#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <termios.h>
#include <stdarg.h>
#include <signal.h>
#include <errno.h>

static struct termios       save_termios;
static int                  ttysavefd = -1;
static enum { RESET, RAW, CBREAK } ttystate = RESET;

int
tty_cbreak(int fd) /* put terminal into a cbreak mode */
{
    int              err;
    struct termios   buf;

    if (ttystate != RESET) {
        errno = EINVAL;
        return(-1);
    }
    if (tcgetattr(fd, &buf) < 0)
        return(-1);
    save_termios = buf; /* structure copy */

    /*
     * Echo off, canonical mode off.
     */
    buf.c_lflag &= ~(ECHO | ICANON);

    /*
     * Case B: 1 byte at a time, no timer.
     */
    buf.c_cc[VMIN] = 1;
    buf.c_cc[VTIME] = 0;
    if (tcsetattr(fd, TCSAFLUSH, &buf) < 0)
        return(-1);

    /*
     * Verify that the changes stuck. tcsetattr can return 0 on
     * partial success.
     */
    if (tcgetattr(fd, &buf) < 0) {
        err = errno;
        tcsetattr(fd, TCSAFLUSH, &save_termios);
        errno = err;
        return(-1);
    }
    if ((buf.c_lflag & (ECHO | ICANON)) || buf.c_cc[VMIN] != 1 ||
      buf.c_cc[VTIME] != 0) {
        /*
         * Only some of the changes were made. Restore the
         * original settings.
         */
        tcsetattr(fd, TCSAFLUSH, &save_termios);
        errno = EINVAL;
        return(-1);
    }

    ttystate = CBREAK;
    ttysavefd = fd;
    return(0);
}

int
tty_raw(int fd)     /* put terminal into a raw mode */
{
    int             err;
    struct termios  buf;

    if (ttystate != RESET) {
        errno = EINVAL;
        return(-1);
    }
    if (tcgetattr(fd, &buf) < 0)
        return(-1);
    save_termios = buf; /* structure copy */

    /*
     * Echo off, canonical mode off, extended input
     * processing off, signal chars off.
     */
    buf.c_lflag &= ~(ECHO | ICANON | IEXTEN | ISIG);

    /*
     * No SIGINT on BREAK, CR-to-NL off, input parity
     * check off, don't strip 8th bit on input, output
     * flow control off.
     */
    buf.c_iflag &= ~(BRKINT | ICRNL | INPCK | ISTRIP | IXON);

    /*
     * Clear size bits, parity checking off.
     */
    buf.c_cflag &= ~(CSIZE | PARENB);

    /*
     * Set 8 bits/char.
     */
    buf.c_cflag |= CS8;

    /*
     * Output processing off.
     */
    buf.c_oflag &= ~(OPOST);

    /*
     * Case B: 1 byte at a time, no timer.
     */
    buf.c_cc[VMIN] = 1;
    buf.c_cc[VTIME] = 0;
    if (tcsetattr(fd, TCSAFLUSH, &buf) < 0)
        return(-1);

    /*
     * Verify that the changes stuck. tcsetattr can return 0 on
     * partial success.
     */
    if (tcgetattr(fd, &buf) < 0) {
        err = errno;
        tcsetattr(fd, TCSAFLUSH, &save_termios);
        errno = err;
        return(-1);
    }
    if ((buf.c_lflag & (ECHO | ICANON | IEXTEN | ISIG)) ||
      (buf.c_iflag & (BRKINT | ICRNL | INPCK | ISTRIP | IXON)) ||
      (buf.c_cflag & (CSIZE | PARENB | CS8)) != CS8 ||
      (buf.c_oflag & OPOST) || buf.c_cc[VMIN] != 1 ||
      buf.c_cc[VTIME] != 0) {
        /*
         * Only some of the changes were made. Restore the
         * original settings.
         */
        tcsetattr(fd, TCSAFLUSH, &save_termios);
        errno = EINVAL;
        return(-1);
    }

    ttystate = RAW;
    ttysavefd = fd;
    return(0);
}

int tty_reset(int fd)      /* restore terminal's mode */
{
    if (ttystate == RESET)
        return(0);
    if (tcsetattr(fd, TCSAFLUSH, &save_termios) < 0)
        return(-1);
    ttystate = RESET;
    return(0);
}
void tty_atexit(void)        /* can be set up by atexit(tty_atexit) */
{
    if (ttysavefd >= 0)
        tty_reset(ttysavefd);
}

struct termios * tty_termios(void)       /* let caller see original tty state */
{
    return(&save_termios);
}

static void
sig_catch(int signo)
{
    printf("signal caught\n");
    tty_reset(STDIN_FILENO);
    exit(0);
}

void err_sys(char *fmt, ...)
{
   char buf[1024];

   va_list ap;

   va_start(ap, fmt);
   vsnprintf(buf, sizeof(buf), fmt, ap);

   fprintf(stderr, "%s", buf);

   va_end(ap);

   exit(EXIT_FAILURE);
}

int
main(void)
{
    int    i;
    char   c;

    if (signal(SIGINT, sig_catch) == SIG_ERR)   /* catch signals */
        err_sys("signal(SIGINT) error");
    if (signal(SIGQUIT, sig_catch) == SIG_ERR)
        err_sys("signal(SIGQUIT) error");
    if (signal(SIGTERM, sig_catch) == SIG_ERR)
        err_sys("signal(SIGTERM) error");

    if (tty_raw(STDIN_FILENO) < 0)
        err_sys("tty_raw error");
    printf("Enter raw mode characters, terminate with DELETE\n");
    while ((i = read(STDIN_FILENO, &c, 1)) == 1) {
        if ((c &= 255) == 0177)     /* 0177 = ASCII DELETE */
            break;
        printf("%o\n", c);
    }
    if (tty_reset(STDIN_FILENO) < 0)
        err_sys("tty_reset error");
    if (i <= 0)
        err_sys("read error");
    if (tty_cbreak(STDIN_FILENO) < 0)
        err_sys("tty_cbreak error");
    printf("\nEnter cbreak mode characters, terminate with SIGINT\n");
    while ((i = read(STDIN_FILENO, &c, 1)) == 1) {
        c &= 255;
        printf("%o\n", c);
    }
    if (tty_reset(STDIN_FILENO) < 0)
        err_sys("tty_reset error");
    if (i <= 0)
        err_sys("read error");
    exit(0);
}