• An API key should be provided in the Dockerfile to enable API calls. Although I have provided mine, I cannot guarantee its functionality as I could have reach usage limit (Alphavantage).
• Please subscribe to a currency supported by the forex API.

Nestpaths are not considered due to the potential for excessive data in documents, depending on timeserie granularity and the application's age. Once a significant number of time series points are reached, considering pagination for historical points will be necessary. Modeling time series points as a relation to currencies simplifies this process.

Deleting a time series point will not remove the relation from a currency because it is expected that they will be updated rather than removed, but it can be implemented.

Time series points are modeled as a relation of currencies. Given the requirement to return only subscribed currencies, I chose to use the existing endpoint [GET] /api/currencies with an additional history query parameter to include or exclude historical points of subscribed currencies. To provide immediate access to data upon subscription, I modified the [PUT] /api/currency/:code endpoint to also return data points.

Even though currency data is only relevant to a single component and does not need to be persisted after the component is destroyed, I chose to centralize all data in a service. This data could have easily been kept in the currency-list component.

• The FOREX API does not have an endpoint to return supported currencies, which means you might subscribe to a currency that will never have data.
• The FOREX API has a call rate limit, so a lower frequency for the cron job should be considered.

• To prevent the user from subscribing to unsupported currencies we could:

1. Allow the user to subscribe only to currencies that are in database.
2. Use a queue to reschedule events.
3. Choose a better API than forex.

• Improve responsiveness