Nostalrius Begins - Quality wow vanilla realm (1.12)

Looking for a macro that will allow me to heal my target's target if my target is an enemy and his target is an ally. For example if i am in a battleground and I am targetting an enemy warrior who is targetting (and attacking) a friendly hunter, I want to be able to maintain my target on the warrior, cast my heal, and have the heal go to the hunter. I had a macro like this in vanilla, was wondering if anyone got it working here. Please help thank you

try

/run if UnitCanAttack("player","target") and not UnitCanAttack("player","targettarget") then TargetUnit("targettarget") CastSpellByName("Heal") TargetLastTarget() end