Refresh client hourly when inactive

[StachuDotNet]

Changelog:

Editor
- refresh the editor when it is outdated and inactive

How this works:

• appsupport.js listens for changes in whether the page is in focus or not, with windowFocusChange
• upon change of hidden/visible, it sends a message to a BrowserSubscription in ReScript land, which in turn triggers a PageVisibilityChange Msg
• that triggers a PageVisibilityChange Msg, which results in an update to a pageVisibility field in our main model
  • new: the 'hidden' variant of PageVisibility now has a since field in it, which is used to track how long it's been since a page became hidden
• separately, a timer runs every minute, triggering a CheckIfClientIsOutdated Msg; that results in an API call being made to a new endpoint in dark-editor, made possible by Add DarkInternal::serverBuildHash fn that returns the git hash of the server's current deploy #4649:
  
• when the result of that API (the hash) is returned, we assess a few variables, and refresh the page if all are true:
  • the client hash and the server hash don't match (i.e. the client is out of date)
  • the page is 'safe to refresh'[1]
  • the page is not currently in focus, and has been 'hidden' for at least an hour

[1] later, we can/should expand this criteria - currently, only the Architecture and FocusedPackageManagerFn pages are considered safely refreshable

I ran into some confusion when trying to tunnel my static assets in prod, so wrote some external docs in darklang/docs, and referenced those in the relevant portion of the Contributor settings.

[pbiggar]

I think we should get a little bit better logic in here:

• ensure we'll only refresh when there's a new client
• ensure we won't do it if the user is currently active (not hidden)

[StachuDotNet]

As of #4649 and a tiny HTTP handler, https://dark-editor.builtwithdark.com/latest-backend-build-hash is now available.

Given that, and this conversation, my current plan for this is:

• (rip out the current commits in favor of this new plan)
• store a new field in our app state, lastActive, representing when the page was last active/visible
• add a timer every minute that checks if the tab is active.
  • If active, set lastActive to 'now'.
  • If inactive, check if it's been an hour since lastActive.
    • if it has been at least an hour, fire off a process (event) to:
      • query that new endpoint for the most recent hash
      • if the hashes differ and the page is 'refreshable', refresh

[StachuDotNet]

My local testing so far has been to raise the RefreshClientIfOutdated Msg with a known-incorrect build hash. I suppose the next step, to better test, will be to set up a tunnel.

[pbiggar]

Looks pretty good.

However, I think the ordering is wrong, leading it to do the API call every minute instead of every hour.

What it does:

• each minute check if there's a new client
• then checks if it's safe to update to it

What it should do:

• check if we're in a position to update (eg it's been an hour)
• then check if there is an update

[StachuDotNet]

Updated - do you mean like this?

[pbiggar]

Perfect!