Three buffs can occur from "Flask of the North"  (47 sp, 80 ap OR 40 str).
Priest/Mage/WL get Spell Power
Rogue/Hunter get Attack Power
DeathKnigts/Warrior get Strenght

But Druid/Paladin/Shaman get Spell Power OR Attack Power / Strengh

So I want to rebuff until the right buff comes up (47 sp, 80 ap OR 40 str).
Two possible ways:
1) Smart per active Talents
2) Dumb per Checkbox (needs Class recognizing too)

This are the IDs of the spells:
67016 "Flask of the North" SP
67017 "Flask of the North" AP
67018 "Flask of the North" Str

If the buff is up, check for its ID (Spell Power). :
local _, _, _, _, _, _, _, _, _, _, fotn = UnitBuff("player", flask_buff_index);
-- ckeck for hybrid class in spellpower spec
if  ((druid and (moonkin or tree)) or (shaman and (resto or ele)) or (paladin and holy)) then
     -- check for wrong spell_id
     if (fotn ~= spellpower_id) then reuse flask;end;
else
     -- check rest of hybrid class specs for wrong spell_id
     if ((druid or shaman or paladin) and (fotn == spellpower_id)) then reuse flask;end;
end;