Rainbow - Backend Take-Home Assignment

Please create a private fork of this repo and complete the objectives.
Once you are finished, send us an email with a link to your private repo.

To Create A Private Fork

Clone the repository to your local machine

git clone git@github.com:rainbowmga/timetravel.git
cd timetravel

Create a new private repository on your GitHub account

https://github.com/new

Add your new private repo as a remote:

git remote rename origin upstream
git remote add origin https://github.com/YOUR_USERNAME/NEW_PRIVATE_REPO.git

Push the code to your new private repo:

git push -u origin master

To Run The Server

Compile and run the Go application:

cd timetravel
go run .

Test the server using the healthcheck endpoint:

curl -X POST http://localhost:8000/api/v1/health

You should see the following response:

{"ok":true}

The Assignment

A core part of any insurance platform is a reliable and auditable
record-keeping system. It must store all relevant data used to underwrite
policies. Policyholders periodically submit and update information about the
risks they want covered, such as their desired liability limits or changes to
their workforce. These changes can significantly affect the policy's risk
profile and, consequently, the premium.

The current codebase represents a very simplified version of this system, with:

GET /api/v1/record/{id} – retrieves a record (a simple JSON mapping of
strings to strings)
POST /api/v1/record/{id} – creates or updates a record

The Problem

Maintaining only the current state of each record is not enough. For
compliance and proper risk assessment, we must also understand how that state
evolved.

Consider the following example. A business buys a policy in January. In March,
they change their business hours, but they don't notify us until July. During
that four-month gap, we are unknowingly covering a risk that has changed.
Depending on the nature of the change, we may need to:

Retroactively adjust the premium
Or even void the policy if the change introduces unacceptable risk

To resolve this, we need a versioned, historical view of the data:

What did we know and when?
When did the change actually occur?

Objective 1: Persist Data with SQLite

Replace the in-memory storage backend with a persistent SQLite database. The
goal is to ensure that all record data is retained even if the server is shut
down and restarted.

Objective 2: Implement Time Travel Functionality

Introduce a “time travel” feature that allows querying the state of any record
at a specific point in time. This enables accurate reconstructions for
compliance, audits, and risk recalculations.

This objective is open-ended and may require significant changes across the
codebase. You'll introduce record versioning and history tracking.

Build out a new set of endpoints under /api/v2 with the following
functionality:

Retrieve records at specific versions (not just the latest)
Apply updates to the latest version while preserving history
List all available versions of a record
Ensure full backward compatibility: /api/v1 endpoints should continue to
work as-is, with no changes in behavior

Notes on the Assignment

You are free to use any tools, libraries, or frameworks you prefer — even building
the solution in a different programming language if desired.

We expect you to work on this task as if it was a normal project at work. So please write
your code in a way that fits your intuitive notion of operating within best practices.

We recommend making separate commits for each objective to help illustrate how you approached
and broke down the assignment. Don't hesitate to commit work that you later revise or remove
— it's valuable to see your process evolve over time.

Parts of this assignment are left intentionally ambiguous. How you resolve these
ambiguities will help us understand your decision-making process.

However, if you do have questions, don't hesitate to reach out!

FAQ

Can I use a different language?

Yes! We've had successful submissions in Python, Java, and others. Just make sure the
functionality replicates what's provided in the Go starter code.

Did you really end up implementing something like this at Rainbow?

Yes, but unfortunately it wasn't as simple as this in practice. For insurance a
number of requirements force us to maintain historic records across many
different object types. So in fact we implemented this across multiple different
tables in our database.

Reference -- The Current API

The current API consists of just two endpoints:

GET /api/v1/records/{id}
POST /api/v1/records/{id},

All ids must be positive integers.

`GET /api/v1/records/{id}`

Retrieves a record by its ID. If the record exists, the server returns it in
JSON format. If the record does not exist, an error message is returned.

✅ Successful Response Example

> GET /api/v1/records/2323 HTTP/1.1

< HTTP/1.1 200 OK
< Content-Type: application/json; charset=utf-8

{"id": 2323, "data": {"david": "hey", "davidx": "hey"}}

❌ Error Response Example

> GET /api/v1/records/32 HTTP/1.1

< HTTP/1.1 400 Bad Request
< Content-Type: application/json; charset=utf-8

{"error": "record of id 32 does not exist"}

`POST /api/v1/records/{id}`

Creates or updates a record at the specified ID.

If the record does not exist, it will be created.
If the record already exists, it will be updated.
Payload values must be a JSON object with string keys and values (or null).
Keys with null values will be deleted from the record.

✅ Create a Record

> POST /api/v1/records/1 HTTP/1.1
> Content-Type: application/json

{"hello": "world"}

< HTTP/1.1 200 OK
< Content-Type: application/json; charset=utf-8

{"id": 1, "data": {"hello": "world"}}

🔁 Update a Record

> POST /api/v1/records/1 HTTP/1.1
> Content-Type: application/json

{"hello": "world 2", "status": "ok"}

< HTTP/1.1 200 OK
< Content-Type: application/json; charset=utf-8

{"id": 1, "data": {"hello": "world 2", "status": "ok"}}

❌ Delete a field from a record

> POST /api/v1/records/1 HTTP/1.1
> Content-Type: application/json

{"hello": null}

< HTTP/1.1 200 OK
< Content-Type: application/json; charset=utf-8

{"id": 1, "data": {"status": "ok"}}

markiskorova/timetravel