/*
    * Copyright 2023 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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.netty.handler.codec.quic;
  
  import io.netty.util.concurrent.FastThreadLocal;
  
  import javax.crypto.Mac;
  import javax.crypto.spec.SecretKeySpec;
  import java.nio.ByteBuffer;
  import java.security.InvalidKeyException;
  import java.security.NoSuchAlgorithmException;
  import java.security.SecureRandom;
  import java.util.Arrays;
  
  final class Hmac {
  
      private static final String ALGORITHM = "HmacSHA256";
  
      // Two independent keys so that CID signing and reset-token signing are
      // cryptographically decoupled: an observer cannot derive one output from
      // the other even when both use the same input value (RFC 9000 §21.11).
      private static final byte[] CID_KEY   = new byte[32];
      private static final byte[] TOKEN_KEY = new byte[32];
  
      static {
          SecureRandom rng = new SecureRandom();
          rng.nextBytes(CID_KEY);
          rng.nextBytes(TOKEN_KEY);
      }
  
      private static final FastThreadLocal<Mac> CID_MACS = new FastThreadLocal<Mac>() {
          @Override
          protected Mac initialValue() {
              return newMac(CID_KEY);
          }
      };
  
      private static final FastThreadLocal<Mac> TOKEN_MACS = new FastThreadLocal<Mac>() {
          @Override
          protected Mac initialValue() {
              return newMac(TOKEN_KEY);
          }
      };
  
      private static Mac newMac(byte[] key) {
          try {
              SecretKeySpec keySpec = new SecretKeySpec(key, ALGORITHM);
              Mac mac = Mac.getInstance(ALGORITHM);
              mac.init(keySpec);
              return mac;
          } catch (NoSuchAlgorithmException | InvalidKeyException exception) {
              throw new IllegalStateException(exception);
          }
      }
  
      private static ByteBuffer sign(Mac mac, ByteBuffer input, int outLength) {
          mac.reset();
          mac.update(input);
          byte[] signBytes = mac.doFinal();
          if (signBytes.length != outLength) {
              signBytes = Arrays.copyOf(signBytes, outLength);
          }
          return ByteBuffer.wrap(signBytes);
      }
  
      static ByteBuffer signCid(ByteBuffer input, int outLength) {
          return sign(CID_MACS.get(), input, outLength);
      }
  
      static ByteBuffer signToken(ByteBuffer input, int outLength) {
          return sign(TOKEN_MACS.get(), input, outLength);
      }
  
      private Hmac() { }
  }