#define TRIG_PIN 5
#define ECHO_PIN 18
#define GREEN_LED 19
#define RED_LED 21

long duration;
int distance;
int threshold = 15; // cm, adjust as needed

void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
}

void loop() {
  // Clear trigger
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  
  // Send pulse
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  // Read echo
  duration = pulseIn(ECHO_PIN, HIGH);
  distance = duration * 0.034 / 2; // cm
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Parking logic
  if(distance < threshold) {
    digitalWrite(RED_LED, HIGH);   // Space full
    digitalWrite(GREEN_LED, LOW);
  } else {
    digitalWrite(RED_LED, LOW);
    digitalWrite(GREEN_LED, HIGH); // Space free
  }

  delay(500);
}