#include <SPI.h>
#include <MFRC522.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const int RST_PIN = D0;     // Reset pin
const int SS_PIN = D1;      // SDA 

#define I2C_ADDR 0x27  // LCD I2C address 
LiquidCrystal_I2C lcd(I2C_ADDR, 16, 2);

MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance

void setup() {
  Serial.begin(9600);
  SPI.begin();          // Init SPI bus
  mfrc522.PCD_Init();   // Init MFRC522

  // I2C pin config 
  Wire.setSDA(6);       // D4 
  Wire.setSCL(7);       // D5 
  Wire.begin();

  lcd.init();           // Initialize LCD
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Scan RFID tag...");
}

void loop() {
  // Check for new RFID card
  if (!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) {
    return;
  }

  // Create a string to hold the UID
  String uidString = "";
  for (byte i = 0; i < mfrc522.uid.size; i++) {
    if (mfrc522.uid.uidByte[i] < 0x10) {
      uidString += "0"; // Leading zero for single hex digits
    }
    uidString += String(mfrc522.uid.uidByte[i], HEX);
  }
  uidString.toUpperCase(); // Optional: make it uppercase

  // Print to Serial
  Serial.print("UID tag: ");
  Serial.println(uidString);

  // Print to LCD
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("RFID UID:");
  lcd.setCursor(0, 1);
  lcd.print(uidString);

  delay(2000); // Display for 2 seconds before next scan
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Scan RFID tag...");

  mfrc522.PICC_HaltA(); // Halt PICC
}