ADC/net/adc_netserver.h

#pragma once

/*

ABSTRACT DEVICE COMPONENTS LIBRARY

*/

#include <filesystem>
#include <functional>
#include <set>
#include <unordered_map>

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


#include "adc_net_concepts.h"

namespace adc
{


/*  SOME USEFULL PRIVITIVES  */

// Ageneric implementation pf POSIX OS daemon
class AdcPosixGenericDaemon
{
public:
    virtual ~AdcPosixGenericDaemon() = default;

    // run server as daemon (still only on POSIX OSes)
    void daemonize()
    {
        daemonizePrepare();

// reference implementation of forking for POSIX OSes
#ifdef FORK_EXISTS
        // get TEMP directory in OS

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

        // _ioContext.notify_fork(asio::execution_context::fork_prepare);

        if (pid_t pid = fork()) {
            if (pid > 0) {
                exit(0);
            } else {
                throw std::system_error(errno, std::generic_category(), "CANNOT FORK 1-STAGE");
            }
        }

        if (setsid() == -1) {
            throw std::system_error(errno, std::generic_category(), "CANNOT FORK SETSID");
        }

        std::filesystem::current_path(tmp_path);

        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");
            }
        }

        close(0);
        close(1);
        close(2);

// _ioContext.notify_fork(asio::io_context::fork_child);
#endif
        daemonizeFinalize();
    }

protected:
    virtual void daemonizePrepare() = 0;
    virtual void daemonizeFinalize() = 0;
};


// a basic network session manager (basic start and stop functionality)

class AdcNetSessionManager
{
public:
    virtual ~AdcNetSessionManager() = default;

protected:
    template <interfaces::adc_netsession_c SessionT>
    constexpr static bool anySessionPredicate(const typename SessionT::netsession_ident_t&)
    {
        return true;
    }

    // started sessions weak pointers
    template <interfaces::adc_netsession_c SessionT>
    static std::unordered_map<const AdcNetSessionManager*, std::set<std::weak_ptr<SessionT>>> _serverSessions;
    std::vector<std::function<bool()>> _stopSessionFunc;

    template <interfaces::adc_netsession_c SessionT>
    void startSession(std::shared_ptr<SessionT>& sess_ptr)
    {
        auto res = _serverSessions<SessionT>[this].emplace(sess_ptr);
        if (res.second) {
            sess_ptr.start();

            _stopSessionFunc.emplace_back([res]() {
                if (!res.first.expired()) {  // session is still existing
                    auto sess = res.first.lock();
                    sess->stop();
                    return true;
                } else {
                    return false;
                }
            });
        }
    }


    template <interfaces::adc_netsession_c SessionT,
              std::predicate<typename SessionT::netsession_ident_t> PredT = decltype(anySessionPredicate<SessionT>)>
    size_t stopSessions(PredT&& comp_func = anySessionPredicate<SessionT>())
    {
        size_t N = 0;

        for (auto& wptr : _serverSessions<SessionT>[this]) {
            if (std::shared_ptr<SessionT> sptr = wptr.lock()) {
                if constexpr (std::same_as<PredT, decltype(anySessionPredicate<SessionT>)>) {
                    sptr->stop();
                    ++N;
                } else {
                    if (std::forward<PredT>(comp_func)(sptr->ident())) {
                        sptr->stop();
                        ++N;
                    }
                }
            }
        }

        return N;
    }


    size_t stopAllSessions()
    {
        size_t N = 0;

        for (auto& func : _stopSessionFunc) {
            func() ? ++N : 0;
        }

        return N;
    }
};



/*  very generic network server  */

class AdcGenericNetServer : public AdcPosixGenericDaemon, public AdcNetSessionManager
{
protected:
public:
    typedef std::string server_ident_t;


    virtual ~AdcGenericNetServer() = default;


    virtual server_ident_t ident() const
    {
        return _serverIdent;
    }

    // start accepting remote connections, create and start given network session
    // It must be assumed that this is asynchronous operation!!!
    template <interfaces::adc_netsession_c SessionT, typename... AcceptorCtorArgTs>
    void start(const typename SessionT::netsession_ident_t& id,
               const typename SessionT::netsession_ctx_t& sess_ctx,
               AcceptorCtorArgTs&&... ctor_args)
    {
        if (!_isListening<SessionT>[this]) {
            auto acceptor = std::make_shared<typename SessionT::netservice_t::acceptor_t>(
                std::forward<AcceptorCtorArgTs>(ctor_args)...);

            doAccept<SessionT>(acceptor, id, sess_ctx);
        }
    };


    template <interfaces::adc_netsession_c SessionT>
    bool isListening() const
    {
        return _isListening<SessionT>[this];
    }

    virtual void start() = 0;

    virtual void stop()
    {
        stopAllSessions();
    };



protected:
    template <interfaces::adc_netsession_c SessionT>
    inline static std::unordered_map<const AdcGenericNetServer*, bool> _isListening{};

    server_ident_t _serverIdent;

    template <typename SessionT, typename AT, typename IDT, typename CTXT>
    void doAccept(std::shared_ptr<AT> acceptor, const IDT& id, const CTXT& sess_ctx)
    {
        acceptor.asyncAccept([acceptor, &id, &sess_ctx, this](auto ec, typename SessionT::netservice_t srv) mutable {
            if (!ec) {
                auto sess = std::make_shared<SessionT>(id, std::move(srv), sess_ctx);
                startSession(sess);

                _isListening<SessionT>[this] = true;
                doAccept(acceptor, id, sess_ctx);
            } else {
                _isListening<SessionT>[this] = false;
            }
        });
    }
};


}  // namespace adc