/* Copyright (C) 2020  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 <err.h>
#include <errno.h>
#include <fcntl.h>
#include <fnmatch.h>
#include <grp.h>
#include <paths.h>
#include <poll.h>
#include <pwd.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <sysexits.h>
#include <syslog.h>
#include <unistd.h>

#include "daemon.h"

#define WS " \t"

struct Set256 stopExits;
struct timespec restartInterval = { .tv_sec = 1 };
struct timespec resetInterval = { .tv_sec = 15 * 60 };

static volatile sig_atomic_t signals[NSIG];
static void signalHandler(int signal) {
	signals[signal] = 1;
}

static ssize_t getlinecont(char **line, size_t *lcap, FILE *file) {
	size_t cap = 0;
	char *buf = NULL;
	ssize_t llen = getline(line, lcap, file);
	while (llen > 1 && (*line)[llen - 1] == '\n' && (*line)[llen - 2] == '\\') {
		llen -= 2;
		ssize_t len = getline(&buf, &cap, file);
		if (len < 0) {
			llen = -1;
			break;
		}
		size_t req = llen + len + 1;
		if (req > *lcap) {
			char *ptr = realloc(*line, req);
			if (!ptr) {
				llen = -1;
				break;
			}
			*line = ptr;
			*lcap = req;
		}
		strlcpy(*line + llen, buf, *lcap - llen);
		llen += len;
	}
	free(buf);
	return llen;
}

static int parseConfig(const char *path) {
	int ret = -1;
	size_t cap = 0;
	char *buf = NULL;

	FILE *file = fopen(path, "r");
	if (!file) {
		syslog(LOG_WARNING, "%s: %m", path);
		goto err;
	}

	prependClear();

	int line = 1;
	for (ssize_t len; 0 <= (len = getlinecont(&buf, &cap, file)); ++line) {
		if (buf[len - 1] == '\n') buf[len - 1] = '\0';

		char *ptr = &buf[strspn(buf, WS)];
		if (!ptr[0] || ptr[0] == '#') {
			continue;
		} else if (ptr[0] == '%') {
			ptr++;
			int error = prependAdd(&ptr[strspn(ptr, WS)]);
			if (error) {
				syslog(LOG_WARNING, "cannot add prepend command: %m");
				goto err;
			}
		} else {
			char *name = strsep(&ptr, WS);
			if (!ptr) {
				syslog(
					LOG_WARNING, "%s:%d: no command line for service %s",
					path, line, name
				);
				goto err;
			}
			int error = serviceAdd(name, &ptr[strspn(ptr, WS)]);
			if (error) {
				syslog(LOG_WARNING, "cannot add service: %m");
				goto err;
			}
		}
	}
	if (ferror(file)) {
		syslog(LOG_WARNING, "%s: %m", path);
		goto err;
	}
	ret = 0;

err:
	free(buf);
	if (file) fclose(file);
	return ret;
}

typedef void Action(struct Service *service);
static void parseControl(char *command) {
	char *action = strsep(&command, WS);
	if (!command) {
		syslog(LOG_NOTICE, "no service names for %s", action);
		return;
	}

	bool drop = false;
	Action *fn = NULL;
	int signal = 0;
	if (!strcmp(action, "start")) {
		fn = serviceStart;
	} else if (!strcmp(action, "stop")) {
		fn = serviceStop;
	} else if (!strcmp(action, "restart")) {
		fn = serviceRestart;
	} else if (!strcmp(action, "status")) {
		fn = serviceStatus;
	} else if (!strcmp(action, "drop")) {
		drop = true;
	} else {
		for (int i = 1; i < NSIG; ++i) {
			if (strcasecmp(action, sys_signame[i])) continue;
			signal = i;
			break;
		}
	}
	if (!drop && !fn && !signal) {
		syslog(LOG_NOTICE, "unknown action or signal %s", action);
		return;
	}

	while (command) {
		bool found = false;
		char *pattern = strsep(&command, WS);
		for (size_t i = services.len - 1; i < services.len; --i) {
			struct Service *service = &services.ptr[i];
			if (fnmatch(pattern, service->name, 0)) continue;
			if (drop) {
				serviceDrop(i);
			} else if (signal) {
				serviceSignal(service, signal);
			} else {
				fn(service);
			}
			found = true;
		}
		if (!found) syslog(LOG_NOTICE, "no services matching %s", pattern);
	}
}

static void parseExits(char *list) {
	setClear(&stopExits);
	while (*list) {
		byte exit = strtoul(list, &list, 10);
		if (*list) {
			if (*list != ',') errx(EX_USAGE, "invalid exit status %s", list);
			list++;
		}
		setAdd(&stopExits, exit);
	}
}

static void parseInterval(struct timespec *interval, const char *millis) {
	unsigned long ms = strtoul(millis, NULL, 10);
	interval->tv_sec = ms / 1000;
	interval->tv_nsec = 1000000 * (ms % 1000);
}

static void setTitle(void) {
	size_t started = 0;
	for (size_t i = 0; i < services.len; ++i) {
		if (services.ptr[i].state == Start) started++;
	}
	setproctitle("%zu/%zu services", started, services.len);
}

int main(int argc, char *argv[]) {
	int error;
	openlog(getprogname(), LOG_NDELAY | LOG_PID | LOG_PERROR, LOG_DAEMON);

	bool daemonize = true;
	setAdd(&stopExits, EX_USAGE);
	setAdd(&stopExits, EX_DATAERR);
	setAdd(&stopExits, EX_NOINPUT);
	setAdd(&stopExits, EX_OSFILE);
	setAdd(&stopExits, EX_CANTCREAT);

	const char *pidPath = NULL;
	const char *configPath = ETCDIR "/catsit.conf";
	const char *fifoPath = RUNDIR "/catsitd.pipe";

	const char *userName = NULL;
	const char *groupName = NULL;

	for (int opt; 0 < (opt = getopt(argc, argv, "C:c:df:g:p:r:s:t:u:"));) {
		switch (opt) {
			break; case 'C': serviceDir = optarg;
			break; case 'c': fifoPath = optarg;
			break; case 'd': daemonize = false;
			break; case 'f': configPath = optarg;
			break; case 'g': groupName = optarg;
			break; case 'p': pidPath = optarg;
			break; case 'r': parseInterval(&resetInterval, optarg);
			break; case 's': parseExits(optarg);
			break; case 't': parseInterval(&restartInterval, optarg);
			break; case 'u': userName = optarg;
			break; default:  return EX_USAGE;
		}
	}

	error = access(configPath, R_OK);
	if (error) err(EX_NOINPUT, "%s", configPath);

	error = access(serviceDir, X_OK);
	if (error) err(EX_NOINPUT, "%s", serviceDir);

	errno = 0;
	struct passwd *user = (userName ? getpwnam(userName) : getpwuid(getuid()));
	if (errno) err(EX_OSFILE, "getpwnam");
	if (!user) errx(EX_USAGE, "no such user %s", userName);
	serviceUID = user->pw_uid;

	if (groupName) {
		errno = 0;
		struct group *group = getgrnam(groupName);
		if (errno) err(EX_OSFILE, "getgrnam");
		if (!group) errx(EX_USAGE, "no such group %s", groupName);
		serviceGID = group->gr_gid;
	} else {
		serviceGID = user->pw_gid;
	}

	int len = asprintf(&serviceEnviron[USER], "USER=%s", user->pw_name);
	if (len < 0) err(EX_OSERR, "asprintf");

	len = asprintf(&serviceEnviron[HOME], "HOME=%s", user->pw_dir);
	if (len < 0) err(EX_OSERR, "asprintf");

	int pidFile = -1;
	if (pidPath) {
		pidFile = open(pidPath, O_WRONLY | O_CREAT | O_CLOEXEC, 0600);
		if (pidFile < 0) err(EX_CANTCREAT, "%s", pidPath);

		error = flock(pidFile, LOCK_EX | LOCK_NB);
		if (error && errno != EWOULDBLOCK) err(EX_IOERR, "%s", pidPath);
		if (error) errx(EX_CANTCREAT, "%s: file is locked", pidPath);

		error = ftruncate(pidFile, 0);
		if (error) err(EX_IOERR, "%s", pidPath);
	}

	// We can't lock a named pipe, so just warn if it already exists.
	error = mkfifo(fifoPath, 0600);
	if (error) {
		if (errno != EEXIST) err(EX_CANTCREAT, "%s", fifoPath);
		warn("%s", fifoPath);
	}

	struct Line fifoLine = {0};
	int fifo = open(fifoPath, O_RDONLY | O_NONBLOCK | O_CLOEXEC);
	if (fifo < 0) err(EX_CANTCREAT, "%s", fifoPath);

	// XXX: Keep a writer open so the reader never gets EOF.
	int writer = open(fifoPath, O_WRONLY | O_NONBLOCK | O_CLOEXEC);
	if (writer < 0) err(EX_CANTCREAT, "%s", fifoPath);

	if (daemonize) {
		error = daemon(0, 0);
		if (error) {
			syslog(LOG_WARNING, "daemon: %m");
			return EX_OSERR;
		}
	}

#ifdef __OpenBSD__
	error = 0
		|| unveil(fifoPath, "c")
		|| unveil(configPath, "r")
		|| unveil(serviceDir, "r")
		|| unveil(_PATH_BSHELL, "x");
	if (error) err(EX_OSERR, "unveil");
	if (pidPath) {
		error = unveil(pidPath, "c");
		if (error) err(EX_OSERR, "unveil");
	}
	error = pledge("stdio rpath cpath proc exec id", NULL);
	if (error) err(EX_OSERR, "pledge");
#endif

	if (pidPath) {
		int len = dprintf(pidFile, "%ju", (uintmax_t)getpid());
		if (len < 0) syslog(LOG_WARNING, "%s: %m", pidPath);
	}

	signal(SIGHUP, signalHandler);
	signal(SIGINT, signalHandler);
	signal(SIGTERM, signalHandler);
	signal(SIGCHLD, signalHandler);
	signal(SIGINFO, signalHandler);

	parseConfig(configPath);
	for (size_t i = 0; i < services.len; ++i) {
		serviceStart(&services.ptr[i]);
	}
	setTitle();

	struct pollfd *fds = calloc(1 + 2 * services.len, sizeof(*fds));
	if (!fds) {
		syslog(LOG_ERR, "calloc: %m");
		goto shutdown;
	}
	fds[0].fd = fifo;
	fds[0].events = POLLIN;

	sigset_t mask;
	sigemptyset(&mask);
	for (;;) {
		if (signals[SIGCHLD]) {
			int status;
			pid_t pid;
			while (0 < (pid = waitpid(-1, &status, WNOHANG))) {
				serviceReap(pid, status);
			}
			if (pid < 0 && errno != ECHILD) syslog(LOG_WARNING, "waitpid: %m");
			setTitle();
			signals[SIGCHLD] = 0;
		}

		if (signals[SIGINT] || signals[SIGTERM]) {
			break;
		}
		if (signals[SIGHUP]) {
			parseConfig(configPath);
			fds = reallocarray(fds, 1 + 2 * services.len, sizeof(*fds));
			if (!fds) {
				syslog(LOG_ERR, "reallocarray: %m");
				goto shutdown;
			}
			setTitle();
			signals[SIGHUP] = 0;
		}
		if (signals[SIGINFO]) {
			char command[] = "status *";
			parseControl(command);
			signals[SIGINFO] = 0;
		}

		struct timespec deadline = {0};
		for (size_t i = 0; i < services.len; ++i) {
			struct Service *service = &services.ptr[i];

			fds[1 + 2 * i].fd = service->outPipe[0];
			fds[2 + 2 * i].fd = service->errPipe[0];
			fds[1 + 2 * i].events = POLLIN;
			fds[2 + 2 * i].events = POLLIN;

			if (service->intent != Start) continue;
			if (service->state == Start) continue;
			if (
				!timespecisset(&deadline) ||
				timespeccmp(&service->restartDeadline, &deadline, <)
			) deadline = service->restartDeadline;
		}

		struct timespec now = {0};
		struct timespec timeout = {0};
		if (timespecisset(&deadline)) {
			clock_gettime(CLOCK_MONOTONIC, &now);
			timespecsub(&deadline, &now, &timeout);
		}
		if (timeout.tv_sec < 0 || timeout.tv_nsec < 0) {
			timespecclear(&timeout);
		}

		int nfds = ppoll(
			fds, 1 + 2 * services.len,
			(timespecisset(&deadline) ? &timeout : NULL),
			&mask
		);
		if (nfds < 0 && errno != EINTR) {
			syslog(LOG_WARNING, "ppoll: %m");
			continue;
		}

		if (nfds > 0 && fds[0].revents) {
			const char *line;
			while (NULL != (line = lineRead(&fifoLine, fifo))) {
				char buf[LineCap];
				snprintf(buf, sizeof(buf), "%s", line);
				parseControl(buf);
			}
			if (errno != EAGAIN) syslog(LOG_WARNING, "read: %m");
			setTitle();
		}

		if (nfds > 0) {
			for (size_t i = 0; i < services.len; ++i) {
				if (fds[1 + 2 * i].revents || fds[2 + 2 * i].revents) {
					serviceRead(&services.ptr[i]);
				}
			}
		}

		if (timespecisset(&deadline)) {
			clock_gettime(CLOCK_MONOTONIC, &now);
			for (size_t i = 0; i < services.len; ++i) {
				struct Service *service = &services.ptr[i];
				if (service->intent != Start) continue;
				if (service->state == Start) continue;
				if (timespeccmp(&service->restartDeadline, &now, <=)) {
					serviceStart(service);
				}
			}
			setTitle();
		}
	}

shutdown:
	close(fifo);
	unlink(fifoPath);

	setproctitle("stopping");
	size_t count = 0;
	for (size_t i = 0; i < services.len; ++i) {
		serviceStop(&services.ptr[i]);
		if (services.ptr[i].state == Start) count++;
	}
	while (count--) {
		int status;
		pid_t pid = wait(&status);
		if (pid < 0) {
			syslog(LOG_WARNING, "wait: %m");
			continue;
		}
		serviceReap(pid, status);
	}
	
	if (pidPath) {
		close(pidFile);
		unlink(pidPath);
	}
}