#include <NewPing.h>
#include <LiquidCrystal_I2C.h>
#include <Servo.h>
#include <DHT11.h>

// ================= PIN DEFINITIONS =================

#define TRIG_PIN 6
#define ECHO_PIN 7
#define SERVO_PIN 5
#define DHT_PIN 8

#define MAX_DISTANCE 500


// ================= OBJECTS =================

NewPing sonar(TRIG_PIN, ECHO_PIN, MAX_DISTANCE);

LiquidCrystal_I2C lcd(0x27, 16, 2);

Servo myServo;

DHT11 dht11(DHT_PIN);


// ================= VARIABLES =================

int temperature;
int humidity;

float speedOfSound;
float distance;

int servo_pos = 0;
int servo_direction = 1;


// ==================================================
// SETUP
// ==================================================

void setup() {

  Serial.begin(115200);

  // LCD
  lcd.init();
  lcd.backlight();

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

  // Startup message
  lcd.setCursor(0, 0);
  lcd.print("Hello, System");

  delay(2000);

  lcd.clear();
}


// ==================================================
// LOOP
// ==================================================

void loop() {

  // ================================================
  // READ DHT11
  // ================================================

  int result = dht11.readTemperatureHumidity(
    temperature,
    humidity
  );


  // ================================================
  // CHECK DHT11 RESULT
  // ================================================

  if (result != 0) {

    Serial.print("DHT11 Error: ");
    Serial.println(result);

    lcd.clear();

    lcd.setCursor(0, 0);
    lcd.print("DHT11 Error");

    delay(1000);

    return;
  }


  // ================================================
  // CALCULATE SPEED OF SOUND
  // ================================================

  /*
     Speed of sound:

     v = 331.3 + (0.606 × T)

     T = temperature in Celsius
     v = speed in meters/second
  */

  speedOfSound = 331.3 + (0.606 * temperature);


  // ================================================
  // READ ULTRASONIC SENSOR
  // ================================================

  unsigned int duration = sonar.ping();


  if (duration == 0) {

    distance = -1;

  }
  else {

    /*
       Distance:

       distance = time × speed / 2

       duration:
       microseconds

       speedOfSound:
       meters/second

       ×100:
       meters → centimeters

       /1,000,000:
       microseconds → seconds

       /2:
       because the ultrasonic wave travels
       to the object and back
    */

    distance =
      (duration * speedOfSound * 100.0)
      / (2.0 * 1000000.0);
  }


  // ================================================
  // SERVO MOVEMENT
  // ================================================

  myServo.write(servo_pos);

  servo_pos += servo_direction;


  // Reached 180°
  if (servo_pos >= 180) {

    servo_pos = 180;

    servo_direction = -10;
  }


  // Reached 0°
  if (servo_pos <= 0) {

    servo_pos = 0;

    servo_direction = 10;
  }


  // ================================================
  // SERIAL MONITOR
  // ================================================

  Serial.println("---------------------------");

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" C");

  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");

  Serial.print("Speed of Sound: ");
  Serial.print(speedOfSound);
  Serial.println(" m/s");

  Serial.print("Distance: ");

  if (distance < 0) {

    Serial.println("No Echo");

  }
  else {

    Serial.print(distance, 2);
    Serial.println(" cm");
  }

  Serial.print("Servo: ");
  Serial.print(servo_pos);
  Serial.println(" degrees");


  // ================================================
  // LCD
  // ================================================

  lcd.clear();


  // First row
  lcd.setCursor(0, 0);

  lcd.print("T:");
  lcd.print(temperature);

  lcd.print("C H:");
  lcd.print(humidity);


  // Second row
  lcd.setCursor(0, 1);

  if (distance < 0) {

    lcd.print("No Echo");

  }
  else {

    lcd.print("D:");
    lcd.print(distance, 1);
    lcd.print("cm");
  }


  // ================================================
  // DHT11 READING INTERVAL
  // ================================================

  delay(1000);
}