/*
  MuTech Robotics - GP1 Pet Safety Tracker (4G + GPS geofence SMS)
  Board : ESP32 development board (30-pin)
  Modem : 4G + GPS module board (Raspberry-Pi-style header)
  Power : 3S 18650 pack (11.1V) -> HAT 12V terminal, and -> MP1584 buck set to 5.0V -> ESP32 VIN

  Wiring
    Battery +  -> HAT +12V terminal and buck IN+
    Battery -  -> HAT GND terminal and buck IN-
    Buck OUT+  -> ESP32 VIN (set the buck to 5.0V BEFORE connecting!)
    Buck OUT-  -> ESP32 GND
    ESP32 D32 (TX) -> module header pin 8  (Pi TXD position)
    ESP32 D33 (RX) <- module header pin 10 (Pi RXD position)
    Fit the LTE antenna and the GPS antenna to the HAT. Insert a 4G SIM with SMS enabled.

  CHECK YOUR HAT: this HAT is made for a Raspberry Pi, so the ESP32 takes the Pi's place on
  pins 8/10. Confirm on your HAT's pin chart that the modem UART is on pins 8/10 at 3.3V logic.
  If the modem does not answer "AT", it may need its PWR (power-key) pin pulsed - see the HAT notes.

  How it works
    AT+QGPS=1      start GNSS
    AT+QGPSLOC=2   read position (decimal degrees)
    If the pet is more than SAFE_RADIUS_M from HOME -> one SMS with a Google Maps link.
    When it comes back inside -> "Back home" SMS, and the alarm re-arms.
*/

const char* OWNER_PHONE = "+91XXXXXXXXXX";   // your mobile number
const double HOME_LAT = 17.448600;            // set to your home location
const double HOME_LON = 78.390800;
const double SAFE_RADIUS_M = 150.0;
const unsigned long CHECK_MS = 10000;         // read GPS every 10 s

HardwareSerial& modem = Serial2;
bool outsideAlerted = false;

String sendAT(const String& cmd, unsigned long waitMs = 1000) {
  while (modem.available()) modem.read();
  modem.println(cmd);
  String resp; unsigned long t0 = millis();
  while (millis() - t0 < waitMs) {
    while (modem.available()) resp += (char)modem.read();
    if (resp.indexOf("OK") >= 0 || resp.indexOf("ERROR") >= 0) break;
  }
  return resp;
}

bool sendSMS(const String& text) {
  sendAT("AT+CMGF=1");
  modem.print("AT+CMGS=\""); modem.print(OWNER_PHONE); modem.println("\"");
  unsigned long t0 = millis();
  while (millis() - t0 < 3000 && modem.read() != (int)'>') {}
  modem.print(text);
  modem.write(26);                              // Ctrl+Z sends the message
  String r = ""; t0 = millis();
  while (millis() - t0 < 10000) { while (modem.available()) r += (char)modem.read(); if (r.indexOf("OK") >= 0) return true; }
  return false;
}

// +QGPSLOC: <utc>,<lat>,<lon>,<hdop>,<alt>,<fix>,<cog>,<spkm>,<spkn>,<date>,<nsat>
bool readGPS(double& lat, double& lon, int& sats) {
  String r = sendAT("AT+QGPSLOC=2", 1500);
  int p = r.indexOf("+QGPSLOC:");
  if (p < 0) return false;                      // no fix yet (CME ERROR 516)
  String s = r.substring(p + 9);
  int c1 = s.indexOf(','), c2 = s.indexOf(',', c1 + 1), c3 = s.indexOf(',', c2 + 1);
  lat = s.substring(c1 + 1, c2).toDouble();
  lon = s.substring(c2 + 1, c3).toDouble();
  int last = s.lastIndexOf(',');
  sats = s.substring(last + 1).toInt();
  return lat != 0.0 && lon != 0.0;
}

double distanceM(double lat1, double lon1, double lat2, double lon2) {
  const double R = 6371000.0;
  double dLat = radians(lat2 - lat1), dLon = radians(lon2 - lon1);
  double a = sin(dLat / 2) * sin(dLat / 2) + cos(radians(lat1)) * cos(radians(lat2)) * sin(dLon / 2) * sin(dLon / 2);
  return 2 * R * atan2(sqrt(a), sqrt(1 - a));
}

String mapLink(double lat, double lon) {
  return "https://maps.google.com/?q=" + String(lat, 6) + "," + String(lon, 6);
}

void setup() {
  Serial.begin(115200);
  modem.begin(115200, SERIAL_8N1, 33, 32);       // RX = D33, TX = D32
  delay(3000);
  Serial.println(sendAT("AT"));
  Serial.println(sendAT("AT+CPIN?"));
  Serial.println(sendAT("AT+QGPS=1"));            // start GNSS (OK, or ERROR 504 if already on)
}

void loop() {
  static unsigned long last = 0;
  if (millis() - last < CHECK_MS) return;
  last = millis();

  double lat, lon; int sats;
  if (!readGPS(lat, lon, sats)) { Serial.println("Waiting for GPS fix..."); return; }
  double d = distanceM(HOME_LAT, HOME_LON, lat, lon);
  Serial.printf("lat %.6f lon %.6f sats %d  from home %.0f m\n", lat, lon, sats, d);

  if (d > SAFE_RADIUS_M && !outsideAlerted) {
    outsideAlerted = sendSMS("ALERT: Your pet left the SAFE ZONE! " + String(d, 0) + " m from home. " + mapLink(lat, lon));
  } else if (d < SAFE_RADIUS_M * 0.8 && outsideAlerted) {   // 20% margin stops repeat alerts at the edge
    sendSMS("Back home: your pet is inside the safe zone again. " + mapLink(lat, lon));
    outsideAlerted = false;
  }
}