Stats endpoint

[swantzter]

I'm thinking an endpoint at

GET /libera/stats which returns either of the following based on the accept header:

application/json: A json payload with: currently receiving per month, received YTD
text/html: The same thing but as a cute little ifram friendly widget we can put on libera.chat without client JS
or do we do the latter with image/svg+xml maybe?

Most likely the thing to do here is:

1. Retrieve the current balance of account 3993 from spiris using /v2/accountbalances/{accountNumber}/{date} which will tell you how much has been donated YTD
2. Retrieve all currently active subscriptions from stripe tagged with the appropriate libera donations tag, and sum their amount per momth in SEK, likely using the preview stripe FX Quotes API to get the conversion rates, this gives a figure for money / month
3. Can we receive the current sum from Liberapay? I don't think we can in a good way, but for the html version we might be able to use one of the widgets, like
4. Cache these values in memory for 24 hours or something like that, also utilise HTTP cache headers to cache it upstream
5. Add cors for the endpoint to allow getting the data via JS

[swantzter]

A way to register a yearly goal (maybe just a config var via the env) would also be nice to allow rendering a progress bar

[swantzter]

Thinking about it some more a html version might be better than an svg for a11y (not ont of my core areas, unfortunately).

Also, it would be nice to maybe render a progress bar in two colours:

1. As a baseline 100% of the progress bar is the budget goal set for the year
2. Color+pattern A represents collected donations for the fiscal year (both one-time and recurring)
3. Color+Pattern B represents projected recurring donations for the remainder of the year

This would probably also be written out below, like
2026 Goal: 13 000 SEK
Donations so far 2026: 5 000 SEK
Projected recurring donations 2026: 7 000 SEK
Missing to hit our goal: 1 000 SEK

Perhaps there'd be some value in accounting for currency volatility and donation cancellations by subtracting 10% from expected recurring, or something, not sure where that number should be (yet)