#include <Servo.h>
#include <LiquidCrystal.h>
#include <TimerOne.h>

LiquidCrystal lcd(12, 11, 10, 8, 5, 4);

Servo myservo;

int distanceThreshold = 100;

int parkingAvailable = 3;
int barrierState = 0;

const int TRIGGER_PIN_SLOT_1 = A0;
const int ECHO_PIN_SLOT_1 = A1;

const int TRIGGER_PIN_SLOT_2 = A2;
const int ECHO_PIN_SLOT_2 = A3;

const int TRIGGER_PIN_SLOT_3 = A4;
const int ECHO_PIN_SLOT_3 = A5;

const int TRIGGER_PIN_ENTER = 3;
const int ECHO_PIN_ENTER = 2;

const int TRIGGER_PIN_EXIT = 13;
const int ECHO_PIN_EXIT = 9;

const int TIMER = 25000; 

volatile long echo_start = 0; 


volatile long distance_enter = 0;

void ultrasonicEcho(){
    if(echo_start != 0){
        distance_enter = (micros() - echo_start) / 58;
        echo_start = 0;
    }
}

void ultrasonicPulse(){
    digitalWrite(TRIGGER_PIN_ENTER, LOW);
    delayMicroseconds(2);
    digitalWrite(TRIGGER_PIN_ENTER, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIGGER_PIN_ENTER, LOW);
    echo_start = micros();
}

void setup() {
  lcd.begin(16,2);
  lcd.setCursor(0,0);
  Serial.begin (9600);
  myservo.attach(6);
  myservo.write(0);
  pinMode(TRIGGER_PIN_ENTER, OUTPUT);
  pinMode(ECHO_PIN_ENTER, INPUT_PULLUP);
  Timer1.initialize(TIMER);
  Timer1.attachInterrupt(ultrasonicPulse);
  attachInterrupt(digitalPinToInterrupt(ECHO_PIN_ENTER), ultrasonicEcho, FALLING);
}

long readDistance(int triggerPin, int echoPin)
{
  pinMode(triggerPin, OUTPUT);
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  pinMode(echoPin, INPUT);
  return pulseIn(echoPin, HIGH);
}


void loop()
{
  float distance_slot_1 = readDistance(TRIGGER_PIN_SLOT_1, ECHO_PIN_SLOT_1) / 58;
  float distance_slot_2 = readDistance(TRIGGER_PIN_SLOT_2, ECHO_PIN_SLOT_2) / 58;
  float distance_slot_3 = readDistance(TRIGGER_PIN_SLOT_3, ECHO_PIN_SLOT_3) / 58;
  float distance_exit = readDistance(TRIGGER_PIN_EXIT, ECHO_PIN_EXIT) / 58;
  
  Serial.println("Distance slot 1 = " + String(distance_slot_1) + "cm");
  Serial.println("Distance slot 2 = " + String(distance_slot_2) + "cm");
  Serial.println("Distance slot 3 = " + String(distance_slot_3) + "cm");
  Serial.println("Distance enter = " + String(distance_enter) + "cm");
  Serial.println("Distance exit = " + String(distance_exit) + "cm");
  
if (barrierState == 0)
{
  if (distance_enter<100 && distance_exit>=100 && parkingAvailable>0)
  {
     parkingAvailable -= 1;
     barrierState = -1;
     myservo.write(90);
  }
  if (distance_enter>=100 && distance_exit<100 && parkingAvailable<3)
  {
     parkingAvailable += 1;
     barrierState = 1;
     myservo.write(90);
  }
}
else if (barrierState == -1)
{
  if (distance_enter>=100 && distance_exit<100)
  {
     barrierState = -2;
     myservo.write(0);
  }
}  
 else if (barrierState == 1)
{
    if (distance_exit>=100 && distance_enter<100)
  {
     barrierState = 2;
     myservo.write(0);
  }
}
 else if (barrierState == -2)
{
    if (distance_exit>=100)
  {
     barrierState = 0;
  }
}  
else if (barrierState == 2)
{
    if (distance_enter>=100)
  {
     barrierState = 0;
  }
}  

lcd.setCursor(0,0);
if (parkingAvailable == 0)
{
  lcd.print("Parking Full  ");
}
else
{
  lcd.print("Parking left ");
  lcd.print(parkingAvailable);
}

  
  
if (distance_slot_1 > 100 & distance_slot_2 > 100 & distance_slot_3 > 100)
{
	lcd.setCursor(0,1);
	lcd.print("Slot 1 2 3 Free");
	delay(500);
	}
else if((distance_slot_1>100 & distance_slot_2>100)|(distance_slot_2>100 & distance_slot_3>100)|(distance_slot_3>100 & distance_slot_1>100))
  {
	lcd.setCursor(0,1);
  	if(distance_slot_1>100 & distance_slot_2>100)
		lcd.print("Slot 1 & 2 Free");
  	else if(distance_slot_1>100 & distance_slot_3>100)
		lcd.print("Slot 1 & 3 Free");
  	else
		lcd.print("Slot 2 & 3 Free");
	}
else if(distance_slot_1<100 & distance_slot_2<100 & distance_slot_3<100)
  {
	lcd.setCursor(0,1);
	lcd.print("Parking Full   ");
	}
else if((distance_slot_1<100 & distance_slot_2<100)|(distance_slot_2<100 & distance_slot_3<100)|(distance_slot_3<100 & distance_slot_1<100))
  {
	lcd.setCursor(0,1);
  	if(distance_slot_1>100)
      lcd.print("Slot 1 is Free ");
	else if (distance_slot_2>100)
       lcd.print("Slot 2 is Free ");
    else
       lcd.print("Slot 3 is Free ");
   }
  delay(100);
}