/*
   Collect GPS data from a file, COM port or Serial port.  Parse NEMA-183 format
   GPS sentences, convert from degrees minutes to decimal degrees, and write
   the result to a text file.  The resulting file can then be used in ArcView GIS.

   Compiles on: Windows, DOS, Linux and other POSIX Compatible Unix systems.
   Author: Bryce Nesbitt
   Website: http://www.obviously.com
 */
#include <stdio.h>
#include <string.h>

#define unless(x)   if(!(x))
#define LINEBUF_SIZE    1024
#define FILEBUF_SIZE	80

#define VERSION "0.5"

#undef Linux
#ifdef	Linux
char infilename[]  = "nema.txt";
char outfilename[] = "/tmp/gpsfix.txt";
#else
char infilename[]  = "COM1";
char outfilename[] = "c:\\gpsfix.txt";
#endif

char linebuf[LINEBUF_SIZE];
char filebuf[FILEBUF_SIZE];

struct gpsfix {
    float   time;
    float   lat;
    float   lon;
    float   lat_deg;
    float   lon_deg;
    int     quality;
};

int parse_nema( char * , struct gpsfix * );

int main(int argc, char *argv[])
{					 
FILE *fp_in;
FILE *fp_out;
struct gpsfix fix;
char *portname = infilename;

	printf("GPS Fixit for ArcView 3.x %s\n", VERSION);

	// First argument overrides default input source
    if( argc == 2 ) {
		portname = argv[1];
		}

    unless( fp_in = fopen(portname, "r") ) {
            printf("Unable to open %s for reading\n", portname);
            return(5);
            }

    printf("Reading data from %s, writing to %s\n", portname, outfilename);

	// Set line buffering.  But with Windows _IOLBF is ignored, how nice.
	// So instead we set a small buffer that gets full all the time.
	setvbuf( fp_in, filebuf, _IOLBF, FILEBUF_SIZE );
    while( fgets( linebuf, LINEBUF_SIZE, fp_in ) ) {

        if( parse_nema( linebuf, &fix ) ) {
            // write gps data to temporary file...
            // snprintf(linebuf,LINEBUF_SIZE, "%f,%f\n", fix.lat/100, fix.lon/100);
            sprintf(linebuf,"%f,%f,%06.0f\n", fix.lat_deg, fix.lon_deg, fix.time);
            if( fp_out = fopen(outfilename, "w") ) {
                    fputs( linebuf, fp_out );
                    fclose( fp_out );
                    printf(" %s", linebuf);
                    }
            }
        }

    fclose( fp_in );
	printf("Exiting...\n");
	unlink( outfilename );

    return(0);
}

int parse_nema( char * nema_gps_string, struct gpsfix * fixit  )
{
char	latdir,londir;
int     latDegrees;
float   latMinutes;
int     lonDegrees;
float   lonMinutes;

    // $GPGAA,hhmmss.ss,ddmm.mmmm,n,dddmm.mmmm,e,q,ss,y.y,a.a,z,g.g,z,t.t,iii*CC    
    if( 0 == strncmp( "$GPGGA", nema_gps_string, 6 ) ) {

        printf("%s", nema_gps_string);

        sscanf( nema_gps_string,
                "$GPGGA,%f,%f,%c,%f,%c,%d", 
                &fixit->time,&fixit->lat,&latdir,&fixit->lon,&londir,&fixit->quality);

        if(latdir == 'S')
            fixit->lat = 0-(fixit->lat);
        if(londir == 'W')
            fixit->lon = 0-(fixit->lon);

        latDegrees = (int)(fixit->lat/100);
        latMinutes = (float)(fixit->lat - latDegrees*100);
        fixit->lat_deg  = latDegrees + (latMinutes/60);	// Concert to decimal degrees

        lonDegrees = (int)(fixit->lon/100);
        lonMinutes = (float)(fixit->lon - lonDegrees*100);
        fixit->lon_deg  = lonDegrees + (lonMinutes/60);	// Convert to decimal degrees

        printf(" %+02d Degrees  %+2.6f Minutes Latitude\n", latDegrees, latMinutes);
        printf(" %+02d Degrees %+2.6f Minutes Longitude\n", lonDegrees, lonMinutes);
    
        return(1);
        }
    return(0);
}