ADC/net/asio/adc_netservice_asio.h

#pragma once

#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>
#include <set>

#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"
#include "../adc_netproto.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
{

// typedef for ASIO streambuf iterators
using asio_streambuff_iter_t = asio::buffers_iterator<asio::streambuf::const_buffers_type>;

// ASIO match condition result typedef
using asio_matchcond_result_t = std::pair<asio_streambuff_iter_t, bool>;

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_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>;


// class adc_asio_async_call_ctx_t
// {
// };


// template <typename T, typename SignatureT = void>
// concept adc_completion_token_c =
//     std::same_as<T, adc_asio_async_call_ctx_t> ||
//     (traits::adc_is_callable<T> &&
//      std::conditional_t<std::same_as<SignatureT, void>,
//                         std::true_type,
//                         std::bool_constant<asio::completion_token_for<T, SignatureT>>>::value);



template <adc_asio_transport_proto_c TRANSPORT_PROTOT,
          interfaces::adc_netsession_proto_c<std::string_view> SESSION_PROTOT,
          traits::adc_output_char_range RMSGT =
              std::vector<char>>  // used only for inner storing of message byte sequence
class AdcNetServiceASIOBase : public SESSION_PROTOT
{
public:
    // 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::function<void(std::error_code)> async_accept_callback_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;


    // acceptor
    class acceptor_t
    {
    public:
        static constexpr std::chrono::duration DEFAULT_ACCEPT_TIMEOUT = std::chrono::seconds::max();

        acceptor_t(asio::io_context& io_ctx)
            : _ioContext(io_ctx), _endpoint(), _socket(_ioContext), _acceptor(_ioContext)
        {
        }
        acceptor_t(asio::io_context& io_ctx, const AdcNetServiceASIOBase::endpoint_t& endpoint) : acceptor_t(io_ctx)
        {
            if (_endpoint != endpoint) {
                _endpoint = endpoint;
                _acceptor = _acceptor_t(_ioContext, _endpoint);
            }
        }

        typedef AdcNetServiceASIOBase netservice_t;
        typedef std::shared_ptr<netservice_t> sptr_netservice_t;

        // typedef std::function<void(std::error_code, AdcNetServiceASIOBase)> async_accept_callback_t;
        typedef std::function<void(std::error_code, sptr_netservice_t)> async_accept_callback_t;

        // template <asio::completion_token_for<void(std::error_code, AdcNetServiceASIOBase)> TokenT,
        template <asio::completion_token_for<void(std::error_code, sptr_netservice_t)> TokenT,
                  traits::adc_time_duration_c DT = decltype(DEFAULT_ACCEPT_TIMEOUT)>
        auto asyncAccept(TokenT&& token, const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            // no acceptor for UDP-sockets
            if constexpr (std::is_null_pointer_v<_acceptor_t>) {
                static_assert(false, "INVALID TRANSPORT PROTOCOL TYPE!");
            }

            _socket = AdcNetServiceASIOBase::socket_t{_ioContext};
            auto timer = getDeadlineTimer(_acceptor, timeout);

            // return asio::async_compose<TokenT, void(std::error_code, AdcNetServiceASIOBase)>(
            return asio::async_compose<TokenT, void(std::error_code, sptr_netservice_t)>(
                [timer = std::move(timer), start = true, this](auto& self, std::error_code ec = {}) mutable {
                    if (!ec) {
                        if (start) {
                            start = false;
                            try {
                                if (!_acceptor.is_open() || (_acceptor.local_endpoint() != _endpoint)) {
                                    _acceptor = _acceptor_t(_ioContext, _endpoint);
                                }
                            } catch (std::system_error err) {
                                timer->cancel();
                                // self.complete(err.code(), AdcNetServiceASIOBase(_ioContext));
                                self.complete(err.code(), std::make_shared<netservice_t>(_ioContext));
                                return;
                            }

                            return _acceptor.async_accept(_socket, std::move(self));
                        }
                    }

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

                    // self.complete(ec, AdcNetServiceASIOBase(std::move(_socket)));
                    self.complete(ec, std::make_shared<netservice_t>(std::move(_socket)));
                },
                token, _ioContext);
        }

        template <asio::completion_token_for<void(std::error_code, AdcNetServiceASIOBase)> TokenT,
                  traits::adc_time_duration_c DT = decltype(DEFAULT_ACCEPT_TIMEOUT)>
        auto asyncAccept(const AdcNetServiceASIOBase::endpoint_t& endpoint,
                         TokenT&& token,
                         const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            _endpoint = 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)
        // AdcNetServiceASIOBase 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)
        // AdcNetServiceASIOBase accept(const endpoint_t& endpoint, const DT& timeout = DEFAULT_ACCEPT_TIMEOUT)
        {
            return accept(endpoint, timeout);
        }

    private:
        asio::io_context& _ioContext;
        AdcNetServiceASIOBase::endpoint_t _endpoint;
        AdcNetServiceASIOBase::socket_t _socket;

        using _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>;

        _acceptor_t _acceptor;
    };



    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);

    AdcNetServiceASIOBase(asio::io_context& ctx)
        : SESSION_PROTOT(), _ioContext(ctx), _receiveStrand(_ioContext), _receiveQueue(), _socket(_ioContext)
    {
    }


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


    // NOTE: CANNOT MOVE asio::streambuf CORRECTLY?!!!
    AdcNetServiceASIOBase(AdcNetServiceASIOBase&& other) = delete;
    // AdcNetServiceASIOBase(AdcNetServiceASIOBase&& other)
    //     : SESSION_PROTOT(std::move(other)),
    //       _ioContext(other._ioContext),
    //       _receiveStrand(std::move(other._receiveStrand)),
    //       _receiveQueue(std::move(_receiveQueue)),
    //       _socket(std::move(other._socket)),
    //       _streamBuffer()
    // {
    //     if (this == &other)
    //         return;

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

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

    virtual ~AdcNetServiceASIOBase() {}


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

    AdcNetServiceASIOBase& operator=(AdcNetServiceASIOBase&& other)
    {
        if (this != &other) {
            close();
            _streamBuffer.consume(_streamBuffer.size());

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

            _ioContext = other._ioContext;
            _receiveStrand = std::move(other._receiveStrand), _socket = std::move(other._socket);

            _receiveQueue = other._receiveQueue;
        }

        return *this;
    }


    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)
    {
        auto timer = getDeadlineTimer(_socket, timeout);

        return asio::async_compose<TokenT, void(std::error_code)>(
            [start = true, endpoint, timer = std::move(timer), this](auto& self, std::error_code ec = {}) mutable {
                if (!ec) {
                    if (start) {
                        start = false;
                        return _socket.async_connect(endpoint, std::move(self));
                    }
                }

                if (isTimeout(timer, ec)) {
                    ec = std::make_error_code(std::errc::timed_out);
                } else {  // an error occured in async_connect
                    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 (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, 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)
    {
        // constexpr auto is_async_ctx_t = std::same_as<std::remove_cvref_t<TokenT>, async_call_ctx_t>;

        // 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;
                        }

                        if constexpr (std::derived_from<socket_t,
                                                        asio::basic_stream_socket<typename socket_t::protocol_type>>) {
                            return asio::async_read(_socket, _streamBuffer, 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.receive(_streamBuffer, 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.receive(_streamBuffer, *out_flags, std::move(self));
                        } else {
                            static_assert(false, "UNKNOWN ASIO-LIBRARY SOCKET TYPE!!!");
                        }
                    }

                    // 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();
    }

    std::error_code close()
    {
        std::error_code ec;

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

        return ec;
    }

    /*   additional ASIO-related methods  */

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

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

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

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;


    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));

            timer->expires_after(timeout < max_d ? timeout : max_d);  // to avoid overflow!
            // timer->expires_after(timeout);

            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);
    }
};


static_assert(adc::interfaces::adc_netservice_c<AdcNetServiceASIOBase<asio::ip::tcp, adc::AdcStopSeqSessionProto<>>>,
              "");

static_assert(adc::interfaces::adc_netsession_proto_c<adc::AdcStopSeqSessionProto<>>, "");



/*  EVENT-BASED SERVICE  */
template <adc_asio_transport_proto_c TRANSPORT_PROTOT,
          interfaces::adc_netsession_proto_c<std::string_view> SESSION_PROTOT>
class AsioNetService : public SESSION_PROTOT
{
public:
    // typedefs from transport protocol
    using endpoint_t = typename TRANSPORT_PROTOT::endpoint;
    using socket_t = typename TRANSPORT_PROTOT::socket;
    using 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>;

    typedef std::function<void(AsioNetService*, std::error_code, endpoint_t)> connect_event_hndl_t;
    typedef std::function<void(AsioNetService*, std::error_code)> send_event_hndl_t;
    typedef std::function<void(AsioNetService*, std::error_code)> close_event_hndl_t;
    typedef std::function<void(AsioNetService*, std::error_code, std::span<const char>)> message_event_hndl_t;

    struct Events {
        bool listening = false;  // true - server role, false - client role
        connect_event_hndl_t onConnect = [](auto...) {};
        send_event_hndl_t onSend = [](auto...) {};
        close_event_hndl_t onClose = [](auto...) {};
        message_event_hndl_t onMessage = [](auto...) {};
    };

    AsioNetService(asio::io_context& ctx, Events events)
        : SESSION_PROTOT(),
          _ioContext(ctx),
          _receiveStrand(_ioContext),
          _receiveQueue(),
          _acceptor(_ioContext),
          _socket(_ioContext),
          _events(events),
          _stopReceiving(false),
          _waitTimer(_ioContext)
    {
    }


    template <traits::adc_time_duration_c DT>
    static void start(AsioNetService& srv, const endpoint_t& endpoint, const DT& timeout)
    {
        // no acceptor for UDP-sockets
        if constexpr (std::is_null_pointer_v<acceptor_t>) {
            srv.startReceiving();
            srv._events.onConnect(&srv, std::error_code{}, endpoint_t());
            return;
        }

        auto token = [&endpoint, &timeout, &srv](std::error_code ec) {
            if (!ec) {
                srv.startReceiving();
            }

            // post event
            srv._events.onConnect(&srv, ec, srv._socket.remote_endpoint());
        };

        if (srv._events.listening) {  // server role (accept connections to given endpoint)

            auto timer = getDeadlineTimer(srv._acceptor, timeout);

            asio::async_compose<decltype(token), void(std::error_code)>(
                [timer = std::move(timer), start = true, &endpoint, &srv](auto& self, std::error_code ec = {}) mutable {
                    if (!ec) {
                        if (start) {
                            start = false;
                            try {
                                if (!srv._acceptor.is_open() || (srv._acceptor.local_endpoint() != endpoint)) {
                                    srv._acceptor = acceptor_t(srv._ioContext, endpoint);
                                }
                            } catch (std::system_error err) {
                                timer->cancel();
                                self.complete(err.code());
                                return;
                            }

                            // return acc.async_accept(_socket, std::move(self));
                            return srv._acceptor.async_accept(srv._socket, std::move(self));
                        }
                    }

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

                    self.complete(ec);
                },
                std::move(token), srv._ioContext);

        } else {  // client role (connect to remote host)

            auto timer = getDeadlineTimer(srv._socket, timeout);

            asio::async_compose<decltype(token), void(std::error_code)>(
                [start = true, endpoint, timer = std::move(timer), &srv](auto& self, std::error_code ec = {}) mutable {
                    if (!ec) {
                        if (start) {
                            start = false;
                            return srv._socket.async_connect(endpoint, std::move(self));
                        }
                    }

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

                    self.complete(ec);
                },
                std::move(token), srv._socket);
        }
    }


    void stop()
    {
        std::error_code ec;

        _stopReceiving = true;

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

        _events.onClose(ec);
    }

    template <traits::adc_input_char_range R, traits::adc_time_duration_c DT>
    auto send(const R& msg, const DT& timeout)
    {
        auto token = [this](std::error_code ec, size_t) {
            //
            _events.onSend(this, ec);
        };

        // 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); });

        auto timer = getDeadlineTimer(_socket, timeout);

        return asio::async_compose<decltype(token), void(std::error_code)>(
            [start = true, buff_seq = std::move(buff_seq), timer = std::move(timer), this](
                auto& self, std::error_code ec = {}) mutable {
                if (!ec) {
                    if (start) {
                        start = false;
                        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, 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);
            },
            std::move(token), _socket);
    }

    template <traits::adc_time_duration_c DT>
    bool wait(const DT& timeout)
    {
        if (_receiveQueue.size()) {
            return true;
        }

        std::error_code ec;

        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));

        auto res = _waitTimers.emplace(_ioContext);
        if (res.second) {
            (*(res.first))->expires_after(timeout < max_d ? timeout : max_d);

            // _waitTimer.expires_after(timeout < max_d ? timeout : max_d); // to avoid overflow!

            // auto f = _waitTimer.async_wait(asio::use_future);

            auto f = (*(res.first))->async_wait(asio::use_future);
            try {
                f.get();
                _waitTimers.erase(res.first);
            } catch (std::system_error& ex) {
                if (ex.code() == asio::error::operation_aborted) {  // canceled in startReceiving (message was received)
                    return true;
                } else {
                    return false;
                }
            }
        }
    }

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

    socket_t _socket;

    acceptor_t _acceptor;

    asio::streambuf _streamBuffer;

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

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

    std::atomic_bool _stopReceiving;

    Events _events;

    asio::steady_timer _waitTimer;
    std::set<std::unique_ptr<asio::steady_timer>> _waitTimers;

    void startReceiving()
    {
        auto get_msg = [this](std::error_code ec, size_t) {
            if (!ec) {
                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()) {
                    _receiveQueue.emplace();
                    std::ranges::copy(this->fromProto(net_pack), std::back_inserter(_receiveQueue.back()));
                    _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
                        }
                    }

                    auto msg = _receiveQueue.front();
                    _events.onMessage(this, ec, std::span<const char>(msg.begin(), msg.end()));

                    _receiveQueue.pop();
                }

                if (!_stopReceiving) {
                    startReceiving();  // initiate consequence socket's read operation
                }
            } else {
                _events.onMessage(this, ec, std::span<const char>());
            }
        };


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

        if constexpr (std::derived_from<socket_t, asio::basic_stream_socket<typename socket_t::protocol_type>>) {
            return asio::async_read(_socket, _streamBuffer, asio::transfer_at_least(1), std::move(get_msg));
        } 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.receive(_streamBuffer, std::move(get_msg));
        } 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.receive(_streamBuffer, *out_flags, std::move(get_msg));
        } else {
            static_assert(false, "UNKNOWN ASIO-LIBRARY SOCKET TYPE!!!");
        }
    }


    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 (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));

            timer->expires_after(timeout < max_d ? timeout : max_d);  // to avoid overflow!
            // timer->expires_after(timeout);

            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);
    }
};

}  // namespace adc::impl