Currency Convertor App

This is the result of evaluation task for a Full-Stack Developer position.

App consists of

• Currency Convertor
• Today's rates
• Historical rates

Overview

The result is an application, consisting of Node.js, Express.js, PostgresQL, Redis backend services and React client app with Material UI library.

All services are containerized with optimized image size, meaning they can be run with Docker with ease, and images will take minimal space.
However, for production use, orchestration services (like kubernetes) should be used.

Architecture follows Domain Drive Design, as all code is separated by domain model.

Backend service makes use of MVC approach, while UI is MVVM with react hooks. State management was not used on UI, because there is only one page to show.
If app is to grow, mobx or redux should be introduced.

All services are made with Standard JS (not TypeScript) with functional approach as per requirements by evaluator. I would personally use TypeScript instead.

Client app utilizes Adaptive and Responsive design, allowing for smooth UX on all devices.

App utilizes an external service FreeCurrencyApi.com as a source for data for currency rates. Data is fetched periodically with job queue schedule. Free external API has strict limit for requests, that's why we have to cache all data in our db.

Task was completed in 8 days. Process of task completion can be seen from commit history.

Demo

Demo is available here.

Credentials:
user
12345

Development

How to run

1. Set up ENV variables as per ./app/.env.development
2. Run docker compose

docker compose up

OR

2. You can manually run individual services using

npm start

What is yet to be done (TODO)

• write lots of tests!
• production deploy with kubernetes
• add WS (or long-polling?) to update rates online. No need now, since FreeCurrencyApi updates rates rarely
• use better service for external currencies (faster updates, better api, more currencies)
• linting
• use TypeScript instead
• better error handling (network errors, offline app usage, toasts)
• databases auto-clean up
• standalone auth service, for proper auth token refresh, reaction for password change
• proper unique design (i.e. company logo, favicon, ui-kit)

Limitations

• All amounts should be rounded for 0.05 steps (floored) - this one cannot be done properly, since user can type both source amount and target amount. This way he will get different results for same amounts. Which is a bad UX.
• Have to cache yearly amount of rates in DB, because of limits in external API.
• Low amount of time given, led to lack of tests
• Requirement for AED currencies being always on top of the list, - is not doable, because there is no AED rates provided by freecurrency.com. I've used EUR instead of it.
• App calculates any rate, using USD as a base rate. Due to higher precision in storage (6 digits), it allows us to store less data, and still have precise (4 digits) rates on UI. This also allows us to cache data once for all rates, instead of requesting it each time (and potentially hitting limits). BUT one might say, that rates are less precise, that directly from external api.

Additional requirements

• All rates should be rounded for four decimal places.
• All amounts should be rounded in 0.05 steps (floored) for two decimal places.
• The user should login with Username & Password before he can interact with the server.
• The app should not call the currency API directly. It should call a NodeJS service that will hold the API Key to make the currency requests on the app behalf. All calls (except login) should be authenticated
• All rates should be rounded for four decimal places.
• Preferred authentication method is JWT
• If user is not authenticated. He’s not allowed to access the converter screen
• The default amount of source currency is 1000.00
• User can change the source and target currencies, the change of the above should immediately reflect on target amount
• Today’s rates will be displayed for 5 predefined currencies (EUR, GBP, CAD, MXN and JPY) related to the selected source currency.
• If one of the above currencies is selected as the source currency USD will be used instead of it.
• User can select four different time frames to show historical data:
  • Last month
  • Last 3 month
  • Last 6 month
  • Last 12 month