/*
 * 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.bouncycastle.pqc.crypto.falcon.FalconParameters;

/**
 * AERE PQC precompile: Falcon-512 signature verification (NIST round-3 reference encoding).
 *
 * <p>Input: {@code pk(897) || sm(rest)} where pk is the reference public key (header 0x09) and sm is
 * the reference signed-message blob. Output: 32-byte word, {@code ...01} if valid else {@code ...00}.
 */
public class Falcon512PrecompiledContract extends AbstractPrecompiledContract {

  static final int PK_LEN = 897;
  private static final int LOGN = 9;
  private static final long GAS = 40_000L;

  /**
   * Instantiates a new Falcon-512 precompiled contract.
   *
   * @param gasCalculator the gas calculator
   */
  Falcon512PrecompiledContract(final GasCalculator gasCalculator) {
    super("AereFalcon512", 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) {
      final byte[] pk = input.slice(0, PK_LEN).toArrayUnsafe();
      final byte[] sm = input.slice(PK_LEN).toArrayUnsafe();
      valid = AereFalconSupport.verify(FalconParameters.falcon_512, LOGN, pk, sm);
    }
    return PrecompileContractResult.success(AereFalconSupport.resultWord(valid));
  }
}