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

// Define LCDs (I2C address 0x27 for user display, 0x26 for reference display)
LiquidCrystal_I2C userLCD(0x27, 16, 2);      
LiquidCrystal_I2C referenceLCD(0x26, 16, 2); 

// Define ultrasonic sensor pins
#define TRIG_LEFT 6
#define ECHO_LEFT 7
#define TRIG_RIGHT 8
#define ECHO_RIGHT 9

// Define button pins
#define BUTTON_BIKE 2
#define BUTTON_CAR 3

// Constants for better readability
#define TOTAL_SLOT_WIDTH 250      // Total parking slot width in cm (2.5 meters)
#define BIKE_WIDTH_MIN 60         // Minimum bike width in cm
#define BIKE_WIDTH_MAX 90         // Maximum bike width in cm
#define CAR_WIDTH_MIN 200         // Minimum car width in cm
#define CAR_WIDTH_MAX 220         // Maximum car width in cm
#define MAX_BIKES 2               // Maximum number of bikes in the slot
#define DISPLAY_CHANGE_TIME 2000  // 2 seconds display time
#define DEBOUNCE_DELAY 250        // Button debounce delay

// System states
enum SystemState {
  ASK_VEHICLE_TYPE,     // Display "Which is your vehicle?"
  SHOW_AVAILABILITY,    // Show if slot #17 is available
  UPDATE_OCCUPANCY      // Internal state to update occupancy
};

// Global variables
SystemState currentState = ASK_VEHICLE_TYPE;
unsigned long stateChangeTime = 0;
unsigned long lastButtonPress = 0;
int occupiedWidth = 0;        // Currently occupied width in cm
int remainingWidth = TOTAL_SLOT_WIDTH;  // Remaining width in cm
int bikeCount = 0;
bool carParked = false;

void setup() {
  // Configure ultrasonic sensor pins
  pinMode(TRIG_LEFT, OUTPUT);
  pinMode(ECHO_LEFT, INPUT);
  pinMode(TRIG_RIGHT, OUTPUT);
  pinMode(ECHO_RIGHT, INPUT);
  
  // Configure button pins with internal pull-up resistors
  pinMode(BUTTON_BIKE, INPUT_PULLUP);
  pinMode(BUTTON_CAR, INPUT_PULLUP);
  
  // Initialize LCDs
  userLCD.init();
  userLCD.backlight();
  referenceLCD.init();
  referenceLCD.backlight();
  
  // Initialize serial for debugging
  Serial.begin(9600);
  Serial.println("Smart Parking System Initialized");
  
  // Reset system to default state
  resetSystem();
}

void loop() {
  // Measure distance for reference
  int leftDistance = getDistance(TRIG_LEFT, ECHO_LEFT);
  int rightDistance = getDistance(TRIG_RIGHT, ECHO_RIGHT);
  int currentWidth = 0;
  
  if (leftDistance > 0 && rightDistance > 0 && leftDistance < 400 && rightDistance < 400) {
    currentWidth = rightDistance - leftDistance;
  }
  
  // State machine for display and interaction
  switch (currentState) {
    case ASK_VEHICLE_TYPE:
      // Display "Which is your vehicle?"
      displayVehicleQuestion();
      
      // Check if buttons are pressed (with debouncing)
      if ((millis() - lastButtonPress) > DEBOUNCE_DELAY) {
        // Bike button pressed
        if (digitalRead(BUTTON_BIKE) == LOW) {
          // Check if a bike can fit
          if (remainingWidth >= BIKE_WIDTH_MAX) {
            // Enough space for a bike
            bikeCount++;
            occupiedWidth += BIKE_WIDTH_MAX;
            remainingWidth = TOTAL_SLOT_WIDTH - occupiedWidth;
            
            Serial.print("Bike added. Count: ");
            Serial.print(bikeCount);
            Serial.print(", Remaining width: ");
            Serial.println(remainingWidth);
            
            // Change state to show availability
            currentState = SHOW_AVAILABILITY;
            stateChangeTime = millis();
          }
          lastButtonPress = millis();
        }
        
        // Car button pressed
        if (digitalRead(BUTTON_CAR) == LOW) {
          // Check if a car can fit
          if (remainingWidth >= CAR_WIDTH_MIN && bikeCount == 0) {
            // Enough space for a car
            carParked = true;
            occupiedWidth += CAR_WIDTH_MAX;
            remainingWidth = TOTAL_SLOT_WIDTH - occupiedWidth;
            
            Serial.println("Car added. No more space available.");
            
            // Change state to show availability
            currentState = SHOW_AVAILABILITY;
            stateChangeTime = millis();
          }
          lastButtonPress = millis();
        }
        
        // Reset system if both buttons pressed simultaneously
        if (digitalRead(BUTTON_BIKE) == LOW && digitalRead(BUTTON_CAR) == LOW) {
          resetSystem();
          lastButtonPress = millis();
        }
      }
      break;
      
    case SHOW_AVAILABILITY:
      // Display slot availability
      displaySlotAvailability();
      
      // Change back to vehicle question after 2 seconds
      if (millis() - stateChangeTime >= DISPLAY_CHANGE_TIME) {
        currentState = ASK_VEHICLE_TYPE;
      }
      break;
      
    case UPDATE_OCCUPANCY:
      // This state is for internal updates if needed
      currentState = ASK_VEHICLE_TYPE;
      break;
  }
  
  // Always update the reference display with current status
  updateReferenceDisplay(currentWidth);
  
  // Short delay to prevent excessive processing
  delay(50);
}

// Function to display "Which is your vehicle?"
void displayVehicleQuestion() {
  userLCD.clear();
  userLCD.setCursor(0, 0);
  userLCD.print("Which is your");
  userLCD.setCursor(0, 1);
  userLCD.print("vehicle?");
}

// Function to display slot availability
void displaySlotAvailability() {
  userLCD.clear();
  userLCD.setCursor(0, 0);
  userLCD.print("Slot #17: ");
  userLCD.setCursor(0, 1);
  
  // Check if slot is available
  if (remainingWidth >= BIKE_WIDTH_MAX) {
    userLCD.print("Available");
  } else {
    userLCD.print("FULL");
  }
}

// Function to update reference display with detailed information
void updateReferenceDisplay(int currentWidth) {
  referenceLCD.clear();
  referenceLCD.setCursor(0, 0);
  
  // First line shows occupancy status
  if (carParked) {
    referenceLCD.print("Car Parked");
  } else if (bikeCount > 0) {
    referenceLCD.print(bikeCount);
    referenceLCD.print(" Bike");
    if (bikeCount > 1) referenceLCD.print("s");
    referenceLCD.print(" Parked");
  } else {
    referenceLCD.print("Slot Empty");
  }
  
  // Second line shows width information
  referenceLCD.setCursor(0, 1);
  referenceLCD.print("Rem:");
  referenceLCD.print(remainingWidth);
  referenceLCD.print("cm");
  
  if (currentWidth > 0) {
    referenceLCD.print(" W:");
    referenceLCD.print(currentWidth);
  }
}

// Function to measure distance with error checking
int getDistance(int trigPin, int echoPin) {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Measure the response time
  long duration = pulseIn(echoPin, HIGH, 30000); // Added timeout
  
  // Check for invalid readings
  if (duration == 0) {
    return 400; // Return max distance if timeout
  }
  
  // Calculate and return distance in centimeters
  int distance = duration * 0.034 / 2;
  
  // Sanity check on the distance value
  return (distance > 0 && distance < 400) ? distance : 400;
}

// Function to reset the system
void resetSystem() {
  occupiedWidth = 0;
  remainingWidth = TOTAL_SLOT_WIDTH;
  bikeCount = 0;
  carParked = false;
  currentState = ASK_VEHICLE_TYPE;
  Serial.println("System reset - slot now empty");
}