#pragma once

#include <filesystem>
#include <set>

#include <asio/awaitable.hpp>
#include <asio/co_spawn.hpp>
#include <asio/deferred.hpp>
#include <asio/detached.hpp>
#include <asio/experimental/awaitable_operators.hpp>
#include <asio/ip/tcp.hpp>
#include <asio/local/seq_packet_protocol.hpp>
#include <asio/local/stream_protocol.hpp>
#include <asio/read.hpp>
#include <asio/redirect_error.hpp>
#include <asio/serial_port.hpp>
#include <asio/steady_timer.hpp>
#include <asio/streambuf.hpp>
#include <asio/write.hpp>

#include <spdlog/sinks/null_sink.h>
#include <spdlog/spdlog.h>

#if __has_include(<unistd.h>)  // POSIX
#define FORK_EXISTS 1
#include <sys/stat.h>
#include <unistd.h>
#include <cerrno>
#endif



#include "comm_server_endpoint.h"
#include "control_proto.h"
#include "mount.h"

namespace mcc
{


namespace traits
{

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

template <typename T>
static constexpr bool is_serial_proto = std::derived_from<T, asio::serial_port>;

// template <typename T>
// static constexpr bool is_tcp_proto = std::derived_from<typename T::protocol_type, asio::ip::tcp>;

// template <typename T>
// static constexpr bool is_local_stream_proto =
//     std::derived_from<typename T::protocol_type, asio::local::stream_protocol>;

// template <typename T>
// static constexpr bool is_local_seqpack_proto =
//     std::derived_from<typename T::protocol_type, asio::local::seq_packet_protocol>;


template <typename T>
static constexpr bool is_tcp_proto =
    std::derived_from<T, asio::ip::tcp::endpoint> || std::derived_from<T, asio::ip::tcp::socket>;

template <typename T>
static constexpr bool is_local_stream_proto = std::derived_from<T, asio::local::stream_protocol::endpoint> ||
                                              std::derived_from<T, asio::local::stream_protocol::socket>;

template <typename T>
static constexpr bool is_local_seqpack_proto = std::derived_from<T, asio::local::seq_packet_protocol::endpoint> ||
                                               std::derived_from<T, asio::local::seq_packet_protocol::socket>;


template <typename T>
concept mcc_time_duration_c = requires {
    []<class RT, class PT>(std::type_identity<std::chrono::duration<RT, PT>>) {

    }(std::type_identity<std::remove_cvref_t<T>>());
};


}  // namespace traits


class MccMountServer
{
public:
    static constexpr std::chrono::duration DEFAULT_RCV_TIMEOUT = std::chrono::hours(12);
    static constexpr std::chrono::duration DEFAULT_SND_TIMEOUT = std::chrono::milliseconds(2000);

    MccMountServer(asio::io_context& ctx, std::shared_ptr<spdlog::logger> logger = spdlog::null_logger_mt("NULL"))
        : _asioContext(ctx), _serverLogger(std::move(logger))
    {
        std::stringstream st;
        st << std::this_thread::get_id();

        _serverLogger->info("Create mount server instance (thread ID = {})", st.str());
    }

    ~MccMountServer()
    {
        std::stringstream st;
        st << std::this_thread::get_id();

        _serverLogger->info("Delete mount server instance (thread ID = {})", st.str());
    }


    template <typename... CtorArgTs>
    asio::awaitable<void> listen(std::derived_from<MccServerEndpoint> auto endpoint, CtorArgTs&&... ctor_args)
    {
        if (!endpoint.isValid()) {
            _serverLogger->error("Cannot start listening! Invalid endpoint string representation ('{}')!",
                                 endpoint.endpoint());
            co_return;
        }

        // add root path to endpoint one
        std::filesystem::path pt("/");


        if (endpoint.isLocalSerial()) {
            pt += endpoint.path();

            asio::serial_port s_port(_asioContext);

            std::error_code ec;

            if constexpr (sizeof...(CtorArgTs)) {  // options
                setSerialOpts(s_port, std::forward<CtorArgTs>(ctor_args)...);
            }

            s_port.open(pt.string(), ec);
            if (ec) {
                _serverLogger->error("Cannot open serial device '{}' (Error = '{}')!", pt.string(), ec.message());
                co_return;
            }

            // asio::co_spawn(_asioContext, listen(std::move(s_port)), asio::detached);
            co_await listen(std::move(s_port));
        } else if (endpoint.isLocal()) {
            // create abstract namespace socket endpoint if its path starts from '@' symbol
            endpoint.makeAbstract('@');

            if (endpoint.path()[0] == '\0') {  // abstract namespace
                std::string p;
                std::ranges::copy(endpoint.path(), std::back_inserter(p));
                p.insert(p.begin() + 1, '/');  // insert after '\0' symbol
                pt = p;
            } else {
                pt += endpoint.path();
            }

            if (endpoint.isLocalStream()) {
                co_await listen(asio::local::stream_protocol::endpoint(pt.string()));
                // asio::co_spawn(_asioContext, listen(asio::local::stream_protocol::endpoint(pt.string())),
                //                asio::detached);
            } else if (endpoint.isLocalSeqpacket()) {
                co_await listen(asio::local::seq_packet_protocol::endpoint(pt.string()));
                // asio::co_spawn(_asioContext, listen(asio::local::seq_packet_protocol::endpoint(pt.string())),
                //                asio::detached);
            } else {
                co_return;  // it must not be!!!!
            }
        } else if (endpoint.isTCP()) {
            // resolve hostname
            try {
                asio::ip::tcp::resolver res(_asioContext);

                auto r_result = co_await res.async_resolve(endpoint.host(), endpoint.portView(), asio::use_awaitable);

                _serverLogger->info("Resolve hostname <{}> to {} IP-addresses", endpoint.host(), r_result.size());


                bool exit_flag = false;
                asio::ip::tcp::acceptor acc(_asioContext);

                for (auto const& epn : r_result) {
                    try {
                        // std::stringstream st;

                        // _serverLogger->debug("Create connection acceptor for endpoint <{}> ...",
                        //                      epn.address().to_string());
                        acc = asio::ip::tcp::acceptor(_asioContext, epn);
                        // st << acc.local_endpoint();
                        exit_flag = true;
                        break;
                    } catch (const std::system_error& err) {
                        _serverLogger->error("An error occuring while creating connection acceptor (ec = {})",
                                             err.what());
                        continue;
                    }
                }
                if (!exit_flag) {
                    _serverLogger->error("Cannot start listening on any resolved endpoints!");
                    co_return;
                }

                _tcpAcceptors.emplace_back(&acc);

                _serverLogger->info("Start listening at <{}> endpoint ...", acc.local_endpoint().address().to_string());

                // start accepting connections
                for (;;) {
                    auto sock = co_await acc.async_accept(asio::use_awaitable);
                    // start new client session
                    asio::co_spawn(_asioContext, startSession(std::move(sock)), asio::detached);
                }

            } catch (const std::system_error& err) {
                _serverLogger->error("An error occured while trying to start accepting connections! ec = '{}'",
                                     err.what());
            }
        }
    }

    template <traits::mcc_endpoint_c EpnT>
    asio::awaitable<void> listen(EpnT endpoint)
    {
        using epn_t = std::decay_t<decltype(endpoint)>;

        std::error_code ec;

        if constexpr (traits::is_serial_proto<epn_t>) {
            // first, check if port is open
            if (!endpoint.is_open()) {
                if (ec) {
                    // ??????????
                    _serverLogger->error("Serial port was not open! Do not start waiting for commands!");
                }
            } else {
                asio::co_spawn(_asioContext, startSession(std::move(endpoint)), asio::detached);
            }

        } else if constexpr (traits::is_tcp_proto<epn_t> || traits::is_local_stream_proto<epn_t> ||
                             traits::is_local_seqpack_proto<epn_t>) {
            try {
                std::stringstream st;

                st << endpoint;
                _serverLogger->debug("Create connection acceptor for endpoint <{}> ...", st.str());
                auto acc = typename epn_t::protocol_type::acceptor(_asioContext, endpoint);

                st.str("");
                st << acc.local_endpoint();
                _serverLogger->info("Start listening at <{}> endpoint ...", st.str());


                if constexpr (traits::is_tcp_proto<epn_t>) {
                    _tcpAcceptors.emplace_back(&acc);
                } else if constexpr (traits::is_local_stream_proto<epn_t>) {
                    _localStreamAcceptors.emplace_back(&acc);
                } else if constexpr (traits::is_local_seqpack_proto<epn_t>) {
                    _localSeqpackAcceptors.emplace_back(&acc);
                } else {
                    static_assert(false, "INVALID ENDPOINT!!!");
                }

                // start accepting connections
                for (;;) {
                    auto sock = co_await acc.async_accept(asio::use_awaitable);
                    // start new client session
                    asio::co_spawn(_asioContext, startSession(std::move(sock)), asio::detached);
                }


            } catch (const std::system_error& err) {
                _serverLogger->error("An error occured while trying to start accepting connections! ec = '{}'",
                                     err.what());
            }
        } else {
            static_assert(false, "INVALID ENDPOINT!!!");
        }

        co_return;
    }


    // close listening on all endpoints
    void stopListening()
    {
        std::error_code ec;

        _serverLogger->info("Close all listening endpoints ...");

        auto num =
            _serialPorts.size() + _tcpAcceptors.size() + _localStreamAcceptors.size() + _localSeqpackAcceptors.size();
        if (!num) {
            _serverLogger->info("There are no listening ports/sockets!");
            return;
        }

        auto close_func = [this](auto& acc_ptrs, std::string_view desc) {
            size_t N = 0, M = 0;
            std::error_code ec;

            if (acc_ptrs.size()) {
                _serverLogger->info("Close {} acceptors ...", desc);

                for (auto& acc : acc_ptrs) {
                    acc->close(ec);
                    if (ec) {
                        _serverLogger->error("Cannot close {} acceptor! ec = '{}'", desc, ec.message());
                        ++M;
                    }
                    ++N;
                }

                _serverLogger->debug("{} from {} {} acceptors were closed!", M, N, desc);

                // pointers are invalidated here, so clear its container
                acc_ptrs.clear();
            }
        };

        close_func(_tcpAcceptors, "TCP socket");
        close_func(_localStreamAcceptors, "local stream socket");
        close_func(_localSeqpackAcceptors, "local seqpack socket");


        _serverLogger->info("The all server listening endpoints were closed!");
    }

    void disconnectClients() {}

    void daemonize()
    {
#ifdef FORK_EXISTS
        _serverLogger->info("Daemonize the server ...");

        _asioContext.notify_fork(asio::execution_context::fork_prepare);

        auto tmp_path = std::filesystem::temp_directory_path();
        if (tmp_path.empty()) {
            tmp_path = std::filesystem::current_path().root_path();
        }


        if (pid_t pid = fork()) {
            if (pid > 0) {
                exit(0);
            } else {
                // throw std::system_error(errno, std::generic_category(), "CANNOT FORK 1-STAGE");
                _serverLogger->error("CANNOT FORK 1-STAGE! The server was not daemonized!");
                return;
            }
        }

        if (setsid() == -1) {
            // throw std::system_error(errno, std::generic_category(), "CANNOT FORK SETSID");
            _serverLogger->error("CANNOT FORK SETSID! The server was not daemonized!");
            return;
        }

        _serverLogger->info("Try to set the daemon current path to '{}' ...", tmp_path.string());

        std::error_code ec{};

        std::filesystem::current_path(tmp_path, ec);
        if (!ec) {
            _serverLogger->warn("Cannot change current path to '{}'! Ignore!", tmp_path.string());
        }

        umask(0);

        if (pid_t pid = fork()) {
            if (pid > 0) {
                exit(0);
            } else {
                // throw std::system_error(errno, std::generic_category(), "CANNOT FORK 2-STAGE");
                _serverLogger->error("CANNOT FORK 2-STAGE! The server was not daemonized!");
                return;
            }
        }

        // stdin, stdout, stderr
        close(0);
        close(1);
        close(2);

        _asioContext.notify_fork(asio::io_context::fork_child);

        _serverLogger->info("The server was daemonized successfully!");

#else
        _serverLogger->warn("Host platform is not POSIX one, so cannot daemonize the server!");
#endif
    }

private:
    asio::io_context& _asioContext;
    std::shared_ptr<spdlog::logger> _serverLogger;

    std::vector<asio::serial_port*> _serialPorts;

    std::vector<asio::ip::tcp::acceptor*> _tcpAcceptors;
    std::vector<asio::local::stream_protocol::acceptor*> _localStreamAcceptors;
    std::vector<asio::local::seq_packet_protocol::acceptor*> _localSeqpackAcceptors;

    std::set<asio::ip::tcp::socket*> _tcpSockets;
    std::set<asio::local::stream_protocol::socket*> _localStreamSockets;
    std::set<asio::local::seq_packet_protocol::socket*> _localSeqpackSockets;
    // std::vector<asio::ip::tcp::socket*> _tcpSockets;
    // std::vector<asio::local::stream_protocol::socket*> _localStreamSockets;
    // std::vector<asio::local::seq_packet_protocol::socket*> _localSeqpackSockets;


    // helpers
    template <typename OptT, typename... OptTs>
    void setSerialOpts(asio::serial_port& s_port, OptT&& opt, OptTs&&... opts)
    {
        std::error_code ec;

        s_port.set_option(opt, ec);
        if (ec) {
            std::string_view opt_name;

            if constexpr (std::same_as<OptT, asio::serial_port::baud_rate>) {
                opt_name = "baud rate";
            } else if constexpr (std::same_as<OptT, asio::serial_port::parity>) {
                opt_name = "parity";
            } else if constexpr (std::same_as<OptT, asio::serial_port::flow_control>) {
                opt_name = "flow control";
            } else if constexpr (std::same_as<OptT, asio::serial_port::stop_bits>) {
                opt_name = "stop bits";
            } else if constexpr (std::same_as<OptT, asio::serial_port::character_size>) {
                opt_name = "char size";
            }

            _serverLogger->error("Cannot set serial port '{}' option! Just skip!", opt_name);
        }

        if constexpr (sizeof...(OptTs)) {
            setSerialOpts(s_port, std::forward<OptTs>(opts)...);
        }
    }


    std::vector<char> handleClientCommand(std::string_view command)
    {
        std::vector<char> resp{BM700::CONTROL_PROTO_STR_RESP_ACK.begin(), BM700::CONTROL_PROTO_STR_RESP_ACK.end()};

        return resp;
    }


    template <traits::mcc_time_duration_c RCVT = decltype(DEFAULT_RCV_TIMEOUT),
              traits::mcc_time_duration_c SNDT = decltype(DEFAULT_SND_TIMEOUT)>
    asio::awaitable<void> startSession(auto socket,
                                       const RCVT& rcv_timeout = DEFAULT_RCV_TIMEOUT,
                                       const SNDT& snd_timeout = DEFAULT_SND_TIMEOUT)
    {
        using namespace asio::experimental::awaitable_operators;

        using sock_t = std::decay_t<decltype(socket)>;


        auto look_for_whole_msg = [](auto const& bytes) {
            auto found = std::ranges::search(bytes, BM700::CONTROL_PROTO_STOP_SEQ);
            return found.empty() ? std::span(bytes.begin(), bytes.begin()) : std::span(bytes.begin(), found.end());
        };

        auto watchdog = [this](const std::chrono::steady_clock::time_point& deadline) -> asio::awaitable<void> {
            // asio::steady_timer timer(_asioContext);
            asio::steady_timer timer(co_await asio::this_coro::executor);

            auto now = std::chrono::steady_clock::now();
            while (deadline > now) {
                timer.expires_at(deadline);
                co_await timer.async_wait(asio::use_awaitable);
                now = std::chrono::steady_clock::now();
            }

            throw std::system_error(std::make_error_code(std::errc::timed_out));
        };


        asio::streambuf sbuff;
        size_t nbytes;
        std::stringstream st;
        std::string r_epn;

        st << std::this_thread::get_id();
        std::string thr_id = st.str();
        st.str("");

        if constexpr (traits::is_serial_proto<sock_t>) {
            st << "serial port: " << socket.native_handle();
        } else {  // network sockets
            st << socket.remote_endpoint();
        }

        r_epn = st.str();
        if (r_epn.empty()) {  // UNIX domain sockets
            r_epn = "local";
        }

        _serverLogger->info("Start client session: remote endpoint <{}> (session thread ID = {})", r_epn, thr_id);

        try {
            if constexpr (!traits::is_serial_proto<sock_t>) {
                _serverLogger->trace("Set socket option KEEP_ALIVE to TRUE");
                socket.set_option(asio::socket_base::keep_alive(true));
            }

            if constexpr (traits::is_serial_proto<sock_t>) {
                _serialPorts.emplace_back(&socket);
            } else if constexpr (traits::is_tcp_proto<sock_t>) {
                // _tcpSockets.emplace_back(&socket);
                _tcpSockets.insert(&socket);
            } else if constexpr (traits::is_local_stream_proto<sock_t>) {
                // _localStreamSockets.emplace_back(&socket);
                _localStreamSockets.insert(&socket);
            } else if constexpr (traits::is_local_seqpack_proto<sock_t>) {
                // _localSeqpackSockets.emplace_back(&socket);
                _localSeqpackSockets.insert(&socket);
            } else {
                static_assert(false, "INVALID SOCKET TTYPE!!!");
            }


            // send buffer sequence
            // initiate the second element by "stop-sequence" symbols
            std::vector<asio::const_buffer> snd_buff_seq{
                {}, {BM700::CONTROL_PROTO_STOP_SEQ.data(), BM700::CONTROL_PROTO_STOP_SEQ.size()}};

            asio::steady_timer timeout_timer(_asioContext);
            std::variant<size_t, std::monostate> op_res;

            std::error_code ec;

            bool do_read = true;

            // main client request -- server respond cycle
            for (;;) {
                // receive message

                if (do_read) {
                    _serverLogger->trace("Start socket/port reading operation with timeout {} ...", rcv_timeout);

                    if constexpr (traits::is_serial_proto<sock_t>) {
                        nbytes = 1024;
                    } else {
                        nbytes = socket.available();
                    }

                    auto buff = sbuff.prepare(nbytes ? nbytes : 1);

                    // timeout_timer.expires_after(std::chrono::seconds(5));
                    timeout_timer.expires_after(rcv_timeout);

                    if constexpr (traits::is_local_seqpack_proto<sock_t>) {
                        asio::socket_base::message_flags oflags;

                        op_res = co_await (
                            socket.async_receive(buff, oflags, asio::redirect_error(asio::use_awaitable, ec)) ||
                            timeout_timer.async_wait(asio::use_awaitable));

                    } else {
                        op_res = co_await (asio::async_read(socket, buff, asio::transfer_at_least(1),
                                                            asio::redirect_error(asio::use_awaitable, ec)) ||
                                           timeout_timer.async_wait(asio::use_awaitable));
                    }

                    if (ec) {
                        throw std::system_error(ec);
                    }

                    if (op_res.index()) {
                        throw std::system_error(std::make_error_code(std::errc::timed_out));
                    } else {
                        nbytes = std::get<0>(op_res);

                        _serverLogger->trace("{} bytes were received", nbytes);

                        if constexpr (traits::is_local_seqpack_proto<sock_t>) {
                            if (!nbytes) {  // EOF!
                                throw std::system_error(std::error_code(asio::error::misc_errors::eof));
                            }
                        }
                    }

                    sbuff.commit(nbytes);
                }  // here, the input stream buffer still contains remaining bytes. try to handle its

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

                auto msg = look_for_whole_msg(std::span(start_ptr, sbuff.size()));
                if (msg.empty()) {  // still not whole message
                    _serverLogger->trace(
                        "It seems a partial command message was received, so waiting for remaining part ...");
                    do_read = true;
                    continue;
                }


                // extract command without stop sequence symbols
                // std::string comm;
                // std::ranges::copy(msg | std::views::take(msg.size() - BM700::CONTROL_PROTO_STOP_SEQ.size()),
                //                   std::back_inserter(comm));

                std::string_view comm{msg.begin(), msg.end() - BM700::CONTROL_PROTO_STOP_SEQ.size()};

                _serverLogger->debug("A command [{}] was received from client (remote endpoint <{}>, thread ID = {})",
                                     comm, r_epn, thr_id);

                auto resp = handleClientCommand(comm);

                // remove received message from the input stream buffer. NOTE: 'msg' is now invalidated!!!
                sbuff.consume(msg.size());
                do_read = sbuff.size() == 0;


                _serverLogger->debug("Send respond [{}] to client (remote endpoint <{}>, thread ID = {})",
                                     std::string_view(resp.begin(), resp.end()), r_epn, thr_id);

                // send server respond to client
                snd_buff_seq[0] = {resp.data(), resp.size()};

                timeout_timer.expires_after(snd_timeout);
                if constexpr (traits::is_local_seqpack_proto<sock_t>) {
                    op_res =
                        co_await (socket.async_send(snd_buff_seq, 0, asio::redirect_error(asio::use_awaitable, ec)) ||
                                  timeout_timer.async_wait(asio::use_awaitable));
                } else {
                    // nbytes = co_await asio::async_write(socket, snd_buff_seq, asio::use_awaitable);
                    op_res = co_await (
                        asio::async_write(socket, snd_buff_seq, asio::redirect_error(asio::use_awaitable, ec)) ||
                        timeout_timer.async_wait(asio::use_awaitable));
                }

                if (ec) {
                    throw std::system_error(ec);
                }

                if (op_res.index()) {
                    throw std::system_error(std::make_error_code(std::errc::timed_out));
                } else {
                    nbytes = std::get<0>(op_res);
                    _serverLogger->trace("{} bytes were sent", nbytes);
                }

                if (nbytes != (resp.size() + BM700::CONTROL_PROTO_STOP_SEQ.size())) {  // !!!!!!!!!!
                }
            }

        } catch (const std::system_error& ex) {
            if (ex.code() == std::error_code(asio::error::misc_errors::eof)) {
                _serverLogger->info(
                    "It seems client or server closed the connection (remote endpoint <{}>, thread ID = {})", r_epn,
                    thr_id);
            } else {
                _serverLogger->error("An error '{}' occured in client session (remote endpoint <{}>, thread ID = {})",
                                     ex.what(), r_epn, thr_id);
            }
        } catch (const std::exception& ex) {
            _serverLogger->error(
                "An unhandled error '{}' occured in client sesssion (remote endpoint <{}>, thread ID = {})", ex.what(),
                r_epn, thr_id);
        } catch (...) {
            _serverLogger->error("An unhandled error occured in client sesssion (remote endpoint <{}>, thread ID = {})",
                                 r_epn, thr_id);
        }

        if constexpr (traits::is_serial_proto<sock_t>) {
            // _serialPorts.emplace_back(&socket);
        } else if constexpr (traits::is_tcp_proto<sock_t>) {
            _tcpSockets.erase(&socket);
        } else if constexpr (traits::is_local_stream_proto<sock_t>) {
            _localStreamSockets.erase(&socket);
        } else if constexpr (traits::is_local_seqpack_proto<sock_t>) {
            _localSeqpackSockets.erase(&socket);
        } else {
            static_assert(false, "INVALID SOCKET TTYPE!!!");
        }

        _serverLogger->info("Close client session: remote endpoint <{}> (thread ID = {})", r_epn, thr_id);
    }
};

}  // namespace mcc