/**
   An ATM that accesses a bank.
*/
public class ATM 
{  
   public static final int CHECKING = 1;
   public static final int SAVINGS = 2;

   private int state;
   private int customerNumber;
   private Customer currentCustomer;
   private BankAccount currentAccount;
   private Bank theBank;
   
   public static final int START = 1;
   public static final int PIN = 2;
   public static final int ACCOUNT = 3;
   public static final int TRANSACT = 4;

   /**
      Constructs an ATM for a given bank.
      @param aBank the bank to which this ATM connects
   */    
   public ATM(Bank aBank)
   {
      theBank = aBank;
      reset();
   }

   /**
      Resets the ATM to the initial state.
   */
   public void reset()
   {
      customerNumber = -1;
      currentAccount = null;
      state = START;             
   }

   /** 
      Sets the current customer number 
      and sets state to PIN. 
      (Precondition: state is START)
      @param number the customer number.
   */
   public void setCustomerNumber(int number) 
   {
      assert state == START;
      customerNumber = number;
      state = PIN;
   }

   /** 
      Finds customer in bank.
      If found sets state to ACCOUNT, else to START.
      (Precondition: state is PIN)
      @param pin the PIN of the current customer
   */
   public void selectCustomer(int pin)
   {  
      assert state == PIN;
      currentCustomer 
         = theBank.findCustomer(customerNumber, pin);
      if (currentCustomer == null) 
         state = START;
      else 
         state = ACCOUNT;
   }
   
   /** 
      Sets current account to checking or savings. Sets 
      state to TRANSACT. 
      (Precondition: state is ACCOUNT or TRANSACT)
      @param account one of CHECKING or SAVINGS
   */
   public void selectAccount(int account)
   {
      assert state == ACCOUNT || state == TRANSACT;
      if (account == CHECKING)
         currentAccount = currentCustomer.getCheckingAccount();
      else
         currentAccount = currentCustomer.getSavingsAccount();
      state = TRANSACT;
   }

   /** 
      Withdraws amount from current account. 
      (Precondition: state is TRANSACT)
      @param value the amount to withdraw
   */
   public void withdraw(double value)
   {  
      assert state == TRANSACT;
      currentAccount.withdraw(value);
   }

   /** 
      Deposits amount to current account. 
      (Precondition: state is TRANSACT)
      @param value the amount to deposit
   */
   public void deposit(double value)
   {  
      assert state == TRANSACT;
      currentAccount.deposit(value);
   }

   /** 
      Gets the balance of the current account. 
      (Precondition: state is TRANSACT)
      @return the balance
   */
   public double getBalance()
   {  
      assert state == TRANSACT;
      return currentAccount.getBalance();
   }

   /**
      Moves back to the previous state.
   */
   public void back()
   {
      if (state == TRANSACT)
         state = ACCOUNT;
      else if (state == ACCOUNT)
         state = PIN;
      else if (state == PIN)
         state = START;
   }

   /**
      Gets the current state of this ATM.
      @return the current state
   */
   public int getState()
   {
      return state;
   }
}