/* Copyright (c) 2018, Curtis McEnroe <programble@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <err.h>
#include <poll.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/wait.h>
#include <sysexits.h>
#include <termios.h>
#include <unistd.h>

#if defined __FreeBSD__
#include <libutil.h>
#elif defined __linux__
#include <pty.h>
#else
#include <util.h>
#endif

static struct termios saveTerm;
static void restoreTerm(void) {
    tcsetattr(STDERR_FILENO, TCSADRAIN, &saveTerm);
}

int main(int argc, char *argv[]) {
    int error;

    if (argc > 1) {
        argv++;
    } else {
        uid_t uid = getuid();
        struct passwd *user = getpwuid(uid);
        if (!user) err(EX_OSFILE, "/etc/passwd");
        argv[0] = user->pw_shell;
    }

    int input = STDIN_FILENO;
    int local = STDERR_FILENO;
    int remote = STDOUT_FILENO;

    error = tcgetattr(local, &saveTerm);
    if (error) err(EX_IOERR, "tcgetattr");
    atexit(restoreTerm);

    struct termios raw;
    cfmakeraw(&raw);
    error = tcsetattr(local, TCSADRAIN, &raw);
    if (error) err(EX_IOERR, "tcsetattr");

    struct winsize window;
    error = ioctl(local, TIOCGWINSZ, &window);
    if (error) err(EX_IOERR, "ioctl(%d, TIOCGWINSZ, ...)", local);

    ssize_t size = write(remote, &window, sizeof(window));
    if (size < 0) err(EX_IOERR, "write(%d)", remote);
    if ((size_t)size < sizeof(window)) errx(EX_IOERR, "short write(%d)", remote);

    int pty;
    pid_t pid = forkpty(&pty, NULL, NULL, &window);
    if (pid < 0) err(EX_OSERR, "forkpty");

    if (!pid) {
        execvp(*argv, argv);
        err(EX_USAGE, "%s", *argv);
    }

    char buf[4096];
    struct pollfd fds[2] = {
        { .fd = input, .events = POLLIN },
        { .fd = pty, .events = POLLIN },
    };
    while (0 < poll(fds, 2, -1)) {
        if (fds[0].revents) {
            ssize_t readSize = read(input, buf, sizeof(buf));
            if (readSize < 0) err(EX_IOERR, "read(%d)", input);

            ssize_t writeSize = write(pty, buf, readSize);
            if (writeSize < 0) err(EX_IOERR, "write(%d)", pty);
            if (writeSize < readSize) errx(EX_IOERR, "short write(%d)", pty);
        }

        if (fds[1].revents) {
            ssize_t readSize = read(pty, buf, sizeof(buf));
            if (readSize < 0) err(EX_IOERR, "read(%d)", pty);

            ssize_t writeSize = write(local, buf, readSize);
            if (writeSize < 0) err(EX_IOERR, "write(%d)", local);
            if (writeSize < readSize) errx(EX_IOERR, "short write(%d)", local);

            writeSize = write(remote, buf, readSize);
            if (writeSize < 0) err(EX_IOERR, "write(%d)", remote);
            if (writeSize < readSize) errx(EX_IOERR, "short write(%d)", remote);
        }

        int status;
        pid_t dead = waitpid(pid, &status, WNOHANG);
        if (dead < 0) err(EX_OSERR, "waitpid");
        if (dead) return WIFEXITED(status) ? WEXITSTATUS(status) : EX_SOFTWARE;
    }
    err(EX_IOERR, "poll");
}