feat: limit possible new internship states for employers

frontend/app/types/internship_status.ts

@@ -1,3 +1,4 @@
+import { Role } from "./role";
 import type { User } from "./user";
 
 export interface InternshipStatusData {
@@ -34,13 +35,25 @@ export function prettyInternshipStatus(status: InternshipStatus) {
     }
 }
 
-export function possibleNextStates(status: InternshipStatus) {
+export function possibleNextStates(status: InternshipStatus, user_role: Role) {
     switch (status) {
         case InternshipStatus.SUBMITTED:
+            if (user_role === Role.EMPLOYER) {
+                return [];
+            }
+
             return [InternshipStatus.CONFIRMED, InternshipStatus.DENIED];
         case InternshipStatus.CONFIRMED:
+            if (user_role === Role.EMPLOYER) {
+                return [InternshipStatus.DENIED];
+            }
+
             return [InternshipStatus.SUBMITTED, InternshipStatus.DENIED, InternshipStatus.DEFENDED, InternshipStatus.NOT_DEFENDED];
         case InternshipStatus.DENIED:
+            if (user_role === Role.EMPLOYER) {
+                return [InternshipStatus.CONFIRMED];
+            }
+
             return [InternshipStatus.SUBMITTED, InternshipStatus.CONFIRMED];
         case InternshipStatus.DEFENDED:
             return [];