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

// Pin Definitions
#define DHTPIN 2
#define DHTTYPE DHT22
#define RELAY_PIN 3

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

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW); // Start with fan off
  
  dht.begin();
  
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { 
    for(;;); // Don't proceed if OLED fails
  }
  
  display.clearDisplay();
  display.setTextColor(WHITE);
}

void loop() {
  float t = dht.readTemperature();

  // Check if reading failed
  if (isnan(t)) {
    return; // Skip this loop iteration if the sensor fails
  }

  // Set up the display for the temperature reading
  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(0,0);
  display.print("Temp: ");
  display.print(t);
  display.print(" C");

  // --- HYSTERESIS LOGIC ---
  const float turnOnTemp = 30.0;
  const float turnOffTemp = 28.0; 
  
  display.setCursor(0, 30);
  display.setTextSize(2);
  
  // 1. If it gets too hot, turn the fan ON
  if (t >= turnOnTemp) {
    digitalWrite(RELAY_PIN, HIGH); 
    display.print("FAN: ON");
  } 
  // 2. If it has cooled down enough, turn the fan OFF
  else if (t <= turnOffTemp) {
    digitalWrite(RELAY_PIN, LOW);  
    display.print("FAN: OFF");
  } 
  // 3. If the temperature is between 28.0 and 30.0 (the deadband), 
  // do nothing to the relay and just print its current state.
  else {
    if (digitalRead(RELAY_PIN) == HIGH) {
      display.print("FAN: ON");
    } else {
      display.print("FAN: OFF");
    }
  }

  display.display();
  delay(2000); // DHT22 needs ~2 seconds between readings
}