Office Hours Backend Coding Challenge

Introduction

Thanks for your interest in joining the Office Hours engineering team! Before we proceed with more formal interviews, we ask that all candidates submit a coding challenge. The coding challenge is a foundational piece of our process and it's referenced later in our process during the technical interviews.

You should not expect to spend more than 1-2 hours on the challenge. We want to be respectful of your time, so if you find yourself exceeding the suggested time limit, there's a chance you may be over-engineering your solution.

If at any point you have questions concerning the coding challenge and/or interview process, please do not hesitate to email coding-challenge@officehours.com.

Challenge Overview

The coding challenge is inspired by a real task our engineering team worked on: building out our system for sending payments to advisors. This is a multi-step task that involves creating a payment and executing a payment (initiating the sending of the funds through a vendor service e.g. Stripe).

This repo has all the scaffolding you'll need so you should be able to jump right in. When you fire up the dev environment, the API will be accessible at http://localhost:3000. You can interact with it through cURL commands to verify your implementation is working correctly.

The libraries and frameworks used mirror the stack we use at Office Hours:

• Node.js
• TypeScript
• Express
• Jest
• MongoDB

You do not need to be an expert in any of the above to successfully complete the coding challenge.

Challenge Details

Your job is to implement two operations and their test suites: createPayment and executePayment. In order to do this, you will also need to expand the schema of the payment document that is stored in Mongo.

createPayment

This is the simpler of the two operations as it is already partially implemented. Your primary task here is to implement a validation check and finish the test suite.

executePayment

This is where things get more interesting. The intent of this operation is to tell our payment vendor to move amount cents to recipient. You can use sendVendorPayment (available from src/scaffolding/vendor) for this. However, this is an asynchronous operation and we want to ensure there are protections in place to avoid double sending the payment.

To implement this, you will need to expand the PaymentDoc schema. How you choose to do this is up to you.

Getting Started

In order to get started, clone this repo to your local machine. You can then install the dependencies and fire up the dev environment by running:

$ npm install
$ npm run dev

You can now access the API at http://localhost:3000.

Here are some cURL commands to help you interact with the API:

# create payment
$ curl --request POST \
  --header "Content-Type: application/json" \
  --data '{"recipient":"$RECIPIENT","amount": $AMOUNT}' \
  http://localhost:3000/payments

# execute payment
$ curl --request POST \
  http://localhost:3000/payments/$PAYMENT_ID/execute

# list all payments
$ curl http://localhost:3000/payments

# list one payments
$ curl http://localhost:3000/payments/$PAYMENT_ID

You should not modify the code in src/scaffolding. You should only need to modify the code in src/operations and src/types.ts.

Submission

To submit your coding challenge, ensure all of your changes have been committed to the main branch and run the following command:

git bundle create coding-challenge.bundle HEAD main

This will generate a coding-challenge.bundle file which you can then email to coding-challenge@officehours.com. We do our best to review and respond to submissions within 1-2 business days.

Thanks for taking the time to do this coding challenge and here's hoping we talk soon!

Joey Dafforn submission

Here's my changes:

• Added status field to PaymentDoc
• createPayment: added validation for negative amounts (and add status=pending)
• createPayment.test:
  • test for negative amount should fail
  • payment should persist
• executePayment:
  • finds the existing payment with the correct status (if there is one)
  • blocks double execution of a payment
  • processes payment using vendor service and gets final status
  • finally, updates payment with final status
• exectuePayment.test:
  • executes successful payment
  • executes a failed payment twice
  • prevents a successful payment from being executed twice
  • prevents multiple payments from executing concurrently