CALCULATOR API built with NodeJS, MongoDB and Mongoose

Description

This is NodeJS application that serves endpoints to perform calculator operations, such addition, sustraction, multiplication, square root, and also an endpoint to generate random strings.

Every registered user gets a credit of 500 units. This units are spent with every request to perform calculations. You can configure the initial amount of credits and also the cost per operations with the environment variables.

Since this is a calculator application in Node.js, which is a relatively simple application, and you don't need complex queries or transactions, MongoDB may be a better choice than a relational database like PostgreSQL. MongoDB's flexibility and ease of use make it a good fit for simple applications like this.

A Bearer token will be needed to excecute all endpoints.

The app provides two endpoints to register a new user and to login with an existing user.

NOTE: all endpoints should have the base url prefix api/v1 in order to handle the api versioning. For expample: the url for a login post request should look like this <host>/api/v1/auth/login

Here is a list of the endponts:

endpoint	method	description	response OK
/calc/adition	POST	Perform an addition operation	{ result: operationResult }
/calc/substraction	POST	Perform a substraction operation	{ result: operationResult }
/calc/multiplication	POST	Perform a multiplication operation	{ result: operationResult }
/calc/division	POST	Perform a division operation	{ result: operationResult }
/calc/square-root	POST	Perform a square root operation	{ result: operationResult }
/calc/random-string	GET	Retrieves a random string	{ result: someRandomString }
---	---	---	---
/operations/list	GET	Retrieves a paginated list of operations requested by the user	{ data: Array<Operations>, totalPages: Total pages, currentPage: Current page }
/operations/:id	DELETE	Soft deletes an operation register	{ message: 'Operation deleted' }
---	---	---	---
/auth/login	POST	Login with one of the creted users (Body requires email and password)	{token: "SomeValidToken"}
/auth/register	POST	Create a new user (Body requires email and password)	{ message: 'User created succesfully' }
/seed	GET	Create users and operations with preloaded data	{ message: SEED OK }

After succesfully seed, a valid user to login to the app is

• email: jose@gmail.com
• password: 123456

Entities

There are two main entities in this project, 'User' and ' Operation'.

User refers to the user who performs an operation

User {
    email: string, valid email,
    password: string,
    status: string,
    balance: number
}

Operation refers to the operation that can be performed on calculator (addition, substraction, multiplication, division, square root, random string)

Operation {
    type: string, Enum value,
    cost: number,
    date: Date,
    user: id of the user who made the operation,
    result: parsed as string,
    isDeleted: boolean
}

This entities structure can be built in a more decoupled way adding a third entity, for example Records, who would be responsible for storing every operation made by an user. This would allow Operation entity to act as a validator entity who would store every valid operation in the app. In this case it was made only with two entities due to a typo in the description of the challenge.

Environment Variables

It is important to configure required environment variables in order to run the project, here is an example with all the required env variables

.env

RANDOM_ORG_API_KEY='apiKeyOfRandom.org'
RANDOM_ORG_URL='https://api.random.org/json-rpc/4/invoke'
STRINGS_TO_GENERATE='abcdefghijklmnopqrstuvwxyz123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'

ADDITION_COST=20
SUBSTRACTION_COST=20
MULTIPLICATION_COST=40
DIVISION_COST=40
SQRT_COST=50
STRING_GENERATOR_COST=60
INITIAL_BALANCE=500

JWT_SECRET=YourJWTSecret
SALT_ROUNDS=25

MONGO_URL="yourMongoURLDatabase"
DB_NAME='databaseName'

variable	description
RANDOM_ORG_API_KEY	Api key from random.org to generate the random strings
RANDOM_ORG_URL	Api URL from random.org
STRINGS_TO_GENERATE	Available strings to generate a random combination
ADDITION_COST	Cost per addition operation
SUBSTRACTION_COST	Cost per substraction operation
MULTIPLICATION_COST	Cost per multiplication operation
DIVISION_COST	Cost per division operation
SQRT_COST	Cost per square root operation
STRING_GENERATOR_COST	Cost per random string generator operation
INITIAL_BALANCE	Initial amount of credit a user gets to perform operations
JWT_SECRET	Secret to configure hash of login tokens
SALT_ROUNDS	Numeric value to configure the encrypt for password when creating and saving a new user
MONGO_URL	Url of a provisioned mongo database
DB_NAME	database name

Running the app

# development
$ npm run start

# watch mode
$ npm run start:dev

Test

Unit tests are built with jest

# unit tests
$ npm test