#include <errno.h>
#include <fcntl.h>
#include <linux/if.h>
#include <linux/if_tun.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

#define DEVICE_NODE_TUN /dev/net/tun
#define BUFFER_SIZE 0x1000

#define EXIT_SUCCESS 0
#define EXIT_USAGE 1
#define EXIT_RUNTIME 2

int file_descriptor;
char buffer[BUFFER_SIZE];
struct ifreq ifr;

int main(int argc, char** argv) {
  if (argc != 2) {
    fprintf(stderr, "Usage: %s TAP\n", argv[0]);
    return EXIT_USAGE;
  } else if ((strlen(argv[1])==2 && strncmp(argv[1], "-h", 2)==0) || (strlen(argv[1])==6 &&strncmp(argv[1], "--help", 6))) {
    fprintf(stdout, "Usage: %s TAP\n", argv[0]);
    return EXIT_SUCCESS;
  }

  memset(&ifr, 0, sizeof(ifr));
  ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
  strncpy(ifr.ifr_name, argv[1], IFNAMSIZ);

  file_descriptor = open("/dev/net/tun", O_RDWR);
  if (file_descriptor == -1) {
    fprintf(stderr, "An error occurred while trying to open DEVICE_NODE_TUN: %i\n", errno);
    return EXIT_RUNTIME;
  }

  if (ioctl(file_descriptor, TUNSETIFF, &ifr) == -1) {
    fprintf(stderr, "An error occurred while trying to ioctl: %i\n", errno);
    close(file_descriptor);
    return EXIT_RUNTIME;
  }

  //TODO:
  // while input not EOF
  // and the tap is still a valid device (it might go away)
  // read from tap to stdout
  // read from stdin to tap

  //TODO: signal handler for SIGINT (and SIGHUP? maybe others?)

  if (fcntl(fd, F_GETFD) != -1 || errno != EBADF) {
    close(file_descriptor);
  }
  return EXIT_SUCCESS;
}