#define MQ2_PIN 2
#define BUZZER 12

int leds[5] = {16, 17, 5, 18, 19};

void setup() {
  Serial.begin(115200);

  for (int i = 0; i < 5; i++) {
    pinMode(leds[i], OUTPUT);
  }

  pinMode(BUZZER, OUTPUT);
}

void loop() {
  int gasValue = analogRead(MQ2_PIN);
  Serial.print("Air Quality Value: ");
  Serial.println(gasValue);

  // Turn OFF everything first
  for (int i = 0; i < 5; i++) {
    digitalWrite(leds[i], LOW);
  }
  digitalWrite(BUZZER, LOW);

  // Air quality levels
  if (gasValue > 500) digitalWrite(leds[0], HIGH);
  if (gasValue > 1000) digitalWrite(leds[1], HIGH);
  if (gasValue > 1500) digitalWrite(leds[2], HIGH);
  if (gasValue > 2000) digitalWrite(leds[3], HIGH);
  
  if (gasValue > 2500) {
    digitalWrite(leds[4], HIGH);
    digitalWrite(BUZZER, HIGH); // danger mode 💀
  }

  delay(500);
}