/****************************************************************
    * 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.IOException;
  import java.io.InputStream;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  /**
   * Performs Base-64 decoding on an underlying stream.
   */
  public class Base64InputStream extends InputStream {
      private static Log log = LogFactory.getLog(Base64InputStream.class);
  
      private static final int ENCODED_BUFFER_SIZE = 1536;
  
      private static final int[] BASE64_DECODE = new int[256];
  
      static {
          for (int i = 0; i < 256; i++)
              BASE64_DECODE[i] = -1;
          for (int i = 0; i < Base64OutputStream.BASE64_TABLE.length; i++)
              BASE64_DECODE[Base64OutputStream.BASE64_TABLE[i] & 0xff] = i;
      }
  
      private static final byte BASE64_PAD = '=';
  
      private static final int EOF = -1;
  
      private final byte[] singleByte = new byte[1];
  
      private boolean strict;
  
      private final InputStream in;
      private boolean closed = false;
  
      private final byte[] encoded = new byte[ENCODED_BUFFER_SIZE];
      private int position = 0; // current index into encoded buffer
      private int size = 0; // current size of encoded buffer
  
      private final ByteQueue q = new ByteQueue();
  
      private boolean eof; // end of file or pad character reached
  
      public Base64InputStream(InputStream in) {
          this(in, false);
      }
  
      public Base64InputStream(InputStream in, boolean strict) {
          if (in == null)
              throw new IllegalArgumentException();
  
          this.in = in;
          this.strict = strict;
      }
  
      @Override
      public int read() throws IOException {
          if (closed)
              throw new IOException("Base64InputStream has been closed");
  
          while (true) {
              int bytes = read0(singleByte, 0, 1);
              if (bytes == EOF)
                  return EOF;
  
              if (bytes == 1)
                  return singleByte[0] & 0xff;
          }
      }
  
      @Override
      public int read(byte[] buffer) throws IOException {
          if (closed)
              throw new IOException("Base64InputStream has been closed");
  
          if (buffer == null)
              throw new NullPointerException();
  
          if (buffer.length == 0)
             return 0;
 
         return read0(buffer, 0, buffer.length);
     }
 
     @Override
     public int read(byte[] buffer, int offset, int length) throws IOException {
         if (closed)
             throw new IOException("Base64InputStream has been closed");
 
         if (buffer == null)
             throw new NullPointerException();
 
         if (offset < 0 || length < 0 || offset + length > buffer.length)
             throw new IndexOutOfBoundsException();
 
         if (length == 0)
             return 0;
 
         return read0(buffer, offset, offset + length);
     }
 
     @Override
     public void close() throws IOException {
         if (closed)
             return;
 
         closed = true;
     }
 
     private int read0(final byte[] buffer, final int from, final int to)
             throws IOException {
         int index = from; // index into given buffer
 
         // check if a previous invocation left decoded bytes in the queue
 
         int qCount = q.count();
         while (qCount-- > 0 && index < to) {
             buffer[index++] = q.dequeue();
         }
 
         // eof or pad reached?
 
         if (eof)
             return index == from ? EOF : index - from;
 
         // decode into given buffer
 
         int data = 0; // holds decoded data; up to four sextets
         int sextets = 0; // number of sextets
 
         while (index < to) {
             // make sure buffer not empty
 
             while (position == size) {
                 int n = in.read(encoded, 0, encoded.length);
                 if (n == EOF) {
                     eof = true;
 
                     if (sextets != 0) {
                         // error in encoded data
                         handleUnexpectedEof(sextets);
                     }
 
                     return index == from ? EOF : index - from;
                 } else if (n > 0) {
                     position = 0;
                     size = n;
                 } else {
                     assert n == 0;
                 }
             }
 
             // decode buffer
 
             while (position < size && index < to) {
                 int value = encoded[position++] & 0xff;
 
                 if (value == BASE64_PAD) {
                     index = decodePad(data, sextets, buffer, index, to);
                     return index - from;
                 }
 
                 int decoded = BASE64_DECODE[value];
                 if (decoded < 0) // -1: not a base64 char
                     continue;
 
                 data = (data << 6) | decoded;
                 sextets++;
 
                 if (sextets == 4) {
                     sextets = 0;
 
                     byte b1 = (byte) (data >>> 16);
                     byte b2 = (byte) (data >>> 8);
                     byte b3 = (byte) data;
 
                     if (index < to - 2) {
                         buffer[index++] = b1;
                         buffer[index++] = b2;
                         buffer[index++] = b3;
                     } else {
                         if (index < to - 1) {
                             buffer[index++] = b1;
                             buffer[index++] = b2;
                             q.enqueue(b3);
                         } else if (index < to) {
                             buffer[index++] = b1;
                             q.enqueue(b2);
                             q.enqueue(b3);
                         } else {
                             q.enqueue(b1);
                             q.enqueue(b2);
                             q.enqueue(b3);
                         }
 
                         assert index == to;
                         return to - from;
                     }
                 }
             }
         }
 
         assert sextets == 0;
         assert index == to;
         return to - from;
     }
 
     private int decodePad(int data, int sextets, final byte[] buffer,
             int index, final int end) throws IOException {
         eof = true;
 
         if (sextets == 2) {
             // one byte encoded as "XY=="
 
             byte b = (byte) (data >>> 4);
             if (index < end) {
                 buffer[index++] = b;
             } else {
                 q.enqueue(b);
             }
         } else if (sextets == 3) {
             // two bytes encoded as "XYZ="
 
             byte b1 = (byte) (data >>> 10);
             byte b2 = (byte) ((data >>> 2) & 0xFF);
 
             if (index < end - 1) {
                 buffer[index++] = b1;
                 buffer[index++] = b2;
             } else if (index < end) {
                 buffer[index++] = b1;
                 q.enqueue(b2);
             } else {
                 q.enqueue(b1);
                 q.enqueue(b2);
             }
         } else {
             // error in encoded data
             handleUnexpecedPad(sextets);
         }
 
         return index;
     }
 
     private void handleUnexpectedEof(int sextets) throws IOException {
         if (strict)
             throw new IOException("unexpected end of file");
         else
             log.warn("unexpected end of file; dropping " + sextets
                     + " sextet(s)");
     }
 
     private void handleUnexpecedPad(int sextets) throws IOException {
         if (strict)
             throw new IOException("unexpected padding character");
         else
             log.warn("unexpected padding character; dropping " + sextets
                     + " sextet(s)");
     }
 }