#include <Wire.h>
#include <MFRC522.h>
#include <Keypad.h>
#include <RTClib.h>
#include <LiquidCrystal_I2C.h>

#define SS_PIN 5
#define RST_PIN 4
#define BUZZER_PIN 15
#define SWITCH_PIN 2
#define RELAY_PIN 16

MFRC522 rfid(SS_PIN, RST_PIN);
RTC_DS3231 rtc;
LiquidCrystal_I2C lcd(0x27, 16, 2);
const byte ROWS = 4, COLS = 4;
char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};
byte rowPins[ROWS] = {13, 12, 14, 27};
byte colPins[COLS] = {26, 25, 33, 32};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

const char* validRFID = "abcd1234"; // Simulated RFID tag ID
char enteredOTP[5];
char generatedOTP[5];

void setup() {
  Serial.begin(115200);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(SWITCH_PIN, INPUT_PULLUP);
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW);
  Wire.begin();
  rfid.PCD_Init();
  rtc.begin();
  lcd.init();
  lcd.backlight();
  lcd.print("Scan RFID");
  rtc.adjust(DateTime(2025, 3, 2, 9, 0, 0)); // Simulated exam time
}

void loop() {
  if (!checkTime()) {
    lcd.clear();
    lcd.print("Time Restricted");
    delay(2000);
    lcd.clear();
    lcd.print("Scan RFID");
    return;
  }

  if (rfid.PICC_IsNewCardPresent() && rfid.PICC_ReadCardSerial()) {
    String tag = readRFID();
    if (tag == validRFID) {
      generateAndSendOTP();
      if (verifyOTP()) {
        unlockSystem();
      } else {
        tamperAlert();
      }
    } else {
      lcd.clear();
      lcd.print("Invalid RFID");
      delay(2000);
    }
    lcd.clear();
    lcd.print("Scan RFID");
    rfid.PICC_HaltA();
  }

  if (digitalRead(SWITCH_PIN) == LOW) {
    tamperAlert();
  }
}

String readRFID() {
  String tag = "";
  for (byte i = 0; i < rfid.uid.size; i++) {
    tag += String(rfid.uid.uidByte[i], HEX);
  }
  return tag;
}

void generateAndSendOTP() {
  randomSeed(millis());
  for (int i = 0; i < 4; i++) {
    generatedOTP[i] = '0' + random(0, 10);
  }
  generatedOTP[4] = '\0';
  lcd.clear();
  lcd.print("OTP Sent");
  Serial.println("SMS: Your OTP: " + String(generatedOTP)); // Simulated GSM
  lcd.clear();
  lcd.print("Enter OTP");
}

bool verifyOTP() {
  int pos = 0;
  while (pos < 4) {
    char key = keypad.getKey();
    if (key && isDigit(key)) {
      enteredOTP[pos] = key;
      lcd.setCursor(pos, 1);
      lcd.print(key);
      pos++;
    }
  }
  enteredOTP[4] = '\0';
  return (strcmp(enteredOTP, generatedOTP) == 0);
}

void unlockSystem() {
  lcd.clear();
  lcd.print("Access Granted");
  digitalWrite(RELAY_PIN, HIGH);
  delay(2000);
  digitalWrite(RELAY_PIN, LOW);
  lcd.clear();
  lcd.print("Scan RFID");
}

void tamperAlert() {
  digitalWrite(BUZZER_PIN, HIGH);
  lcd.clear();
  lcd.print("Leak Detected");
  Serial.println("SMS: System Tampered!"); // Simulated GSM
  delay(2000);
  digitalWrite(BUZZER_PIN, LOW);
  lcd.clear();
  lcd.print("Scan RFID");
}

bool checkTime() {
  DateTime now = rtc.now();
  DateTime examTime(2025, 3, 2, 9, 0, 0);
  return (now >= examTime && now <= examTime + TimeSpan(0, 0, 5, 0)); // 5-min window
}