#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// MQ Sensor Pins
#define MQ135_BEFORE A0  
#define MQ135_AFTER A1   
#define MQ2_BEFORE A2    
#define MQ2_AFTER A3     

// LED & Buzzer Pins
#define GREEN_LED 5  
#define YELLOW_LED 6 
#define RED_LED 7    
#define BUZZER 8     

void setup() {
    Serial.begin(9600);
    
    if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { 
        Serial.println(F("OLED not found!"));
        while (true);
    }
    
    display.clearDisplay();
    display.setTextSize(1);
    display.setTextColor(WHITE);
    
    pinMode(GREEN_LED, OUTPUT);
    pinMode(YELLOW_LED, OUTPUT);
    pinMode(RED_LED, OUTPUT);
    pinMode(BUZZER, OUTPUT);
}

void loop() {
    int mq135_value = analogRead(MQ135_BEFORE);
    int mq2_value = analogRead(MQ2_BEFORE);

    Serial.print("MQ-135: "); Serial.println(mq135_value);
    Serial.print("MQ-2: "); Serial.println(mq2_value);

    display.clearDisplay();
    display.setCursor(0, 0);
    display.print("MQ-135: "); display.print(mq135_value);

    display.setCursor(0, 10);
    display.print("MQ-2: "); display.print(mq2_value);

    String status = controlIndicators(mq135_value, mq2_value);
    
    display.setCursor(0, 20);
    display.print("Status: "); display.print(status);
    
    display.display();
    delay(1000);
}

// Function to Control LEDs & Buzzer
String controlIndicators(int mq135_value, int mq2_value) {
    String level = "";

    if (mq135_value < 200 && mq2_value < 500) {
        digitalWrite(GREEN_LED, HIGH);
        digitalWrite(YELLOW_LED, LOW);
        digitalWrite(RED_LED, LOW);
        digitalWrite(BUZZER, LOW);
        level = "Good";
    } 
    else if ((mq135_value >= 200 && mq135_value < 400) || (mq2_value >= 500 && mq2_value < 700)) {
        digitalWrite(GREEN_LED, LOW);
        digitalWrite(YELLOW_LED, HIGH);
        digitalWrite(RED_LED, LOW);
        digitalWrite(BUZZER, LOW);
        level = "Warn";
    } 
    else {
        digitalWrite(GREEN_LED, LOW);
        digitalWrite(YELLOW_LED, LOW);
        digitalWrite(RED_LED, HIGH);
        digitalWrite(BUZZER, HIGH);
        level = "DANGER!";
    }

    return level;
}