }
     }
 
 
     // in order to function as a filter, these streams need to override the different
     // read() signature.
 
     public int read() throws IOException
     {
         return getByte();
     }
 
 
     public int read(byte [] buffer, int offset, int length) throws IOException {
         return getBytes(buffer, offset, length);
     }
 
 
     public boolean markSupported() {
         return false;
     }
 
 
     public int available() throws IOException {
         return ((in.available() / 4) * 3) + decodedCount;
     }
 }