Order calculator

Treat this exercise as you would a real-life business problem. You can ask for clarification of any domain name or rule. If the business requirement is not clear, assume you have access to a business owner to answer your questions.

There is no requirement to complete this exercise, we are more looking at your thought process & how you approach the problem.

The problem

Farmdrop would like to build a system to calculate the final total of an order.

Based on customer feedback we have noticed customers would like to see an itemised breakdown of their order. This should include a following items:

• Cost of all line items
• Cost of delivery
• Total to pay

What to build

Build an application that returns itemised billing for an order.

A seperate order service will send you the required data, so the application should accept line_items and a delivery_slot_id. Based on this an itemised bill should be returned.

There is already a postgres database populated with a delivery_slots and delivery_costs table. You can see the details of the tables at db/structure.sql

A delivery_slot can have multiple delivery_costs. The delivery_cost defines the minimum spend, and the cost to charge if that minimum spend is met. If a delivery cost is not found we can assume the cost is 0.

This is the structure for line_items:

{
  id: 32433,
  quantity: 1,
  price_pence: 150
}

You can assume the interviewer is the business owner and ask any clarification on the above.

Example

Given the following data was sent from the order service:

[
  {
    id: 53888,
    quantity: 2,
    price_pence: 299
  },
  {
    id: 99633,
    quantity: 1,
    price_pence: 125
  }
]

and a delivery slot id was also provided, allowing us to which allows us to retrieve the following delivery_cost record in the database

delivery_slot_id: 342344

{
  id: 343424,
  delivery_slot_id: 342344,
  cost_pence: 100,
  minimum_spend_pence: 500,
  label: "£1 delivery when you spend over £5"
}

The application will return the following response:

{
 item_total_pence: 723,
 shipment_total_pence: 100,
 total_pence: 823
}

Docker installation

Run the following commands to setup the application.

docker-compose build
docker-compose run --rm app rake db:setup
docker-compose up

Standard installation

Firstly, open the .env file, then modify the host portion of the DATABASE_URL && INITIAL_DATABASE_URL from db to localhost.

Then run the following commands

bundle install
rake db:setup
thor app:server
thor app:console # if you would like a console