// Define pin numbers
const int trigPin = 12;
const int echoPin = 14;
const int redLED = 2;
const int yellowLED = 13;
const int greenLED = 4;

// Define variables for the duration and the distance
long duration;
int distance;

void setup() {
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
  pinMode(echoPin, INPUT); // Sets the echoPin as an Input
  pinMode(redLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  Serial.begin(9600); // Starts the serial communication
}

void loop() {
  // Clears the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  // Reads the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH);
  // Calculating the distance
  distance = duration * 0.034 / 2; // Speed of sound wave divided by 2 (go and back)
  Serial.print("Distance: ");
  Serial.println(distance);

  if (distance > 10 && distance < 50) {
    // Car is detected
    if (digitalRead(redLED) == HIGH) {
      // Transition from red to green through yellow
      digitalWrite(redLED, LOW); // Turn Red LED off
      digitalWrite(yellowLED, HIGH); // Turn Yellow LED on
      delay(3000); // Yellow light duration
      digitalWrite(yellowLED, LOW); // Turn Yellow LED off
    }
    digitalWrite(greenLED, HIGH); // Turn Green LED on
  } else {
    // No car is detected
    digitalWrite(greenLED, LOW); // Turn Green LED off
    digitalWrite(yellowLED, LOW); // Ensure Yellow LED is off
    digitalWrite(redLED, HIGH); // Turn Red LED on
  }
  delay(1000); // Delay a second for better visualization
}