/*
    * GordianKnot: Security Suite
    * Copyright 2012-2026. Tony Washer
    *
    * 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 io.github.tonywasher.joceanus.gordianknot.impl.ext.engines;
  
  import io.github.tonywasher.joceanus.gordianknot.impl.ext.digests.GordianBlake3Digest;
  import io.github.tonywasher.joceanus.gordianknot.impl.ext.params.GordianBlake3Parameters;
  import org.bouncycastle.crypto.CipherParameters;
  import org.bouncycastle.crypto.DataLengthException;
  import org.bouncycastle.crypto.OutputLengthException;
  import org.bouncycastle.crypto.StreamCipher;
  import org.bouncycastle.crypto.params.KeyParameter;
  import org.bouncycastle.crypto.params.ParametersWithIV;
  import org.bouncycastle.util.Memoable;
  
  /**
   * Blake3 used as a stream Cipher.
   */
  public class GordianBlake3Engine
          implements StreamCipher, Memoable {
      /**
       * index of next byte in keyStream.
       */
      private int theIndex;
  
      /**
       * Advanced stream.
       */
      private final byte[] theKeyStream;
  
      /**
       * Underlying kMac.
       */
      private final GordianBlake3Digest theDigest;
  
      /**
       * Reset state.
       */
      private GordianBlake3Digest theResetState;
  
      /**
       * Constructor.
       */
      public GordianBlake3Engine() {
          theDigest = new GordianBlake3Digest();
          theKeyStream = new byte[theDigest.getDigestSize() << 1];
      }
  
      /**
       * Constructor.
       *
       * @param pSource the source engine
       */
      private GordianBlake3Engine(final GordianBlake3Engine pSource) {
          this();
          reset(pSource);
      }
  
      /**
       * initialise a Blake3 cipher.
       *
       * @param forEncryption whether or not we are for encryption.
       * @param params        the parameters required to set up the cipher.
       * @throws IllegalArgumentException if the params argument is inappropriate.
       */
      public void init(final boolean forEncryption,
                       final CipherParameters params) {
          /*
           * Blake3 encryption and decryption is completely symmetrical, so the 'forEncryption' is
           * irrelevant. (Like 90% of stream ciphers)
           */
  
          /* Determine parameters */
          CipherParameters myParams = params;
          byte[] newKey = null;
          byte[] newIV = null;
          if ((myParams instanceof ParametersWithIV ivParams)) {
              newIV = ivParams.getIV();
              myParams = ivParams.getParameters();
          }
          if (myParams instanceof KeyParameter keyParam) {
              newKey = keyParam.getKey();
          }
          if (newKey == null || newIV == null) {
              throw new IllegalArgumentException("A key and IV  must be provided");
          }
 
         /* Initialise engine and mark as initialised */
         theDigest.init(GordianBlake3Parameters.key(newKey));
         theDigest.update(newIV, 0, newIV.length);
 
         /* Save reset state */
         theResetState = theDigest.copy();
 
         /* Initialise the stream block */
         theIndex = 0;
         makeStreamBlock();
     }
 
     @Override
     public String getAlgorithmName() {
         return theDigest.getAlgorithmName();
     }
 
     @Override
     public int processBytes(final byte[] in,
                             final int inOff,
                             final int len,
                             final byte[] out,
                             final int outOff) {
         /* Check for errors */
         if (theResetState == null) {
             throw new IllegalStateException(getAlgorithmName() + " not initialised");
         }
         if ((inOff + len) > in.length) {
             throw new DataLengthException("input buffer too short");
         }
         if ((outOff + len) > out.length) {
             throw new OutputLengthException("output buffer too short");
         }
 
         /* Loop through the input bytes */
         for (int i = 0; i < len; i++) {
             out[i + outOff] = returnByte(in[i + inOff]);
         }
         return len;
     }
 
     @Override
     public void reset() {
         if (theResetState != null) {
             theDigest.reset(theResetState);
             theIndex = 0;
             makeStreamBlock();
         }
     }
 
     @Override
     public byte returnByte(final byte in) {
         final byte out = (byte) (theKeyStream[theIndex] ^ in);
         theIndex = (theIndex + 1) % theKeyStream.length;
 
         if (theIndex == 0) {
             makeStreamBlock();
         }
         return out;
     }
 
     /**
      * Generate keystream.
      */
     private void makeStreamBlock() {
         /* Generate next output block */
         theDigest.doOutput(theKeyStream, 0, theKeyStream.length);
     }
 
     @Override
     public GordianBlake3Engine copy() {
         return new GordianBlake3Engine(this);
     }
 
     @Override
     public void reset(final Memoable pState) {
         final GordianBlake3Engine e = (GordianBlake3Engine) pState;
         if (theKeyStream.length != e.theKeyStream.length) {
             throw new IllegalArgumentException();
         }
         theDigest.reset(e.theDigest);
         System.arraycopy(e.theKeyStream, 0, theKeyStream, 0, theKeyStream.length);
         theIndex = e.theIndex;
         theResetState = e.theResetState;
     }
 }