Automated Teller Machine - ATM

We've embarked on the journey to create a speculative new bank, and our mission is to implement a simple ATM machine. The ATM comprises two crucial components:

1. Register: Keeps track of the physical cash on hand within the ATM machine.
2. Terminal: Enables customers to access their account, view their balance, and withdraw cash.

Your Mission

The initial parts of the terminal UI prompt for a customer's account number. Once entered and found, we'd like to provide three options to the customer:

1. Show Balance: Displays the current balance for the customer.
2. Withdraw Cash: Prompts for the amount they wish to withdraw, following certain rules.
3. Exit: Returns the UI to the main terminal.

We need your help to complete the functionality of our ATM machine.

Rules

1. Do not allow withdrawals exceeding $500 at a time.
2. Do not permit withdrawals exceeding the available balance in the account.
3. Manage remaining bills in the register – if a customer requests $200 and only one $100 bill remains, they should receive that $100 and smaller bills for the remaining balance.
4. Alert the customer if there's insufficient money in the register or in their account for the withdrawal.

Admin Access

For added security, bank tellers can access super-secret internal account details by entering admin into the account number prompt. This grants access to the overall balance of the register, including the number of each respective bill.

The possible bills in the register are $1, $5, $10, $20, $50, and $100.

Running the ATM

To run the ATM, execute the following command in your terminal:

ruby atm.rb

Running the Tests

To run the tests, execute the following command in your terminal:

rspec

Implementation and Architecture

The implementation follows a modular structure with distinct classes for the Account, Register, and AutomatedTellerMachine. The ATM relies on user input to navigate through account details, display balances, and facilitate cash withdrawals.

Trade-offs and Potential Improvements

1. User Experience: Enhancements in the user interface and experience could be implemented for a more intuitive interaction.
2. Error Handling: Implement more detailed error messages to guide users in case of invalid inputs.
3. Code Refactoring: Continuously refactor code to adhere to best practices and improve maintainability.