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

// --- LCD Configuration ---
// Find your I2C LCD address. Common addresses: 0x27, 0x3F.
// Use an I2C scanner sketch if you're unsure.
LiquidCrystal_I2C lcd(0x27, 16, 2); // Address, columns, rows

// --- Keypad Configuration ---
const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
// Define GPIO pins for rows and columns
byte rowPins[ROWS] = {19, 18, 5, 17}; // Connect to R1, R2, R3, R4
byte colPins[COLS] = {16, 4, 0, 2};   // Connect to C1, C2, C3, C4
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

// --- LED Configuration ---
const int RED_LED_PIN = 13;
const int GREEN_LED_PIN = 12;
const int BLUE_LED_PIN = 14;
// For Common Anode LED (HIGH = OFF, LOW = ON)
#define LED_ON LOW
#define LED_OFF HIGH

// --- Button Configuration ---
const int BUTTON_PIN = 15;

// --- Password and State ---
#define PASSWORD "1234"
const int PASSWORD_LENGTH = strlen(PASSWORD);

typedef enum {
    STATE_IDLE,
    STATE_WAITING_FOR_START,
    STATE_ENTERING_PASSWORD,
    STATE_PASSWORD_CORRECT_GET_NUMBER,
    STATE_SHOW_WELCOME
} SystemState_t;

SystemState_t currentState = STATE_IDLE;
int passwordIndex = 0;
char enteredPassword[PASSWORD_LENGTH + 1];
char doorNumberChar = '\0';

unsigned long lastDebounceTime = 0;
unsigned long debounceDelay = 50;
int lastButtonState = HIGH;
int buttonState;


void setup() {
  Serial.begin(115200); // For debugging output to Serial Monitor

  // --- Initialize LCD ---
  lcd.init();
  lcd.backlight();
  lcd.clear();

  // --- Initialize LEDs ---
  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(GREEN_LED_PIN, OUTPUT);
  pinMode(BLUE_LED_PIN, OUTPUT);
  setLed(LED_OFF, LED_OFF, LED_OFF); // All off

  // --- Initialize Button ---
  pinMode(BUTTON_PIN, INPUT_PULLUP); // Use internal pull-up

  // --- Initial State ---
  displayPrompt("System Ready", "Press Button");
  currentState = STATE_WAITING_FOR_START;
  Serial.println("System Initialized. Press button to start.");
}

void loop() {
  char key = keypad.getKey();

  // --- Handle Button Press to Start ---
  if (currentState == STATE_WAITING_FOR_START) {
    int reading = digitalRead(BUTTON_PIN);
    if (reading != lastButtonState) {
        lastDebounceTime = millis();
    }
    if ((millis() - lastDebounceTime) > debounceDelay) {
        if (reading != buttonState) {
            buttonState = reading;
            if (buttonState == LOW) { // Button pressed (active LOW due to PULLUP)
                currentState = STATE_ENTERING_PASSWORD;
                resetPasswordEntry();
                displayPrompt("Enter Code:", "");
                setLed(LED_OFF, LED_OFF, LED_ON); // Blue: entry mode
                Serial.println("Password entry started.");
            }
        }
    }
    lastButtonState = reading;
  }

  // --- Process Keypad Input based on State ---
  if (key != NO_KEY) { // Keypad library returns NO_KEY if nothing pressed
    Serial.print("Key Pressed: "); Serial.println(key);

    if (currentState == STATE_ENTERING_PASSWORD) {
      if (passwordIndex < PASSWORD_LENGTH) {
        lcd.setCursor(passwordIndex, 1); // Display on second line
        lcd.print(key); // Or print '*' for security

        if (key == PASSWORD[passwordIndex]) {
          enteredPassword[passwordIndex] = key;
          passwordIndex++;
          setLed(LED_OFF, LED_ON, LED_OFF); // Green: correct digit
          delay(200);
          setLed(LED_OFF, LED_OFF, LED_ON); // Blue: back to entry

          if (passwordIndex == PASSWORD_LENGTH) {
            currentState = STATE_PASSWORD_CORRECT_GET_NUMBER;
            setLed(LED_OFF, LED_ON, LED_OFF); // Green: password correct
            displayPrompt("Correct Code!", "Enter Door #:");
            Serial.println("Password correct! Enter door number.");
          }
        } else {
          setLed(LED_ON, LED_OFF, LED_OFF); // Red: wrong digit
          Serial.print("Wrong digit at index "); Serial.print(passwordIndex);
          Serial.print(". Expected "); Serial.print(PASSWORD[passwordIndex]);
          Serial.print(", got "); Serial.println(key);
          delay(1000);
          setLed(LED_OFF, LED_OFF, LED_ON); // Blue: back to entry
          // For "index didn't increase, next user input will be checked by the same index"
          // We just show error and wait for next key press for the same index.
          // To make it more obvious, re-prompt and clear the wrongly entered digit.
          displayPrompt("Enter Code:", "");
          lcd.setCursor(0,1);
          for(int i=0; i < passwordIndex; i++) lcd.print(PASSWORD[i]); // Or '*'
        }
      }
    } else if (currentState == STATE_PASSWORD_CORRECT_GET_NUMBER) {
      if (isDigit(key)) { // Check if the key is a digit '0'-'9'
        doorNumberChar = key;
        currentState = STATE_SHOW_WELCOME;
        setLed(LED_OFF, LED_ON, LED_OFF); // Green

        char welcomeMsg[17]; // 16 chars + null
        sprintf(welcomeMsg, "Welcome to %c", doorNumberChar);
        displayPrompt(welcomeMsg, "");
        Serial.print("Door "); Serial.print(doorNumberChar); Serial.println(" rung.");

        delay(3000);
        setLed(LED_OFF, LED_OFF, LED_OFF); // All off
        displayPrompt("System Ready", "Press Button");
        currentState = STATE_WAITING_FOR_START;
        Serial.println("System reset to waiting state.");
      } else {
        setLed(LED_ON, LED_OFF, LED_OFF); // Red: invalid door #
        displayPrompt("Invalid Door #", "Use 0-9");
        delay(1000);
        setLed(LED_OFF, LED_ON, LED_OFF); // Green (password was correct)
        displayPrompt("Correct Code!", "Enter Door #:"); // Re-prompt
      }
    }
  }
  // A small delay to prevent loop from running too fast if not much is happening
  // Keypad library handles debouncing internally. Button has its own debounce.
  delay(10);
}

// --- Helper Functions ---
void setLed(int r, int g, int b) {
  digitalWrite(RED_LED_PIN, r);
  digitalWrite(GREEN_LED_PIN, g);
  digitalWrite(BLUE_LED_PIN, b);
}

void displayPrompt(const char* line1, const char* line2) {
  lcd.clear();
  if (line1) {
    lcd.setCursor(0, 0);
    lcd.print(line1);
  }
  if (line2) {
    lcd.setCursor(0, 1);
    lcd.print(line2);
  }
}

void resetPasswordEntry() {
  passwordIndex = 0;
  for (int i = 0; i <= PASSWORD_LENGTH; i++) {
    enteredPassword[i] = '\0';
  }
  // Optionally clear the part of the LCD where digits were shown
  lcd.setCursor(0,1);
  for(int i=0; i < PASSWORD_LENGTH; ++i) lcd.print(" ");
}