Salt Crypto Challenge

A challenge for a Back End Engineer position at Salt Lending.

General Application Notes

Architecture

A simple react front end with a Node Typescript Express back end and a postgres sql database hosted in AWS RDS.

General App Useage

There are 3 features created here. The first is the user can enter a valid btc address (validated) and check spent or unspent. The balance will be returned. The 2nd feature is handled by the same input as the first, but displays a pie chart showing spent vs unspent balance as well as a percent of balance available (unspent). The third is that a user can enter a btc address and choose either an amount, or full amount to spend. the balance and pie chart are updated upon spend.

.env

I know that commiting a .env is bad practice. But for the sake of ease for this challenge, the fact that there is no sensitive information involved, and that this isn't a production application, I've decided to include the .env in git.

Certain refactors/breaking out of functions

Certain functions in the back end have been broken out, others have not. Breaking functions out for reuse is incredibly helpful for when changes need to be made, however, when trying to read on function it can be cumbersome to jump back and forth between functions and files to decipher what's going on. I'm a fan of "wet" code (opposite of D.R.Y. get it?). This doesn't mean I don't break anything out, but to keep a balance between readability and maintainability, my general rule of thumb is that if I have to write something more than twice (or believe I will use a certain function more than twice), then I will break it out into it's own function and err on the side of maintainability. Hopefully that answers some of the structure questions, especially in the balanceService.spend function.

Use of the balanceService.spend function

The balance service.spend function will mutate and create data (mutation is setting spent to true). If you are expecting certain numbers to be returned given the main requirement of returning a balance given a BTC Address and spent boolean, know that running the spend function or using the spend feature will alter the numbers returned. I have tested this in a duplicate copy of the database, so the original data that was sent to me will be intact and unchanged upon reaching you.

Demo Ids

The following id is a good example of a BTC Address with a good mix of spent and unspent rows. This id will get you the best result when demoing/testing certain functions:

3L72RKvX1hWbqbzQcogCm4hJbQBDKs3Boi

Back End

Run Locally

Clone the project (Should already be cloned with front end, same repo)

  git clone [email protected]:amoses12/salt-crypto-test.git

Go to the project directory

  cd backend

Install dependencies

  npm install

Start the server

  npm run dev

General Notes

Following backend code

I know there's a lot to follow here and wanted to give some context on the pieces you will most likely be interested in. Here's a quick guide on how to follow the back end code and where to find files/code of interest:

Main server file:

index.js

API endpoints imported into server file:

routers/balance.router.ts

Service functions (this is probably of most interest):

services/balance.service.ts

There are 2 helper functions in the /helpers directory. balanceHelper has a function that may be of interest when it comes to dynamically creating sql queries for the balanceService.spend function:

helpers/balanceHelpers.ts

Models/Types can all be found in the models directory

Front End

Run Locally

Clone the project (should already be cloned from back end)

  git clone https://link-to-project

Make sure the back end is running (see above)

Go to the project directory

  cd frontend/salt-challenge-frontend

Install dependencies (I'm using yarn, but npm should work just fine)

  yarn install

Start the server

  yarn start

Troubleshooting

If you're using npm and having trouble with the start script, try replacing your start script in the front end package.json to:

"start": "react-scripts --openssl-legacy-provider start"

Following Front End Code

Main App:

App.js

Main balance page:

pages/balance/index.js

Components:

Each component has it's own component folder in the /components directory containing an index.js and .css file

Redux:

Store:

store.js

Redux Toolkit Slice:

slices/balanceSlice.js

Utility functions (API setup)

utils/API.js

General Notes

The front end is built on react and uses redux toolkit as well is nivo charts for the pie chart. The purpose of this was to demonstrate my versatility, but I spent more time on the back end since this is for a back end position. By no means is it perfect or incredibly pretty, but it is entirely functional and mostly mobile responsive. Hopefully it demonstrates that I can be useful on the front end when needed as well.