#include <DHT.h>
#include <Servo.h>

// ---------------- PIN DEFINITIONS ----------------
#define MQ2_PIN A0

#define DHT_PIN 2
#define DHT_TYPE DHT22

#define TRIG_PIN 3
#define ECHO_PIN 4

#define BUZZER_PIN 5
#define LED_PIN 6

#define SERVO_PIN 9

#define STEP_PIN 10
#define DIR_PIN 11
#define ENABLE_PIN 12

// ---------------- SETTINGS ----------------
#define GAS_THRESHOLD 400
#define DISTANCE_THRESHOLD 15   // cm
#define TEMP_THRESHOLD 50       // Celsius

DHT dht(DHT_PIN, DHT_TYPE);
Servo myServo;

// Stepper settings
int stepDelay = 1000; // microseconds
int stepperSteps = 200; // one revolution for a 1.8-degree motor

// ------------------------------------------------

void setup() {
  Serial.begin(9600);

  // Sensors
  dht.begin();

  // Ultrasonic
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  // Outputs
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);

  // Stepper driver
  pinMode(STEP_PIN, OUTPUT);
  pinMode(DIR_PIN, OUTPUT);
  pinMode(ENABLE_PIN, OUTPUT);

  // Enable A4988
  digitalWrite(ENABLE_PIN, LOW);

  // Servo
  myServo.attach(SERVO_PIN);
  myServo.write(0);

  digitalWrite(BUZZER_PIN, LOW);
  digitalWrite(LED_PIN, LOW);

  Serial.println("System Started");
}

// ------------------------------------------------

void loop() {

  // ---------- MQ2 GAS SENSOR ----------
  int gasValue = analogRead(MQ2_PIN);

  // ---------- DHT22 ----------
  float temperature = dht.readTemperature();
  float humidity = dht.readHumidity();

  // ---------- ULTRASONIC ----------
  long duration;
  float distance;

  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);

  digitalWrite(TRIG_PIN, LOW);

  duration = pulseIn(ECHO_PIN, HIGH, 30000);

  if (duration == 0) {
    distance = 999;
  } else {
    distance = duration * 0.0343 / 2;
  }

  // ---------- SERIAL MONITOR ----------
  Serial.println("-------------------------");

  Serial.print("MQ2 Gas Value: ");
  Serial.println(gasValue);

  if (!isnan(temperature)) {
    Serial.print("Temperature: ");
    Serial.print(temperature);
    Serial.println(" C");
  } else {
    Serial.println("DHT22 temperature error");
  }

  if (!isnan(humidity)) {
    Serial.print("Humidity: ");
    Serial.print(humidity);
    Serial.println(" %");
  } else {
    Serial.println("DHT22 humidity error");
  }

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // =================================================
  // GAS / SMOKE DETECTION
  // =================================================

  if (gasValue > GAS_THRESHOLD) {

    Serial.println("!!! GAS/SMOKE DETECTED !!!");

    // Turn ON LED
    digitalWrite(LED_PIN, HIGH);

    // Buzzer ON
    digitalWrite(BUZZER_PIN, HIGH);

    // Move servo to safety position
    myServo.write(90);

    // Stop for a short time
    delay(500);
  }

  else {
    digitalWrite(LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, LOW);

    // Normal servo position
    myServo.write(0);
  }

  // =================================================
  // HIGH TEMPERATURE
  // =================================================

  if (!isnan(temperature) && temperature > TEMP_THRESHOLD) {

    Serial.println("!!! HIGH TEMPERATURE !!!");

    digitalWrite(LED_PIN, HIGH);

    // Beep buzzer
    tone(BUZZER_PIN, 2000);
    delay(200);
    noTone(BUZZER_PIN);
  }

  // =================================================
  // ULTRASONIC OBJECT DETECTION
  // =================================================

  if (distance < DISTANCE_THRESHOLD) {

    Serial.println("Object detected nearby");

    // Turn LED ON
    digitalWrite(LED_PIN, HIGH);

    // Rotate stepper clockwise
    digitalWrite(DIR_PIN, HIGH);

    rotateStepper(stepperSteps);
  }

  delay(1000);
}

// =================================================
// STEPPER MOTOR FUNCTION
// =================================================

void rotateStepper(int steps) {

  for (int i = 0; i < steps; i++) {

    digitalWrite(STEP_PIN, HIGH);
    delayMicroseconds(stepDelay);

    digitalWrite(STEP_PIN, LOW);
    delayMicroseconds(stepDelay);
  }
}