Senior Backend Engineering Code Challenge

Please spend a maximum of 2 hours on this challenge.

This should be taken as way to demonstrate your:

• How you structure projects
  • formatting, organization, linting, etc.
• Skills/understanding of TypeScript
• Skills/understanding of NestJS
• Integration with external APIs
• Databases
  • design, queries, migrations, etc.
• Caching
  • design, implementation, strategies, etc.

The Task

The participant will build a NestJS application that:

1. Accepts coordinates via a protected webhook (POST endpoint).
2. Performs a transformation on the coordinates.
3. Calls the Overpass API to get nearby landmarks.
4. Saves these landmarks in a SQLite database.
5. Caches the results.
6. Exposes a GET endpoint that retrieves them from the cache (fallback to DB).

NestJS + Overpass Code Challenge

Overview & Requirements

1. Protected Webhook Endpoint (POST /webhook)

• Receives a JSON payload with lat and lng.

• For example:

  {
    "lat": 48.8584,
    "lng": 2.2945
  }

• Be sure to have some validation in place and return proper HTTP status codes.

• Require Authorization header with a secret

2. Overpass API Call

• Query the Overpass API at https://overpass-api.de/api/interpreter to find nearby tourist attractions within a 500m (or configurable) radius of the coordinates.

• Example Curl command:

  curl -X POST \
     -H "Content-Type: text/plain" \
     --data '[out:json];
     (
       way["tourism"="attraction"](around:500,{{lat}},{{lng}});
       relation["tourism"="attraction"](around:500,{{lat}},{{lng}});
     );
  

• Expect a JSON response containing ways or relations with metadata in the tags property (including name if available).

3. Store in SQLite

• Parse the JSON response and store relevant data in a SQLite database.
  • Perform some transformation on the data to simplify what is stored about landmarks
• If nothing is found, store the original request coordinates.

4. Caching

• Use some form of caching to store the landmarks that will be used for fetching.
• Implement a write-through cache.

5. Data Retrieval Endpoint (GET /landmarks)

• Accepts query parameters lat and lng.
• Use your best judgement on how to design the data that is returned.

6. Error Handling & Validation

• If the Overpass API is unreachable or returns an error, handle gracefully (e.g., return 500 with an error message).
• Validate that lat and lng are valid floats in the expected range (-90 to 90, -180 to 180). Return 400 if invalid.

7. Testing

• Demonstrate how to call the POST /webhook endpoint with sample coordinates (e.g., near the Eiffel Tower: 48.8584, 2.2945).
• Show how to retrieve the landmarks using GET /landmarks?lat=48.8584&lng=2.2945.
• Verify data is served from the cache after the first retrieval.

8. Submission

• Provide instructions in a README on how to install dependencies, run the application, and test the endpoints with curl or a REST client.
• Include the commands you used, for example:

Create or migrate the SQLite DB (if needed)

npm run db:migrate

Post some coordinates

curl -X POST -H "Content-Type: application/json" \
  -d '{"lat":48.8584,"lng":2.2945}' \
  http://localhost:3000/webhook

Retrieve the landmarks

curl "http://localhost:3000/landmarks?lat=48.8584&lng=2.2945"