Checkout Service

A simple service to calculate the total amount to be paid on a checkout process.

Requirements

npm
node >= 14.7.0 (will likely work with older versions, but has never been tested)

Installation

npm install

Running

npm start will start the application at http://localhost:8080 (set environment variable PORT to change the port).

Cases to execute with curl

curl --data '{"codes": "VOUCHER, TSHIRT, MUG"}' -H "Content-Type: application/json" http://localhost:8080/checkout

curl --data '{"codes": "VOUCHER, TSHIRT, VOUCHER"}' -H "Content-Type: application/json" http://localhost:8080/checkout

curl --data '{"codes": "TSHIRT, TSHIRT, TSHIRT, VOUCHER, TSHIRT"}' -H "Content-Type: application/json" http://localhost:8080/checkout

curl --data '{"codes": "VOUCHER, TSHIRT, VOUCHER, VOUCHER, MUG, TSHIRT, TSHIRT"}' -H "Content-Type: application/json" http://localhost:8080/checkout

Testing

Tests can be run with npm test.

All tests are colocated with their respective source files in *.spec.js files, using Jest with default settings.

Resolution process

Configure Node API basic config to interact with it as an RestFull API
Configure an app for this service pourpose
Design a json schema to store the products and the rules, which ended up to be

{
  // list of all the products that can purchased
  "products": [
    { "code": "UpperSnakeCase String", "name": "String", "price": "Double" },
    ...
  ],
  // list of rules that need to be applied
  "rules": [
    {
      // There is a defined number of rules at config rules.js which can be used
      "ruleCode": "lowerCamelCase String",
      // Product's code which this rule applies
      "productCode": "TSHIRT",
      // additional constant variables that needs the rule
      "inputs": {...}
    },
    ...
  ]
}

Add test for rules functions
Design and implement the rule functions and define the input & output
- Added a rule template function as a helper for new functions in the future
Execute test and bug-fixing
Add notes at test for service, just define because it's a simple service and it would require to much time to add the tests
Implement the service, controller and router
Add JSDoc to type input params at rules and service
Test API with given cases

Proposal improvements

Rules: We're only considering one product per rule as the requiremnts consider 1 product as most. For scalability and more rule capabilities we should change it to be able to accept an array of products.
Rules config: For a JSON like this it may be convenient to define some jsonSchema schema, for time constraints I'm adding this as a improvement.
Rules config: If the changes are something really consistent it may be convenient to configure a database to store the products and rulse configuration so it's not required to restart the app to update the config each time.
API Rest: Add test for proper error handling
API Rest: add input validation with Joi
Rules: It can be improved by using classes and inheritance, an interface or abstract classes so each rule extends/implements a predefined class/interface

CristianPQ / checkout-with-rules