/*
    * GordianKnot: Security Suite
    * Copyright 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.bc.sign;
  
  import io.github.tonywasher.joceanus.gordianknot.api.base.GordianException;
  import io.github.tonywasher.joceanus.gordianknot.api.sign.GordianNewSignParams;
  import io.github.tonywasher.joceanus.gordianknot.api.sign.spec.GordianSignatureSpec;
  import io.github.tonywasher.joceanus.gordianknot.impl.bc.keypair.BouncyEllipticKeyPair.BouncyECPrivateKey;
  import io.github.tonywasher.joceanus.gordianknot.impl.bc.keypair.BouncyEllipticKeyPair.BouncyECPublicKey;
  import io.github.tonywasher.joceanus.gordianknot.impl.bc.keypair.BouncyKeyPair;
  import io.github.tonywasher.joceanus.gordianknot.impl.bc.sign.BouncySignature.BouncyDSACoder;
  import io.github.tonywasher.joceanus.gordianknot.impl.core.base.GordianBaseFactory;
  import io.github.tonywasher.joceanus.gordianknot.impl.core.spec.sign.GordianCoreSignatureSpec;
  import org.bouncycastle.crypto.params.ParametersWithRandom;
  import org.bouncycastle.crypto.signers.ECGOST3410Signer;
  
  import java.math.BigInteger;
  
  /**
   * GOST signer.
   */
  public class BouncyGOSTSignature
          extends BouncyDigestSignature {
      /**
       * The Signer.
       */
      private final ECGOST3410Signer theSigner;
  
      /**
       * The Coder.
       */
      private final BouncyGOSTCoder theCoder;
  
      /**
       * Constructor.
       *
       * @param pFactory the factory
       * @param pSpec    the signatureSpec.
       * @throws GordianException on error
       */
      BouncyGOSTSignature(final GordianBaseFactory pFactory,
                          final GordianSignatureSpec pSpec) throws GordianException {
          /* Initialise underlying class */
          super(pFactory, pSpec);
  
          /* Create the signer and Coder */
          theSigner = new ECGOST3410Signer();
          theCoder = new BouncyGOSTCoder(((GordianCoreSignatureSpec) pSpec).getDigestSpec().getDigestLength().getByteLength() << 1);
      }
  
      @Override
      public void initForSigning(final GordianNewSignParams pParams) throws GordianException {
          /* Initialise detail */
          super.initForSigning(pParams);
          final BouncyKeyPair myPair = getKeyPair();
          BouncyKeyPair.checkKeyPair(myPair);
  
          /* Initialise and set the signer */
          final BouncyECPrivateKey myPrivate = (BouncyECPrivateKey) myPair.getPrivateKey();
          final ParametersWithRandom myParms = new ParametersWithRandom(myPrivate.getPrivateKey(), getRandom());
          theSigner.init(true, myParms);
      }
  
      @Override
      public void initForVerify(final GordianNewSignParams pParams) throws GordianException {
          /* Initialise detail */
          super.initForVerify(pParams);
          final BouncyKeyPair myPair = getKeyPair();
          BouncyKeyPair.checkKeyPair(myPair);
  
          /* Initialise and set the signer */
          final BouncyECPublicKey myPublic = (BouncyECPublicKey) myPair.getPublicKey();
          theSigner.init(false, myPublic.getPublicKey());
      }
  
      @Override
      public byte[] sign() throws GordianException {
          /* Check that we are in signing mode */
          checkMode(GordianSignatureMode.SIGN);
  
          /* Sign the message */
          final BigInteger[] myValues = theSigner.generateSignature(getDigest());
          return theCoder.dsaEncode(myValues[0], myValues[1]);
      }
 
     @Override
     public boolean verify(final byte[] pSignature) throws GordianException {
         /* Check that we are in verify mode */
         checkMode(GordianSignatureMode.VERIFY);
 
         /* Verify the message */
         final BigInteger[] myValues = theCoder.dsaDecode(pSignature);
         return theSigner.verifySignature(getDigest(), myValues[0], myValues[1]);
     }
 
     /**
      * GOST encoder.
      */
     static final class BouncyGOSTCoder
             implements BouncyDSACoder {
         /**
          * The fixed length (if any).
          */
         private final Integer theLen;
 
         /**
          * Constructor.
          *
          * @param pLen the fixed length (or null)
          */
         BouncyGOSTCoder(final Integer pLen) {
             theLen = pLen;
         }
 
         @Override
         public byte[] dsaEncode(final BigInteger r,
                                 final BigInteger s) {
             /* Access byteArrays */
             final byte[] myFirst = makeUnsigned(s);
             final byte[] mySecond = makeUnsigned(r);
             final byte[] myResult = new byte[theLen];
 
             /* Build array and return */
             System.arraycopy(myFirst, 0, myResult, theLen / 2 - myFirst.length, myFirst.length);
             System.arraycopy(mySecond, 0, myResult, theLen - mySecond.length, mySecond.length);
             return myResult;
         }
 
         /**
          * Make the value unsigned.
          *
          * @param pValue the value
          * @return the unsigned value
          */
         private static byte[] makeUnsigned(final BigInteger pValue) {
             /* Convert to byteArray and return if OK */
             final byte[] myResult = pValue.toByteArray();
             if (myResult[0] != 0) {
                 return myResult;
             }
 
             /* Shorten the array */
             final byte[] myTmp = new byte[myResult.length - 1];
             System.arraycopy(myResult, 1, myTmp, 0, myTmp.length);
             return myTmp;
         }
 
         @Override
         public BigInteger[] dsaDecode(final byte[] pEncoded) {
             /* Build the value arrays */
             final byte[] myFirst = new byte[pEncoded.length / 2];
             final byte[] mySecond = new byte[pEncoded.length / 2];
             System.arraycopy(pEncoded, 0, myFirst, 0, myFirst.length);
             System.arraycopy(pEncoded, myFirst.length, mySecond, 0, mySecond.length);
 
             /* Create the signature values and return */
             final BigInteger[] sig = new BigInteger[2];
             sig[1] = new BigInteger(1, myFirst);
             sig[0] = new BigInteger(1, mySecond);
             return sig;
         }
     }
 }