const int trigPin = 9;
const int echoPin = 10;
const int ledPin = 13;
const int buzzerPin = 8;

bool visitorAlerted = false;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
  digitalWrite(ledPin, LOW);
}

void loop() {
  long duration;
  float distance;

  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH, 30000);

  if (duration == 0) {
    digitalWrite(ledPin, LOW);
    noTone(buzzerPin);
    visitorAlerted = false;
    delay(100);
    return;
  }

  distance = duration * 0.0343 / 2;

  if (distance > 100) {
    digitalWrite(ledPin, LOW);
    noTone(buzzerPin);
    visitorAlerted = false;
  } else if (distance >= 50) {
    digitalWrite(ledPin, HIGH);
    delay(200);
    digitalWrite(ledPin, LOW);
    delay(200);
  } else {
    digitalWrite(ledPin, HIGH);
    if (!visitorAlerted) {
      tone(buzzerPin, 1000, 300);
      visitorAlerted = true;
    }
  }

  delay(50);
}