/* Copyright (C) 2021  C. McEnroe <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 <sys/types.h>

#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/event.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <sysexits.h>
#include <unistd.h>

static void watch(int kq, char *path) {
	int fd = open(path, O_RDONLY | O_CLOEXEC);
	if (fd < 0) err(EX_TEMPFAIL, "%s", path);

	struct kevent event;
	EV_SET(
		&event, fd, EVFILT_VNODE, EV_ADD | EV_CLEAR,
		NOTE_WRITE | NOTE_DELETE, 0, path
	);
	int nevents = kevent(kq, &event, 1, NULL, 0, NULL);
	if (nevents < 0) err(EX_OSERR, "kevent");
}

static void run(char *argv[]) {
	pid_t pid = fork();
	if (pid < 0) err(EX_OSERR, "fork");
	if (!pid) {
		execvp(argv[0], argv);
		err(126, "%s", argv[0]);
	}

	int status;
	pid = wait(&status);
	if (pid < 0) err(EX_OSERR, "wait");
	if (WIFEXITED(status)) {
		status = WEXITSTATUS(status);
		if (status) exit(status);
	} else {
		exit(status);
	}
}

int main(int argc, char *argv[]) {
	int kq = kqueue();
	if (kq < 0) err(EX_OSERR, "kqueue");
	fcntl(kq, F_SETFD, FD_CLOEXEC);

	int init = 0;
	int delay = 0;
	int append = 0;
	for (int opt; 0 < (opt = getopt(argc, argv, "ad:f:i"));) {
		switch (opt) {
			break; case 'a': append = 1;
			break; case 'd': delay = strtol(optarg, NULL, 10);
			break; case 'f': watch(kq, optarg);
			break; case 'i': init = 1;
			break; default: return EX_USAGE;
		}
	}
	argc -= optind;
	argv += optind;
	if (!argc) errx(EX_USAGE, "command required");

	char **rest = argv;
	if (append) {
		rest = calloc(argc + 2, sizeof(*rest));
		if (!rest) err(EX_OSERR, "calloc");
		memcpy(rest, argv, sizeof(*argv) * argc);
	}

#ifdef __OpenBSD__
	int error = pledge("stdio proc exec", NULL);
	if (error) err(EX_OSERR, "pledge");
#endif

	if (init) run(rest);
	for (;;) {
		struct kevent event;
		int nevents = kevent(kq, NULL, 0, &event, 1, NULL);
		if (nevents < 0) err(EX_OSERR, "kevent");

		if (delay) {
			struct kevent timer;
			EV_SET(
				&timer, 0, EVFILT_TIMER, EV_ADD | EV_ONESHOT,
				0, delay, event.udata
			);
			nevents = kevent(kq, &timer, 1, NULL, 0, NULL);
			if (nevents < 0) err(EX_OSERR, "kevent");
			while (
				event.filter != EVFILT_TIMER
				&& !(event.fflags & NOTE_DELETE)
			) {
				nevents = kevent(kq, NULL, 0, &event, 1, NULL);
				if (nevents < 0) err(EX_OSERR, "kevent");
			}
		}

		if (event.filter == EVFILT_VNODE && event.fflags & NOTE_DELETE) {
			errx(EX_TEMPFAIL, "%s: file removed", (char *)event.udata);
		}

		if (append) rest[argc] = (char *)event.udata;
		run(rest);
	}
}