// Define Pin Allocations
const int gasSensorPin = A0;  // MQ2 Analog pin
const int greenLedPin = 2;    // Safe Status LED
const int redLedPin = 3;      // Alarm Status LED
const int buzzerPin = 4;      // Piezo Alarm

// Set the gas threshold limit
// In Wokwi, default clean air sits around 300.
const int gasThreshold = 400; 

void setup() {
  // Initialize digital pins as outputs
  pinMode(greenLedPin, OUTPUT);
  pinMode(redLedPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
  
  // Set the gas pin as input
  pinMode(gasSensorPin, INPUT);
  
  // Initialize the Serial Monitor
  Serial.begin(9600);
  Serial.println("--- MQ2 Gas Detection System Active ---");
}

void loop() {
  // Read the analog value from the MQ2 sensor
  int gasValue = analogRead(gasSensorPin);
  
  // Print value to screen so you can find your ideal threshold
  Serial.print("Current Gas Level: ");
  Serial.println(gasValue);
  
  // Check if gas levels cross the danger zone
  if (gasValue > gasThreshold) {
    // DANGER: Gas Detected!
    digitalWrite(greenLedPin, LOW);   // Turn off green
    digitalWrite(redLedPin, HIGH);    // Turn on red
    
    // Play a distinct 1000Hz frequency alarm sound
    tone(buzzerPin, 1000); 
    
    Serial.println("[ALERT] Gas Leak Detected! Alarm sounding!");
  } 
  else {
    // SAFE: Normal Environment
    digitalWrite(greenLedPin, HIGH);  // Green stays on
    digitalWrite(redLedPin, LOW);     // Red stays off
    
    // Silence the alarm
    noTone(buzzerPin); 
  }
  
  // Wait 300ms before reading again
  delay(300);
}