#include <Keypad.h>
#include <LiquidCrystal_I2C.h>
#include <EEPROM.h>
#include <string.h>

/* ================= LCD ================= */
LiquidCrystal_I2C lcd(0x27, 16, 2);   // change to 0x3F if needed

/* ================= PASSWORD ================= */
char password[5];
char entered[5];
int pos = 0;
int attempts = 0;
bool locked = false;
bool changeMode = false;
unsigned long lastFailTime = 0;

/* ================= KEYPAD ================= */
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'}
};

byte rowPins[ROWS] = {PA0, PA1, PA2, PA3};
byte colPins[COLS] = {PA4, PA5, PA6, PA7};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

/* ================= OUTPUT PINS ================= */
#define GREEN_LED PB0
#define RED_LED   PB1
#define BUZZER    PB2
#define RESET_BTN PB3

/* ================= SETUP ================= */
void setup() {
  Serial.begin(115200);
  Serial.println("Hello, STM32!");
  Serial.println("Multi-Level Security System");

  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
  pinMode(BUZZER, OUTPUT);
  pinMode(RESET_BTN, INPUT_PULLUP);

  digitalWrite(GREEN_LED, LOW);
  digitalWrite(RED_LED, LOW);
  digitalWrite(BUZZER, LOW);

  lcd.init();
  lcd.backlight();

  // Load password from EEPROM (default 1234)
  for (int i = 0; i < 4; i++) {
    char v = EEPROM.read(i);
    if (v < '0' || v > '9')
      password[i] = '2' + i;
    else
      password[i] = v;
  }
  password[4] = '\0';

  lcd.clear();
  lcd.print("Enter Password");
}

/* ================= LOOP ================= */
void loop() {

  /* -------- ADMIN RESET -------- */
  if (digitalRead(RESET_BTN) == LOW) {
    locked = false;
    attempts = 0;
    changeMode = false;
    lastFailTime = 0;

    digitalWrite(BUZZER, LOW);
    digitalWrite(RED_LED, LOW);

    lcd.clear();
    lcd.print("System Reset");
    delay(1500);
    lcd.clear();
    lcd.print("Enter Password");
  }

  /* -------- LOCK STATE -------- */
  if (locked) {
    digitalWrite(RED_LED, HIGH);
    digitalWrite(BUZZER, HIGH);
    lcd.setCursor(0, 1);
    lcd.print("SYSTEM LOCKED ");
    delay(500);
    return;
  }

  /* -------- TIMEOUT AFTER FAIL -------- */
  if (lastFailTime != 0 && millis() - lastFailTime < 5000) {
    lcd.setCursor(0, 1);
    lcd.print("Wait 5 seconds ");
    return;
  }

  char key = keypad.getKey();

  if (key) {
    Serial.print("Key Pressed: ");
    Serial.println(key);

    // Enter password change mode
    if (key == '#' && pos == 0) {
      changeMode = true;
      lcd.clear();
      lcd.print("New Password:");
      return;
    }

    entered[pos] = key;
    lcd.setCursor(pos, 1);
    lcd.print("*");
    pos++;

    if (pos == 4) {
      entered[4] = '\0';

      // Change password
      if (changeMode) {
        for (int i = 0; i < 4; i++) {
          password[i] = entered[i];
          EEPROM.write(i, entered[i]);
        }
        changeMode = false;
        lcd.clear();
        lcd.print("Pwd Changed!");
        Serial.println("Password Updated");
        delay(1500);
      }

      // Correct password
      else if (strcmp(entered, password) == 0) {
        lcd.clear();
        lcd.print("Access Granted");
        digitalWrite(GREEN_LED, HIGH);
        attempts = 0;
        lastFailTime = 0;
        Serial.println("ACCESS GRANTED");
      }

      // Wrong password
      else {
        lcd.clear();
        lcd.print("Access Denied");
        digitalWrite(RED_LED, HIGH);
        digitalWrite(BUZZER, HIGH);
        delay(300);
        digitalWrite(BUZZER, LOW);
        attempts++;
        lastFailTime = millis();
        Serial.print("Wrong Attempt: ");
        Serial.println(attempts);
      }

      // Lock system
      if (attempts >= 3) {
        locked = true;
        lcd.clear();
        lcd.print("LOCKED!");
        Serial.println("SYSTEM LOCKED");
      }

      pos = 0;
      delay(1500);
      digitalWrite(GREEN_LED, LOW);
      digitalWrite(RED_LED, LOW);
      lcd.clear();
      lcd.print("Enter Password");
    }
  }
}