RFID Smart Door Access

#include <Arduino.h>
#include <SPI.h>
#include <Wire.h>
#include <MFRC522.h>
#include <LiquidCrystal_I2C.h>
#include <ESP32Servo.h>
#include <Preferences.h>


// Forward declarations
String uidToString(const MFRC522::Uid &uid);
void showMessage(const String &line1, const String &line2);
void beep(unsigned int durationMs);
void lockDoor(bool announce);
void unlockDoor();
void denyAccess();

constexpr uint8_t RFID_SS_PIN = 4;
constexpr uint8_t RFID_RST_PIN = 26;
constexpr uint8_t RFID_SCK_PIN = 18;
constexpr uint8_t RFID_MISO_PIN = 19;
constexpr uint8_t RFID_MOSI_PIN = 23;
constexpr uint8_t LCD_SDA_PIN = 21;
constexpr uint8_t LCD_SCL_PIN = 22;
constexpr uint8_t SERVO_PIN = 25;
constexpr uint8_t BUZZER_PIN = 33;
constexpr int LOCK_ANGLE = 10;
constexpr int UNLOCK_ANGLE = 90;
constexpr unsigned long UNLOCK_TIME_MS = 5000;
constexpr unsigned long CARD_COOLDOWN_MS = 1200;

MFRC522 rfid(RFID_SS_PIN, RFID_RST_PIN);
LiquidCrystal_I2C lcd(0x27, 16, 2);
Servo latchServo;
Preferences preferences;
String enrolledUid;
String lastMessage;
unsigned long unlockStartedAt = 0;
unsigned long lastCardAt = 0;
bool doorUnlocked = false;

String uidToString(const MFRC522::Uid &uid) {
  String value;
  for (byte i = 0; i < uid.size; ++i) {
    if (uid.uidByte[i] < 0x10) value += "0";
    value += String(uid.uidByte[i], HEX);
  }
  value.toUpperCase();
  return value;
}

void showMessage(const String &line1, const String &line2) {
  String message = line1 + "\n" + line2;
  if (message == lastMessage) return;
  lastMessage = message;
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print(line1.substring(0, 16));
  lcd.setCursor(0, 1);
  lcd.print(line2.substring(0, 16));
}

void beep(unsigned int durationMs) {
  digitalWrite(BUZZER_PIN, HIGH);
  delay(durationMs);
  digitalWrite(BUZZER_PIN, LOW);
}

void lockDoor(bool announce = true) {
  latchServo.write(LOCK_ANGLE);
  doorUnlocked = false;
  if (announce) showMessage("Door locked", "Present card");
}

void unlockDoor() {
  latchServo.write(UNLOCK_ANGLE);
  doorUnlocked = true;
  unlockStartedAt = millis();
  showMessage("Access granted", "Door unlocked");
  beep(90);
  delay(70);
  beep(90);
}

void denyAccess() {
  showMessage("Access denied", "Unknown card");
  beep(600);
}

void setup() {
  Serial.begin(115200);
  pinMode(BUZZER_PIN, OUTPUT);
  digitalWrite(BUZZER_PIN, LOW);
  Wire.begin(LCD_SDA_PIN, LCD_SCL_PIN);
  lcd.init();
  lcd.backlight();
  showMessage("Smart Door", "Starting...");
  latchServo.setPeriodHertz(50);
  latchServo.attach(SERVO_PIN, 500, 2400);
  lockDoor(false);
  SPI.begin(RFID_SCK_PIN, RFID_MISO_PIN, RFID_MOSI_PIN, RFID_SS_PIN);
  rfid.PCD_Init();
  preferences.begin("door-access", false);
  enrolledUid = preferences.getString("adminUid", "");
  if (enrolledUid.length() == 0) {
    showMessage("Enroll first card", "Scan RFID card");
    Serial.println("Enrollment mode: scan the first card to authorize it.");
  } else {
    showMessage("Door locked", "Present card");
  }
}

void loop() {
  if (doorUnlocked && millis() - unlockStartedAt >= UNLOCK_TIME_MS) lockDoor();
  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) return;
  if (millis() - lastCardAt < CARD_COOLDOWN_MS) {
    rfid.PICC_HaltA();
    rfid.PCD_StopCrypto1();
    return;
  }
  lastCardAt = millis();
  const String scannedUid = uidToString(rfid.uid);
  Serial.println("Scanned UID: " + scannedUid);
  if (enrolledUid.length() == 0) {
    enrolledUid = scannedUid;
    preferences.putString("adminUid", enrolledUid);
    showMessage("Card enrolled", "Scan to unlock");
    beep(120);
    delay(80);
    beep(120);
  } else if (scannedUid == enrolledUid) {
    unlockDoor();
  } else {
    denyAccess();
  }
  rfid.PICC_HaltA();
  rfid.PCD_StopCrypto1();
}