/*
    * 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 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;
  
  import java.util.Arrays;
  
  /**
   * StreamCipher implementation based on the SosemanukFast java implementation.
   * <p>
   * Based on http://www.ecrypt.eu.org/stream/e2-rabbit.html.
   */
  @SuppressWarnings("checkstyle:MagicNumber")
  public class GordianRabbitEngine
          implements StreamCipher, Memoable {
      /**
       * Number of variables.
       */
      private static final int NUM_VARS = 8;
  
      /**
       * Advanced stream length.
       */
      private static final int STREAM_LEN = 80;
  
      /**
       * context.
       */
      static class GordianRabbitContext {
          /**
           * X state.
           */
          private int[] x = new int[NUM_VARS];
  
          /**
           * c stat.
           */
          private int[] c = new int[NUM_VARS];
  
          /**
           * carry state.
           */
          private int carry;
  
          /**
           * Copy from.
           *
           * @param pSource the source context
           */
          void copyFrom(final GordianRabbitContext pSource) {
              System.arraycopy(pSource.x, 0, x, 0, NUM_VARS);
              System.arraycopy(pSource.c, 0, c, 0, NUM_VARS);
              carry = pSource.carry;
          }
      }
  
      /**
       * Work context.
       */
      private GordianRabbitContext work = new GordianRabbitContext();
  
      /**
       * master context.
       */
      private GordianRabbitContext master = new GordianRabbitContext();
  
      /**
       * index of next byte in keyStream.
       */
      private int theIndex;
  
      /**
       * Advanced stream.
       */
      private final byte[] keyStream = new byte[STREAM_LEN];
  
      /**
       * Reset state.
      */
     private GordianRabbitEngine theResetState;
 
     /**
      * Constructor.
      */
     public GordianRabbitEngine() {
     }
 
     /**
      * Constructor.
      *
      * @param pSource the source engine
      */
     private GordianRabbitEngine(final GordianRabbitEngine pSource) {
         reset(pSource);
     }
 
     /**
      * initialise a Rabbit 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) {
         /*
          * 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();
         }
 
         /* Initialise engine and mark as initialised */
         theIndex = 0;
         setKey(newKey);
         setIV(newIV);
         makeKeyStream();
 
         /* Save reset state */
         theResetState = copy();
     }
 
     @Override
     public String getAlgorithmName() {
         return "Rabbit";
     }
 
     @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) {
             reset(theResetState);
         }
     }
 
     @Override
     public byte returnByte(final byte in) {
         final byte out = (byte) (keyStream[theIndex] ^ in);
         theIndex = (theIndex + 1) % STREAM_LEN;
 
         if (theIndex == 0) {
             makeKeyStream();
         }
         return out;
     }
 
     /**
      * Decode a 32-bit value from a buffer (little-endian).
      *
      * @param buf the input buffer
      * @param off the input offset
      * @return the decoded value
      */
     private static int decode32le(final byte[] buf, final int off) {
         return (buf[off] & 0xFF)
                 | ((buf[off + 1] & 0xFF) << 8)
                 | ((buf[off + 2] & 0xFF) << 16)
                 | ((buf[off + 3] & 0xFF) << 24);
     }
 
     /**
      * Encode a 32-bit value into a buffer (little-endian).
      *
      * @param val the value to encode
      * @param buf the output buffer
      * @param off the output offset
      */
     private static void encode32le(final int val, final byte[] buf, final int off) {
         buf[off] = (byte) val;
         buf[off + 1] = (byte) (val >> 8);
         buf[off + 2] = (byte) (val >> 16);
         buf[off + 3] = (byte) (val >> 24);
     }
 
     /* Square a 32-bit unsigned integer to obtain the 64-bit result and return */
     /* the upper 32 bits XOR the lower 32 bits */
     static int rabbitGFunc(final int x) {
         /* Construct high and low argument for squaring */
         final int a = x & 0xFFFF;
         final int b = x >>> 16;
 
         /* Calculate high and low result of squaring */
         final int h = ((((a * a) >>> 17) + (a * b)) >>> 15) + b * b;
         final int l = x * x;
 
         /* Return high XOR low */
         return (h ^ l);
     }
 
     /* Calculate the next internal state */
     static void rabbitNextState(final GordianRabbitContext pContext) {
         /* Save old counter values */
         final int[] cOld = Arrays.copyOf(pContext.c, NUM_VARS);
         final int[] g = new int[NUM_VARS];
 
         /* Calculate new counter values */
         pContext.c[0] = (pContext.c[0] + 0x4D34D34D + pContext.carry);
         pContext.c[1] = (pContext.c[1] + 0xD34D34D3 + (Integer.compareUnsigned(pContext.c[0], cOld[0]) < 0 ? 1 : 0));
         pContext.c[2] = (pContext.c[2] + 0x34D34D34 + (Integer.compareUnsigned(pContext.c[1], cOld[1]) < 0 ? 1 : 0));
         pContext.c[3] = (pContext.c[3] + 0x4D34D34D + (Integer.compareUnsigned(pContext.c[2], cOld[2]) < 0 ? 1 : 0));
         pContext.c[4] = (pContext.c[4] + 0xD34D34D3 + (Integer.compareUnsigned(pContext.c[3], cOld[3]) < 0 ? 1 : 0));
         pContext.c[5] = (pContext.c[5] + 0x34D34D34 + (Integer.compareUnsigned(pContext.c[4], cOld[4]) < 0 ? 1 : 0));
         pContext.c[6] = (pContext.c[6] + 0x4D34D34D + (Integer.compareUnsigned(pContext.c[5], cOld[5]) < 0 ? 1 : 0));
         pContext.c[7] = (pContext.c[7] + 0xD34D34D3 + (Integer.compareUnsigned(pContext.c[6], cOld[6]) < 0 ? 1 : 0));
         pContext.carry = Integer.compareUnsigned(pContext.c[7], cOld[7]) < 0 ? 1 : 0;
 
         /* Calculate the g-values */
         for (int i = 0; i < 8; i++) {
             g[i] = rabbitGFunc(pContext.x[i] + pContext.c[i]);
         }
 
         /* Calculate new state values */
         pContext.x[0] = (g[0] + rotl32(g[7], 16) + rotl32(g[6], 16));
         pContext.x[1] = (g[1] + rotl32(g[0], 8) + g[7]);
         pContext.x[2] = (g[2] + rotl32(g[1], 16) + rotl32(g[0], 16));
         pContext.x[3] = (g[3] + rotl32(g[2], 8) + g[1]);
         pContext.x[4] = (g[4] + rotl32(g[3], 16) + rotl32(g[2], 16));
         pContext.x[5] = (g[5] + rotl32(g[4], 8) + g[3]);
         pContext.x[6] = (g[6] + rotl32(g[5], 16) + rotl32(g[4], 16));
         pContext.x[7] = (g[7] + rotl32(g[6], 8) + g[5]);
     }
 
     static int rotl32(final int v, final int n) {
         return (((v) << (n)) | ((v) >>> (32 - (n))));
     }
 
     /* Key setup */
     void setKey(final byte[] key) {
         /* Check lengths */
         if (key == null || key.length != 16) {
             throw new IllegalArgumentException("A key of 16 bytes is needed");
         }
 
         /* Generate four subkeys */
         final int k0 = decode32le(key, 0);
         final int k1 = decode32le(key, 4);
         final int k2 = decode32le(key, 8);
         final int k3 = decode32le(key, 12);
 
         /* Generate initial state variables */
         master.x[0] = k0;
         master.x[2] = k1;
         master.x[4] = k2;
         master.x[6] = k3;
         master.x[1] = (k3 << 16) | (k2 >>> 16);
         master.x[3] = (k0 << 16) | (k3 >>> 16);
         master.x[5] = (k1 << 16) | (k0 >>> 16);
         master.x[7] = (k2 << 16) | (k1 >>> 16);
 
         /* Generate initial counter values */
         master.c[0] = rotl32(k2, 16);
         master.c[2] = rotl32(k3, 16);
         master.c[4] = rotl32(k0, 16);
         master.c[6] = rotl32(k1, 16);
         master.c[1] = (k0 & 0xFFFF0000) | (k1 & 0xFFFF);
         master.c[3] = (k1 & 0xFFFF0000) | (k2 & 0xFFFF);
         master.c[5] = (k2 & 0xFFFF0000) | (k3 & 0xFFFF);
         master.c[7] = (k3 & 0xFFFF0000) | (k0 & 0xFFFF);
 
         /* Clear carry bit */
         master.carry = 0;
 
         /* Iterate the system four times */
         for (int i = 0; i < 4; i++) {
             rabbitNextState(master);
         }
 
         /* Modify the counters */
         for (int i = 0; i < NUM_VARS; i++) {
             master.c[i] ^= master.x[(i + 4) & 0x7];
         }
 
         /* Copy master instance to work instance */
         for (int i = 0; i < NUM_VARS; i++) {
             work.x[i] = master.x[i];
             work.c[i] = master.c[i];
         }
         work.carry = master.carry;
     }
 
     /* ------------------------------------------------------------------------- */
 
     /* IV setup */
     void setIV(final byte[] iv) {
         /* Check lengths */
         if (iv == null || iv.length != 8) {
             throw new IllegalArgumentException("An IV of 8 bytes is needed");
         }
 
         /* Generate four subvectors */
         final int i0 = decode32le(iv, 0);
         final int i2 = decode32le(iv, 4);
         final int i1 = (i0 >>> 16) | (i2 & 0xFFFF0000);
         final int i3 = (i2 << 16) | (i0 & 0x0000FFFF);
 
         /* Modify counter values */
         work.c[0] = master.c[0] ^ i0;
         work.c[1] = master.c[1] ^ i1;
         work.c[2] = master.c[2] ^ i2;
         work.c[3] = master.c[3] ^ i3;
         work.c[4] = master.c[4] ^ i0;
         work.c[5] = master.c[5] ^ i1;
         work.c[6] = master.c[6] ^ i2;
         work.c[7] = master.c[7] ^ i3;
 
         /* Copy state variables */
         for (int i = 0; i < NUM_VARS; i++) {
             work.x[i] = master.x[i];
         }
         work.carry = master.carry;
 
         /* Iterate the system four times */
         for (int i = 0; i < 4; i++) {
             rabbitNextState(work);
         }
     }
 
     /* Generate keystream */
     void makeKeyStream() {
         /* Generate five blocks */
         for (int i = 0; i < STREAM_LEN; i += 16) {
             /* Iterate the system */
             rabbitNextState(work);
 
             /* Generate 16 bytes of pseudo-random data */
             encode32le(work.x[0] ^ (work.x[5] >>> 16) ^ (work.x[3] << 16), keyStream, i + 0);
             encode32le(work.x[2] ^ (work.x[7] >>> 16) ^ (work.x[5] << 16), keyStream, i + 4);
             encode32le(work.x[4] ^ (work.x[1] >>> 16) ^ (work.x[7] << 16), keyStream, i + 8);
             encode32le(work.x[6] ^ (work.x[3] >>> 16) ^ (work.x[1] << 16), keyStream, i + 12);
         }
     }
 
     @Override
     public GordianRabbitEngine copy() {
         return new GordianRabbitEngine(this);
     }
 
     @Override
     public void reset(final Memoable pState) {
         final GordianRabbitEngine e = (GordianRabbitEngine) pState;
         work.copyFrom(e.work);
         master.copyFrom(e.master);
         System.arraycopy(e.keyStream, 0, keyStream, 0, STREAM_LEN);
         theIndex = e.theIndex;
     }
 }