/*
    * 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.base.GordianDataConverter;
  import io.github.tonywasher.joceanus.gordianknot.impl.core.exc.GordianCryptoException;
  import org.bouncycastle.asn1.ASN1OctetString;
  import org.bouncycastle.asn1.ASN1Primitive;
  import org.bouncycastle.asn1.DEROctetString;
  import org.bouncycastle.asn1.ua.DSTU4145Params;
  import org.bouncycastle.crypto.Digest;
  import org.bouncycastle.crypto.digests.GOST3411Digest;
  import org.bouncycastle.crypto.params.ParametersWithRandom;
  import org.bouncycastle.crypto.signers.DSTU4145Signer;
  
  import java.math.BigInteger;
  
  /**
   * DSTU signer.
   */
  public class BouncyDSTUSignature
          extends BouncyDigestSignature {
      /**
       * Expanded sandBox length.
       */
      private static final int EXPANDED_LEN = 128;
  
      /**
       * The Signer.
       */
      private final DSTU4145Signer theSigner;
  
      /**
       * The Coder.
       */
      private final BouncyDSTUCoder theCoder;
  
      /**
       * Constructor.
       *
       * @param pFactory the factory
       * @param pSpec    the signatureSpec.
       */
      BouncyDSTUSignature(final GordianBaseFactory pFactory,
                          final GordianSignatureSpec pSpec) {
          /* Initialise underlying class */
          super(pFactory, pSpec, newDigest());
  
          /* Create the signer and Coder */
          theSigner = new DSTU4145Signer();
          theCoder = new BouncyDSTUCoder();
      }
  
      @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]);
     }
 
     /**
      * Obtain new digest for DSTU signer.
      *
      * @return the new digest
      */
     private static Digest newDigest() {
         final byte[] myCompressed = DSTU4145Params.getDefaultDKE();
         final byte[] myExpanded = new byte[EXPANDED_LEN];
 
         for (int i = 0; i < myCompressed.length; i++) {
             myExpanded[i * 2] = (byte) ((myCompressed[i] >> GordianDataConverter.NYBBLE_SHIFT)
                     & GordianDataConverter.NYBBLE_MASK);
             myExpanded[i * 2 + 1] = (byte) (myCompressed[i] & GordianDataConverter.NYBBLE_MASK);
         }
         return new GOST3411Digest(myExpanded);
     }
 
     /**
      * DSTU encoder.
      */
     static final class BouncyDSTUCoder implements BouncyDSACoder {
         @Override
         public byte[] dsaEncode(final BigInteger r,
                                 final BigInteger s) throws GordianException {
             /* Protect against exceptions */
             try {
                 /* Access byteArrays */
                 final byte[] myFirst = s.toByteArray();
                 final byte[] mySecond = r.toByteArray();
                 final byte[] myResult = myFirst.length > mySecond.length
                         ? new byte[myFirst.length * 2]
                         : new byte[mySecond.length * 2];
 
                 /* Build array and return */
                 System.arraycopy(myFirst, 0, myResult, myResult.length / 2 - myFirst.length, myFirst.length);
                 System.arraycopy(mySecond, 0, myResult, myResult.length - mySecond.length, mySecond.length);
                 return new DEROctetString(myResult).getEncoded();
             } catch (Exception e) {
                 throw new GordianCryptoException(BouncySignature.ERROR_SIGGEN, e);
             }
         }
 
         @Override
         public BigInteger[] dsaDecode(final byte[] pEncoded) throws GordianException {
             /* Protect against exceptions */
             try {
                 /* Access the bytes */
                 final byte[] bytes = ((ASN1OctetString) ASN1Primitive.fromByteArray(pEncoded)).getOctets();
 
                 /* Build the value arrays */
                 final byte[] myFirst = new byte[bytes.length / 2];
                 final byte[] mySecond = new byte[bytes.length / 2];
                 System.arraycopy(bytes, 0, myFirst, 0, myFirst.length);
                 System.arraycopy(bytes, 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;
             } catch (Exception e) {
                 throw new GordianCryptoException(BouncySignature.ERROR_SIGPARSE, e);
             }
         }
     }
 }