#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <unistd.h>

#define BUF_SIZE 100
#define PORT 8000
#define LISTEN_BACKLOG 32
#define MAX_EVENTS 10

#define handle_error(msg)                                                      \
  do {                                                                         \
    perror(msg);                                                               \
    exit(EXIT_FAILURE);                                                        \
  } while (0)

int main() {
  struct sockaddr_in addr, remote_addr;
  int sfd, cfd, epollfd;
  int nfds;
  ssize_t num_read;
  socklen_t addrlen = sizeof(struct sockaddr_in);
  char buf[BUF_SIZE];
  struct epoll_event ev, events[MAX_EVENTS];

  sfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sfd == -1)
    handle_error("socket");

  memset(&addr, 0, sizeof(struct sockaddr_in));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(PORT);
  addr.sin_addr.s_addr = htonl(INADDR_ANY);

  if (bind(sfd, (struct sockaddr *)&addr, sizeof(struct sockaddr_in)) == -1)
    handle_error("bind");

  if (listen(sfd, LISTEN_BACKLOG) == -1)
    handle_error("listen");

  epollfd = epoll_create1(0);
  if (epollfd == -1)
    handle_error("epoll_create1");

  ev.events = EPOLLIN | EPOLLOUT;
  ev.data.fd = sfd; // save the accept socket
  if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sfd, &ev) == -1)
    handle_error("epoll_ctl");

  for (;;) {
    nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
    if (nfds == -1)
      handle_error("epoll_wait");

    for (int i = 0; i < nfds; ++i) {
      if (events[i].data.fd == sfd) {
        memset(&remote_addr, 0, sizeof(struct sockaddr_in));
        cfd = accept(sfd, (struct sockaddr *)&remote_addr, &addrlen);
        if (cfd == -1)
          handle_error("accept");

        // Set O_NONBLOCK
        int flags = fcntl(cfd, F_GETFL, 0);
        if (flags == -1)
          handle_error("fcntl");
        flags |= O_NONBLOCK;
        if (fcntl(cfd, F_SETFL, flags) == -1)
          handle_error("fcntl");

        ev.events = EPOLLIN | EPOLLOUT;
        ev.data.fd = cfd;
        if (epoll_ctl(epollfd, EPOLL_CTL_ADD, cfd, &ev) == -1) {
          perror("epoll_ctl: conn_sock");
          exit(EXIT_FAILURE);
        }
      } else {
        while ((num_read = read(events[i].data.fd, buf, BUF_SIZE)) > 0) {
          if (write(STDOUT_FILENO, buf, num_read) != num_read)
            handle_error("write");

          if (num_read == -1)
            handle_error("read");
        }
      }
    }
  }
}