Steve Howell 14396c3e32 presence: Prep for upcoming changes to server data. ...

In the next commit we're going to change what the
server sends for the following:

    - page_params
    - server responses to /json/users/me/presence

We will **not** yet be changing the format of the data
that we get in events when users update their presence.

It's also just a bit in flux what our final formats
will be for various presence payloads, and different
optimizations may lead us to use different data
structures in different payloads.

So for now we decouple these two things:

    raw_info: this is intended to represent a
        snapshot of the latest data from the
        server, including some data like
        timestamps that are only used
        in downstream calculations and not
        user-facing

    exports.presence_info: this is calculated
        info for modules like buddy_data that
        just need to know active vs. idle and
        last_active_date

Another change that happens here is we rename
set_info_for_user to update_info_for_event,
which just makes it clear that the function
expects data in the "event" format (as opposed
to the format for page_params or server
responses).

As of now keeping the intermediate raw_info data
around feels slightly awkward, because we just
immediately calculate presence_info for any kind
of update.  This may be sorta surprising if you
just skim the code and see the various timeout
constants.  You would think we might be automatically
expiring "active" statuses in the client due to
the simple passage of time, but in fact the precise
places we do this are all triggered by new data
from the server and we re-calculate statuses
immediately.

(There are indirect ways that clients
have timing logic, since they ask the
server for new data at various intervals, but a
smarter client could simply expire users on its
own, or at least with a more efficient transfer
of info between it and the server. One of
the thing that complicates client-side logic
is that server and client clocks may be out
of sync.  Also, it's not inherently super expensive
to get updates from the server.)

2020-02-10 14:37:44 -08:00

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