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#include <SoftwareSerial.h>

// Ultrasonic pins
const int trigPin = 7;
const int echoPin = 6;

// GSM pins
const int gsmRx = 8;  // Arduino receives (SIM800 TX)
const int gsmTx = 9;  // Arduino sends   (SIM800 RX via divider)
SoftwareSerial gsm(gsmRx, gsmTx);

const char phoneNumber[] = "+1234567890"; // <-- replace with your phone number

const int floodLevel = 10; // cm threshold
unsigned long lastSmsTime = 0;
const unsigned long smsCooldown = 60000; // 1 min cooldown between SMS

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  Serial.begin(9600);
  gsm.begin(9600);

  delay(1000);
  sendAT("AT");         // Wake up
  sendAT("ATE0");       // Disable echo
  sendAT("AT+CMGF=1");  // SMS text mode

  Serial.println("SIM800L Flood Alert System Ready");
}

void loop() {
  long distance = readDistance();
  Serial.print("Distance: ");
  Serial.println(distance);

  if (distance < floodLevel && millis() - lastSmsTime > smsCooldown) {
    sendSMS("FLOOD ALERT! Water level is too high!");
    lastSmsTime = millis();
  }

  delay(1000);
}

long readDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  long duration = pulseIn(echoPin, HIGH, 30000);
  return duration * 0.034 / 2;
}

void sendAT(const char *cmd) {
  gsm.println(cmd);
  delay(500);
  while (gsm.available()) Serial.write(gsm.read());
}

void sendSMS(const char* msg) {
  gsm.print("AT+CMGS=\"");
  gsm.print(phoneNumber);
  gsm.println("\"");
  delay(500);
  gsm.print(msg);
  delay(500);
  gsm.write(26); // Ctrl+Z ends the SMS
  delay(5000);
  Serial.println("SMS sent.");
}