DEEL BACKEND TASK

💫 Welcome! 🎉

This backend exercise involves building a Node.js/Express.js app that will serve a REST API. We imagine you should spend around 3 hours at implement this feature.

Data Models

All models are defined in src/model.js

Profile

A profile can be either a client or a contractor. clients create contracts with contractors. contractor does jobs for clients and get paid. Each profile has a balance property.

Contract

A contract between and client and a contractor. Contracts have 3 statuses, new, in_progress, terminated. contracts are considered active only when in status in_progress Contracts group jobs within them.

Job

contractor get paid for jobs by clients under a certain contract.

Getting Set Up

The exercise requires Node.js to be installed. We recommend using the LTS version.

Start by cloning this repository.
In the repo root directory, run npm install to gather all dependencies.
Next, npm run seed will seed the local SQLite database. Warning: This will drop the database if it exists. The database lives in a local file database.sqlite3.
Then run npm start which should start both the server and the React client.

❗️ Make sure you commit all changes to the master branch!

Technical Notes

The server is running with nodemon which will automatically restart for you when you modify and save a file.
The database provider is SQLite, which will store data in a file local to your repository called database.sqlite3. The ORM Sequelize is on top of it. You should only have to interact with Sequelize - please spend some time reading sequelize documentation before starting the exercise.
To authenticate users use the getProfile middleware that is located under src/middleware/getProfile.js. users are authenticated by passing profile_id in the request header. after a user is authenticated his profile will be available under req.profile. make sure only users that are on the contract can access their contracts.
The server is running on port 3001.

APIs To Implement

Below is a list of the required API's for the application.

GET /contracts/:id - This API is broken 😵! it should return the contract only if it belongs to the profile calling. better fix that!
GET /contracts - Returns a list of contracts belonging to a user (client or contractor), the list should only contain non terminated contracts.
GET /jobs/unpaid - Get all unpaid jobs for a user (either a client or contractor), for active contracts only.
POST /jobs/:job_id/pay - Pay for a job, a client can only pay if his balance >= the amount to pay. The amount should be moved from the client's balance to the contractor balance.
POST /balances/deposit/:userId - Deposits money into the the the balance of a client, a client can't deposit more than 25% his total of jobs to pay. (at the deposit moment)
GET /admin/best-profession?start=<date>&end=<date> - Returns the profession that earned the most money (sum of jobs paid) for any contactor that worked in the query time range.
GET /admin/best-clients?start=<date>&end=<date>&limit=<integer> - returns the clients the paid the most for jobs in the query time period. limit query parameter should be applied, default limit is 2.

 [
    {
        "id": 1,
        "fullName": "Reece Moyer",
        "paid" : 100.3
    },
    {
        "id": 200,
        "fullName": "Debora Martin",
        "paid" : 99
    },
    {
        "id": 22,
        "fullName": "Debora Martin",
        "paid" : 21
    }
]

Going Above and Beyond the Requirements

Given the time expectations of this exercise, we don't expect anyone to submit anything super fancy, but if you find yourself with extra time, any extra credit item(s) that showcase your unique strengths would be awesome! 🙌

It would be great for example if you'd write some unit test / simple frontend demostrating calls to your fresh APIs.

Submitting the Assignment

When you have finished the assignment, create a github repository and send us the link.

Thank you and good luck! 🙏

Developer Notes:

The Node version used was 16.14.2. LTS: Gallium. Sequelize Version: 6.17.0. TODO: Add library check-node into package.json to avoid inconsistencies between node versions in the developers PCs. npm v8.5.0
ESLint was installed for organization and readability. eslintConfig is in the package.json but could be placed as a file in the root directory as best practice.
express-async-handler was installed to handle routes better.
JEST. For Unit Testing.

Project structure:

Application → Controllers. Their responsibility is to receive and parse the data in the incoming request. If all data is correct, it call the respective service to handle the request.
Service → Services. Their responsibility is to handle the business logic. From here you can call the repositories, but the logic is placed inside each service.
Repository → Their responsibility is to connect and query the DB.

Next steps and TODOs:

Centralized error handling for the controllers.
Inputs validation.
getProfile should call profileRepository.
Authorization middleware for admin endpoints.
Unit testing.
Swagger.
Replace all console.logs with logger.

Concurrency notes:

By default, sequelize uses the isolation level of the database. SQLite uses Serializable.

This means that if two different requests try to perform payJob at the same time (even though the clients nor the contractors are the same), one of the transactions will lock the tables and only one of the requests will succeed.

In order to increment the concurrency level and be able to pay many jobs at the same time (if their clients and contractors are not equal) I would implement an Optimistic Locking approach, with a version column at the Profile and Job tables. This way, the isolation level would be at a row level and each row would be protected, without locking the entire table.

Josega149/Deel-BackEnd-Challenge