/*
 * Copyright contributors to the AERE Network.
 *
 * 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.
 *
 * SPDX-License-Identifier: Apache-2.0
 */
package org.hyperledger.besu.evm.precompile;

import org.hyperledger.besu.evm.frame.MessageFrame;
import org.hyperledger.besu.evm.gascalculator.GasCalculator;

import jakarta.validation.constraints.NotNull;
import org.apache.tuweni.bytes.Bytes;
import org.apache.tuweni.bytes.Bytes32;
import org.bouncycastle.pqc.crypto.slhdsa.SLHDSAParameters;
import org.bouncycastle.pqc.crypto.slhdsa.SLHDSAPublicKeyParameters;
import org.bouncycastle.pqc.crypto.slhdsa.SLHDSASigner;

/**
 * AERE PQC precompile: SLH-DSA-SHA2-128s (SPHINCS+, FIPS 205) signature verification via the
 * INTERNAL interface (slh_verify_internal, Algorithm 20 — message hashed directly, no prefix).
 *
 * <p>Input: {@code pk(32) || sig(7856) || message(rest)}. Output: 32-byte word, {@code ...01} valid
 * else {@code ...00}. The internal verifier is reached by subclassing Bouncy Castle's
 * {@link SLHDSASigner} and calling its {@code protected internalVerifySignature}.
 */
public class SLHDSA128sPrecompiledContract extends AbstractPrecompiledContract {

  static final int PK_LEN = 32;
  static final int SIG_LEN = 7856;
  private static final long GAS = 350_000L;

  /** Subclass exposing Bouncy Castle's protected internal (slh_verify_internal) verifier. */
  private static final class InternalVerifier extends SLHDSASigner {
    boolean verifyInternal(final byte[] message, final byte[] signature) {
      return internalVerifySignature(message, signature);
    }
  }

  /**
   * Instantiates a new SLH-DSA-128s precompiled contract.
   *
   * @param gasCalculator the gas calculator
   */
  SLHDSA128sPrecompiledContract(final GasCalculator gasCalculator) {
    super("AereSLHDSA128s", gasCalculator);
  }

  @Override
  public long gasRequirement(final Bytes input) {
    return GAS;
  }

  @NotNull
  @Override
  public PrecompileContractResult computePrecompile(
      final Bytes input, @NotNull final MessageFrame messageFrame) {
    boolean valid = false;
    if (input.size() >= PK_LEN + SIG_LEN) {
      try {
        final byte[] pk = input.slice(0, PK_LEN).toArrayUnsafe();
        final byte[] sig = input.slice(PK_LEN, SIG_LEN).toArrayUnsafe();
        final byte[] message = input.slice(PK_LEN + SIG_LEN).toArrayUnsafe();
        final SLHDSAPublicKeyParameters pub =
            new SLHDSAPublicKeyParameters(SLHDSAParameters.sha2_128s, pk);
        final InternalVerifier verifier = new InternalVerifier();
        verifier.init(false, pub);
        valid = verifier.verifyInternal(message, sig);
      } catch (final Throwable t) {
        valid = false;
      }
    }
    return PrecompileContractResult.success(
        valid ? Bytes32.leftPad(Bytes.of((byte) 1)) : Bytes32.ZERO);
  }
}