/* 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 <fcntl.h>
#include <poll.h>
#include <sys/ioctl.h>
#include <sys/ioctl.h>
#include <sysexits.h>
#include <unistd.h>

extern int winch(void);

static struct {
    int winch;
    int local;
    int remote;
} fd = { -1, -1, STDIN_FILENO };

int main(int argc, char *argv[]) {
    if (argc < 2) errx(EX_USAGE, "missing private id");
    if (!isatty(STDERR_FILENO)) errx(EX_USAGE, "no terminal (use ssh -t)");

    const char *path = argv[1];
    fd.local = open(path, O_WRONLY);
    if (fd.local < 0) err(EX_NOINPUT, "%s", path);

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

    for (;;) {
        int error = ftruncate(fd.local, 0);
        if (error) err(EX_IOERR, "%s", path);

        off_t off = lseek(fd.local, 0, SEEK_SET);
        if (off < 0) err(EX_IOERR, "%s", path);

        ssize_t size = write(fd.local, &window, sizeof(window));
        if (size < 0) err(EX_IOERR, "write(%d)", fd.local);
        if ((size_t)size < sizeof(window)) {
            errx(EX_IOERR, "short write(%d)", fd.local);
        }

        char buf[4096];
        struct pollfd fds[2] = {
            { .fd = fd.remote, .events = POLLIN },
            { .fd = fd.winch, .events = POLLIN },
        };
        for (ssize_t totalSize = 0; totalSize < 1024 * 1024;) {
            int nfds = poll(fds, 2, -1);
            if (nfds < 0) {
                if (errno == EINTR) continue;
                err(EX_IOERR, "poll");
            }

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

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

                totalSize += readSize;
            }

            if (fds[0].revents & POLLHUP) return EX_OK;

            if (fds[1].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);
                }
                break;
            }
        }
    }
}