// Copyright (c) Vitaliy Filippov, 2019+
// License: VNPL-1.1 or GNU GPL-2.0+ (see README.md for details)

#include <sys/epoll.h>
#include <sys/poll.h>
#include <poll.h>
#include <unistd.h>
#include <stdexcept>

#include "epoll_manager.h"

#define MAX_EPOLL_EVENTS 64

epoll_manager_t::epoll_manager_t(ring_loop_t *ringloop)
{
    this->ringloop = ringloop;
    this->pending = false;

    epoll_fd = epoll_create(1);
    if (epoll_fd < 0)
    {
        throw std::runtime_error(std::string("epoll_create: ") + strerror(errno));
    }

    tfd = new timerfd_manager_t([this](int fd, bool wr, std::function<void(int, int)> handler) { set_fd_handler(fd, wr, handler); });

    if (ringloop)
    {
        consumer.loop = [this]()
        {
            if (pending)
                handle_uring_event();
        };
        ringloop->register_consumer(&consumer);
        handle_uring_event();
    }
}

epoll_manager_t::~epoll_manager_t()
{
    if (ringloop)
    {
        ringloop->unregister_consumer(&consumer);
    }
    if (tfd)
    {
        delete tfd;
        tfd = NULL;
    }
    close(epoll_fd);
}

int epoll_manager_t::get_fd()
{
    return epoll_fd;
}

void epoll_manager_t::set_fd_handler(int fd, bool wr, std::function<void(int, int)> handler)
{
    if (handler != NULL)
    {
        bool exists = epoll_handlers.find(fd) != epoll_handlers.end();
        epoll_event ev;
        ev.data.fd = fd;
        ev.events = (wr ? EPOLLOUT : 0) | EPOLLIN | EPOLLRDHUP | EPOLLET;
        if (epoll_ctl(epoll_fd, exists ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev) < 0)
        {
            if (errno == ENOENT)
            {
                // The FD is probably already closed
                epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, NULL);
                epoll_handlers.erase(fd);
                return;
            }
            throw std::runtime_error(std::string("epoll_ctl: ") + strerror(errno));
        }
        epoll_handlers[fd] = handler;
        // We use edge-triggered epoll so it may miss events which already happened
        // on the FD at the moment of adding it to epoll. So check for these with poll()
        struct pollfd initpoll = { .fd = fd, .events = (short)((wr ? POLLOUT : 0) | POLLIN | POLLRDHUP) };
        int r = poll(&initpoll, 1, 0);
        if (r < 0)
            throw std::runtime_error(std::string("poll: ") + strerror(errno));
        if (r > 0)
        {
            auto events = ((initpoll.revents & POLLOUT) ? EPOLLOUT : 0) |
                ((initpoll.revents & POLLIN) ? EPOLLIN : 0) |
                ((initpoll.revents & POLLRDHUP) ? EPOLLRDHUP : 0);
            tfd->set_timer_us(1, false, [this, fd, events](int)
            {
                auto cb_it = epoll_handlers.find(fd);
                if (cb_it != epoll_handlers.end())
                {
                    auto & cb = cb_it->second;
                    cb(fd, events);
                }
            });
        }
    }
    else
    {
        if (epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, NULL) < 0 && errno != ENOENT)
        {
            throw std::runtime_error(std::string("epoll_ctl: ") + strerror(errno));
        }
        epoll_handlers.erase(fd);
    }
}

void epoll_manager_t::handle_uring_event()
{
    io_uring_sqe *sqe = ringloop->get_sqe();
    if (!sqe)
    {
        // Don't handle epoll events until we manage to post the next event handler
        // otherwise we'll fall out of sync with EPOLLET
        pending = true;
        ringloop->wakeup();
        return;
    }
    pending = false;
    ring_data_t *data = ((ring_data_t*)sqe->user_data);
    io_uring_prep_poll_add(sqe, epoll_fd, POLLIN);
    data->callback = [this](ring_data_t *data)
    {
        if (data->res < 0 && data->res != -ECANCELED)
        {
            throw std::runtime_error(std::string("epoll failed: ") + strerror(-data->res));
        }
        handle_uring_event();
    };
    ringloop->submit();
    handle_events(0);
}

void epoll_manager_t::handle_events(int timeout)
{
    int nfds;
    epoll_event events[MAX_EPOLL_EVENTS];
    do
    {
        nfds = epoll_wait(epoll_fd, events, MAX_EPOLL_EVENTS, timeout);
        timeout = 0;
        for (int i = 0; i < nfds; i++)
        {
            auto cb_it = epoll_handlers.find(events[i].data.fd);
            if (cb_it != epoll_handlers.end())
            {
                auto & cb = cb_it->second;
                cb(events[i].data.fd, events[i].events);
            }
        }
    } while (nfds == MAX_EPOLL_EVENTS);
}