#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Servo.h>

#define TRIGGER_ENTRANCE_PIN 4
#define ECHO_ENTRANCE_PIN 5
#define TRIGGER_EXIT_PIN 6
#define ECHO_EXIT_PIN 7
#define SERVO_PIN 3
#define SLOT_CAPACITY 4

LiquidCrystal_I2C lcd(0x27, 16, 2);
Servo parkingServo;
int availableSlots = SLOT_CAPACITY;

void setup() {
  pinMode(TRIGGER_ENTRANCE_PIN, OUTPUT);
  pinMode(ECHO_ENTRANCE_PIN, INPUT);
  pinMode(TRIGGER_EXIT_PIN, OUTPUT);
  pinMode(ECHO_EXIT_PIN, INPUT);

  lcd.begin(16, 2);
  lcd.setCursor(0, 0);
  lcd.print("GOD IS MY LIGHT");
  delay(2000);
  lcd.clear();

  parkingServo.attach(SERVO_PIN);
  parkingServo.write(0); // Set servo to initial position
}

void loop() {
  int entranceDistance = detectDistance(TRIGGER_ENTRANCE_PIN, ECHO_ENTRANCE_PIN);
  int exitDistance = detectDistance(TRIGGER_EXIT_PIN, ECHO_EXIT_PIN);

  lcd.setCursor(0, 0);
  lcd.print("Welcome");
  lcd.setCursor(0, 1);
  
  if (availableSlots > 0 || exitDistance <= 30) { // Allow exit when parking is full if exitDistance is within limit
    lcd.print("Slots: ");
    lcd.print(availableSlots);
    delay(1000);
    lcd.clear();
    
    if (entranceDistance <= 30) {
      lcd.setCursor(0, 0);
      lcd.print("Car Entering!");
      delay(2000);
      lcd.clear();
      availableSlots--;
      moveServo(); // Move servo to allow the car in
    }
    
    if (exitDistance <= 30) {
      lcd.setCursor(0, 0);
      lcd.print("Car Exiting!");
      delay(2000);
      lcd.clear();
      availableSlots++;
      moveServo(); // Move servo to allow the car out
    }
  } else {
    lcd.print("Parking full!");
    delay(1000);
    lcd.clear();
  }
}

int detectDistance(int triggerPin, int echoPin) {
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  
  int duration = pulseIn(echoPin, HIGH);
  int distance = duration * 0.034 / 2;
  
  return distance;
}

void moveServo() {
  parkingServo.write(90); // Move the servo to open position
  delay(2000);
  parkingServo.write(0); // Move the servo back to initial position
  delay(500);
}