#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <getopt.h>
#include <syslog.h>
#include <signal.h>

#define MAX_BACKLOG		5
#define MAX_BUFFER		1024

short int recivedCloseSignal = 0;
short int iAmDaemon = 0;

void myprint(char * message)
{
	if (iAmDaemon)
	{
		syslog(LOG_INFO, "%s", message);
	} else {
		printf("%s\n", message);
	}
}

void handleEndSignal(int s)
{
	char buffer[MAX_BUFFER];
	snprintf(buffer, MAX_BUFFER, "Recived signal %i. Program will shut down after ending current connections. Please wait.", s);
	myprint(buffer);
	recivedCloseSignal = 1;
}

void HandleClient(int connectionFd, struct sockaddr * echoKlientAdr, socklen_t rozm)
{
	time_t currentTime;
	int ret;

	currentTime = htonl(time(NULL) + 2208988800UL);
	errno = (int)NULL;
	ret = sendto(connectionFd, &currentTime, sizeof(time_t), 0, (struct sockaddr *) echoKlientAdr, rozm);
	if (ret != sizeof(time_t))
	{
		perror("sendto() client");
		printf("sendto returned (%i)\n", ret);
	}
}

void usage(char * name)
{
	fprintf(stderr, "Usage: %s [-h] [-d] [-p PORT]\n-h\tthis help\n-d\trun server in daemon mode, all messages will be sent to syslog\n-p PORT\tlisten on given port instead on default 37\n\nYou can close it by sending SIGINT ([Ctlr]+[C]) or SIGKILL (kill PID).\nPid will be written to ./serwerUDP.pid.\n", name);
	exit(1);
}

int serverLoop(int * serverFd)
{
	struct sockaddr_in clientaddr;
	unsigned int clientSize;
	char buffer[MAX_BUFFER];
	void handleEndSignal(int);
	struct sigaction sigactionEnd;
	int recived = 0;
	unsigned int klientDl;

	klientDl = sizeof(clientaddr);
	sigactionEnd.sa_handler = handleEndSignal;

	sigaction(SIGINT, &sigactionEnd, NULL);
	sigaction(SIGTERM, &sigactionEnd, NULL);

	if (iAmDaemon)
	{
		myprint("Time daemon successfully daemonized.");
	} else {
		myprint("Time daemon successfully started.");
	}

	clientSize = sizeof(clientaddr);
	while (1)
	{
		errno = (int)NULL;
		recived = recvfrom(*serverFd, buffer, sizeof(buffer), 0, (struct sockaddr *) &clientaddr, &klientDl);
		if (recived == 0) {
			snprintf(buffer, MAX_BUFFER, "Handling client %s.", inet_ntoa(clientaddr.sin_addr));
			myprint(buffer);
			HandleClient(*serverFd, (struct sockaddr *) & clientaddr, sizeof(clientaddr));
		} else if (recived == -1) {
			myprint(strerror(errno));
			myprint("was error during recvfrom()");
		}
		if (recivedCloseSignal) return(0);
	}
}

void writePid(void)
{
	char buffer[MAX_BUFFER];
	FILE * pidFile;
	errno = (int)NULL;
	pidFile = fopen("./serwerUDP.pid", "w");
	snprintf(buffer, MAX_BUFFER, "%i\n", getpid());

	if (pidFile == NULL)
	{
		perror("can't write pid file");
		exit(1);
	}
	fwrite(buffer, strlen(buffer), sizeof(char), pidFile);
	fclose(pidFile);
}

int main ( int argc, char *argv[])
{
	int serverFd;
	struct sockaddr_in servaddr;
	int daytimePort = 37;
	int c;
	char buffer[MAX_BUFFER];

	while((c = getopt(argc, argv, "hdp:")) != -1)
	{
		switch (c)
		{
			case 'd':
				iAmDaemon = 1;
				break;
			case 'p':
				daytimePort = atoi(optarg);
				break;
			default:
				usage(argv[0]);
				break;
		}
	}

	if (iAmDaemon) openlog("serwerUDP", LOG_PID, LOG_DAEMON);
	snprintf(buffer, MAX_BUFFER, "Running time daemon in %s mode. Will listen on port %i.", iAmDaemon ? "daemon" : "standard", daytimePort);
	myprint(buffer);

	errno = (int)NULL;
	serverFd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if (serverFd == -1)
	{
		perror("socket() error");
		exit(1);
	}

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(daytimePort);

	errno = (int)NULL;
	if (bind(serverFd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1)
	{
		perror("bind() error");
		exit(1);
	}

	if (iAmDaemon)
	{
		if (fork() == 0) /* child */
		{
			writePid();
			fclose(stdin);
			fclose(stderr);
			fclose(stdout);
			chdir("/");
			serverLoop(&serverFd);
			myprint("Time server shutting down.");
		} else {
			_exit(0);
		}
	} else {
		writePid();
		serverLoop(&serverFd);
		myprint("Time server shutting down.");
	}
	exit(0);
}