Camille passive

How exactly does her shield calculate "Primary damage type" because if it is based around kit (say, for instance Janna) is would give her a magic damage shield, but if you were to give that Janna a BF Sword then she would more than likely do more physical damage, or if there is a champion with a sheen/ hextech with an on hit passive how would that be calculated in? What about hybrid champions like Corki? There is a lot about this new champ that I like, but her passive seems like it wouldn't be the most reasonably done ability, given that most champions could build something off meta that they don't scale with and Camille passive sounds like it would just be buggy.