/*   To compile : gcc -o TnHserver TnHserver.c */
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>

// The ESP12 is going to send Temperature and Humidity as two strings
// into the UDP packet payload on the port 7777
// The maximum payload would be something like this:
// |-12.4\0100.0\0|
// A smaller packet could look like this:
// |15.7\0\056.7\0\0|
// The \0 is a byte with all zeros and in the C-language \0 is the string termination.

#define BUFLEN 12
#define PORT 7777

int main(void)
{
    struct sockaddr_in si_me, si_client;
    int udp_sock, nb, slen=sizeof(si_client);
    char buf[BUFLEN];
    char oke[4] = "OK!";
    char command[80];

    bzero((char *) &si_me, sizeof(si_me));
    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(PORT);
    si_me.sin_addr.s_addr = htonl(INADDR_ANY);
    // Create a UDP socket
    if ((udp_sock=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))<0)
	   { printf("Error opening UDP socket.\n"); 
	     exit(1); 
	   }
    // Bind the socket to our IP address and our port
	   if (bind(udp_sock, &si_me, sizeof(si_me))<0) 
	   { printf("Error binding UDP socket.\n"); 
         exit(1);
	   }
    printf("We are listening on: %s:%d\n\n\n",inet_ntoa(si_me.sin_addr), ntohs(si_me.sin_port));
    // we enter an endless loop, waiting for UDP packets with the readings...
    while (1) {
      // recvfrom is going to wait till our socket has received a packet		
      nb = recvfrom(udp_sock, buf, BUFLEN, 0, &si_client, &slen);
      if (nb<0) {
        // if you get a negative number of byte, chances are that the server/socket has a problem.
		// I send an alert to my gmail account.
		system("echo \"TnHserver died!\" | mail -s \"RPI TnHserver has crashed!\" user@gmail.com");
        close(udp_sock);
        return 0;
      }
	  // We're still here so we got a packet, I am not going to do any checks, just send "OK!" back to sender.
      sendto(udp_sock, oke, 3, 0, &si_client, slen);
      printf("Received packet from %s:%d\n",inet_ntoa(si_client.sin_addr), ntohs(si_client.sin_port));
      printf("Byte: %d\t\tData:>%s:%s<\n", nb, buf, &buf[6]);
	  // Now we create the command line to update the RRD
      sprintf(command,"/usr/bin/rrdtool update /home/user/data/TnHdatabase.rrd N:%s:%s\n",buf,&buf[6]);
	  // ... and we execute the command!  Easy peasy!
      system(command);
	  // Good practice to clear the buffer once we have registered the values...
      bzero(buf,BUFLEN);
    }
	// If we get here, something must have gone wrong... sending an e-mail alert.
    system("echo \"TnHserver died!\" | mail -s \"RPI TnHserver has crashed!\" user@gmail.com");
    close(udp_sock);
    return 0;
}