//    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) 2012-2022 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/>.

// Base class for OpenVPN data channel encryption/decryption

#ifndef OPENVPN_CRYPTO_CRYPTODC_H
#define OPENVPN_CRYPTO_CRYPTODC_H

#include <utility> // for std::move
#include <cstdint> // for std::uint32_t, etc.

#include <openvpn/common/exception.hpp>
#include <openvpn/buffer/buffer.hpp>
#include <openvpn/error/error.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/frame/frame.hpp>
#include <openvpn/crypto/static_key.hpp>
#include <openvpn/crypto/packet_id.hpp>
#include <openvpn/crypto/cryptoalgs.hpp>
#include <openvpn/compress/compress.hpp>

namespace openvpn {

// Base class for encryption/decryption of data channel
class CryptoDCInstance : public RC<thread_unsafe_refcount>
{
  public:
    typedef RCPtr<CryptoDCInstance> Ptr;

    // Encrypt/Decrypt

    // returns true if packet ID is close to wrapping
    virtual bool encrypt(BufferAllocated &buf, const PacketID::time_t now, const unsigned char *op32) = 0;

    virtual Error::Type decrypt(BufferAllocated &buf, const PacketID::time_t now, const unsigned char *op32) = 0;

    // Initialization

    // return value of defined()
    enum
    {
        CIPHER_DEFINED = (1 << 0),               // may call init_cipher method
        HMAC_DEFINED = (1 << 1),                 // may call init_hmac method
        CRYPTO_DEFINED = (1 << 2),               // may call encrypt or decrypt methods
        EXPLICIT_EXIT_NOTIFY_DEFINED = (1 << 3), // may call explicit_exit_notify method
    };
    virtual unsigned int defined() const = 0;

    virtual void init_cipher(StaticKey &&encrypt_key,
                             StaticKey &&decrypt_key)
        = 0;

    virtual void init_hmac(StaticKey &&encrypt_key,
                           StaticKey &&decrypt_key)
        = 0;

    virtual void init_pid(const int send_form,
                          const int recv_mode,
                          const int recv_form,
                          const char *recv_name,
                          const int recv_unit,
                          const SessionStats::Ptr &recv_stats_arg)
        = 0;

    virtual void init_remote_peer_id(const int remote_peer_id)
    {
    }

    virtual bool consider_compression(const CompressContext &comp_ctx) = 0;

    virtual void explicit_exit_notify()
    {
    }

    // Rekeying

    enum RekeyType
    {
        ACTIVATE_PRIMARY,
        ACTIVATE_PRIMARY_MOVE,
        NEW_SECONDARY,
        PRIMARY_SECONDARY_SWAP,
        DEACTIVATE_SECONDARY,
        DEACTIVATE_ALL,
    };

    virtual void rekey(const RekeyType type) = 0;
};

// Factory for CryptoDCInstance objects
class CryptoDCContext : public RC<thread_unsafe_refcount>
{
  public:
    explicit CryptoDCContext(const CryptoAlgs::KeyDerivation method)
        : key_derivation(method)
    {
    }

    typedef RCPtr<CryptoDCContext> Ptr;

    virtual CryptoDCInstance::Ptr new_obj(const unsigned int key_id) = 0;

    // cipher/HMAC/key info
    struct Info
    {
        Info()
        {
        }
        CryptoAlgs::Type cipher_alg = CryptoAlgs::NONE;
        CryptoAlgs::Type hmac_alg = CryptoAlgs::NONE;
        CryptoAlgs::KeyDerivation key_derivation = CryptoAlgs::KeyDerivation::OPENVPN_PRF;
    };
    virtual Info crypto_info() = 0;

    // Info for ProtoContext::link_mtu_adjust
    virtual size_t encap_overhead() const = 0;

  protected:
    CryptoAlgs::KeyDerivation key_derivation = CryptoAlgs::KeyDerivation::OPENVPN_PRF;
};

// Factory for CryptoDCContext objects
class CryptoDCFactory : public RC<thread_unsafe_refcount>
{
  public:
    typedef RCPtr<CryptoDCFactory> Ptr;

    virtual CryptoDCContext::Ptr new_obj(const CryptoAlgs::Type cipher,
                                         const CryptoAlgs::Type digest,
                                         const CryptoAlgs::KeyDerivation method)
        = 0;
};

// Manage cipher/digest settings, DC factory, and DC context.
class CryptoDCSettings
{
  public:
    OPENVPN_SIMPLE_EXCEPTION(no_data_channel_factory);

    CryptoDCSettings()
    {
    }

    void set_factory(const CryptoDCFactory::Ptr &factory)
    {
        factory_ = factory;
        context_.reset();
        dirty = false;
    }

    void set_cipher(const CryptoAlgs::Type cipher)
    {
        if (cipher != cipher_)
        {
            cipher_ = cipher;
            dirty = true;
        }
    }

    void set_digest(const CryptoAlgs::Type digest)
    {
        if (digest != digest_)
        {
            digest_ = digest;
            dirty = true;
        }
    }

    CryptoDCContext &context()
    {
        if (!context_ || dirty)
        {
            if (!factory_)
                throw no_data_channel_factory();
            context_ = factory_->new_obj(cipher_, digest_, key_derivation_);
            dirty = false;
        }
        return *context_;
    }

    void reset()
    {
        factory_.reset();
        context_.reset();
        dirty = false;
    }

    CryptoAlgs::Type cipher() const
    {
        return cipher_;
    }

    /**
     *  Retrieve the digest configured for the data channel.
     *  If the configured data channel cipher does not use any
     *  additional digest, CryptoAlgs::NONE is returned.
     *
     * @return  Returns the cipher digest in use
     */
    CryptoAlgs::Type digest() const
    {
        return (CryptoAlgs::use_cipher_digest(cipher_) ? digest_ : CryptoAlgs::NONE);
    }


    CryptoDCFactory::Ptr factory() const
    {
        return factory_;
    }

    void set_key_derivation(CryptoAlgs::KeyDerivation method)
    {
        key_derivation_ = method;
    }

    CryptoAlgs::KeyDerivation key_derivation() const
    {
        return key_derivation_;
    }

  private:
    CryptoAlgs::Type cipher_ = CryptoAlgs::NONE;
    CryptoAlgs::Type digest_ = CryptoAlgs::NONE;
    CryptoAlgs::KeyDerivation key_derivation_ = CryptoAlgs::KeyDerivation::OPENVPN_PRF;

    CryptoDCFactory::Ptr factory_;
    CryptoDCContext::Ptr context_;
    bool dirty = false;
};
} // namespace openvpn

#endif
