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:

Accepts coordinates via a protected webhook (POST endpoint).
Performs a transformation on the coordinates.
Calls the Overpass API to get nearby landmarks.
Saves these landmarks in a SQLite database.
Caches the results.
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"

superrare/snr-bck-eng-code-challenge

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