Weak Auras cast counter for Blackrock Barrage

[Vile 9]

I'm trying to make a reliable cast counter for our Mythic Oregorger interrupt rotation but my LUA skills are very lacking and I need some help. So far the trigger looks something like this:

function(event,source,spellName,_,_,_) 
    if event == "ENCOUNTER_START" then 
        castNum = 1
    else 
        if spellName == "Blackrock Barrage" and source == "boss1" then 
            if castNum == nil then 
                castNum = 1
            else
                castNum = castNum + 1
                if castNum == 6 then
                    castNum = 1
                end
                if castNum % 5 == 0 then 
                    return true 
                end
            end 
        end 
    end 
    return false 
end

 I haven't had the opportunity to try it yet so I'm not sure if that'll work the way I think it will. I'd like to make some changes however, and this is where I need some help.

 

Is there a way to trigger a castNum + 1 on Blackrock Barrage being interrupted/successfully cast rather than it starting being cast? If yes, how?

 

Is there a way to have it reset the counter whenever we hit phase 2? I'm thinking one could use either UNIT_AURA_REMOVED for the Blackrock Spines buff, UNIT_AURA_APPLIED for the Hungry buff (I think he gets some buff or other during p2? Not sure) or have his energy being depleted somehow triggering a reset. These are all ideas I don't know how to translate into custom code.

 

The general idea is to have this Weak Aura together with a simple cast bar WA that will only show his Blackrock Barrage cast as to avoid having trigger happy melee interrupt the wrong spell. I want the number 1 to show as soon as we start the encounter, the number 2 to show as soon as the first cast has been interrupted (or failed to be interrupted), to give every player in the interrupt rotation a heads up on their turn to interrupt. This would also help for when anyone in the rotation dies and their spot in the chain needs to be covered.

 

Obviously this shouldn't be necessary but could help simplifying the interrupt order.

 

Any help and/or suggestions are greatly appreciated.