Target macro help

Hello guys, i was trying to make a very specific macro, which i can't find an example of online, or wrap my head around making one myself with the conditionals and stuff, basically, i want to have a macro that casts at my focus' target if my current target is invalid in any way, meaning me having no target, friendly, or a dead target

which spell?

Btw this should work:
/cast [@target,harm,nodead,exists] SPELLNAME
/cast [@focus] SPELLNAME

Edit:
I guess this is the same:
/cast [@target,harm,nodead,exists] [@focus] SPELLNAME

Thanks, I'm gonna give it a try