Ki take home exercise

Background

The Ki website allows customers to open an account and purchase shares in one or more funds. Before a customer can buy shares, they top up their account with a desired amount, using a debit card.

The website is supported by an underlying investment platform, consisting of modules that each perform a specific role. Each module is a separate package, installed on the platform as a dependency. One of these modules is tasked with processing an incoming payments CSV file, then generating a share order CSV, consumed by another module.

This report contains the customer_id and the number of shares their payment(s) will purchase, given the share price.

"customer_id","shares"
"123","100"
"987","3400"

For development, the module can be invoked with the LocalRunner class, which simulates how it is integrated with the investment platform. This is configured as the main class of the package. To run this locally, build the project with Maven:

mvn package

You can now call the JAR file directly:

java -jar target/ki-takehome-kotlin-1.0-SNAPSHOT.jar <path_to_payments_csv> <source> <share_price>

To see example output:

java -jar target/ki-takehome-kotlin-1.0-SNAPSHOT.jar card_payments_example.csv card 1.20

Exercise

Some customers have indicated they would prefer to top up their account by making a bank transfer, rather than using their debit card.

Update the com.ki.services.PaymentProcessor class to support both card and bank transfer payments. We will receive a separate CSV file from our payment provider, in a similar format to card payments:

customer_id,date,amount,bank_account_id
789,2018-10-25,900,20
345,2018-11-03,900,60

Unlike card payments, our payment provider will only update us once a bank transfer has been successfully processed.

Remember, the module is installed on the platform as a dependency, therefore the API to both the PaymentProcessor and ShareEngine service classes must not change.

You can check your implementation by using the example CSV:

java -jar target/ki-takehome-kotlin-1.0-SNAPSHOT.jar bank_payments_example.csv bank 1.20

This should produce the result:

"customer_id","shares"
"789","735"
"345","735"

NOTE content fin, order wrong -- due to grouping and ordering by custid

Tests

You can run the tests from the root of the project with:

mvn test

Notes

The code base has been written to compile under Java 8 (and Kotlin 1.6.0-RC2) and upwards. Dependencies are managed via Maven, see the pom.xml file.

Notes and Assumptions

I am assuming, from this wording:

Unlike card payments, our payment provider will only update us once a bank transfer has been successfully processed.

That the bank payment CSV contains only successful transfers. n.b., I am aware that another interpretation of this could have been that the success of the payments must be asynchronously confirmed, following the file's processing, with the csv containing payments with no guarantee of successful processing. Given there was no further alluding to this idea, it was opted to not pursue it.

Discrepancies

It also appears that the expected output, as stated in this readme file, is misaligned vs the actual output when using the local runner files. I will assume this is simply a stale readme, as tests pass.