/* _XOPEN_SOURCE unlocks <stdlib.h> pty/ptmx/pts declarations. */
#define _XOPEN_SOURCE 600
/* _GNU_SOURCE unlocks the ptsname_r declaration*/
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <asm/termbits.h>  /* TIOC* constants */
#include <sys/ioctl.h>

#ifdef PATH_MAX
# define SNAME_MAX PATH_MAX
#else
# define SNAME_MAX 512
#endif /* PATH_MAX */

/* Allocate PTY master and slave file descriptors.
 * errno will have been set if newpty() fails.
 *
 * NOTE: This function is my alternative to GLibC's
 * openpty() function. It exists as a learning resource.
 * REF: glibc.git:/login/openpty.c
 */
int mkpty(int *fdmx, int *fds) {
  int _fdmx = -1, _fds = -1;
  char sname[SNAME_MAX];  

  // Configure PTY master (file descriptor)
  _fdmx = posix_openpt(O_RDWR | O_NOCTTY);
  if (_fdmx == -1)
    return EXIT_FAILURE;

  if (grantpt(_fdmx))
    goto fail;
  if (unlockpt(_fdmx))
    goto fail;

#ifdef TIOCGPTPEER
  /* Try to allocate slave fd solely based on PTMX fd first. */
  _fds = ioctl(_fdmx, TIOCGPTPEER, O_RDWR | O_NOCTTY);
#endif
  if (_fds == -1) {
    /* Fallback to path-based slave fd allocation
     * (if the kernel doesn't support TIOCGPTPEER, ie Linux <4.13) */
    if(ptsname_r(_fdmx, sname, sizeof(sname)))
      goto fail;

    _fds = open(sname, O_RDWR | O_NOCTTY);
    if (_fds == -1)
      goto fail;
  }

  // Propagate file descriptors via parameters
  *fdmx = _fdmx;
  *fds = _fds;
  return EXIT_SUCCESS;

fail:
  if (_fdmx == -1) {
    close(_fdmx);
    if (_fds == -1)
      close(_fds);
  }
  return EXIT_FAILURE;
}

/*
 */
pid_t forkmkpty() {
  int fdmx, fds;
  pid_t pid;
  if (mkpty(&fdmx, &fds))
    return EXIT_FAILURE;

  switch (pid = fork()) {
  case -1:
    close(fdmx);
    close(fds);
    return -1;    
  case 0:
    /* Child Process */
    close(fdmx);
    break;
    
  default:
    /* Parent Process */
    close(fds);
    break;
  }

  /* Both Processes */
  return pid;
}

/* Set pseudoterminal slave's window size.
 * Returns 0 on success, and fails with -1 if the kernel doesn't
 * implement this, or 1 for general errors (errno will be set).
 * NOTE: Typically this is part of a glibc openpty() call.
 */
int setptsxy(const unsigned short rows, const unsigned short cols, const int fds) {
#ifndef TIOCSWINSZ
  /* Fail if kernel doesn't support TIOCSWINSZ. */
  return -1;
#else
  struct winsize win = {
    .ws_row = rows,
    .ws_col = cols,
  };
  
  if (ioctl(fds, TIOCSWINSZ, &win))
    return EXIT_FAILURE;
  return EXIT_SUCCESS;
#endif /* TIOCSWINSZ */
}

/* Get pseudoterminal slave's window size.
 * Returns 0 on success, and fails with -1 if the kernel doesn't
 * implement this, or 1 for general errors (errno will be set).
 */
int getptsxy(unsigned short *rows, unsigned short *cols, const int fds) {
#ifndef TIOCGWINSZ
  /* Fail if kernel doesn't support TIOCGWINSZ. */
  return -1;
#else
  struct winsize win = (struct winsize){ 0 };
  if (ioctl(fds, TIOCGWINSZ, &win))
    return EXIT_FAILURE;
  *rows = win.ws_row;
  *cols = win.ws_col;
  return EXIT_SUCCESS;
#endif /* TIOCGWINSZ */
}