Implement listener for PaperMC's AsyncPlayerSendCommandsEvent

[lokka30]

Context

BlackWidow's command blocking module requires a listener to review and manage command suggestions that the server/proxy implementation wants to send to players.

The Bukkit API has PlayerCommandSendEvent, which works great, with one major caveat: the server calls it synchronously.

On PaperMC server implementations, we can instead listen to AsyncPlayerSendCommandsEvent.html, which is (usually - but not guaranteed to.. anyways,) be called asynchronously by the server.

Challenges

This event seems to not be well-known and thus isn't utilized often in plugins. With rather limited documentation on the event and (very) poor knowledge with Brigadier, I'm ill-equipped as of posting this issue to tackle this.

To expand on the Brigadier challenge: the Paper event presents a Brigadier command node - a more contemporary API choice, which is great, but requires a new style of parser. Furthermore, instead of rather simple lists of arguments suggestions, we get a root command tree which needs to be managed entirely differently than just simply removing offending strings from a mutable list (Bukkit API / legacy approach).

That being said, I think it may be worth going through the server software source code and checking how PlayerCommandSendEvent adapts Brigadier commands into standard Bukkit command strings. Or, there is a better way to do it, research to be done...

Goals

• Detect when PaperMC (or derivative) server software implementation is running.
• To be completed together:
  • Disable listener PlayerCommandSendListener when PaperMC is used.
  • Implement AsyncPlayerSendCommandsListener.
  • Enable AsyncPlayerSendCommandsListener when PaperMC is used.
• Test it works.
  • Detecting suggestions (can see them coming in)
  • Managing suggestions (removing those which are blocked for the player)
  • Listener handles the event asynchronously only
  • Not being accessed on SpigotMC servers (i.e., no Paper API present; NOT PaperMC or derivatives).

Other

I plan to work on this. If you have worked with this event before, please feel free to let me know below, I would love some assistance :)