typescript-data-manipulation: A TypeScript repository from rcoedo

Code Challenge

To solve the proposed challenge I built a backend using NestJS with an endpoint that returns the required stats.

Running the application 🚀

First of all you need to provide the environment file. There's a sample in config/local.env.sample. Create a new file config/local.env using this one as template, so the application can fetch the right data.

An example of a config/local.env file:

API_ENDPOINT=https://api.supermetrics.com/assignment
API_CLIENT_ID=your_client_id
API_EMAIL=your_email
API_NAME=your_name
API_TOKEN_TTL=3600

After that, you can run the application using yarn:

$ yarn # To install dependencies
$ yarn start # To start the server

Alternatively, you can run the application using docker:

$ docker compose up

This will start the NestJS server in http://localhost:3000.

Once the server is up and running, you can query the endpoint for the stats in the url http://localhost:3000/stats

The stack 👩‍💻

I've chosen NestJS because I think it's one of the best Node frameworks available at the moment. It has great support for TypeScript out of the box, and it is really easy to set up a new project with all the necessary tooling, like jest, supertest for e2e tests, prettier, eslint etc.

I also used RxJS to manipulate the data, since it makes it easy to pipe through it and split it in different streams to be processed by different stats processors.

To manipulate Dates, I used momentjs, and to generate data for testing purposes I used faker.

The architecture 🏗️

Client: The client fetches data from the API and handles authentication + token caching.
PostsService: Its purpose is to fetch posts using the client, and to encapsulate pagination behavior. Pagination is transparent and from the outside the user only sees a stream of posts.
StatsService: Its main purpose is, given a stream of Posts, to calculate a set of statistics. The stream is split in many, and each of those passed to a processor. A processor is a pure function that receives a stream of Posts and returns the corresponding statistic result.
StatsController: Has a single endpoint that returns the stats for the first 1000 posts.

Testing

There are unit tests for the different parts of the application. There's also an e2e test under test/app.e2e-spec.ts that hits the API and checks the result using Snapshot Testing.

To run the unit tests:

$ yarn test

To run the e2e test:

$ yarn test:e2e

Keep in mind that, since these tests are hitting the provided API, and the data is not static, they will fail. I still decided to include it because it is a good way to test the application. To update the snapshots:

$ yarn test:e2e -u

That's it! 🎊