#define ECHO_PIN 8
#define TRIG_PIN 7
#define RED_LED_PIN 5
#define GREEN_LED_PIN 6
#define TIMEOUT 5000

float readDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  int duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.034 / 2;
}

void setup() {
  Serial.begin(9600);
  pinMode(ECHO_PIN, INPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(GREEN_LED_PIN, OUTPUT);
}

void loop() {
  static unsigned long timeCapture;

  if (!timeCapture && readDistance() <= 31) {  // Door is Open - Waiting for Timeout...
    timeCapture = millis();
    digitalWrite(RED_LED_PIN, LOW);
  }

   if (readDistance() >= 30) { // Door is Closed - Room Occupied
    digitalWrite(RED_LED_PIN, HIGH);
    digitalWrite(GREEN_LED_PIN, LOW);
    timeCapture = 0;
  }

  
  if(timeCapture && (millis() - timeCapture) >= TIMEOUT) { // Open Timeout expired - Room Available
    digitalWrite(GREEN_LED_PIN, HIGH);
    timeCapture = 1;
  }
}