/* 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 <assert.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <paths.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <syslog.h>
#include <time.h>
#include <unistd.h>

#include "daemon.h"

enum {
	ExitNotFound = 127,
	ExitNoExec   = 126,
};

const char *serviceDir = "/";
uid_t serviceUID;
gid_t serviceGID;
char *serviceEnviron[EnvironLen] = {
	[SHELL] = "SHELL=" _PATH_BSHELL,
	[PATH]  = "PATH=" _PATH_DEFPATH,
};

struct Prepend prepend;
struct Services services;

static void serviceFree(struct Service *service) {
	free(service->name);
	free(service->command);
	if (service->outPipe[0] >= 0) {
		close(service->outPipe[0]);
		close(service->outPipe[1]);
	}
	if (service->errPipe[0] >= 0) {
		close(service->errPipe[0]);
		close(service->errPipe[1]);
	}
}

int serviceAdd(const char *name, const char *command) {
	struct Service *service = NULL;
	for (size_t i = 0; i < services.len; ++i) {
		if (!strcmp(services.ptr[i].name, name)) {
			service = &services.ptr[i];
			break;
		}
	}

	if (service) {
		char *dup = strdup(command);
		if (!dup) return -1;
		free(service->command);
		service->command = dup;
		return 0;
	}

	if (services.len == services.cap) {
		size_t cap = (services.cap ? services.cap * 2 : 8);
		void *ptr = realloc(services.ptr, sizeof(*services.ptr) * cap);
		if (!ptr) return -1;
		services.cap = cap;
		services.ptr = ptr;
	}
	service = &services.ptr[services.len];
	*service = (struct Service) {
		.outPipe = { -1, -1 },
		.errPipe = { -1, -1 },
		.restartInterval = restartInterval,
	};

	service->name = strdup(name);
	if (!service->name) goto err;

	service->command = strdup(command);
	if (!service->command) goto err;

	int error = pipe2(service->outPipe, O_CLOEXEC);
	if (error) goto err;

	error = pipe2(service->errPipe, O_CLOEXEC);
	if (error) goto err;

	fcntl(service->outPipe[0], F_SETFL, O_NONBLOCK);
	fcntl(service->errPipe[0], F_SETFL, O_NONBLOCK);

	services.len++;
	return 0;

err:
	serviceFree(service);
	return -1;
}

void serviceStatus(struct Service *service) {
	if (service->state == Stop && service->intent == Stop) {
		syslog(LOG_NOTICE, "%s[] is stopped", service->name);
	} else if (service->state == Stop && service->intent == Start) {
		struct timespec now, timeleft;
		clock_gettime(CLOCK_MONOTONIC, &now);
		timespecsub(&service->restartDeadline, &now, &timeleft);
		syslog(
			LOG_NOTICE, "%s[] is restarting in %lds",
			service->name, (long)timeleft.tv_sec
		);
	} else if (service->state == Stop && service->intent == Restart) {
		syslog(LOG_NOTICE, "%s[] is restarting", service->name);
	} else if (service->state == Start && service->intent == Start) {
		syslog(LOG_NOTICE, "%s[%d] is started", service->name, service->pid);
	} else if (service->state == Start && service->intent == Stop) {
		syslog(LOG_NOTICE, "%s[%d] is stopping", service->name, service->pid);
	} else if (service->state == Start && service->intent == Restart) {
		syslog(
			LOG_NOTICE, "%s[%d] is stopping for restart",
			service->name, service->pid
		);
	}
}

static void setDeadline(struct Service *service) {
	clock_gettime(CLOCK_MONOTONIC, &service->restartDeadline);
	timespecadd(
		&service->restartDeadline, &service->restartInterval,
		&service->restartDeadline
	);
}

void serviceStart(struct Service *service) {
	if (service->state != Stop) return;

	if (service->intent == Start) {
		struct timespec backoff = service->restartInterval;
		timespecadd(&backoff, &backoff, &service->restartInterval);
	} else {
		service->restartInterval = restartInterval;
	}
	setDeadline(service);

	service->intent = Start;
	service->pid = fork();
	if (service->pid < 0) {
		syslog(LOG_WARNING, "fork: %m");
		return;
	}
	if (service->pid) {
		service->state = Start;
		clock_gettime(CLOCK_MONOTONIC, &service->startTime);
		syslog(LOG_NOTICE, "%s[%d] started", service->name, service->pid);
		return;
	}

	setpgid(0, 0);
	dup2(service->outPipe[1], STDOUT_FILENO);
	dup2(service->errPipe[1], STDERR_FILENO);

	int error = chdir(serviceDir);
	if (error) err(ExitNoExec, "%s", serviceDir);

	error = setgid(serviceGID);
	if (error) err(ExitNoExec, "setgid");

	error = setgroups(1, &serviceGID);
	if (error) err(ExitNoExec, "setgroups");

	error = setuid(serviceUID);
	if (error) err(ExitNoExec, "setuid");

	size_t len = 0;
	char command[ARG_MAX];
	for (size_t i = 0; i < prepend.len; ++i) {
		int n = snprintf(
			&command[len], sizeof(command) - len, "%s;", prepend.commands[i]
		);
		assert(n > 0);
		len += n;
	}
	snprintf(&command[len], sizeof(command) - len, "exec %s", service->command);

	execle(
		_PATH_BSHELL,
		_PATH_BSHELL, "-c", command, service->name, NULL,
		serviceEnviron
	);
	err(ExitNotFound, "%s", _PATH_BSHELL);
}

void serviceSignal(struct Service *service, int signal) {
	if (service->state != Start) return;
	int error = killpg(service->pid, signal);
	if (error) {
		syslog(
			LOG_WARNING, "killpg(%s[%d], %s): %m",
			service->name, service->pid, sys_signame[signal]
		);
	}
}

void serviceStop(struct Service *service) {
	service->intent = Stop;
	serviceSignal(service, SIGTERM);
}

void serviceRestart(struct Service *service) {
	service->intent = Restart;
	if (service->state == Start) {
		serviceSignal(service, SIGTERM);
	} else {
		serviceStart(service);
	}
}

static void serviceLog(struct Service *service, const char *log) {
	syslog(LOG_NOTICE, "%s[%d]: %s", service->name, service->pid, log);
}

void serviceRead(struct Service *service) {
	const char *out;
	while (NULL != (out = lineRead(&service->outLine, service->outPipe[0]))) {
		serviceLog(service, out);
	}
	if (errno != EAGAIN) syslog(LOG_WARNING, "read: %m");
	const char *err;
	while (NULL != (err = lineRead(&service->errLine, service->errPipe[0]))) {
		serviceLog(service, err);
	}
	if (errno != EAGAIN) syslog(LOG_WARNING, "read: %m");
}

static void serviceFlush(struct Service *service) {
	const char *out = lineFlush(&service->outLine);
	const char *err = lineFlush(&service->errLine);
	if (out) serviceLog(service, out);
	if (err) serviceLog(service, err);
}

void serviceReap(pid_t pid, int status) {
	struct Service *service = NULL;
	for (size_t i = 0; i < services.len; ++i) {
		if (services.ptr[i].state != Start) continue;
		if (services.ptr[i].pid != pid) continue;
		service = &services.ptr[i];
		break;
	}
	if (!service) {
		syslog(LOG_WARNING, "reaping unknown child %d", pid);
		return;
	}
	serviceFlush(service);

	service->state = Stop;
	if (WIFEXITED(status)) {
		int exit = WEXITSTATUS(status);
		if (
			exit == ExitNotFound ||
			exit == ExitNoExec ||
			setTest(&stopExits, exit)
		) {
			service->intent = Stop;
		}
		if (exit) {
			syslog(
				LOG_WARNING, "%s[%d] exited %d",
				service->name, pid, exit
			);
		}
	} else if (WIFSIGNALED(status) && WTERMSIG(status) != SIGTERM) {
		syslog(
			LOG_WARNING, "%s[%d] signaled %s",
			service->name, pid, sys_signame[WTERMSIG(status)]
		);
	}

	if (service->intent == Start) {
		struct timespec uptime;
		clock_gettime(CLOCK_MONOTONIC, &uptime);
		timespecsub(&uptime, &service->startTime, &uptime);
		if (timespeccmp(&uptime, &resetInterval, >=)) {
			service->restartInterval = restartInterval;
		}
		setDeadline(service);
		syslog(
			LOG_NOTICE, "%s[%d] restarting in %lds",
			service->name, pid, (long)service->restartInterval.tv_sec
		);
	} else {
		syslog(LOG_NOTICE, "%s[%d] stopped", service->name, pid);
	}
	if (service->intent == Restart) {
		serviceStart(service);
	}
}