/* 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 <poll.h>
#include <pwd.h>
#include <signal.h>
#include <stdarg.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"

#ifndef RUNDIR
#define RUNDIR "/var/run"
#endif

#ifndef ETCDIR
#define ETCDIR "/usr/local/etc"
#endif

#define WS " \t"

struct timespec restartInterval = { .tv_sec = 1 };
struct Set256 stopExits;

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

static void configerr(bool exit, const char *format, ...) {
	va_list ap;
	va_start(ap, format);
	if (exit) {
		verrx(EX_DATAERR, format, ap);
	} else {
		vsyslog(LOG_WARNING, format, ap);
	}
	va_end(ap);
}

static void parseConfig(bool exit, const char *path) {
	size_t cap = 0;
	char *buf = NULL;

	FILE *file = fopen(path, "r");
	if (!file) {
		configerr(exit, "%s: %s", path, strerror(errno));
		goto err;
	}

	prependClear();

	int line = 1;
	for (ssize_t len; 0 <= (len = getline(&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] == '%') {
			int error = prependAdd(&ptr[1]);
			if (error) {
				configerr(
					exit, "cannot add prepend command: %s", strerror(errno)
				);
				goto err;
			}
		} else {
			char *name = strsep(&ptr, WS);
			if (!ptr) {
				configerr(
					exit, "%s:%d: no command line for service %s",
					path, line, name
				);
				goto err;
			}
			int error = serviceAdd(name, ptr);
			if (error) {
				configerr(exit, "cannot add service: %s", strerror(errno));
				goto err;
			}
		}
	}
	if (ferror(file)) configerr(exit, "%s: %s", path, strerror(errno));

err:
	free(buf);
	fclose(file);
}

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;
	}

	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 {
		for (int i = 1; i < NSIG; ++i) {
			if (strcasecmp(action, sys_signame[i])) continue;
			signal = i;
			break;
		}
	}
	if (!fn && !signal) {
		syslog(LOG_NOTICE, "unknown action or signal %s", action);
		return;
	}

	while (command) {
		char *pattern = strsep(&command, WS);
		for (size_t i = 0; i < services.len; ++i) {
			struct Service *service = &services.ptr[i];
			if (fnmatch(pattern, service->name, 0)) continue;
			if (signal) {
				serviceSignal(service, signal);
			} else {
				fn(service);
			}
		}
	}
}

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(const char *millis) {
	unsigned long ms = strtoul(millis, NULL, 10);
	restartInterval.tv_sec = ms / 1000;
	restartInterval.tv_nsec = 1000000 * (ms % 1000);
}

int main(int argc, char *argv[]) {
	setprogname(argv[0]);

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

	const char *pidPath = NULL;
	const char *configPath = ETCDIR "/spawntab";
	const char *fifoPath = RUNDIR "/spawnd.pipe";

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

	for (int opt; 0 < (opt = getopt(argc, argv, "C:c:df:g:p: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 's': parseExits(optarg);
			break; case 't': parseInterval(optarg);
			break; case 'u': userName = optarg;
			break; default:  return EX_USAGE;
		}
	}
	parseConfig(true, configPath);
	
	int 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);

	errno = 0;
	struct group *group = (
		groupName ? getgrnam(groupName) : getgrgid(user->pw_gid)
	);
	if (errno) err(EX_OSFILE, "getgrnam");
	if (!group) errx(EX_USAGE, "no such group %s", groupName);

	serviceUID = user->pw_uid;
	serviceGID = group->gr_gid;

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

	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_EXLOCK | O_CLOEXEC, 0600
		);
		if (pidFile < 0) err(EX_CANTCREAT, "%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);
	}

	// XXX: Make sure there is always at least one writer open, otherwise we
	// get EOF continually.
	int fifo = open(fifoPath, O_RDWR | O_NONBLOCK | O_CLOEXEC);
	if (fifo < 0) err(EX_CANTCREAT, "%s", fifoPath);
	struct Line fifoLine = {0};

	openlog(getprogname(), LOG_NDELAY | LOG_PID | LOG_PERROR, LOG_DAEMON);

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

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

	// TODO: setproctitle to number of services currently running.

	sigset_t mask;
	sigemptyset(&mask);
	for (;;) {
		struct pollfd fds[1 + 2 * services.len];
		fds[0].fd = fifo;
		fds[0].events = POLLIN;

		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");
		}

		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);
				}
			}
		}

		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");
			signals[SIGCHLD] = 0;
		}

		if (signals[SIGINT] || signals[SIGTERM]) {
			break;
		}
		if (signals[SIGHUP]) {
			parseConfig(false, configPath);
			signals[SIGHUP] = 0;
		}
		if (signals[SIGINFO]) {
			char command[] = "status *";
			parseControl(command);
			signals[SIGINFO] = 0;
		}
	}

	close(fifo);
	unlink(fifoPath);

	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);
	}
}