Lichess client / server architechture

[ky28059]

Hi!

Sorry if this is not the right place to ask this, but I was wondering if there's an article / post somewhere detailing how the Lichess client uses the API to display the information that it does? Some friends and I want to make our own spinoff Lichess-inspired site for other games like ultimate tic tac toe and similar, and while it will probably be a fun hobby project we're concerned with doing it "right".

I've tried reading the repository wiki and searching past discussions and blogs, but I haven't really found anything that matches what I'm looking for; the source code is also a bit confusing to me as I haven't worked with Scala before. I've read through the API docs, and while I think I can infer how live games are handled, I guess my questions are:

• I know there's a websocket connection, but what exactly is sent over it? Is it just so the client can send heartbeats to let Lichess know they're online?
• When a game starts, how is the "your record against this player is ..." section at the bottom handled? Fetching all games and filtering by ones against a certain player seems expensive.
• How are statistics like "you are better than x% of ... players" handled? Fetching all users and mapping over all of them seems expensive.
• How are the rating charts on the profile pages generated? Sending every data point seems expensive, especially when theres one point per day per variant played on that day.
• When reading some of the socket code, I noticed references to lag handling; how exactly does this work (both client and server side)? Is the clock purely client-side as well?

Thanks in advance for your time!