ATM machine

As owners of AwesomeSuperPuperBank, we want to have a simple prototype of our new ATM machine that allows our customers to:

• view their account balance
• withdraw money

Our bank already has two clients: Volodymyr and Iryna. We saved their account information in our system (see config.yml). The bank also has liquid assets (i.e. cash) in the amount of ₴337 (in different banknotes) which our ATM machine can operate with.

Use case:

The information about the banknotes in the ATM and all the accounts in the bank is stored in a configuration file:

# config.yml
banknotes:
  500: 0
  200: 0
  100: 2
  50: 1
  20: 2
  10: 4
  5: 1
  2: 0
  1: 2
accounts:
  3321:
    name: 'Volodymyr'
    password: 'mypass'
    balance: 422
  5922:
    name: 'Iryna'
    password: 'ho#ll_§1'
    balance: 5301

We run the app by passing the location of this configuration file as an argument to the program

  ruby atm.rb config.yml

Here’s one of possible application flows:

Please Enter Your Account Number:
> 3321
Enter Your Password:
> mypass

Hello, Volodymyr!

Please Choose From the Following Options:
 1. Display Balance
 2. Withdraw
 3. Log Out

> 1

Your Current Balance is ₴422

Please Choose From the Following Options:
 1. Display Balance
 2. Withdraw
 3. Log Out

> 2

Enter Amount You Wish to Withdraw:
> 100000

ERROR: INSUFFICIENT FUNDS!! PLEASE ENTER A DIFFERENT AMOUNT:
> 420

ERROR: THE MAXIMUM AMOUNT AVAILABLE IN THIS ATM IS ₴337. PLEASE ENTER A DIFFERENT AMOUNT:
> 329

ERROR: THE AMOUNT YOU REQUESTED CANNOT BE COMPOSED FROM BILLS AVAILABLE IN THIS ATM. PLEASE ENTER A DIFFERENT AMOUNT:
> 320

Your New Balance is ₴102

Please Choose From the Following Options:
 1. Display Balance
 2. Withdraw
 3. Log Out

> 1

Your Current Balance is ₴102

Please Choose From the Following Options:
 1. Display Balance
 2. Withdraw
 3. Log Out

> 3

Volodymyr, Thank You For Using Our ATM. Good-Bye!

Please Enter Your Account Number:
> 5922
Enter Your Password:
> 1234567

ERROR: ACCOUNT NUMBER AND PASSWORD DON'T MATCH

Please Enter Your Account Number:
> 5922
Enter Your Password:
> ho#ll_§1

Hello, Iryna!
...

Tips:

Please send us your code even if you haven't fully implemented all the requirements. We understand that the task may turn out to be more complex than it looks at first glance.

When making decisions about your code, keep in mind that the bank owners may request certain changes in functionality in the future. Can your code design allow such changes easily?

What possible security issues do you see in the current app design? What changes would you recommend to improve the security of the app?

In your opinion, what could prevent the bank from integrating the current app into their production systems right now?