/**
 * Copyright 2015 University of Applied Sciences Western Switzerland / Fribourg
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 * Module:	MA-CSEL1 - Building Embedded Systems under Linux
 *
 * Abstract: 	Introduction to the Embedded Linux Development Environment
 *
 * Purpose:	This module implements a simple application to be launched from
 *		/etc/inttab.
 *		-->> tracing with syslog
 *
 * Autĥor:	Daniel Gachet
 * Date:	28.08.2015
 */
#define _XOPEN_SOURCE 600
#define _DEFAULT_SOURCE

#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <grp.h>
#include <pwd.h>
#include <signal.h>
#include <syslog.h>

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#define UNUSED(x) (void)(x)

static int signal_catched = 0; 

static void catch_signal (int signal)
{
	syslog (LOG_INFO, "signal=%d catched\n", signal);
	signal_catched++;
}

int main(int argc, char* argv[])
{
	UNUSED(argc); UNUSED(argv);
	
	// daemon's steps 1 to 3 skipt

	// 4. capture all required signals
	struct sigaction act = {.sa_handler = catch_signal,};
	sigaction (SIGHUP,  &act, NULL);  //  1 - hangup
	sigaction (SIGINT,  &act, NULL);  //  2 - terminal interrupt
	sigaction (SIGQUIT, &act, NULL);  //  3 - terminal quit
	sigaction (SIGABRT, &act, NULL);  //  6 - abort
	sigaction (SIGTERM, &act, NULL);  // 15 - termination
	sigaction (SIGTSTP, &act, NULL);  // 19 - terminal stop signal

	// 5. update file mode creation mask
	umask(0027);

	// 6. change working directory to appropriate place
	if (chdir ("/") == -1) {
		syslog (LOG_ERR, "ERROR while changing to working directory"); 
		exit (1);
	}

	// 7. close all open file descriptors
	for (int fd = sysconf(_SC_OPEN_MAX); fd >= 0; fd--) {
		close (fd);
	}

	// 8. redirect stdin, stdout and stderr to /dev/null
	if (open ("/dev/null", O_RDWR) != STDIN_FILENO) {
		syslog (LOG_ERR, "ERROR while opening '/dev/null' for stdin");
		exit (1);
	}
	if (dup2 (STDIN_FILENO, STDOUT_FILENO) != STDOUT_FILENO) {
		syslog (LOG_ERR, "ERROR while opening '/dev/null' for stdout");
		exit (1);
	}
	if (dup2 (STDIN_FILENO, STDERR_FILENO) != STDERR_FILENO) {
		syslog (LOG_ERR, "ERROR while opening '/dev/null' for stderr");
		exit (1);
	}

	// 9. option: open syslog for message logging
	openlog (NULL, LOG_NDELAY | LOG_PID, LOG_DAEMON); 
	syslog (LOG_INFO, "Daemon has started...");
 
	// 10. option: get effective user and group id for appropriate's one
	struct passwd* pwd = getpwnam ("daemon");
	if (pwd == 0) {
		syslog (LOG_ERR, "ERROR while reading daemon password file entry");
		exit (1);
	}

	// 11. option: change root directory
	if (chroot (".") == -1) {
		syslog (LOG_ERR, "ERROR while changing to new root directory");
		exit (1);
	}

	// 12. option: change effective user and group id for appropriate's one
	if (setegid (pwd->pw_gid) == -1) {
		syslog (LOG_ERR, "ERROR while setting new effective group id");
		exit (1);
	}
	if (seteuid (pwd->pw_uid) == -1) {
		syslog (LOG_ERR, "ERROR while setting new effective user id");
		exit (1);
	}
 
	// 13. implement daemon body...
	int t = 30;
	do {
		t = sleep(t);
	} while (t > 0);

	syslog (LOG_INFO, "daemon stopped. Number of signals catched=%d\n", signal_catched);
	closelog();

	return 0;
}