Delivery Fee Calculator API

Solution to Wolt's engineering internship (backend) assignment

Description

• The Delivery Fee Calculator API provides a single-endpoint that responds to POST requests.
• Request body format:

{"cart_value": 975, "delivery_distance": 3520, "number_of_items": 3, "time": "2024-01-31T17:00:00Z"}

Field details:

Field	Type	Description	Example value
cart_value	Integer	Value of the shopping cart in cents.	975 (975 cents = 9.75€)
delivery_distance	Integer	The distance between the store and customer’s location in meters.	3520 (3520 meters = 3.520 km)
number_of_items	Integer	The number of items in the customer's shopping cart.	3 (customer has 3 items in the cart)
time	String	Order time in UTC in ISO format.	2024-01-31T17:00:00Z

Response: Calculated delivery fee (in cents)

{"delivery_fee": 825}

• delivery fee will be 8.25€ (825 cents)

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Getting started

Using a virtual environment (Python 3.10 or higher):

Linux, macOS:

python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
uvicorn app.main:app --reload

Windows:

PowerShell	CMD
python3 -m venv .venv .venv/Scripts/Activate.ps1 pip install -r requirements.txt uvicorn app.main:app --reload	python3 -m venv .venv .venv/Scripts/activate.bat pip install -r requirements.txt uvicorn app.main:app --reload

To exit the virtual environment:

deactivate

Using Docker:

Prerequisites

• Docker and docker-compose installed on your system.

Build and Run Docker Container

docker compose up or docker-compose up

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Try it out:

• Send POST requests to 127.0.0.1:8000/delivery_fee or localhost:8000/delivery_fee
• Access fastAPI's documentation and interact with the API: http://127.0.0.1:8000/docs
• Send a POST request from terminal:

curl -X "POST" -H "Content-Type: application/json" -d "{\"cart_value\": 975, \"delivery_distance\": 3520, \"number_of_items\": 3, \"time\": \"2024-01-31T17:00:00Z\"}" localhost:8000/delivery_fee

Running the tests

Tests	Commands
All tests:	pytest
Unit tests:	pytest tests/unit
Integration tests:	pytest tests/integration
Show coverage:	pytest --cov=.

Requirements

(No need to worry about these if you followed the steps under 'Getting started')

fastapi==0.109.0
httpx==0.26.0
pydantic==2.5.3
pytest==7.4.4
pytest-cov==4.1.0
uvicorn==0.27.0
python-dateutil==2.8.2
types-python-dateutil==2.8.19.20240106

Clarifications/interpretations

• Rush hour in UTC: although it does not make much sense in a real-life scenario, I interpret it as any timezone converted to UTC; rush hour in UTC, no matter the local time of the order.
• Rush hour 3-7 PM is interpreted as 15:00:00.000 – 18:59:59.999 (3 inclusive, 7 exclusive).
• As stated in the docstrings of models.py: extra fields of the request body do not raise errors, but are disregarded. This is true only if the required fields are present and formatted correctly.
• Rounding; in cases where the rush hour multiplication results in a fractional number, banker's rounding is applied.

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Special thanks to Jerry Pussinen for the inspiring FastAPI workshop at Hive Helsinki!