// ============================================================
// Smart Home Fire & Gas Safety System (FINAL FIXED VERSION)
// ============================================================

#include <WiFi.h>
#include <DHT.h>
#include <LiquidCrystal_I2C.h>

// ---------------- PINS ----------------
#define DHT_PIN       4
#define DHT_TYPE      DHT22
#define GAS_PIN       34
#define RED_LED_PIN   25
#define GREEN_LED_PIN 26
#define BUZZER_PIN    27

// ---------------- LCD ----------------
LiquidCrystal_I2C lcd(0x27, 16, 2);

// ---------------- WIFI ----------------
const char* WIFI_SSID = "Wokwi-GUEST";
const char* WIFI_PASSWORD = "";

// ---------------- GAS CALIBRATION ----------------
// Wokwi MQ2 behaves like:
// Clean air ≈ 3000 ADC
// Max gas   ≈ 4095 ADC
#define GAS_BASELINE 3000
#define GAS_MAX      4095

// ---------------- THRESHOLDS ----------------
const int GAS_WARNING = 400;
const int GAS_DANGER  = 700;

// ---------------- STATES ----------------
unsigned long lastBlink = 0;
unsigned long lastBeep  = 0;
bool ledState = false;
bool buzzerState = false;

DHT dht(DHT_PIN, DHT_TYPE);

// ============================================================
// SETUP
// ============================================================
void setup() {
  digitalWrite(25, HIGH);   // turn red ON
  delay(2000);

  digitalWrite(25, LOW);
  digitalWrite(26, HIGH);   // turn green ON
  delay(2000);

  digitalWrite(26, LOW);
  Serial.begin(115200);

  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(GREEN_LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);

  digitalWrite(RED_LED_PIN, LOW);
  digitalWrite(GREEN_LED_PIN, HIGH);
  digitalWrite(BUZZER_PIN, LOW);

  lcd.init();
  lcd.backlight();
  lcd.setCursor(0,0);
  lcd.print("System Starting");
  delay(1500);
  lcd.clear();

  dht.begin();

  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
}

// ============================================================
// LOOP
// ============================================================
void loop() {

  float temp = dht.readTemperature();
  float hum  = dht.readHumidity();

  // -------- GAS FIXED CALIBRATION --------
  int rawADC = analogRead(GAS_PIN);

  int gasPPM = map(rawADC, GAS_BASELINE, GAS_MAX, 0, 1000);
  gasPPM = constrain(gasPPM, 0, 1000);

  // -------- CLASSIFICATION --------
  String status = classify(gasPPM);

  // -------- OUTPUT --------
  triggerAlert(status);
  updateLCD(temp, hum, gasPPM, status);

  // Debug (important for report)
  Serial.print("RAW: "); Serial.print(rawADC);
  Serial.print(" | PPM: "); Serial.print(gasPPM);
  Serial.print(" | Status: "); Serial.println(status);

  delay(100);
}

// ============================================================
// CLASSIFICATION
// ============================================================
String classify(int gas) {

  if (gas >= GAS_DANGER) return "DANGER";
  else if (gas >= GAS_WARNING) return "WARNING";
  else return "SAFE";
}

// ============================================================
// ALERT SYSTEM (STABLE + NON-BLOCKING)
// ============================================================
void triggerAlert(String status) {

  unsigned long now = millis();

  static String lastStatus = "";

  // Reset states when status changes
  if (status != lastStatus) {
    lastStatus = status;
    ledState = false;
    buzzerState = false;
    lastBlink = now;
    lastBeep = now;
  }

  if (status == "DANGER") {

    // Fast blink (200ms)
    if (now - lastBlink >= 200) {
      lastBlink = now;
      ledState = !ledState;
      digitalWrite(RED_LED_PIN, ledState);
    }

    digitalWrite(GREEN_LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, HIGH);

  }
  else if (status == "WARNING") {

    digitalWrite(RED_LED_PIN, HIGH);
    digitalWrite(GREEN_LED_PIN, LOW);

    // Slow beep
    if (now - lastBeep >= 800) {
      lastBeep = now;
      buzzerState = !buzzerState;
      digitalWrite(BUZZER_PIN, buzzerState);
    }

  }
  else {

    digitalWrite(RED_LED_PIN, LOW);
    digitalWrite(GREEN_LED_PIN, HIGH);
    digitalWrite(BUZZER_PIN, LOW);
  }
}

// ============================================================
// LCD DISPLAY (NO FLICKER)
// ============================================================
void updateLCD(float t, float h, int gas, String status) {

  static int lastGas = -1;

  if (gas == lastGas) return;
  lastGas = gas;

  lcd.clear();

  lcd.setCursor(0,0);
  lcd.print("T:");
  lcd.print(t,1);
  lcd.print("C H:");
  lcd.print((int)h);

  lcd.setCursor(0,1);
  lcd.print("G:");
  lcd.print(gas);

  lcd.setCursor(8,1);
  lcd.print(status);
}