The pistons have popped out of the caliper. For this you either need to get a rebuild kit and learn how to rebuild a caliper or purchase one that’s already been rebuilt and slap it on. Because good luck trying to put this back together as it is and have it not leak, seals are probably destroyed. Either the brakes pads/rotor was worn so thin the piston exceeded it’s travel and popped out, or the brake pedal was pressed while the caliper was off