/* Copyright (C) 2018  Causal Agent June <june@causal.agency>
 *
 * 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 <errno.h>
#include <poll.h>
#include <pwd.h>
#include <stdlib.h>
#include <sys/ioctl.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

extern int winch(void);

static struct {
    int pty;
    int winch;
    int input;
    int local;
    int remote;
} fd = { -1, -1, STDIN_FILENO, STDERR_FILENO, STDOUT_FILENO };

static struct termios saveTerm;
static void restoreTerm(void) {
    tcsetattr(fd.local, TCSADRAIN, &saveTerm);
}

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

    if (isatty(fd.remote)) {
        errx(EX_USAGE, "stdout is not redirected");
    }

    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;
    }

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

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

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

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

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

    char buf[4096];
    ssize_t totalSize = 0;
    struct pollfd fds[3] = {
        { .fd = fd.input, .events = POLLIN },
        { .fd = fd.pty, .events = POLLIN },
        { .fd = fd.winch, .events = POLLIN },
    };
    for (;;) {
        int nfds = poll(fds, 3, -1);
        if (nfds < 0) {
            if (errno == EINTR) continue;
            err(EX_IOERR, "poll");
        }

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

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

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

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

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

            if ((totalSize += readSize) >= 1024 * 1024) {
                struct winsize original = window;
                window.ws_row = 1;
                window.ws_col = 1;

                int error = ioctl(fd.pty, TIOCSWINSZ, &window);
                if (error) err(EX_IOERR, "TIOCSWINSZ");

                window = original;
                error = ioctl(fd.pty, TIOCSWINSZ, &window);
                if (error) err(EX_IOERR, "TIOCWINSZ");

                totalSize = 0;
            }
        }

        if (fds[2].revents == POLLIN) {
            ssize_t readSize = read(fd.winch, &window, sizeof(window));
            if (readSize < 0) err(EX_IOERR, "read(%d)", fd.winch);
            if ((size_t)readSize < sizeof(window)) {
                errx(EX_IOERR, "short read(%d)", fd.winch);
            }

            int error = ioctl(fd.pty, TIOCSWINSZ, &window);
            if (error) err(EX_IOERR, "TIOCSWINSZ");
        }

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