/* DESC: This script sends the local GPS NMEA stream (incl. serial/checksum) to a remote UDP server.
 * Copyright (C) 2013-2015 NetModule AG, Switzerland
 */

void usage() 
{
    nb_syslog("Usage: gps-udp-client.are <server> <port>");
    exit(1);
}

int connect_gpsd ()
{
    for (attempt = 0; attempt < 60; attempt++) {
        sleep(1);

        sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        if (sock < 0) {
            nb_syslog("Unable to create socket");
            continue;
        }
        nb_syslog("Connecting to GPS daemon");
        if (connect(sock, "127.0.0.1", 2947) < 0){
            nb_syslog("Could not connect to GPS daemon");
            close(sock);
            continue;
        }
        nb_syslog("Requesting raw NMEA stream");
        if (send(sock, "R\n") < 0) {
            nb_syslog("Unable to request raw NMEA stream");
            close(sock);
            continue;
        }

        nb_syslog("Successfully connected to GPS daemon");
        return sock;
    }

    return -1;
}

if (argc < 2) {
    usage();
}

SERVER = trim((string) argv[1]);
PORT = (int) argv[2];

SERIAL = struct_get(nb_status("system"), "SERIAL_NUMBER");
if (SERIAL == "") {
    nb_syslog("Unable to obtain serial number");
    exit(1);
}

gpsd = connect_gpsd();
if (gpsd < 0) {
    exit(1);
}

/* open UDP server socket */
server = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (server < 0) {
    nb_syslog("Unable to open server socket");
    close(gpsd);
    exit(1);
}

/* process NMEA stream */
nb_syslog("Processing NMEA data");

while (1) {
    /* wait for socket data  */
    rv = select(gpsd, 10);
    if (rv > 0) {
        data = recv(gpsd);
        len = strlen(data);
    } else if (rv < 0) {
        nb_syslog("select failed");
        len = -1;
    } else {
        nb_syslog("nothing received");
        len = -1;
    } 
    if (len <= 0) {
        nb_syslog("Receive failed, re-connecting to GPS daemon");
        close(gpsd);
        gpsd = connect_gpsd();
        if (gpsd < 0) {
            exit(1);
        }
    } else {
        str = strcat("PNMID,", SERIAL);
        chars = explode(str);

        checksum = 0;
        for (i = 0; i < length(chars); i++) {
            c = ord(chars[i]);
            checksum ^= c;
        }
        sentence = sprintf("$%s*%02X\r\n", str, checksum);
        data = strcat(data, sentence);
        len = strlen(data);

        if (len > 0) {
            sent = sendto(server, data, SERVER, PORT);
            if (sent != len) {
                nb_syslog("Unable to send message to %s:%d", SERVER, PORT);
            }
        }
    }
}

close(gpsd);
close(server);

exit(0);