Implement IRC client presence (with caveats)

[hifi]

It would look a lot better if everyone who are on a channel show up "online" rather than "unavailable". We can update the presence status to "offline" if we see a client quit but it's really a best effort as it's only visible to you if that happens on a channel you're in.

The very least we should set all users online that we know are currently on a channel. This can be flushed through a slow background queue.

[piegamesde]

I don't fully understand the description. Is it about bridging a user's presence to IRC or about other users' presence to Matrix? (Does IRC even have some presence-like features?)

[hifi]

Showing an IRC puppet online if we have a good guess they are like being on a channel with a Matrix user.

Them showing up as unavailable looks dull on Element so either force every puppet online or do best effort tracking from known events.

If an IRC user is not on any known channel and PMs someone we can set them online and if a PM to IRC user replies with "no such nick" we can set them offline. It isn't perfect but we could also do background checking with WHO if really wanted.

[piegamesde]

I'd say that explicit calls to check if users are online are a bit intrusive towards the server (imagine doing this for all people in a larger room). But a passive "the bridge has seen that persons in the last five minutes" would be good enough. Heck, even simply saying that all people in a room are online (if they weren't they'd left that room) would be fine for me.

[hifi]

Of course it doesn't need to do that for people that are in known rooms. It would only need to poll anyone in a DM without a common channel.

Though this is not a high priority feature, mostly just put it up that it should be implemented at some point.