Add: Extend UserRegistry to remove Disconnected User, reassign User to new session and get all users

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/domain/user/UserRegistry.java

@@ -1,6 +1,8 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.domain.user;
 
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionId;
+
+import java.util.Collection;
 import java.util.Iterator;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
@@ -49,4 +51,29 @@ public class UserRegistry {
         }
     }
 
-}
+    public synchronized boolean removeIfStillDisconnected(UserId userId) {
+        User user = byId.get(userId);
+        if (user == null) {
+            return false;
+        }
+
+        if (user.getSessionId().isPresent()) {
+            return false;
+        }
+
+        byId.remove(user.getId());
+        return true;
+    }
+
+    public synchronized Optional<User> reassignSession(UserId userId, SessionId sessionId) {
+        User user = byId.get(userId);
+        if (user == null) return Optional.empty();
+ 
+        user.reassignSession(sessionId);
+        return Optional.of(user);
+    }
+
+    public Collection<User> getAllUsers() {
+        return byId.values();
+    }
+}