//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// Wrap the OpenSSL HMAC API defined in <openssl/hmac.h> so
// that it can be used as part of the crypto layer of the OpenVPN core.

#ifndef OPENVPN_OPENSSL_CRYPTO_HMAC_H
#define OPENVPN_OPENSSL_CRYPTO_HMAC_H

#include <string>

#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/openssl/crypto/digest.hpp>

#include <openvpn/openssl/compat.hpp>

namespace openvpn {
  namespace OpenSSLCrypto {
    class HMACContext
    {
      HMACContext(const HMACContext&) = delete;
      HMACContext& operator=(const HMACContext&) = delete;

    public:
      OPENVPN_SIMPLE_EXCEPTION(openssl_hmac_uninitialized);
      OPENVPN_EXCEPTION(openssl_hmac_error);

      enum {
	MAX_HMAC_SIZE = EVP_MAX_MD_SIZE
      };

      HMACContext() = default;

      HMACContext(const CryptoAlgs::Type digest, const unsigned char *key, const size_t key_size)
      {
	init(digest, key, key_size);
      }

      ~HMACContext() { erase() ; }

      void init(const CryptoAlgs::Type digest, const unsigned char *key, const size_t key_size)
      {
	erase();
	ctx = HMAC_CTX_new ();
	if (!HMAC_Init_ex (ctx, key, int(key_size), DigestContext::digest_type(digest), nullptr))
	  {
	    openssl_clear_error_stack();
	    HMAC_CTX_free(ctx);
	    ctx = nullptr;
	    throw openssl_hmac_error("HMAC_Init_ex (init)");
	  }
      }

      void reset()
      {
	check_initialized();
	if (!HMAC_Init_ex (ctx, nullptr, 0, nullptr, nullptr))
	  {
	    openssl_clear_error_stack();
	    throw openssl_hmac_error("HMAC_Init_ex (reset)");
	  }
      }

      void update(const unsigned char *in, const size_t size)
      {
	check_initialized();

	if (!HMAC_Update(ctx, in, int(size)))
	  {
	    openssl_clear_error_stack();
	    throw openssl_hmac_error("HMAC_Update");
	  }
      }

      size_t final(unsigned char *out)
      {
	check_initialized();
	unsigned int outlen;
	if (!HMAC_Final(ctx, out, &outlen))
	  {
	    openssl_clear_error_stack();
	    throw openssl_hmac_error("HMAC_Final");
	  }
	return outlen;
      }

      size_t size() const
      {
	check_initialized();
	return size_();
      }

      bool is_initialized() const { return ctx != nullptr; }

    private:
      void erase()
      {
	  HMAC_CTX_free(ctx);
	  ctx = nullptr;
      }

      size_t size_() const
      {
	return HMAC_size(ctx);
      }

      void check_initialized() const
      {
#ifdef OPENVPN_ENABLE_ASSERT
	if (!ctx)
	  throw openssl_hmac_uninitialized();
#endif
      }

      HMAC_CTX* ctx = nullptr;
    };
  }
}

#endif