#include <assert.h>
#include <curl/curl.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <unistd.h>

void error(const char* string)
{
  perror(string);
  exit(1);
}

int epollFd;
int timeout = -1;

int socketCallback(CURL* easy, curl_socket_t fd, int action, void* u, void* s)
{
  struct epoll_event event;
  event.events = 0;
  event.data.fd = fd;

  if (action == CURL_POLL_REMOVE) {
    int res = epoll_ctl(epollFd, EPOLL_CTL_DEL, fd, &event);
    if (res == -1 && errno != EBADF)
      perror("epoll_ctl(DEL)");
    return 0;
  }

  if (action == CURL_POLL_IN || action == CURL_POLL_INOUT)
    event.events |= EPOLLIN;
  if (action == CURL_POLL_OUT || action == CURL_POLL_INOUT)
    event.events |= EPOLLOUT;

  if (event.events != 0) {
    int res = epoll_ctl(epollFd, EPOLL_CTL_ADD, fd, &event);
    if (res == -1)
      res = epoll_ctl(epollFd, EPOLL_CTL_MOD, fd, &event);
    if (res == -1)
      error("epoll_ctl(MOD)");
  }

  return 0;
}

int timerCallback(CURLM* multi, long timeout_ms, void* u)
{
  timeout = timeout_ms;
  return 0;
}

int main(int argc, char** argv)
{
  // argv[1] == URL
  assert(argc == 2);

  epollFd = epoll_create(1);
  if (epollFd == -1)
    error("epoll_create");

  curl_global_init(CURL_GLOBAL_ALL);
  printf("Using %s\n", curl_version());

  CURL* easy = curl_easy_init();
  curl_easy_setopt(easy, CURLOPT_URL, argv[1]);
  curl_easy_setopt(easy, CURLOPT_FOLLOWLOCATION, 1);

  CURLM* multi = curl_multi_init();
  curl_multi_setopt(multi, CURLMOPT_SOCKETFUNCTION, socketCallback);
  curl_multi_setopt(multi, CURLMOPT_TIMERFUNCTION, timerCallback);

  curl_multi_add_handle(multi, easy);

  int running_handles = 1;
  while (running_handles > 0) {
    struct epoll_event event;
    int res = epoll_wait(epollFd, &event, 1, timeout);
    if (res == -1)
      error("epoll_wait");
    else if (res == 0) {
      curl_multi_socket_action(multi, CURL_SOCKET_TIMEOUT, 0, &running_handles);
    }
    else {
      curl_multi_socket_action(multi, event.data.fd, 0, &running_handles);
    }
  }

  curl_global_cleanup();
  close(epollFd);

  printf("bye bye\n");
  return 0;
}