/*
From: David Huichen Dai <address@hidden>
To: address@hidden
Cc: 张楚文 <address@hidden>
Subject: [gpsd-dev] Example code for libgps using shared memory
Date: Wed, 8 Nov 2017 21:12:46 +0800
*/


#include <gps.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>

int main() {
    int rc;
    struct timeval tv;
    struct gps_data_t gps_data;
    if ((rc = gps_open(GPSD_SHARED_MEMORY, 0, &gps_data)) == -1) {
        printf("code: %d, reason: %s\n", rc, gps_errstr(rc));
        return EXIT_FAILURE;
    }
    gps_stream(&gps_data, WATCH_ENABLE | WATCH_JSON, NULL);
    while (1) {
        /* wait for 2 seconds to receive data */
        if (gps_waiting (&gps_data, 2000000)) {
            /* read data */
            if ((rc = gps_read(&gps_data)) == -1) {
                printf("error occured reading gps data. code: %d, reason: %s\n",
                       rc, gps_errstr(rc));
            } else {
                /* Display data from the GPS receiver. */
                if ((gps_data.status == STATUS_FIX) &&
                        (gps_data.fix.mode == MODE_2D || gps_data.fix.mode ==
                         MODE_3D) &&
                        !isnan(gps_data.fix.latitude) &&
                        !isnan(gps_data.fix.longitude)) {
                    //gettimeofday(&tv, NULL); EDIT: tv.tv_sec isn't actually the timestamp!
                    printf("latitude: %f, longitude: %f, speed: %f, timestamp: %lf\n",
                           gps_data.fix.latitude, gps_data.fix.longitude,
                           gps_data.fix.speed, gps_data.fix.time); 
		   //EDIT: Replaced tv.tv_sec with gps_data.fix.time
                } else {
                    printf("no GPS data available\n");
                }
            }
        }
        else printf("waiting failed.\n");
    }
    /* When you are done... */
    gps_stream(&gps_data, WATCH_DISABLE, NULL);
    gps_close (&gps_data);
    return EXIT_SUCCESS;
}