public class ATM
{
    private boolean userAuthenticated; //whether user is authenticated
    private int currentAccountNumber; // current user's account number
    private Screen screen; //ATM's screen
    private Keypad keypad; //ATM's keypad
    private CashDispenser cashDispenser; //ATM's cash dispenser
    private DepositSlot depositSlot; //ATM's deposit slot
    private BankDatabase bankDatabase; // account information database

    //constants corresponding to main menu options
    private static final int BALANCE_INQUIRY = 1;
    private static final int WITHDRAWAL = 2;
    private static final int DEPOSIT = 3;
    private static final int EXIT = 4;

    //no-argument ATM constructor initializes instance variables
    public ATM()
    {
        userAuthenticated = false; //user is not authenticated to start
        currentAccountNumber = 0; //no current account number to start
        screen = new Screen(); //create screen
        keypad = new Keypad(); //create keypad
        cashDispenser = new CashDispenser(); //create cash dispenser
        depositSlot = new DepositSlot(); //crate deposit slot
        bankDatabase = new BankDatabase(); //create acct info database
    } //end no-argument ATM constructor

    //start ATM
    public void run()
    {
        //welcome and authenticate user; perform transaction
        while(true)
        {
            //loop while user is not yet authenticated
            while(!userAuthenticated)
            {
                screen.displayMessageLine("\nSelamat Datang!");
                authenticateUser(); //authenticated user
            }  //end while

            performTransactions(); //user is now authenticated
            userAuthenticated = false;  //reset before next ATM session
            currentAccountNumber = 0;  //reset before next ATM session
            screen.displayMessageLine("\nTerima Kasih!\nSampai Jumpa!");
        }
    } //end method run

    //attempts to authenticate user against database
    private void authenticateUser()
    {
        screen.displayMessage("\nSilahkan masukkan nomor akun anda : ");
        int accountNumber = keypad.getInput(); //input account number
        screen.displayMessage("\nSilahkan masukkan PIN anda : "); //prompt for PIN
        int pin = keypad.getInput(); //input PIN

        //set userAuthenticated to boolean value returned by database
        userAuthenticated = bankDatabase.authenticateUser(accountNumber, pin);

        //check whether authentication succeeded
        if(userAuthenticated)
        {
            currentAccountNumber = accountNumber;  //save user's account
        }
        else
        {
            screen.displayMessageLine("Nomor akun atau PIN anda tidak valid.");
            screen.displayMessageLine("Silahkan coba lagi.");
        }
    }

    //display the main menu and perform transaction
    private void performTransactions()
    {
        //local variable to store transaction currently being processed
        Transaction currentTransaction = null;
        boolean userExited = false;  //user has not chosen to exit.

        //loop while user has not chosen option to exit system
        while(!userExited)
        {
            //show main menu and get user selection
            int mainMenuSelection = displayMainMenu();

            //decide how to proceed based on user's menu selection
            switch(mainMenuSelection)
            {
                //user chose to perform one of three transaction types
                case BALANCE_INQUIRY :
                case WITHDRAWAL :
                case DEPOSIT :
                    //initialize as new object of chosen type
                    currentTransaction = createTransaction(mainMenuSelection);
                    currentTransaction.execute();
                    break;
                case EXIT :
                    screen.displayMessageLine("\nKeluar dari sistem...");
                    userExited = true;
                    break;
                default : //user didn't enter an integer from 1-4
                    screen.displayMessageLine("\nMenu yang anda pilih tidak valid.");
                    screen.displayMessageLine("Silahkan coba lagi.");
                    break;
            }  //end switch
        } //end while
    }   //end method performTransaction

    private int displayMainMenu()
    {
        screen.displayMessageLine("\nMain Menu :");
        screen.displayMessageLine("1. Lihat Saldo"); //view my balance
        screen.displayMessageLine("2. Tarik Uang"); //withdraw cash
        screen.displayMessageLine("3. Simpan Uang"); //deposit funds
        screen.displayMessageLine("4. Keluar\n");
        screen.displayMessage("Masukkan pilihan : ");
        return keypad.getInput(); //return user's selection
    }

    private Transaction createTransaction(int type)
    {
        Transaction temp = null;
        switch(type){
            case BALANCE_INQUIRY :
                temp = new BalanceInquiry(currentAccountNumber, screen, bankDatabase);
                break;
            case WITHDRAWAL :
                temp = new Withdrawal(currentAccountNumber, screen, bankDatabase, keypad, cashDispenser);
                break;
            case DEPOSIT :
                temp = new Deposit(currentAccountNumber, screen, bankDatabase, keypad, depositSlot);
                break;
        }
        return temp;
    }
}