// Smart Parking Sensor with Arduino
const int trigPin = 9;
const int echoPin = 10;

const int greenLED = 3;
const int yellowLED = 4;
const int redLED = 5;
const int buzzer = 6;

long duration;
int distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
  pinMode(redLED, OUTPUT);
  pinMode(buzzer, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Send ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Measure response
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2; // Convert to cm

  // Default state
  digitalWrite(greenLED, LOW);
  digitalWrite(yellowLED, LOW);
  digitalWrite(redLED, LOW);
  digitalWrite(buzzer, LOW);

  if (distance > 30) {
    digitalWrite(greenLED, HIGH); // Safe
  } 
  else if (distance <= 30 && distance > 15) {
    digitalWrite(yellowLED, HIGH); // Caution
    tone(buzzer, 1000, 100); // Short beep
    delay(300);
  } 
  else if (distance <= 15) {
    digitalWrite(redLED, HIGH); // Danger
    tone(buzzer, 1000); // Continuous beep
  }

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  delay(200);
}