int buttonPin = 2;
int buttonState;
int lastButtonState = HIGH;
int systemOn = 0;

unsigned long previousMillis = 0;
int currentLed = 13;

void setup() {
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(9, OUTPUT);

  pinMode(buttonPin, INPUT_PULLUP);
}

void loop() {

  buttonState = digitalRead(buttonPin);

  // Toggle ON/OFF on button press
  if (buttonState == LOW && lastButtonState == HIGH) {
    systemOn = !systemOn;
    delay(200); // debounce
  }
  lastButtonState = buttonState;

  // If OFF → immediately turn everything OFF
  if (systemOn == 0) {
    digitalWrite(13, LOW);
    digitalWrite(12, LOW);
    digitalWrite(11, LOW);
    digitalWrite(10, LOW);
    digitalWrite(9, LOW);
    return;  // stop execution here
  }

  // Non-blocking LED sequence
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= 2000) {
    previousMillis = currentMillis;

    // Turn all OFF first
    digitalWrite(13, LOW);
    digitalWrite(12, LOW);
    digitalWrite(11, LOW);
    digitalWrite(10, LOW);
    digitalWrite(9, LOW);

    // Turn current LED ON
    digitalWrite(currentLed, HIGH);

    // Move to next LED
    if (currentLed == 13) currentLed = 12;
    else if (currentLed == 12) currentLed = 11;
    else if (currentLed == 11) currentLed = 10;
    else if (currentLed == 10) currentLed = 9;
    else currentLed = 13;
  }
}