feat: add function for getting possible new internship statuses based on current one

frontend/app/types/internship_status.ts

@@ -33,3 +33,20 @@ export function prettyInternshipStatus(status: InternshipStatus) {
             throw new Error("Unknown status");
     }
 }
+
+export function possibleNextStates(status: InternshipStatus) {
+    switch (status) {
+        case InternshipStatus.SUBMITTED:
+            return [InternshipStatus.CONFIRMED, InternshipStatus.DENIED];
+        case InternshipStatus.CONFIRMED:
+            return [InternshipStatus.SUBMITTED, InternshipStatus.DENIED, InternshipStatus.DEFENDED, InternshipStatus.NOT_DEFENDED];
+        case InternshipStatus.DENIED:
+            return [InternshipStatus.SUBMITTED, InternshipStatus.CONFIRMED];
+        case InternshipStatus.DEFENDED:
+            return [];
+        case InternshipStatus.NOT_DEFENDED:
+            return [];
+        default:
+            throw new Error("Unknown status");
+    }
+}