/*
    * 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.commons.codec.binary;
  
  import java.util.Arrays;
  
  import org.apache.commons.codec.BinaryDecoder;
  import org.apache.commons.codec.BinaryEncoder;
  import org.apache.commons.codec.DecoderException;
  import org.apache.commons.codec.EncoderException;
  
  /**
   * Abstract superclass for Base-N encoders and decoders.
   *
   * <p>
   * This class is thread-safe.
   * </p>
   *
   * @version $Id: BaseNCodec.html 891688 2013-12-24 20:49:46Z ggregory $
   */
  public abstract class BaseNCodec implements BinaryEncoder, BinaryDecoder {
  
      /**
       * Holds thread context so classes can be thread-safe.
       *
       * This class is not itself thread-safe; each thread must allocate its own copy.
       *
       * @since 1.7
       */
      static class Context {
  
          /**
           * Place holder for the bytes we're dealing with for our based logic.
           * Bitwise operations store and extract the encoding or decoding from this variable.
           */
          int ibitWorkArea;
  
          /**
           * Place holder for the bytes we're dealing with for our based logic.
           * Bitwise operations store and extract the encoding or decoding from this variable.
           */
          long lbitWorkArea;
  
          /**
           * Buffer for streaming.
           */
          byte[] buffer;
  
          /**
           * Position where next character should be written in the buffer.
           */
          int pos;
  
          /**
           * Position where next character should be read from the buffer.
           */
          int readPos;
  
          /**
           * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless,
           * and must be thrown away.
           */
          boolean eof;
  
          /**
           * Variable tracks how many characters have been written to the current line. Only used when encoding. We use
           * it to make sure each encoded line never goes beyond lineLength (if lineLength > 0).
           */
          int currentLinePos;
  
          /**
           * Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This
           * variable helps track that.
           */
          int modulus;
  
          Context() {
          }
  
          /**
           * Returns a String useful for debugging (especially within a debugger.)
           *
           * @return a String useful for debugging.
           */
         @SuppressWarnings("boxing") // OK to ignore boxing here
         @Override
         public String toString() {
             return String.format("%s[buffer=%s, currentLinePos=%s, eof=%s, ibitWorkArea=%s, lbitWorkArea=%s, " +
                     "modulus=%s, pos=%s, readPos=%s]", this.getClass().getSimpleName(), Arrays.toString(buffer),
                     currentLinePos, eof, ibitWorkArea, lbitWorkArea, modulus, pos, readPos);
         }
     }
 
     /**
      * EOF
      *
      * @since 1.7
      */
     static final int EOF = -1;
 
     /**
      *  MIME chunk size per RFC 2045 section 6.8.
      *
      * <p>
      * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
      * equal signs.
      * </p>
      *
      * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 6.8</a>
      */
     public static final int MIME_CHUNK_SIZE = 76;
 
     /**
      * PEM chunk size per RFC 1421 section 4.3.2.4.
      *
      * <p>
      * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
      * equal signs.
      * </p>
      *
      * @see <a href="http://tools.ietf.org/html/rfc1421">RFC 1421 section 4.3.2.4</a>
      */
     public static final int PEM_CHUNK_SIZE = 64;
 
     private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;
 
     /**
      * Defines the default buffer size - currently {@value}
      * - must be large enough for at least one encoded block+separator
      */
     private static final int DEFAULT_BUFFER_SIZE = 8192;
 
     /** Mask used to extract 8 bits, used in decoding bytes */
     protected static final int MASK_8BITS = 0xff;
 
     /**
      * Byte used to pad output.
      */
     protected static final byte PAD_DEFAULT = '='; // Allow static access to default
 
     protected final byte PAD = PAD_DEFAULT; // instance variable just in case it needs to vary later
 
     /** Number of bytes in each full block of unencoded data, e.g. 4 for Base64 and 5 for Base32 */
     private final int unencodedBlockSize;
 
     /** Number of bytes in each full block of encoded data, e.g. 3 for Base64 and 8 for Base32 */
     private final int encodedBlockSize;
 
     /**
      * Chunksize for encoding. Not used when decoding.
      * A value of zero or less implies no chunking of the encoded data.
      * Rounded down to nearest multiple of encodedBlockSize.
      */
     protected final int lineLength;
 
     /**
      * Size of chunk separator. Not used unless {@link #lineLength} > 0.
      */
     private final int chunkSeparatorLength;
 
     /**
      * Note <code>lineLength</code> is rounded down to the nearest multiple of {@link #encodedBlockSize}
      * If <code>chunkSeparatorLength</code> is zero, then chunking is disabled.
      * @param unencodedBlockSize the size of an unencoded block (e.g. Base64 = 3)
      * @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
      * @param lineLength if &gt; 0, use chunking with a length <code>lineLength</code>
      * @param chunkSeparatorLength the chunk separator length, if relevant
      */
     protected BaseNCodec(final int unencodedBlockSize, final int encodedBlockSize,
                          final int lineLength, final int chunkSeparatorLength) {
         this.unencodedBlockSize = unencodedBlockSize;
         this.encodedBlockSize = encodedBlockSize;
         final boolean useChunking = lineLength > 0 && chunkSeparatorLength > 0;
         this.lineLength = useChunking ? (lineLength / encodedBlockSize) * encodedBlockSize : 0;
         this.chunkSeparatorLength = chunkSeparatorLength;
     }
 
     /**
      * Returns true if this object has buffered data for reading.
      *
      * @param context the context to be used
      * @return true if there is data still available for reading.
      */
     boolean hasData(final Context context) {  // package protected for access from I/O streams
         return context.buffer != null;
     }
 
     /**
      * Returns the amount of buffered data available for reading.
      *
      * @param context the context to be used
      * @return The amount of buffered data available for reading.
      */
     int available(final Context context) {  // package protected for access from I/O streams
         return context.buffer != null ? context.pos - context.readPos : 0;
     }
 
     /**
      * Get the default buffer size. Can be overridden.
      *
      * @return {@link #DEFAULT_BUFFER_SIZE}
      */
     protected int getDefaultBufferSize() {
         return DEFAULT_BUFFER_SIZE;
     }
 
     /**
      * Increases our buffer by the {@link #DEFAULT_BUFFER_RESIZE_FACTOR}.
      * @param context the context to be used
      */
     private byte[] resizeBuffer(final Context context) {
         if (context.buffer == null) {
             context.buffer = new byte[getDefaultBufferSize()];
             context.pos = 0;
             context.readPos = 0;
         } else {
             final byte[] b = new byte[context.buffer.length * DEFAULT_BUFFER_RESIZE_FACTOR];
             System.arraycopy(context.buffer, 0, b, 0, context.buffer.length);
             context.buffer = b;
         }
         return context.buffer;
     }
 
     /**
      * Ensure that the buffer has room for <code>size</code> bytes
      *
      * @param size minimum spare space required
      * @param context the context to be used
      */
     protected byte[] ensureBufferSize(final int size, final Context context){
         if ((context.buffer == null) || (context.buffer.length < context.pos + size)){
             return resizeBuffer(context);
         }
         return context.buffer;
     }
 
     /**
      * Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
      * bytes. Returns how many bytes were actually extracted.
      * <p>
      * Package protected for access from I/O streams.
      *
      * @param b
      *            byte[] array to extract the buffered data into.
      * @param bPos
      *            position in byte[] array to start extraction at.
      * @param bAvail
      *            amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
      * @param context
      *            the context to be used
      * @return The number of bytes successfully extracted into the provided byte[] array.
      */
     int readResults(final byte[] b, final int bPos, final int bAvail, final Context context) {
         if (context.buffer != null) {
             final int len = Math.min(available(context), bAvail);
             System.arraycopy(context.buffer, context.readPos, b, bPos, len);
             context.readPos += len;
             if (context.readPos >= context.pos) {
                 context.buffer = null; // so hasData() will return false, and this method can return -1
             }
             return len;
         }
         return context.eof ? EOF : 0;
     }
 
     /**
      * Checks if a byte value is whitespace or not.
      * Whitespace is taken to mean: space, tab, CR, LF
      * @param byteToCheck
      *            the byte to check
      * @return true if byte is whitespace, false otherwise
      */
     protected static boolean isWhiteSpace(final byte byteToCheck) {
         switch (byteToCheck) {
             case ' ' :
             case '\n' :
             case '\r' :
             case '\t' :
                 return true;
             default :
                 return false;
         }
     }
 
     /**
      * Encodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
      * the Encoder interface, and will throw an EncoderException if the supplied object is not of type byte[].
      *
      * @param obj
      *            Object to encode
      * @return An object (of type byte[]) containing the Base-N encoded data which corresponds to the byte[] supplied.
      * @throws EncoderException
      *             if the parameter supplied is not of type byte[]
      */
     @Override
     public Object encode(final Object obj) throws EncoderException {
         if (!(obj instanceof byte[])) {
             throw new EncoderException("Parameter supplied to Base-N encode is not a byte[]");
         }
         return encode((byte[]) obj);
     }
 
     /**
      * Encodes a byte[] containing binary data, into a String containing characters in the Base-N alphabet.
      * Uses UTF8 encoding.
      *
      * @param pArray
      *            a byte array containing binary data
      * @return A String containing only Base-N character data
      */
     public String encodeToString(final byte[] pArray) {
         return StringUtils.newStringUtf8(encode(pArray));
     }
 
     /**
      * Encodes a byte[] containing binary data, into a String containing characters in the appropriate alphabet.
      * Uses UTF8 encoding.
      *
      * @param pArray a byte array containing binary data
      * @return String containing only character data in the appropriate alphabet.
     */
     public String encodeAsString(final byte[] pArray){
         return StringUtils.newStringUtf8(encode(pArray));
     }
 
     /**
      * Decodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
      * the Decoder interface, and will throw a DecoderException if the supplied object is not of type byte[] or String.
      *
      * @param obj
      *            Object to decode
      * @return An object (of type byte[]) containing the binary data which corresponds to the byte[] or String
      *         supplied.
      * @throws DecoderException
      *             if the parameter supplied is not of type byte[]
      */
     @Override
     public Object decode(final Object obj) throws DecoderException {
         if (obj instanceof byte[]) {
             return decode((byte[]) obj);
         } else if (obj instanceof String) {
             return decode((String) obj);
         } else {
             throw new DecoderException("Parameter supplied to Base-N decode is not a byte[] or a String");
         }
     }
 
     /**
      * Decodes a String containing characters in the Base-N alphabet.
      *
      * @param pArray
      *            A String containing Base-N character data
      * @return a byte array containing binary data
      */
     public byte[] decode(final String pArray) {
         return decode(StringUtils.getBytesUtf8(pArray));
     }
 
     /**
      * Decodes a byte[] containing characters in the Base-N alphabet.
      *
      * @param pArray
      *            A byte array containing Base-N character data
      * @return a byte array containing binary data
      */
     @Override
     public byte[] decode(final byte[] pArray) {
         if (pArray == null || pArray.length == 0) {
             return pArray;
         }
         final Context context = new Context();
         decode(pArray, 0, pArray.length, context);
         decode(pArray, 0, EOF, context); // Notify decoder of EOF.
         final byte[] result = new byte[context.pos];
         readResults(result, 0, result.length, context);
         return result;
     }
 
     /**
      * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
      *
      * @param pArray
      *            a byte array containing binary data
      * @return A byte array containing only the basen alphabetic character data
      */
     @Override
     public byte[] encode(final byte[] pArray) {
         if (pArray == null || pArray.length == 0) {
             return pArray;
         }
         final Context context = new Context();
         encode(pArray, 0, pArray.length, context);
         encode(pArray, 0, EOF, context); // Notify encoder of EOF.
         final byte[] buf = new byte[context.pos - context.readPos];
         readResults(buf, 0, buf.length, context);
         return buf;
     }
 
     // package protected for access from I/O streams
     abstract void encode(byte[] pArray, int i, int length, Context context);
 
     // package protected for access from I/O streams
     abstract void decode(byte[] pArray, int i, int length, Context context);
 
     /**
      * Returns whether or not the <code>octet</code> is in the current alphabet.
      * Does not allow whitespace or pad.
      *
      * @param value The value to test
      *
      * @return {@code true} if the value is defined in the current alphabet, {@code false} otherwise.
      */
     protected abstract boolean isInAlphabet(byte value);
 
     /**
      * Tests a given byte array to see if it contains only valid characters within the alphabet.
      * The method optionally treats whitespace and pad as valid.
      *
      * @param arrayOctet byte array to test
      * @param allowWSPad if {@code true}, then whitespace and PAD are also allowed
      *
      * @return {@code true} if all bytes are valid characters in the alphabet or if the byte array is empty;
      *         {@code false}, otherwise
      */
     public boolean isInAlphabet(final byte[] arrayOctet, final boolean allowWSPad) {
         for (int i = 0; i < arrayOctet.length; i++) {
             if (!isInAlphabet(arrayOctet[i]) &&
                     (!allowWSPad || (arrayOctet[i] != PAD) && !isWhiteSpace(arrayOctet[i]))) {
                 return false;
             }
         }
         return true;
     }
 
     /**
      * Tests a given String to see if it contains only valid characters within the alphabet.
      * The method treats whitespace and PAD as valid.
      *
      * @param basen String to test
      * @return {@code true} if all characters in the String are valid characters in the alphabet or if
      *         the String is empty; {@code false}, otherwise
      * @see #isInAlphabet(byte[], boolean)
      */
     public boolean isInAlphabet(final String basen) {
         return isInAlphabet(StringUtils.getBytesUtf8(basen), true);
     }
 
     /**
      * Tests a given byte array to see if it contains any characters within the alphabet or PAD.
      *
      * Intended for use in checking line-ending arrays
      *
      * @param arrayOctet
      *            byte array to test
      * @return {@code true} if any byte is a valid character in the alphabet or PAD; {@code false} otherwise
      */
     protected boolean containsAlphabetOrPad(final byte[] arrayOctet) {
         if (arrayOctet == null) {
             return false;
         }
         for (final byte element : arrayOctet) {
             if (PAD == element || isInAlphabet(element)) {
                 return true;
             }
         }
         return false;
     }
 
     /**
      * Calculates the amount of space needed to encode the supplied array.
      *
      * @param pArray byte[] array which will later be encoded
      *
      * @return amount of space needed to encoded the supplied array.
      * Returns a long since a max-len array will require > Integer.MAX_VALUE
      */
     public long getEncodedLength(final byte[] pArray) {
         // Calculate non-chunked size - rounded up to allow for padding
         // cast to long is needed to avoid possibility of overflow
         long len = ((pArray.length + unencodedBlockSize-1)  / unencodedBlockSize) * (long) encodedBlockSize;
         if (lineLength > 0) { // We're using chunking
             // Round up to nearest multiple
             len += ((len + lineLength-1) / lineLength) * chunkSeparatorLength;
         }
         return len;
     }
 }