/**
  * This is a simple test program for GPS modules and the C-
  * based NMEA sentence parser.  It can optionally print data to
  * the terminal, or display the data on a 4x20 character serial
  * LCD (Parallax #27979).
  *
  * The test program was written specifically to display NMEA
  * sentences received from Parallax's PAM-7Q GPS module
  * (Parallax #28509), but it should work with any module that
  * outputs standard NMEA sentences.
  *
  * Author: Daniel Harris, Parallax Inc.
  * Date:   August 14, 2014
  *
  */

#include "simpletools.h"                      // Include simple tools
//#include "gps.h"                              // include the GPS library
#include <unistd.h>                           // included for usleep
#include <fdserial.h>

//defined constants

#define GPS_RXIN_PIN  1
#define GPS_TXOUT_PIN 0
#define GPS_BAUD      9600

fdserial *gps_ser;

char HasFix = 0;
char SatCount = 0;
int Lat = 0;
int Long = 0;


char Rx(void) {
  return fdserial_rxChar(gps_ser);
}

void SkipField(void) {
  while( Rx() != ',' ) {
    ;
  }    
}


int ParseDegrees( void )
{
  int v = 0;    // Integer
  int lowDigits = 0;
  char ch;

  while(1) {
    ch = Rx();
    if( ch < '0' || ch > '9' ) break;
    v *= 10;
    v += ch - '0';
  }

  if( ch == '.' ) { // Found the decimal, so parse the fractional part
    while(1) {
      ch = Rx();
      if( ch < '0' || ch > '9' ) break;
      if( lowDigits < 5 )
      {
        v *= 10;
        v += ch - '0';
        lowDigits++;
      }        
    }

    while( lowDigits < 5 ) {
      v *= 10;
      lowDigits++;
    }
  }
  else {
    v *= 100000;  // scale it up to the precision expected
  }    

  if( ch == ',' ) { // Next bit should be N/S/E/W
    ch = Rx();
    if( ch == 'N' || ch == 'E' ) {
      v = -v;
    }
  }

  while( Rx() != ',' )  // Skip the terminating ,
    ;

  return v;
}


// http://aprs.gids.nl/nmea/#rmc
void ParseRMC(void) // Recommended minimum specific GPS / transit data
{
  // $GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62
  // $GPRMC,031025.00,A,3814.24788,N,12235.27105,W,0.052,,261115,,,A*69


  Rx();                     // Grab the initial comma
  SkipField();              // Skip the time value
  HasFix = Rx() == 'A';     // Is the sat receiver ok?  (A = OK, V = warning)
  Rx();                     // Skip the 'HasFix' comma

  Lat = ParseDegrees();     // Parse latitude
  Long = ParseDegrees();    // Parse longitude
}


void ParseGGA(void) // Global Positioning System Fix Data
{
  // $GPGGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh

  Rx();                     // Grab the initial comma
  SkipField();              // Skip the time value

  Lat = ParseDegrees();     // Parse latitude
  Long = ParseDegrees();    // Parse longitude

  HasFix = Rx() != '0';
  Rx(); // Skip the comma

  SatCount = 0;
  while(1) {
    char ch = Rx();
    if( ch < '0' || ch > '9' ) break;
    SatCount *= 10;
    SatCount += ch - '0';
  }
}


int main()
{
  pause(1000);

  gps_ser = fdserial_open(GPS_RXIN_PIN, GPS_TXOUT_PIN, 0, GPS_BAUD);

  while( 1 )
  {
    if( Rx() != '$' ) continue;

    // Get the packet type (5 chars, but 1st is always 'G')
    char ch = Rx();
    if( ch != 'G' ) continue;

    int type = 0;
    for( int i=0; i<4; i++ ) {
      type <<= 8;
      type |= Rx();
    }

    char Spew = 0;
    if( type == 'PRMC' ) {
      putChar( 'R' );
      ParseRMC();
      Spew = 1;
    }
    else if( type == 'PGGA' ) {
      putChar( 'G' );
      ParseGGA();
      Spew = 1;
    }            

    if( Spew )
    {
      putChar( ' ' );
      putChar( HasFix ? 'Y' : 'N' );
      putChar(' ');

      putDec( SatCount );
      putChar(' ');
  
      putDec( Lat );
  
      putChar(' ');
      putChar(' ');
  
      putDec( Long );
  
      putChar(13);
    }
  }
}