/*
  NMEA Sentence Builder

  https://www.sparkfun.com/datasheets/GPS/NMEA%20Reference%20Manual1.pdf
  See ReadMe
*/

const char* MSG_IDS[6] = {
  "$GPGGA",
  "$GPGLL",
  "$GPGSA",
  "$GPGSV",
  "$GPRMC",
  "$GPVTG"
};

const char UTC_TIME[] = {"171530.123"}; // hhmmss.sss

char sentence[85];
char csBuffer[3];

//double latitude = 4110.3962;    // ddmm.mmmm N
//double longitude = 07427.1141;  // dddmm.mmmm W
//double longitude = 99999.1141;  // dddmm.mmmm W

int latitude = 0;
int longitude = 0;

int intLat = 0;
int intLong = 0;

int degLat = 0;
int minLat = 0;
char secLat[] = {"1234"};
int degLong = 0;
int minLong = 0;
char secLong[] = {"1234"};
char* ns = {"N"};
char* ew = {"W"};



//Message ID, Mode 1, mode 2, Sats Used, PDOP, HDOP, VDOP
//$GPGSA,A,3,07,02,26,27,09,04,15,,,,,,1.8,1.0,1.5*33

//Message ID , Number of Messages, Message Number1, Sats in view, Sat ID, Elevation, Azimuth, SNR, ...*CS<CR+LF>
//$GPGSV,2,1,07,07,79,048,42,02,51,062,43,26,36,256,42,27,27,138,42*71
//$GPGSV,2,2,07,09,23,313,42,04,19,159,41,15,12,041,42*41

//Message ID, UTC, Status, Lat, N/S, Long, E/W, Speed, Course, Date, Mag, Mode
//$GPRMC,UTC,A,Lat,NS,Long,EW,0.13,309.62,150824,,*CS

//Message ID, Course, Ref, Course, Ref, Speed, Units, Speed, Units, Mode
//$GPVTG,309.62,T,,M,0.13,N,0.2,K,A*23

byte makeChecksum(char *msg) {
  byte checksum = 0;

  for (int i = 1; i < strlen(msg); i++) {
    checksum = checksum ^ (byte)msg[i];
  }

  return checksum;
}

// Message ID, UTC Time, Lat, N/S, Long, E/W, Fix, Sats, HDOP, MSL Altitude, Units, Geoid Separation, Units, Age of Diff. Corr, Diff. Ref. Station ID, Checksum, CR+LF
// $GPGGA,hhmmss.sss,ddmm.mmmm,N,dddmm.mmmm,W,1,07,1.0,100,M,,,,0000*CS<CR+LF>
char* makeGPGGA()  {
  char latBuff[10];
  char longBuff[11];
  char* csBuff;
  //char* msg;

  strncpy(sentence, MSG_IDS[0], 6);
  strncat(sentence, ",", 1);
  strncat(sentence, UTC_TIME, 10);
  strncat(sentence, ",", 1);




  //dtostrf(latitude, 6, 4, latBuff);
  //Serial.print("latBuff: ");
  //Serial.println(latBuff);
  //strncat(latBuff, "\0", 1);

  //if (strlen(latBuff) < 8) {
    //strncat(sentence, "00", 2);
  //} else if (strlen(latBuff) < 9)  {
    //strncat(sentence, "0", 1);
  //}

  if (intLat < 1000)  {
    strncat(sentence, "00", 2);
  } else if (intLat < 100)  {
    strncat(sentence, "0", 1);
  }
  strncat(sentence, itoa(intLat, latBuff, 10), 4);
  strncat(sentence, ".", 1);
  strncat(sentence, secLat, 4);
  //Serial.println(intLat);////////////////////////////////////////
  //strncat(sentence, latBuff, 10);
  //strncat(latBuff, "\0", 1);
  strncat(sentence, ",", 1);
  strncat(sentence, ns, 1);
  strncat(sentence, ",", 1);

  if (intLong < 100)  {
    strncat(sentence, "000", 3);
  } else if (intLong < 1000)  {
    strncat(sentence, "00", 2);
  } else if (intLong < 10000) {
    strncat(sentence, "0", 1);
  }
  strncat(sentence, itoa(intLong, longBuff, 10), 4);
  strncat(sentence, ".", 1);
  strncat(sentence, secLong, 4);


  //dtostrf(longitude, 6, 4, longBuff);
  //strncat(longBuff, "\0", 1);
  //Serial.println(strlen(latLongBuff));
  //if (strlen(longBuff) < 8) {
    //strncat(sentence, "000", 3);
  //} else if (strlen(longBuff) < 9) {
    //strncat(sentence, "00", 2);
  //} else if (strlen(longBuff) < 10) {
    //strncat(sentence, "0", 1);
  //}
  //strncat(sentence, longBuff, 11);
  strncat(sentence, ",", 1);
  strncat(sentence, ew, 1);
  strncat(sentence, ",", 1);
  strncat(sentence, "1,07,1.0,100,M,,,,0000", 22);
  //Serial.println(sentence);
  int cs = makeChecksum(sentence);
  Serial.print("GPGGA cs: ");
  Serial.println(cs);
  //csBuff = decToHexa(cs);
  //strncat(csBuff, "\0", 1);
  //Serial.println(csBuff);
  //Serial.println(decToHexa(cs));
  strncat(sentence, "*", 1);
  csBuff = decToHexa(cs);
  Serial.println(csBuff);
  strncat(sentence, csBuff, 2);
  strncat(sentence, "\r\n", 2);
  strncat(sentence, "\0", 1);
  //strncat(sentence, msg, 5);
  //strncat(sentence, "\0", 1);
  Serial.println(sentence);
  return sentence;
}

// Message ID, Lat, N/S, Long, E/W, UTC, Status, Mode
// $GPGLL,Lat,NS,Long,EW,UTC,A,A*CS
char* makeGPGLL()  {
  char latBuff[12];
  char longBuff[12];
  char* csBuff;

  strncpy(sentence, MSG_IDS[1], 6);
  strncat(sentence, ",", 1);
  dtostrf(latitude, 6, 4, latBuff);
  if (strlen(latBuff) < 8) {
    strncat(sentence, "00", 2);
  } else if (strlen(latBuff) < 9)  {
    strncat(sentence, "0", 1);
  }
  Serial.println(latBuff);
  strncat(sentence, latBuff, 9);
  strncat(sentence, ",", 1);
  strncat(sentence, ns, 1);
  strncat(sentence, ",", 1);
  dtostrf(longitude, 6, 4, longBuff);
  //Serial.println(strlen(latLongBuff));
  if (strlen(longBuff) < 8) {
    strncat(sentence, "000", 3);
  } else if (strlen(longBuff) < 9) {
    strncat(sentence, "00", 2);
  } else if (strlen(longBuff) < 10) {
    strncat(sentence, "0", 1);
  }
  strncat(sentence, longBuff, 10);
  strncat(sentence, ",", 1);
  strncat(sentence, ew, 1);
  strncat(sentence, ",", 1);
  strncat(sentence, UTC_TIME, 10);
  strncat(sentence, ",", 1);
  strncat(sentence, "A,A", 3);

  int cs = makeChecksum(sentence);
  //Serial.print("setup cs: ");
  //Serial.println(cs);
  csBuff = decToHexa(cs);
  //strncat(csBuff, "\0", 1);
  //Serial.println(csBuff);
  //Serial.println(decToHexa(cs));
  strncat(sentence, "*", 1);
  //csBuff = decToHexa(cs);
  strncat(sentence, csBuff, 2);
  strncat(sentence, "\r\n", 2);
  strncat(sentence, "\0", 1);
  //strncat(sentence, msg, 5);
  //strncat(sentence, "\0", 1);
  //Serial.println(sentence);

  //strncat(sentence, "\0", 1);
  //Serial.println(sentence);
  return sentence;
}

char* decToHexa(int n) {
  csBuffer[0] = intToHex(n / 16);
  csBuffer[1] = intToHex(n % 16);
  //csBuffer[0] = '1';
  //csBuffer[1] = 'D';
  csBuffer[2] = '\0';
  return csBuffer;
}

char intToHex(int value) {
  char hexChar;

  if (value < 10) {
    hexChar = value + 48;
  } else  {
    hexChar = value + 55;
  }
  return hexChar;
}



void setup() {
  Serial.begin(115200);
}

void loop() {
  char* msg1;
  char* msg2;
  //char* csBuff;

  degLat = map(analogRead(A1), 0, 1023, -90, 90);
  minLat = 50;
  //secLat = 1234;
  degLong = map(analogRead(A0), 0, 1023, -180, 180);
  minLong = 50;
  //secLong = 1234;

  if (degLat < 0) {
    ns = "S";
    degLat = abs(degLat);
  } else  {
    ns = "N";
  }

  if (degLong < 0)  {
    ew = "W";
    degLong = abs(degLong);
  } else  {
    ew = "E";
  }

  intLat = (degLat * 100) + minLat;
  intLong = (degLong * 100) + minLong;

  Serial.println(latitude);
  Serial.println(longitude);

  msg1 = makeGPGGA();
  Serial.println(msg1);

  //msg2 = makeGPGLL();
  //Serial.println(msg2);
  //Serial.println(makeGPGLL());

  /*
    //char* sentence = {"$GPGGA,171530.123,4110.3960,N,07427.1143,W,1,07,1.0,100,M,,,,0000"};
    //Serial.println(sentence);
    int cs = makeChecksum(msg);
    //int cs = 29;
    Serial.print("setup cs: ");
    Serial.println(cs);
    csBuff = decToHexa(cs);
    strncat(csBuff, "\0", 1);
    Serial.println(csBuff);
    //Serial.println(decToHexa(cs));
    strncat(msg, "*", 1);
    //csBuff = decToHexa(cs);
    strncat(msg, csBuff, 2);
    strncat(msg, "\0", 1);
  */

  delay(3000);
}