#pragma once

#include <asio/any_completion_handler.hpp>
#include <asio/basic_datagram_socket.hpp>
#include <asio/basic_seq_packet_socket.hpp>
#include <asio/basic_stream_socket.hpp>
#include <asio/bind_executor.hpp>
#include <asio/compose.hpp>
#include <asio/deferred.hpp>
#include <asio/ip/tcp.hpp>
#include <asio/ip/udp.hpp>
#include <asio/local/datagram_protocol.hpp>
#include <asio/local/seq_packet_protocol.hpp>
#include <asio/local/stream_protocol.hpp>
#include <asio/read.hpp>
#include <asio/read_until.hpp>
#include <asio/steady_timer.hpp>
#include <asio/strand.hpp>
#include <asio/streambuf.hpp>
#include <asio/use_awaitable.hpp>
#include <asio/use_future.hpp>
#include <asio/write.hpp>

#include <functional>
#include <queue>

#ifdef USE_OPENSSL_WITH_ASIO

#include <asio/ssl.hpp>
#include <asio/ssl/stream.hpp>

#endif


#include "../../common/adc_traits.h"
#include "../adc_net_concepts.h"

namespace adc::traits
{

// special ASIO-related template specializations

template <>
struct adc_func_traits<asio::use_future_t<>> {
    using ret_t = std::nullptr_t;
    using args_t = std::tuple<std::nullptr_t, std::nullptr_t>;
    using arg1_t = std::nullptr_t;
    static constexpr size_t arity = 0;
};

template <>
struct adc_func_traits<asio::use_awaitable_t<>> {
    using ret_t = std::nullptr_t;
    using args_t = std::tuple<std::nullptr_t, std::nullptr_t>;
    using arg1_t = std::nullptr_t;
    static constexpr size_t arity = 0;
};

template <>
struct adc_func_traits<asio::deferred_t> {
    using ret_t = std::nullptr_t;
    using args_t = std::tuple<std::nullptr_t, std::nullptr_t>;
    using arg1_t = std::nullptr_t;
    static constexpr size_t arity = 0;
};

}  // namespace adc::traits


namespace adc::impl
{

template <typename T>
concept adc_asio_transport_proto_c =
    std::derived_from<T, asio::ip::tcp> || std::derived_from<T, asio::ip::udp> ||
    std::derived_from<T, asio::local::seq_packet_protocol> || std::derived_from<T, asio::local::stream_protocol> ||
    std::derived_from<T, asio::local::datagram_protocol>;


template <typename T>
concept adc_asio_tls_transport_proto_c =
    std::derived_from<T, asio::ip::tcp> || std::derived_from<T, asio::local::stream_protocol> ||
    std::derived_from<T, asio::local::seq_packet_protocol>;

template <typename T>
concept adc_asio_stream_transport_proto_c =
    std::derived_from<T, asio::ip::tcp> || std::derived_from<T, asio::local::stream_protocol>;


template <typename T>
concept adc_asio_is_future = requires {
    // [](std::type_identity<asio::use_future_t<>>) {}(std::type_identity<std::remove_cvref_t<T>>());
    []<typename AllocatorT>(std::type_identity<asio::use_future_t<AllocatorT>>) {
    }(std::type_identity<std::remove_cvref_t<T>>{});
};

template <typename T>
concept adc_asio_is_awaitable = requires {
    []<typename ExecutorT>(std::type_identity<asio::use_awaitable_t<ExecutorT>>) {
    }(std::type_identity<std::remove_cvref_t<T>>{});
};


template <typename T>
concept adc_asio_special_comp_token_c =
    adc_asio_is_future<T> || adc_asio_is_awaitable<T> || std::same_as<std::remove_cvref_t<T>, asio::deferred_t>;



template <
    bool USE_TLS,                                 // true - use of asio::ssl::stream<TRANSPORT_PROTOT>
    adc_asio_transport_proto_c TRANSPORT_PROTOT,  // transport-level proto (e.g. asio::ip::tcp)
    interfaces::adc_netsession_proto_c<std::string_view> SESSION_PROTOT,  // session-level proto (see ../adc_netproto.h)
    traits::adc_output_char_range RMSGT = std::vector<char>>  // used only for inner storing of message byte sequence
class AdcBaseNetServiceASIO : public SESSION_PROTOT
{
public:
#ifdef USE_OPENSSL_WITH_ASIO
    // static_assert(!(USE_TLS && adc_asio_tls_transport_proto_c<TRANSPORT_PROTOT>),
    //               "INVALID 'TRANSPORT_PROTOT' TEMPLATE ARGUMENT!");

    static constexpr bool isTLS = USE_TLS;
#else  // ignore USE_TLS
    static constexpr bool isTLS = false;
#endif

    // typedefs to satisfy 'adc_netservice_c' concept
    typedef std::string_view netservice_ident_t;


    typedef std::vector<char> send_msg_t;  // in general, only one of several possible
    typedef RMSGT recv_msg_t;  // in general, only one of several possible (see class template arguments declaration)
    typedef traits::adc_common_duration_t timeout_t;
    using endpoint_t = typename TRANSPORT_PROTOT::endpoint;

    // typedefs for completion tokens (callbacks, required by 'adc_netservice_c' concept)
    typedef std::error_code async_callback_err_t;

    typedef std::function<void(std::error_code)> async_connect_callback_t;
    typedef std::function<void(std::error_code)> async_send_callback_t;
    typedef std::function<void(std::error_code, RMSGT)> async_receive_callback_t;


    // typedefs from transport protocol
    using socket_t = typename TRANSPORT_PROTOT::socket;  // low-level socket type
#ifdef USE_OPENSSL_WITH_ASIO
    using session_level_socket_t = std::conditional_t<isTLS, asio::ssl::stream<socket_t>, std::nullptr_t>;

    // TLS certificate attributes comparison function:
    //     'serial' - as returned by OpenSSL BN_bn2hex
    //     'fingerprint' - as returned by OpenSSL X509_digest
    //     'depth' - depth in chain
    // the function must return 0 - if comparison failed; otherwise - something != 0
    typedef std::function<int(const std::string& serial, const std::vector<unsigned char>& fingerprint, int depth)>
        cert_comp_func_t;
#else
    using session_level_socket_t = socket_t;
#endif


    struct acceptor_t {
        using srv_acceptor_t = std::conditional_t<
            std::derived_from<socket_t, asio::basic_datagram_socket<typename socket_t::protocol_type>>,
            std::nullptr_t,  // there is no acceptor
            typename TRANSPORT_PROTOT::acceptor>;

        static constexpr std::chrono::duration DEFAULT_ACCEPT_TIMEOUT = std::chrono::seconds::max();

        typedef AdcBaseNetServiceASIO netservice_t;
        typedef std::function<void(std::error_code, netservice_t)> async_accept_callback_t;


        acceptor_t(asio::io_context& io_context)
            requires(!netservice_t::isTLS)
            : _ioContext(io_context), _acceptor(io_context)
        {
        }

        acceptor_t(asio::io_context& io_context, const netservice_t::endpoint_t& endpoint)
            requires(!netservice_t::isTLS)
            : _ioContext(io_context), _acceptor(io_context, endpoint)
        {
        }

#ifdef USE_OPENSSL_WITH_ASIO
        acceptor_t(asio::io_context& io_context,
                   asio::ssl::context tls_ctx,
                   asio::ssl::verify_mode tls_verify_mode = asio::ssl::context_base::verify_peer)
            requires netservice_t::isTLS
            : _ioContext(io_context), _acceptor(io_context), _tlsCtx(std::move(tls_ctx)), _tlsVerMode(tls_verify_mode)
        {
        }

        acceptor_t(asio::io_context& io_context,
                   const netservice_t::endpoint_t& endpoint,
                   asio::ssl::context tls_ctx,
                   asio::ssl::verify_mode tls_verify_mode = asio::ssl::context_base::verify_peer)
            requires netservice_t::isTLS
            : _ioContext(io_context),
              _acceptor(io_context, endpoint),
              _tlsCtx(std::move(tls_ctx)),
              _tlsVerMode(tls_verify_mode)
        {
        }
#endif
        template <asio::completion_token_for<void(std::error_code, netservice_t)> TokenT,
                  traits::adc_time_duration_c DT = decltype(DEFAULT_ACCEPT_TIMEOUT)>
        auto asyncAccept(TokenT&& token, const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            enum { sock_accept, handshake, done };

            auto timer = netservice_t::getDeadlineTimer(_acceptor, timeout);

#ifdef USE_OPENSSL_WITH_ASIO
            auto srv = [&, this]() {
                if constexpr (netservice_t::isTLS) {
                    return std::make_unique<netservice_t>(_ioContext, std::move(_tlsCtx), _tlsVerMode);
                } else {
                    return std::make_unique<netservice_t>(_ioContext);
                }
            }();
#else
            auto srv = std::make_unique<netservice_t>(_ioContext);
#endif
            return asio::async_compose<TokenT, void(std::error_code, netservice_t)>(
                [timer = std::move(timer), srv = std::move(srv), state = sock_accept, this](
                    auto& self, std::error_code ec = {}) mutable {
                    if (!ec) {
                        switch (state) {
                            case sock_accept:
                                if constexpr (netservice_t::isTLS) {
                                    state = handshake;
                                } else {
                                    state = done;
                                }
                                return _acceptor.async_accept(srv->_socket, std::move(self));
                                break;
                            case handshake:
                                state = done;
#ifdef USE_OPENSSL_WITH_ASIO
                                if constexpr (netservice_t::isTLS) {
                                    srv->_sessSocket =
                                        netservice_t::session_level_socket_t(std::move(srv->_socket), srv->_tlsContext);
                                    return srv->_sessSocket.async_handshake(asio::ssl::stream_base::server,
                                                                            std::move(self));
                                }
#endif
                                break;
                            case done:
                                break;
                            default:
                                break;
                        }
                    }

                    if (netservice_t::isTimeout(timer, ec)) {
                        ec = std::make_error_code(std::errc::timed_out);
                    } else {  // an error occured in async_accept od async_handshake
                        timer->cancel();
                    }

                    self.complete(ec, std::move(*srv));

                    srv.reset();
                },
                token, _ioContext);
        }

        template <asio::completion_token_for<void(std::error_code, netservice_t)> TokenT,
                  traits::adc_time_duration_c DT = decltype(DEFAULT_ACCEPT_TIMEOUT)>
        auto asyncAccept(const netservice_t::endpoint_t& endpoint,
                         TokenT&& token,
                         const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            _acceptor = srv_acceptor_t(_ioContext, endpoint);
            return asyncAccept(std::forward<TokenT>(token), timeout);
        }

        template <traits::adc_time_duration_c DT = decltype(DEFAULT_ACCEPT_TIMEOUT)>
        auto accept(const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            auto f = asyncAccept(asio::use_future, timeout);

            return f.get();
        }

        template <traits::adc_time_duration_c DT = decltype(DEFAULT_ACCEPT_TIMEOUT)>
        auto accept(const endpoint_t& endpoint, const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            _acceptor = srv_acceptor_t(_ioContext, endpoint);
            return accept(timeout);
        }

        void close(std::error_code& ec)
        {
            _acceptor.close(ec);
        }

    private:
        asio::io_context& _ioContext;
        srv_acceptor_t _acceptor;

#ifdef USE_OPENSSL_WITH_ASIO
        asio::ssl::context _tlsCtx{asio::ssl::context_base::tlsv13};
        asio::ssl::verify_mode _tlsVerMode;
#endif
    };


    static constexpr std::chrono::duration DEFAULT_CONNECT_TIMEOUT = std::chrono::seconds(10);
    static constexpr std::chrono::duration DEFAULT_SEND_TIMEOUT = std::chrono::seconds(5);
    static constexpr std::chrono::duration DEFAULT_RECEIVE_TIMEOUT = std::chrono::seconds(5);

    /*  CONSTRUCTORS AND DESTRUCTOR  */

    AdcBaseNetServiceASIO(asio::io_context& ctx)
        requires(!isTLS)
        : SESSION_PROTOT(), _ioContext(ctx), _receiveStrand(_ioContext), _socket(_ioContext), _receiveQueue()
    {
    }


    // AdcBaseNetServiceASIO(socket_t socket)
    //     : SESSION_PROTOT(),
    //       _ioContext(static_cast<asio::io_context&>(socket.get_executor().context())),
    //       _socket(std::move(socket)),
    //       _receiveStrand(_ioContext),
    //       _receiveQueue()
    // {
    // }

#ifdef USE_OPENSSL_WITH_ASIO
    AdcBaseNetServiceASIO(asio::io_context& ctx,
                          asio::ssl::context tls_context,
                          const asio::ssl::verify_mode& tls_peer_verify_mode = asio::ssl::verify_peer)
        requires isTLS
        : SESSION_PROTOT(),
          _ioContext(ctx),
          _receiveStrand(_ioContext),
          _socket(_ioContext),
          _receiveQueue(),
          _tlsContext(std::move(tls_context)),
          _tlsPeerVerifyMode(tls_peer_verify_mode),
          _sessSocket(_ioContext, _tlsContext)
    {
    }
#endif


    AdcBaseNetServiceASIO(AdcBaseNetServiceASIO&& other)
        requires(!isTLS)
        : _ioContext(other._ioContext),
          _receiveStrand(std::move(other._receiveStrand)),
          _socket(std::move(other._socket)),
          _sessSocket(std::move(other._sessSocket)),
          _streamBuffer(),
          _receiveQueue(std::move(other._receiveQueue))

    {
        auto bytes = asio::buffer_copy(_streamBuffer.prepare(other._streamBuffer.size()), other._streamBuffer.data());
        _streamBuffer.commit(bytes);
    }

#ifdef USE_OPENSSL_WITH_ASIO
    AdcBaseNetServiceASIO(AdcBaseNetServiceASIO&& other)
        requires isTLS
        : _ioContext(other._ioContext),
          _receiveStrand(std::move(other._receiveStrand)),
          _socket(std::move(other._socket)),
          _sessSocket(std::move(other._sessSocket)),
          _streamBuffer(),
          _receiveQueue(std::move(other._receiveQueue)),
          _tlsContext(std::move(other._tlsContext)),
          _tlsPeerVerifyMode(std::move(other._tlsPeerVerifyMode))

    {
        auto bytes = asio::buffer_copy(_streamBuffer.prepare(other._streamBuffer.size()), other._streamBuffer.data());
        _streamBuffer.commit(bytes);
    }
#endif

    AdcBaseNetServiceASIO(const AdcBaseNetServiceASIO&) = delete;  // no copy constructor!

    virtual ~AdcBaseNetServiceASIO() {}


    AdcBaseNetServiceASIO& operator=(const AdcBaseNetServiceASIO&) = delete;

    AdcBaseNetServiceASIO& operator=(AdcBaseNetServiceASIO&& other)
        requires(!isTLS)
    {
        _ioContext = other._ioContext;
        _receiveStrand = std::move(other._receiveStrand);
        _receiveQueue = std::move(other._receiveQueue);
        _socket = std::move(other._socket);

        _streamBuffer.consume(_streamBuffer.size());

        auto bytes = asio::buffer_copy(_streamBuffer.prepare(other._streamBuffer.size()), other._streamBuffer.data());
        _streamBuffer.commit(bytes);

        return *this;
    };

#ifdef USE_OPENSSL_WITH_ASIO
    AdcBaseNetServiceASIO& operator=(AdcBaseNetServiceASIO&& other)
        requires isTLS
    {
        _ioContext = other._ioContext;
        _receiveStrand = std::move(other._receiveStrand);
        _receiveQueue = std::move(other._receiveQueue);
        _socket = std::move(other._socket);

        _sessSocket = std::move(other._sessSocket);
        _tlsContext = std::move(other._tlsContext);
        _tlsPeerVerifyMode = std::move(other._tlsPeerVerifyMode);


        _streamBuffer.consume(_streamBuffer.size());

        auto bytes = asio::buffer_copy(_streamBuffer.prepare(other._streamBuffer.size()), other._streamBuffer.data());
        _streamBuffer.commit(bytes);

        return *this;
    };

#endif
    constexpr netservice_ident_t ident() const
    {
        return _ident;
    }


    /*    asynchronuos methods   */

    template <asio::completion_token_for<void(std::error_code)> TokenT,
              traits::adc_time_duration_c TimeoutT = decltype(DEFAULT_CONNECT_TIMEOUT)>
    auto asyncConnect(const endpoint_t& endpoint, TokenT&& token, const TimeoutT& timeout = DEFAULT_CONNECT_TIMEOUT)
    {
        enum { sock_connect, handshake, done };

        auto timer = getDeadlineTimer(_socket, timeout);

        return asio::async_compose<TokenT, void(std::error_code)>(
            [state = sock_connect, endpoint, timer = std::move(timer), this](auto& self,
                                                                             std::error_code ec = {}) mutable {
                if (!ec) {
                    switch (state) {
                        case sock_connect:
                            if constexpr (isTLS) {
                                state = handshake;
                            } else {
                                state = done;
                            }

                            return _socket.async_connect(endpoint, std::move(self));
                            break;
                        case handshake:
                            state = done;
#ifdef USE_OPENSSL_WITH_ASIO
                            if constexpr (isTLS) {
                                _sessSocket = session_level_socket_t(std::move(_socket), _tlsContext);
                                return _sessSocket.async_handshake(session_level_socket_t::client, std::move(self));
                            }
#endif
                            break;
                        case done:
                            break;
                        default:
                            break;
                    }
                }

                if (isTimeout(timer, ec)) {
                    ec = std::make_error_code(std::errc::timed_out);
                } else {  // an error occured in async_connect or async_handshake
                    timer->cancel();
                }

                self.complete(ec);
            },
            token, _socket);
    }


    template <traits::adc_input_char_range MessageT,
              asio::completion_token_for<void(std::error_code ec)> TokenT,
              traits::adc_time_duration_c TimeoutT = decltype(DEFAULT_SEND_TIMEOUT)>
    auto asyncSend(const MessageT& msg, TokenT&& token, const TimeoutT& timeout = DEFAULT_SEND_TIMEOUT)
    {
        // create buffer sequence of sending session protocol representation of the input message
        std::vector<asio::const_buffer> buff_seq;
        // std::ranges::for_each(this->toProto(msg), [&buff_seq](const auto& el) { buff_seq.emplace_back(el); });
        std::ranges::for_each(this->toProto(msg),
                              [&buff_seq](const auto& el) { buff_seq.emplace_back(el.data(), el.size()); });

        auto timer = getDeadlineTimer(_socket, timeout);

        return asio::async_compose<TokenT, void(std::error_code)>(
            [start = true, buff_seq = std::move(buff_seq), timer = std::move(timer), this](
                auto& self, std::error_code ec = {}, size_t = 0) mutable {
                if (!ec) {
                    if (start) {
                        start = false;
                        if constexpr (isTLS) {
                            return asio::async_write(_sessSocket, buff_seq, std::move(self));
                        } else {
                            if constexpr (std::derived_from<
                                              socket_t, asio::basic_stream_socket<typename socket_t::protocol_type>>) {
                                return asio::async_write(_socket, buff_seq, std::move(self));
                            } else if constexpr (std::derived_from<socket_t, asio::basic_datagram_socket<
                                                                                 typename socket_t::protocol_type>>) {
                                return _socket.async_send(buff_seq, std::move(self));
                            } else if constexpr (std::derived_from<socket_t, asio::basic_seq_packet_socket<
                                                                                 typename socket_t::protocol_type>>) {
                                return _socket.async_send(buff_seq, 0, std::move(self));
                            } else {
                                static_assert(false, "UNKNOWN ASIO-LIBRARY SOCKET TYPE!!!");
                            }
                        }
                    }
                }

                if (isTimeout(timer, ec)) {
                    ec = std::make_error_code(std::errc::timed_out);
                } else {  // an error occured in async_write/async_send
                    timer->cancel();
                }

                self.complete(ec);
            },
            token, _socket);
    }


    template <typename TokenT, traits::adc_time_duration_c TimeoutT = decltype(DEFAULT_RECEIVE_TIMEOUT)>
    auto asyncReceive(TokenT&& token, const TimeoutT& timeout = DEFAULT_RECEIVE_TIMEOUT)
    {
        // static asio::streambuf _streamBuffer;

        // check completion token signature and deduce message type
        // if constexpr (!adc_asio_special_comp_token_c<TokenT> && !is_async_ctx_t) {
        if constexpr (!adc_asio_special_comp_token_c<TokenT>) {
            static_assert(traits::adc_func_traits<TokenT>::arity == 2, "INVALID COMPLETION TOKEN SIGNATURE!");
            static_assert(std::is_same_v<std::remove_cvref_t<traits::adc_func_arg1_t<TokenT>>, std::error_code>,
                          "INVALID COMPLETION TOKEN SIGNATURE!");
            static_assert(traits::adc_output_char_range<
                              std::tuple_element_t<1, typename traits::adc_func_traits<TokenT>::args_t>>,
                          "INVALID COMPLETION TOKEN SIGNATURE!");
        }

        using msg_t = std::conditional_t<
            // adc_asio_special_comp_token_c<TokenT> || is_async_ctx_t, RMSGT,
            adc_asio_special_comp_token_c<TokenT>, RMSGT,
            std::remove_cvref_t<std::tuple_element_t<1, typename traits::adc_func_traits<TokenT>::args_t>>>;

        auto out_flags = std::make_shared<asio::socket_base::message_flags>();

        auto timer = getDeadlineTimer(_socket, timeout);

        return asio::async_compose<TokenT, void(std::error_code, msg_t)>(
            [out_flags, do_read = true, timer = std::move(timer), this](auto& self, std::error_code ec = {},
                                                                        size_t nbytes = 0) mutable {
                msg_t msg;

                if (!ec) {
                    if (do_read) {
                        do_read = false;
                        if (_receiveQueue.size()) {  // return message from queue
                            timer->cancel();
                            auto imsg = _receiveQueue.front();
                            _receiveQueue.pop();
                            if constexpr (std::is_same_v<msg_t, RMSGT>) {
                                self.complete(std::error_code(), std::move(imsg));
                            } else {
                                self.complete(std::error_code(), {imsg.begin(), imsg.end()});
                            }
                            return;
                        }

                        auto n_avail = _socket.available();
                        if (!n_avail) {
                            return _socket.async_wait(asio::ip::tcp::socket::wait_read, std::move(self));
                        }
                        auto buff = _streamBuffer.prepare(n_avail ? n_avail : 1);

                        if constexpr (isTLS) {
                            return asio::async_read(_sessSocket, std::move(buff), asio::transfer_at_least(1),
                                                    std::move(self));
                        } else {
                            if constexpr (std::derived_from<
                                              socket_t, asio::basic_stream_socket<typename socket_t::protocol_type>>) {
                                return asio::async_read(_socket, std::move(buff), asio::transfer_at_least(1),
                                                        std::move(self));
                            } else if constexpr (std::derived_from<socket_t, asio::basic_datagram_socket<
                                                                                 typename socket_t::protocol_type>>) {
                                // datagram, so it should be received at once
                                return _socket.async_receive(std::move(buff), std::move(self));
                            } else if constexpr (std::derived_from<socket_t, asio::basic_seq_packet_socket<
                                                                                 typename socket_t::protocol_type>>) {
                                // datagram, so it should be received at once
                                return _socket.async_receive(std::move(buff), *out_flags, std::move(self));
                            } else {
                                static_assert(false, "UNKNOWN ASIO-LIBRARY SOCKET TYPE!!!");
                            }
                        }
                    }

                    // zero-length message for SEQ_PACK sockets is EOF
                    if constexpr (std::derived_from<socket_t,
                                                    asio::basic_seq_packet_socket<typename socket_t::protocol_type>>) {
                        if (!nbytes) {
                            timer->cancel();
                            self.complete(std::error_code(asio::error::misc_errors::eof), std::move(msg));
                            return;
                        }
                    }

                    _streamBuffer.commit(nbytes);

                    // if (!nbytes) {
                    //     do_read = true;
                    //     asio::post(std::move(self));  // initiate consequence socket's read operation
                    //     return;
                    // }

                    auto start_ptr = static_cast<const char*>(_streamBuffer.data().data());

                    auto net_pack = this->search(std::span(start_ptr, _streamBuffer.size()));
                    if (net_pack.empty()) {
                        do_read = true;
                        asio::post(std::move(self));  // initiate consequence socket's read operation
                        return;
                    }

                    timer->cancel();  // there were no errors in the asynchronous read-operation, so stop timer

                    // here one has at least a single message

                    std::ranges::copy(this->fromProto(net_pack), std::back_inserter(msg));
                    _streamBuffer.consume(net_pack.size());


                    while (_streamBuffer.size()) {  // search for possible additional session protocol packets
                        start_ptr = static_cast<const char*>(_streamBuffer.data().data());

                        net_pack = this->search(std::span(start_ptr, _streamBuffer.size()));

                        if (!net_pack.empty()) {
                            _receiveQueue.emplace();
                            std::ranges::copy(this->fromProto(net_pack), std::back_inserter(_receiveQueue.back()));
                            _streamBuffer.consume(net_pack.size());
                        } else {
                            break;  // exit and hold remaining bytes in stream buffer
                        }
                    }
                }

                if (isTimeout(timer, ec)) {
                    ec = std::make_error_code(std::errc::timed_out);
                } else {  // an error occured in async_*
                    timer->cancel();
                }

                if constexpr (std::is_same_v<msg_t, RMSGT>) {
                    self.complete(ec, std::move(msg));
                } else {
                    self.complete(ec, {msg.begin(), msg.end()});
                }

                // if constexpr (adc_asio_special_comp_token_c<TokenT>) {
                //     self.complete(ec, std::move(msg));
                // } else {  // may be of non-RMSGT type
                //     self.complete(ec, {msg.begin(), msg.end()});
                // }
            },
            token, _receiveStrand);
    }

    /*    blocking methods    */

    template <traits::adc_time_duration_c TimeoutT = decltype(DEFAULT_CONNECT_TIMEOUT)>
    auto connect(const endpoint_t& endpoint, const TimeoutT& timeout = DEFAULT_CONNECT_TIMEOUT)
    {
        std::future<void> ftr = asyncConnect(endpoint, asio::use_future, timeout);
        ftr.get();
    }

    template <traits::adc_input_char_range R, traits::adc_time_duration_c TimeoutT = decltype(DEFAULT_SEND_TIMEOUT)>
    auto send(const R& msg, const TimeoutT& timeout = DEFAULT_SEND_TIMEOUT)
    {
        std::future<void> ftr = asyncSend(msg, asio::use_future, timeout);
        ftr.get();
    }

    template <traits::adc_time_duration_c TimeoutT = decltype(DEFAULT_RECEIVE_TIMEOUT)>
    auto receive(const TimeoutT& timeout = DEFAULT_RECEIVE_TIMEOUT)
    {
        std::future<RMSGT> ftr = asyncReceive(asio::use_future, timeout);
        return ftr.get();
    }

    // one still may receive messages from queue!
    std::error_code close()
    {
        std::error_code ec;

#ifdef USE_OPENSSL_WITH_ASIO
        if constexpr (isTLS) {
            _sessSocket.shutdown(ec);
        }
#endif

        _socket.shutdown(_shutdownType, ec);
        if (!ec) {
            _socket.close(ec);
        }

        return ec;
    }

    /*   additional ASIO-related methods  */

    void clearRcvQueue()
    {
        // clear receiving messages queue
        // NOTE: there is no racing condition here since using asio::strand!
        asio::post(_receiveStrand, [this]() {
            //
            _receiveQueue = {};
        });
    }

    void clearRcvBuff()
    {
        asio::post(_receiveStrand, [this]() {
            //
            _streamBuffer.consume(_streamBuffer.size());
        });
    }

    void clearRcvData()
    {
        asio::post(_receiveStrand, [this]() {
            _receiveQueue = {};
            _streamBuffer.consume(_streamBuffer.size());
        });
    }

    void setShutdownType(asio::socket_base::shutdown_type shutdown_type)
    {
        _shutdownType = shutdown_type;
    }

    asio::socket_base::shutdown_type getShutdownType() const
    {
        return _shutdownType;
    }


    template <typename OutputItT, typename FormatT = std::string_view>
    static void formatError(std::error_code err,
                            OutputItT out_iter,
                            FormatT fmt = "{} (Err category: {}) (Err msg: {})")
    {
        std::format_to(out_iter, fmt, err.value(), err.category().name(), err.message());
    }

protected:
    static constexpr netservice_ident_t _ident =
        std::derived_from<socket_t, asio::basic_stream_socket<typename socket_t::protocol_type>>
            ? "STREAM-SOCKET NETWORK SERVICE"
        : std::derived_from<socket_t, asio::basic_datagram_socket<typename socket_t::protocol_type>>
            ? "DATAGRAM-SOCKET NETWORK SERVICE"
        : std::derived_from<socket_t, asio::basic_seq_packet_socket<typename socket_t::protocol_type>>
            ? "SEQPACKET-SOCKET NETWORK SERVICE"
            : "UNKNOWN";

    asio::io_context& _ioContext;
    asio::io_context::strand _receiveStrand;

    socket_t _socket;

    asio::streambuf _streamBuffer;

    std::queue<std::vector<char>> _receiveQueue;

    asio::socket_base::shutdown_type _shutdownType = asio::socket_base::shutdown_both;

#ifdef USE_OPENSSL_WITH_ASIO
    session_level_socket_t _sessSocket;
    std::conditional_t<isTLS, asio::ssl::context, std::nullptr_t> _tlsContext;
    asio::ssl::verify_mode _tlsPeerVerifyMode;
    cert_comp_func_t _tlsCertCompFunc;
    std::string _tlsCertFingerprintDigest;

    // reference implementation fo certificate verification function
    virtual bool verifyCertificate(int preverified_ok, X509_STORE_CTX* store)
    {
        if (preverified_ok == 0) {
            int err = X509_STORE_CTX_get_error(store);
            auto err_str = X509_verify_cert_error_string(err);
            // log_error("TLS certificate verification error: {}", err_str);

            return preverified_ok;
        }

        char subject_name[256];

        int depth;
        ASN1_INTEGER* serial;
        BIGNUM* bnser;

        X509* cert = X509_STORE_CTX_get_current_cert(store);

        if (cert != NULL) {
            depth = X509_STORE_CTX_get_error_depth(store);
            X509_NAME_oneline(X509_get_subject_name(cert), subject_name, 256);
            serial = X509_get_serialNumber(cert);  // IT IS INTERNAL POINTER SO IT MUST NOT BE FREED UP!!!
            bnser = ASN1_INTEGER_to_BN(serial, NULL);
            auto serial_hex = BN_bn2hex(bnser);

            // log_debug("Received TLS certificate: SUBJECT = {}, SERIAL = {}, DEPTH = {}", subject_name, serial_hex,
            //           depth);

            // if no compare function then do not compute fingerprint
            if (_tlsCertCompFunc) {
                // compute certificate fingerprint
                unsigned char digest_buff[EVP_MAX_MD_SIZE];
                const EVP_MD* digest = EVP_get_digestbyname(_tlsCertFingerprintDigest.c_str());
                unsigned int N;

                if (X509_digest(cert, digest, digest_buff, &N)) {
                    preverified_ok = _tlsCertCompFunc(std::string(serial_hex),
                                                      std::vector<unsigned char>(digest_buff, digest_buff + N), depth);

                } else {
                    // log_error("Cannot compute client certificate fingerprint! Cannot verify the certificate!");
                    preverified_ok = 0;
                }
            }

            BN_free(bnser);
            OPENSSL_free(serial_hex);

        } else {
            // log_error("OpenSSL error: cannot get current certificate");
            preverified_ok = 0;
        }

        return preverified_ok;
    }

#endif


    template <typename CancelableT, traits::adc_time_duration_c TimeoutT>
    static std::unique_ptr<asio::steady_timer> getDeadlineTimer(CancelableT& obj,
                                                                const TimeoutT& timeout,
                                                                bool arm = true)
    {
        auto timer = std::make_unique<asio::steady_timer>(obj.get_executor());

        // if (timeout == std::chrono::duration<typename TimeoutT::rep, typename TimeoutT::period>::max()) {
        //     return timer;  // do not arm the timer if MAX duration are given
        // }

        if (arm) {
            std::chrono::seconds max_d = std::chrono::duration_cast<std::chrono::seconds>(
                std::chrono::steady_clock::time_point::max() - std::chrono::steady_clock::now() -
                std::chrono::seconds(1));

            if (timeout < max_d) {
                timer->expires_after(timeout);
            } else {
                timer->expires_after(max_d);  // to avoid overflow!
            }


            timer->async_wait([&obj](const std::error_code& ec) mutable {
                if (!ec) {
                    obj.cancel();
                }
            });
        }

        return timer;
    }

    template <typename TimerT>
    static bool isTimeout(const std::unique_ptr<TimerT>& timer, const std::error_code& ec)
    {
        auto exp_time = timer->expiry();
        return (exp_time < std::chrono::steady_clock::now()) && (ec == asio::error::operation_aborted);
    }

    template <typename TimerT>
    static bool isTimeout(const std::shared_ptr<TimerT>& timer, const std::error_code& ec)
    {
        auto exp_time = timer->expiry();
        return (exp_time < std::chrono::steady_clock::now()) && (ec == asio::error::operation_aborted);
    }
};



/*  */
template <
    adc_asio_transport_proto_c TRANSPORT_PROTOT,                          // transport-level proto (e.g. asio::ip::tcp)
    interfaces::adc_netsession_proto_c<std::string_view> SESSION_PROTOT,  // session-level proto (see ../adc_netproto.h)
    traits::adc_output_char_range RMSGT = std::vector<char>>  // used only for inner storing of message byte sequence
using AdcNetServiceASIO = AdcBaseNetServiceASIO<false, TRANSPORT_PROTOT, SESSION_PROTOT, RMSGT>;


#ifdef USE_OPENSSL_WITH_ASIO

template <
    adc_asio_transport_proto_c TRANSPORT_PROTOT,                          // transport-level proto (e.g. asio::ip::tcp)
    interfaces::adc_netsession_proto_c<std::string_view> SESSION_PROTOT,  // session-level proto (see ../adc_netproto.h)
    traits::adc_output_char_range RMSGT = std::vector<char>>  // used only for inner storing of message byte sequence
using AdcNetServiceASIOTLS = AdcBaseNetServiceASIO<true, TRANSPORT_PROTOT, SESSION_PROTOT, RMSGT>;

#endif

}  // namespace adc::impl