How to create interruptable weapon charge using Behavior Tree

Hello,
I am modelling the AI of my NPCs using BTs. For one of my bosses (to say) I want to have like a super-weapon that can be interrupted while charging. What I mean is this:

  • The NPC charges the weapon for some time staying at a place
  • If the the charge is successful, the NPC fires
  • The ways to interrupt the charging are
  • if shot, the charge stops and the NPC plays a shot reaction
  • if hit, the charge stops and the NPC plays a hit reaction (note that the two reactions are different, although not cleared out exactly what)

My problem is that I don’t know how to make this interruption using the behavior trees :\ So any help are going to be much appreciated.