package org.djutils.decoderdumper;
   
   import java.io.ByteArrayOutputStream;
   import java.io.IOException;
   
   import org.djutils.logger.CategoryLogger;
   
   /**
    * Decode base64 encoded data and show it as hex bytes. See https://en.wikipedia.org/wiki/Base64
   * <p>
   * Copyright (c) 2013-2024 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://djutils.org/docs/current/djutils/licenses.html">DJUTILS License</a>.
   * </p>
   * @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://www.tudelft.nl/staff/p.knoppers/">Peter Knoppers</a>
   */
  public class Base64Decoder implements Decoder
  {
      /** Assembling space for decoded data. */
      private int notYetDecodedData = 0;
  
      /** Number of accumulated bits in <code>notYetDecodedData</code>. */
      private int accumulatedBits = 0;
  
      /** Dumper used internally to assemble the decoded data into hex values and char values. */
      private final Dumper<Base64Decoder> internalDumper = new Dumper<>();
  
      /** Collector for the output of the internal dumper. */
      private final ByteArrayOutputStream baos;
  
      /** Count number of equals (=) symbols seen. */
      private int endOfInputCharsSeen = 0;
  
      /** Set when an error is detected in the input stream. */
      private boolean errorDetected = false;
  
      /**
       * Construct a new Base64Decoder.
       * @param decodedBytesPerLine int; maximum number of decoded input characters resulting in one output line
       * @param extraSpaceAfterEvery int; insert an extra space after every N output fields (a multiple of 3 makes sense for the
       *            base64 decoder because base64 encodes three bytes into 4 characters)
       */
      public Base64Decoder(final int decodedBytesPerLine, final int extraSpaceAfterEvery)
      {
          this.baos = new ByteArrayOutputStream();
          this.internalDumper.setOutputStream(this.baos);
          int maximumBytesPerOutputLine = (decodedBytesPerLine + 3) / 4 * 3;
          this.internalDumper.addDecoder(new HexDecoder(maximumBytesPerOutputLine, extraSpaceAfterEvery));
          this.internalDumper.addDecoder(new FixedString("  "));
          this.internalDumper.addDecoder(new CharDecoder(maximumBytesPerOutputLine, extraSpaceAfterEvery));
      }
  
      @Override
      public String getResult()
      {
          try
          {
              this.internalDumper.flush();
              String result = this.baos.toString("UTF-8");
              this.baos.reset();
              return result;
          }
          catch (IOException ioe)
          {
              // Cannot happen because writing to a ByteArrayOutputStream should never fail
              return null;
          }
      }
  
      @Override
      public int getMaximumWidth()
      {
          return this.internalDumper.getMaximumWidth();
      }
  
      @Override
      public boolean append(final int address, final byte theByte) throws IOException
      {
          if (theByte == 61)
          {
              this.endOfInputCharsSeen++; // equals
          }
          if (this.endOfInputCharsSeen > 0)
          {
              return false; // This decoder does not handle multiple base64 encoded objects in its input
          }
          int value;
          if (theByte >= 48 && theByte <= 57)
          {
              value = theByte - 48 + 52; // Digit
          }
          else if (theByte >= 65 && theByte <= 90)
          {
              value = theByte - 65 + 0; // Capital letter
          }
          else if (theByte >= 97 && theByte <= 122)
          {
              value = theByte - 97 + 26;
          }
         else if (theByte == 43 || theByte == 45 || theByte == 46)
         {
             value = 62; // Plus or minus or dot
         }
         else if (theByte == 47 || theByte == 95 || theByte == 44)
         {
             value = 63; // Slash or underscore or comma
         }
         else if (theByte <= 32)
         {
             return false; // White space can appear anywhere and should be ignored (but this test for white space is bad)
         }
         else
         {
             // Illegal byte in input
             if (!this.errorDetected) // First error
             {
                 CategoryLogger.always().info("illegal character found in Base64Decoder stream at address {}, character {}",
                         address, theByte);
             }
             this.errorDetected = true;
             return false;
         }
         this.notYetDecodedData = (this.notYetDecodedData << 6) + value;
         this.accumulatedBits += 6;
         if (this.accumulatedBits >= 8)
         {
             int byteValue = this.notYetDecodedData >> (this.accumulatedBits - 8);
             this.accumulatedBits -= 8;
             this.notYetDecodedData -= byteValue << this.accumulatedBits;
             boolean result = this.internalDumper.append((byte) byteValue);
             return result;
         }
         return false;
     }
 
     @Override
     public boolean ignoreForIdenticalOutputCheck()
     {
         return false;
     }
 
 }