Ceiling leaked need guidance on next steps!

Hi please help point me in a direction on where to go to next!! Last night I took a bath in the upstairs bathroom of my house and my chandelier fixture below me started leaking!! In the first pic I put an arrow to where the water leaked from. It wasn’t coming from the outer circle of the part that’s attached from the wall, but instead from like the hanging pole part if that makes sense? My roommate was sleeping on the couch downstairs and said it was POURING to the point it woke him up and our whole dining room was flooded. So referring to pic #2, this is what I think happened.. when I got in the tub, the water level rose and I heard water go down that drain in the tub. Apparently it was screwed in upside down (the opening was facing down), and when I was trying to figure out what happened with the water, I unscrewed that to put it right side up and noticed that when facing the hole upwards it had a path down what looks like a specific pipe.. so what I’m thinking is my bath water missed that pipe and went straight between my upstairs floor to downstairs roof.. I really hope that makes sense but my question now is what do I do next??? Who do I call?? I already put duct tape on the light switch for the chandelier so no one uses it downstairs.. but anyways I’m concerned of the ceiling being filled with water and eventually down the road it turning to mold.. so who do I call first?? A drywall person?? An electrician?? The former president??? I seriously have zero idea on how to handle this at all and I REALLY need some advice on what I need to do.. for context my roommate has NO IDEA what to do either, and he desperately asked for help on asking anybody for advice on where to go from here.. please help us out and thank you soooooo much in advance!!!