#include <WiFi.h>
#include <PubSubClient.h>
#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <DHT_U.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// Pin Definitions
#define DHTPIN 12
#define DHTTYPE DHT22
#define MQ135PIN 34
#define OLED_SDA 21
#define OLED_SCL 22

// OLED Display Settings
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

// Sensor Objects
DHT dht(DHTPIN, DHTTYPE);

// WiFi & MQTT Settings
const char* ssid = "Wokwi-GUEST";
const char* password = "";
const char* mqttServer = "broker.hivemq.com";
const char* clientID = "ESP32-Sensor";
const char* topic = "sensor/data";

WiFiClient espClient;
PubSubClient client(espClient);

// Timing Variables
unsigned long previousMillis = 0;
const long interval = 2000;

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

  // Initialize OLED Display
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED display failed to start");
    while (1);
  }
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);

  // Connect to WiFi
  connectWiFi();

  // Set up MQTT
  client.setServer(mqttServer, 1883);
}

void loop() {
  if (!client.connected()) {
    reconnectMQTT();
  }
  client.loop();

  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;

    // Read DHT22 Sensor
    float temp = dht.readTemperature();
    float hum = dht.readHumidity();

    // Read MQ135 Sensor
    int airQuality = analogRead(MQ135PIN);

    // Print Values
    Serial.print("Temp: "); Serial.print(temp); Serial.print("°C, ");
    Serial.print("Humidity: "); Serial.print(hum); Serial.print("%, ");
    Serial.print("Air Quality: "); Serial.println(airQuality);

    // Display Data on OLED
    display.clearDisplay();
    display.setCursor(0, 10);
    display.print("Temp: "); display.print(temp); display.println(" C");
    display.print("Humidity: "); display.print(hum); display.println(" %");
    display.print("Air Q: "); display.print(airQuality);
    display.display();

    // Send Data to MQTT
    String payload = String(temp) + "," + String(hum) + "," + String(airQuality);
    client.publish(topic, payload.c_str());
  }
}

// WiFi Connection Function
void connectWiFi() {
  Serial.print("Connecting to WiFi...");
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nWiFi Connected!");
  Serial.print("IP Address: "); Serial.println(WiFi.localIP());
}

// MQTT Reconnect Function
void reconnectMQTT() {
  while (!client.connected()) {
    Serial.print("Connecting to MQTT...");
    if (client.connect(clientID)) {
      Serial.println("Connected to MQTT!");
    } else {
      Serial.print("Failed, retrying in 5s...");
      delay(5000);
    }
  }
}