/* zentific-poll: statistics collection daemon for Zentific
 * Copyright (C) 2007, 2008
 *      Steven Maresca, Justin Demaris,
 *      and Zentific LLC
 *
 * All rights reserved.
 * Use is subject to license terms.
 *
 * Please visit http://zentific.com for news and updates
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 */

#ifndef DAEMONIZE_H_
#define DAEMONIZE_H_

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/param.h>
#include <sys/file.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <unistd.h>

extern int errno;

/**
 * Detaches daemon from the terminal and it's caller
 * 
 * @param int ignsigcld 0 if we want to pay attention to child deaths, 1 to ignore.
 */
int daemonize(int ignsigcld) {
	register int childpid;
	
	// If we are a child of init, then we don't need to break out any further
	if ( getppid() != 1 ) {	
		// Ignore most signals that would make us exit
		signal(SIGTTOU, SIG_IGN);
		signal(SIGTTIN, SIG_IGN);
		signal(SIGTSTP, SIG_IGN);
		signal(SIGTERM, SIG_IGN);
	
		// Fork and kill the parent - makes sure we aren't a process group leader
		if ( (childpid = fork()) < 0 )
			perror("ERROR: Can't fork first child.\n");
		else if ( childpid > 0 )
			exit(0);		// parent exits
	
		// Disassociate from controlling terminal and group
		if ( setpgrp() == -1 ){	
			perror("ERROR: Can't become process group leader.\n");
			return -1;
		}

		// ignore group leader death
		signal(SIGHUP, SIG_IGN);	

		// fork and kill parent again - makes sure we can't reaquire a command terminal
		if ( (childpid = fork()) < 0 ) {
			perror("ERROR: Can't fork second child.\n");
		} else if (childpid > 0) {
			// first child exits
			exit(0);				
		}
	}

	// mark no errors so far
	errno = 0;		

	// set file creation 
	umask(027);
	if (chdir("/") < 0)
		return -1;
	
	// Check if we want to ignore children exit statuses
	if ( ignsigcld )
		signal(SIGCLD, SIG_IGN);

	return 0;
}

int detach_daemon(){

	// if pidfile is to be generated, do so before calling this function
	//	(needs stderr to still be open)
	
 	/* redirect fd 0,1,2 to /dev/null */
	int fd;
        if ((fd = open("/dev/null",O_RDWR)) == -1) {
		return -1;
        }
	
	int i;
 	for (i = 0; i <= 2; i++) {
                close(i);
                int dup = dup2(fd, i);

		if(dup == -1)
			return -1;
        }

        close(fd);

	return 0;

}

int make_pidfile(char *filename){

	//NOTE: open is by nature more primitive than fopen, but permits a higher level of granularity in permissions, 
	//	locking, and error handling

	//FIXME: may want O_EXCL here to replace O_TRUNC. the latter truncates the file to 0 if it already exists, 
	//	whereas the former causes it to fail if file exists (implying either that the daemon is already 
	//	running or it exited uncleanly last time. side topic: existence of a pidfile is lockfile enough
	
	// modes for file perms:  the access permission bits in the file mode of the file are set to permit reading and writing by 
	// 	the owner, and to permit reading only by group members and others

	mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
 	int fd = open(filename, O_RDWR | O_EXCL | O_CREAT, mode); // fd = open(pidfile, O_RDWR | O_TRUNC | O_CREAT, mode);

        if (fd == -1) 
		//to signal potential unclean exit and/or daemon is already running
               	return -2; 

        if (lockf(fd, F_TLOCK, 0) == -1) 
                return -1; 

	char buf[100];
        int len = sprintf(buf, "%ld\n", (long)getpid());

        if (write(fd, buf, len) < 0)
           return -1;

	//unlocking can probably fail silently, POSIX locks are generally ignored anyway
        lockf(fd, F_ULOCK, 0);

	int closed = close(fd);

	if(closed == -1)
		return -1;

	return 0;

}

#endif /*DAEMONIZE_H_*/