ATM

interface AtmState {
  void insertCard(Atm atm, Card card);
  void enterPin(Atm atm, Pin pin);
  void withdraw(Atm atm, Money amount);
  void eject(Atm atm);
}

interface WithdrawHandler {
  void setNext(WithdrawHandler next);
  void handle(WithdrawContext ctx);
}

abstract class AbstractWithdrawHandler implements WithdrawHandler {
  private WithdrawHandler next;
  public void setNext(WithdrawHandler next) { this.next = next; }
  protected void pass(WithdrawContext ctx) {
    if (next != null) next.handle(ctx);
  }
}

class PinOkHandler extends AbstractWithdrawHandler {
  public void handle(WithdrawContext ctx) {
    if (!ctx.session.authenticated()) throw new NotAuthenticated();
    pass(ctx);
  }
}

class NoteMultipleHandler extends AbstractWithdrawHandler {
  public void handle(WithdrawContext ctx) {
    if (!ctx.amount.isMultipleOf(ctx.cassette.minNote())) throw new InvalidAmount();
    pass(ctx);
  }
}

class BalanceHandler extends AbstractWithdrawHandler {
  public void handle(WithdrawContext ctx) {
    if (ctx.account.balance().lessThan(ctx.amount)) throw new InsufficientFunds();
    pass(ctx);
  }
}

interface BankPort {
  Account snapshot(Card card);
  void debit(Card card, Money amount);
}

class Atm {
  private AtmState state = new IdleState();
  private final BankPort bank;
  void insertCard(Card card) { state.insertCard(this, card); }
  void enterPin(Pin pin) { state.enterPin(this, pin); }
  void withdraw(Money amount) { state.withdraw(this, amount); }
}