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

@@ -12,7 +12,7 @@ import java.util.concurrent.ConcurrentLinkedQueue;
 /** Represents an authenticated user on the server. */
 public class User {
     private final UserId id;
-    private final String name;
+    private String name;
     private SessionId sessionId;
     private Instant disconnectedAt;
     private final Queue<Message> messages;
@@ -46,10 +46,21 @@ public class User {
      *
      * @return the user name
      */
-    public String getName() {
+    public synchronized String getName() {
         return name;
     }
 
+    /**
+     * Sets a new display name for this user. Thread-safe; callers must ensure the
+     * registry is
+     * updated to maintain uniqueness when needed.
+     *
+     * @param newName the new display name
+     */
+    public synchronized void setName(String newName) {
+        this.name = newName;
+    }
+
     /**
      * Returns the session currently associated with this user, if any.
      *
@@ -62,7 +73,8 @@ public class User {
     /**
      * Returns the time at which this user disconnected, if applicable.
      *
-     * @return an Optional containing the disconnect timestamp, or empty if connected
+     * @return an Optional containing the disconnect timestamp, or empty if
+     *         connected
      */
     public Optional<Instant> getDisconnectedAt() {
         return Optional.ofNullable(disconnectedAt);
@@ -78,7 +90,10 @@ public class User {
         this.disconnectedAt = null;
     }
 
-    /** Marks this user as disconnected by clearing the session and recording the timestamp. */
+    /**
+     * Marks this user as disconnected by clearing the session and recording the
+     * timestamp.
+     */
     public void markDisconnected() {
         this.sessionId = null;
         this.disconnectedAt = Instant.now();

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

@@ -1,10 +1,12 @@
 package ch.unibas.dmi.dbis.cs108.casono.server.domain.user;
 
 import ch.unibas.dmi.dbis.cs108.casono.server.network.sessions.SessionId;
+import java.util.concurrent.atomic.AtomicInteger;
 
 /** Creates new users, resolving name conflicts automatically. */
 public class UserFactory {
     private final UserRegistry registry;
+    private final AtomicInteger anonymousCounter = new AtomicInteger(1);
 
     /**
      * Creates a new UserFactory backed by the given registry.
@@ -16,15 +18,30 @@ public class UserFactory {
     }
 
     /**
-     * Creates and registers a new user with the given name and session. If the name is already
+     * Creates and registers a new user with the given name and session. If the name
-     * taken, a numeric suffix is appended and incremented until a free name is found (e.g.
+     * is already
-     * Lars_001, Lars_002, ...).
+     * taken, a numeric suffix is appended and incremented until a free name is
+     * found (e.g.
+     * Lars_001, Lars_002, ...). If the desiredName is null or empty, an automatic
+     * name of the
+     * form "playerN" is assigned, incrementing N until a free name is found.
      *
      * @param desiredName the preferred display name
      * @param sessionId   the session to associate with the new user
      * @return the newly created and registered user
      */
     public User create(String desiredName, SessionId sessionId) {
+        if (desiredName == null || desiredName.isBlank()) {
+            // assign playerN names for anonymous logins
+            while (true) {
+                String candidate = "player" + anonymousCounter.getAndIncrement();
+                var result = registry.registerIfAvailable(candidate, sessionId);
+                if (result.isPresent()) {
+                    return result.get();
+                }
+            }
+        }
+
         var result = registry.registerIfAvailable(desiredName, sessionId);
         if (result.isPresent()) {
             return result.get();

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

@@ -12,7 +12,8 @@ public class UserRegistry {
     private final ConcurrentHashMap<SessionId, User> bySessionId = new ConcurrentHashMap<>();
 
     /**
-     * Attempts to register a user under the given name atomically. Returns the registered user, or
+     * Attempts to register a user under the given name atomically. Returns the
+     * registered user, or
      * empty if the name is already taken.
      *
      * @param name      the desired display name
@@ -92,8 +93,10 @@ public class UserRegistry {
     }
 
     /**
-     * Removes the user with the given ID, but only if they are still disconnected. This prevents
+     * Removes the user with the given ID, but only if they are still disconnected.
-     * removing a user who has reconnected between the cleanup job's check and its removal call.
+     * This prevents
+     * removing a user who has reconnected between the cleanup job's check and its
+     * removal call.
      *
      * @param userId the ID of the user to remove
      */
@@ -112,7 +115,8 @@ public class UserRegistry {
     }
 
     /**
-     * Marks the user associated with the given session as disconnected, clearing the session
+     * Marks the user associated with the given session as disconnected, clearing
+     * the session
      * association and recording the disconnect timestamp.
      *
      * @param sessionId the session ID of the disconnected client
@@ -127,7 +131,8 @@ public class UserRegistry {
     }
 
     /**
-     * Reassociates a user with a new session, effectively restoring them after a reconnect.
+     * Reassociates a user with a new session, effectively restoring them after a
+     * reconnect.
      *
      * @param userId    the ID of the user to reconnect
      * @param sessionId the new session ID
@@ -148,7 +153,8 @@ public class UserRegistry {
      * Looks up a user by their {@link SessionId}.
      *
      * @param sessionId the SessionId to look up
-     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     * @return an Optional containing the {@link User}, or empty if no user is
+     *         associated with this
      *         SessionId
      */
     public Optional<User> getBySessionId(SessionId sessionId) {
@@ -159,7 +165,8 @@ public class UserRegistry {
      * Looks up a user by their {@link UserId}.
      *
      * @param userId the UserId to look up
-     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     * @return an Optional containing the {@link User}, or empty if no user is
+     *         associated with this
      *         UserId
      */
     public Optional<User> getByUserId(UserId userId) {
@@ -170,7 +177,8 @@ public class UserRegistry {
      * Looks up a user by their username.
      *
      * @param username the username to look up
-     * @return an Optional containing the {@link User}, or empty if no user is associated with this
+     * @return an Optional containing the {@link User}, or empty if no user is
+     *         associated with this
      *         username
      */
     public Optional<User> getByUsername(String username) {
@@ -185,4 +193,31 @@ public class UserRegistry {
     public Collection<User> getAllUsers() {
         return byId.values();
     }
+
+    /**
+     * Attempts to change the username of an existing user. Ensures the new name is
+     * not already
+     * taken and updates internal indices atomically.
+     *
+     * @param userId  the id of the user to rename
+     * @param newName the desired new name
+     * @return true if the rename succeeded, false if the name was already taken or
+     *         user not found
+     */
+    public synchronized boolean changeUsername(UserId userId, String newName) {
+        User user = byId.get(userId);
+        if (user == null) {
+            return false;
+        }
+
+        if (byName.containsKey(newName)) {
+            return false;
+        }
+
+        // remove old mapping and put new mapping
+        byName.remove(user.getName());
+        user.setName(newName);
+        byName.put(newName, user);
+        return true;
+    }
 }