Reflective Mirrors (#11677)

code/datums/observation/entered.dm

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+//	Observer Pattern Implementation: Entered
+//		Registration type: /atom
+//
+//		Raised when: An /atom/movable instance has entered an atom.
+//
+//		Arguments that the called proc should expect:
+//			/atom/entered: The atom that was entered
+//			/atom/movable/enterer: The instance that entered the atom
+//			/atom/old_loc: The atom the enterer came from
+//
+
+var/datum/observ/entered/entered_event = new()
+
+/datum/observ/entered
+	name = "Entered"
+	expected_type = /atom
+
+/*******************
+* Entered Handling *
+*******************/
+
+/atom/Entered(atom/movable/enterer, atom/old_loc)
+	..()
+	entered_event.raise_event(src, enterer, old_loc)

code/datums/observation/exited.dm

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+//	Observer Pattern Implementation: Exited
+//		Registration type: /atom
+//
+//		Raised when: An /atom/movable instance has exited an atom.
+//
+//		Arguments that the called proc should expect:
+//			/atom/entered: The atom that was exited from
+//			/atom/movable/exitee: The instance that exited the atom
+//			/atom/new_loc: The atom the exitee is now residing in
+//
+
+var/datum/observ/exited/exited_event = new()
+
+/datum/observ/exited
+	name = "Exited"
+	expected_type = /atom
+
+/******************
+* Exited Handling *
+******************/
+
+/atom/Exited(atom/movable/exitee, atom/new_loc)
+	. = ..()
+	exited_event.raise_event(src, exitee, new_loc)