#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <syslog.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include "btime_int.h"

static void (*btimed_error)(int level, const char *fmt, ...);

static void btimed(void);
static unsigned int get_btime(void);
static int daemon_init(void);
static void btimed_perror(int level, const char *fmt, ...);
static void sigchld_hdlr(int sig);
static void usage(const char *progname);


int
main(int argc, char **argv)
{
	struct sigaction sa;
	int debug = 0;
	int c;

	while ((c = getopt(argc, argv, "hd")) != -1) {
		switch (c)  {
			case 'd':
				debug = 1;
				break;
			case 'h':
			case '?':
			default:
				usage(argv[0]);
				exit(2);
		}
	}

	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = sigchld_hdlr;
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = SA_NOCLDSTOP | SA_RESTART; 
	sigaction(SIGCHLD, &sa, NULL); 

	if (debug) {
		btimed_error = btimed_perror;
	} else {
		btimed_error = syslog;	
		daemon_init();
	}

	btimed();

	return 0;
}


/*
 *---------------------------------------------------------------------------
 *
 * btimed --
 *
 *	The main loop of the deamon.  It listens on its well know port for
 * messages, responds to the request via a child process.
 *
 * Returns:
 *	Never returns.
 *
 * Side effects:
 *	Child processes are created.
 *---------------------------------------------------------------------------
 */

static void
btimed(void)
{
	int sd;
	char msg[BTIME_MSGLEN];
	struct sockaddr_in cli_addr;
	int cli_addr_len;
	struct sockaddr_in my_addr;
	pid_t pid;
	ssize_t nbytes;

	if ((sd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
		btimed_error(LOG_ERR, "Could not create socket: %s\n", 
		        strerror(errno));
		exit(1);
	}

	memset(&my_addr, 0, sizeof my_addr);
	my_addr.sin_family = AF_INET;
	my_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	my_addr.sin_port = htons(BTIME_PORT);
	if (bind(sd, (struct sockaddr *)&my_addr, sizeof my_addr) < 0) {
		btimed_error(LOG_ERR, "Could not bind to local address: %s\n", 
		        strerror(errno));
		exit(1);
	}

	for (;;) {	
		memset(&cli_addr, 0, sizeof cli_addr);
		cli_addr_len = sizeof cli_addr;
		nbytes = recvfrom(sd, &msg, BTIME_MSGLEN, MSG_WAITALL, 
		         (struct sockaddr *)&cli_addr, &cli_addr_len);

		if ((pid = fork()) < 0) {	
			btimed_error(LOG_ERR, "Could not fork(): %s\n", strerror(errno));
			exit(1);
		}

		if (pid == 0) {
			memset(msg, 0, BTIME_MSGLEN);
			sprintf(msg, "%u\n", get_btime());
			sendto(sd, &msg, BTIME_MSGLEN, MSG_DONTWAIT, 
			       (struct sockaddr *)&cli_addr, cli_addr_len);

			exit(0);
		}
	}

	close(sd);
}



/*
 *---------------------------------------------------------------------------
 *
 * get_btime --
 *
 *	Return machine's boot time.
 *
 * Returns:
 *	0 on failure
 * 	non-zero on success.
 *
 *---------------------------------------------------------------------------
 */

static unsigned int 
get_btime(void)
{
	FILE *statf;
	char line[1024];
	unsigned int btime = 0;

	if ((statf = fopen("/proc/stat", "r")) == NULL) {
		btimed_error(LOG_ERR, "/proc/stat open failure: %s\n", 
		        strerror(errno));
		exit(1);
	}

	while (fgets(line, 1024, statf) != NULL) {
		if (strstr(line, "btime") != NULL) {
			sscanf(line, "%*s%u", &btime); 
		}
			
	}

	fclose(statf);

	return btime;
}


/*
 *---------------------------------------------------------------------------
 *
 * daemon_init --
 *
 *	Set up a basic daemon environment
 *
 * Returns:
 *	0 on success
 * non-zero on failure.
 *
 * Side effects:
 *	All fds are closed and process is now a session leader.
 *
 *---------------------------------------------------------------------------
 */

static int 
daemon_init(void)
{
	pid_t pid;
	int fd;
	int maxfd = sysconf(_SC_OPEN_MAX);
	
	if ((pid = fork()) < 0) {
		return(-1);
	} else if (pid != 0) {
		exit(0);	/* Exit in parent */
	}

	/* 
	 * Child sets up daemon environment 
	 */

	setsid();	/* Become session leader */
	chdir("/");
	umask(0);
	for (fd = 0; fd < maxfd; fd++) {
		close(fd);
	}
	errno = 0;	/* probably set to EBADFD from above loop, reset */

	openlog("btimed", LOG_PID, LOG_USER);

	return 0;
}


/*
 *---------------------------------------------------------------------------
 *
 * btimed_perror --
 *
 * 	Print error messages to stderr, level is not used, it is there
 * 	to have the same calling args as syslog(3) so we can use either
 *	based on debug level.
 *
 * Returns:
 *  NA
 *
 * Side effects:
 * 	None 
 *---------------------------------------------------------------------------
 */

static void 
btimed_perror(int level, const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vfprintf(stderr, fmt, ap);
	va_end(ap);
}


static void 
sigchld_hdlr(int sig)
{
	int status;

	wait(&status);
	return;
}


static void 
usage(const char *progname)
{
	fprintf(stderr, "Usage: %s [OPTION]...\n"
	        "-h\tPrint this help and exit.\n"
	        "-d\tDon't daemonize, send output to stderr.\n",
	        progname);

	return;
}