How to queue an issued order

[MN Lahmar]

Hello guys, i wanna make a trigger where my Unit gets attacked it'll cast Firebolt on the attacker.
But, my Unit has flamestrike which requires 2sec of casting time. In those 2 sec if my unit gets attacked it'll be ordered immediately to cast firebolt on the attacker which will cancel the casting of flamestrike.
I wanna make a trigger where the issued order (cast firebolt on attacker) will be queued.

 

[ZiBitheWand3r3r]

nothing