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Basic Credit Card Processing

Imagine that you're writing software for a credit card provider. Implement a program that will add new credit card accounts, process charges and credits against them, and display summary information.

Requirements:

  • Your program must accept input from two sources: a filename passed in command line arguments and STDIN. For example, on Linux or OSX both './myprogram input.txt' and './myprogram < input.txt' should work.
  • Your program must accept three input commands passed with space delimited arguments.
  • "Add" will create a new credit card for a given name, card number, and limit
    • Card numbers should be validated using Luhn 10
    • New cards start with a $0 balance
  • "Charge" will increase the balance of the card associated with the provided name by the amount specified
    • Charges that would raise the balance over the limit are ignored as if they were declined
    • Charges against Luhn 10 invalid cards are ignored
  • "Credit" will decrease the balance of the card associated with the provided name by the amount specified
    • Credits that would drop the balance below $0 will create a negative balance
    • Credits against Luhn 10 invalid cards are ignored
  • When all input has been read and processed, a summary should be generated and written to STDOUT in the format shown in the example below.
  • The summary should include the name of each person followed by a colon and balance.
  • The names should be displayed alphabetically.
  • Display "error" instead of the balance if the credit card number does not pass Luhn 10.

Input Assumptions:

  • All input will be valid -- there's no need to check for illegal characters or malformed commands.
  • All input will be space delimited.
  • Credit card numbers may vary in length up to 19 characters.
  • Credit card numbers will always be numeric.
  • Amounts will always be prefixed with "$" and will be in whole dollars (no decimals).

Input and Output:

Given the following input:

Add Tom 4111111111111111 $1000
Add Lisa 5454545454545454 $3000
Add Quincy 1234567890123456 $2000
Charge Tom $500
Charge Tom $800
Charge Lisa $7
Credit Lisa $100
Credit Quincy $200

Your program must produce the following output:

Lisa: $-93
Quincy: error
Tom: $500

Implementing and Packaging Your Solution:

Implement your solution in any programming language you wish, but keep in mind we may ask you to explain or extend your code. Please write automated tests and include them with your submission.

You may implement your own Luhn 10 check, or you may use an external library. We do not prefer either approach over the other, but your solution will be assessed on correctness and testing.

In addition to your code and tests, please also include a README that explains:

  • An overview of your design decisions
  • Why you picked the programming language you used
  • How to run your code and tests, including how to compile it if applicable and how to install any dependencies your code may have.

Thank you!

Note: this information is confidential. It is prohibited to share, post online or otherwise publicize without Braintree's prior written consent.