feat: converted UserManager to singleton object

Server/src/main/java/uulm/teamname/marvelous/server/netconnector/UserManager.java

@@ -20,6 +20,19 @@ import java.util.*;
  */
 public class UserManager {
 
+    private static UserManager instance;
+
+    /**
+     * @return the current instance of the UserManager
+     */
+    public static UserManager getInstance() {
+        if (instance == null) {
+            Logger.debug("No instance of UserManager found. Creating new instance...");
+            instance = new UserManager();
+        }
+        return instance;
+    }
+
     /** A set of users that aren't assigned to lobbies or character selection yet */
     private final HashSet<WebSocket> newUsers;
 
@@ -45,7 +58,7 @@ public class UserManager {
     private final JSON json;
 
     /** Constructs a new, empty UserManager */
-    public UserManager() {
+    private UserManager() {
         this.newUsers = new HashSet<>();
         this.readyToConnect = new HashMap<>();
         this.readyToReconnect = new HashMap<>();
@@ -55,7 +68,7 @@ public class UserManager {
     }
 
     /** Called on a new WebSocket connection. Places the WebSocket and its ResourceDescriptor in a HashMap. */
-    public void connectUser(WebSocket conn) {
+    void connectUser(WebSocket conn) {
         newUsers.add(conn);
     }
 
@@ -66,7 +79,7 @@ public class UserManager {
      * @param conn is the {@link WebSocket} that sent the message
      * @param message is the {@link String} sent by the connection
      */
-    public void messageReceived(WebSocket conn, String message) {
+    void messageReceived(WebSocket conn, String message) {
         Logger.trace("Parsing message...");
         var parsedMessageOptional = json.parse(message);
         if (parsedMessageOptional.isEmpty()) {
@@ -148,8 +161,13 @@ public class UserManager {
             var participantToRestore = activeParticipants.get(clientID);
 
             participantToRestore.setConnection(conn);
-            readyToReconnect.remove(conn);
-            inGame.put(conn, participantToRestore);
+
+            synchronized (readyToReconnect) {
+                readyToReconnect.remove(conn);
+            }
+            synchronized (inGame) {
+                inGame.put(conn, participantToRestore);
+            }
             // activeParticipants remains the same, as no players have been removed from the game
         } else {
             Logger.debug(
@@ -157,8 +175,13 @@ public class UserManager {
                     conn);
 
             var clientID = readyToReconnect.get(conn);
-            readyToConnect.put(conn, clientID);
-            readyToReconnect.remove(conn);
+
+            synchronized (readyToConnect) {
+                readyToConnect.put(conn, clientID);
+            }
+            synchronized (readyToReconnect) {
+                readyToReconnect.remove(conn);
+            }
         }
     }
 
@@ -172,6 +195,16 @@ public class UserManager {
     void relayRequestMessage(Participant conn, RequestMessage message) {
     }
 
+    void disconnectUser(WebSocket conn, boolean closedByRemote) {
+        // TODO: notify clients and such if the connection was in fact closed by the remote. Also remove participant
+        synchronized (newUsers) {
+            newUsers.remove(conn);
+        }
+        synchronized (inGame) {
+            inGame.remove(conn);
+        }
+    }
+
     public void sendMessage(WebSocket conn, BasicMessage message) {
         var jsonRepresentingMessage = json.stringify(message);
         if (jsonRepresentingMessage.isEmpty()) {
@@ -189,16 +222,6 @@ public class UserManager {
         sendMessage(conn, errorMessage);
     }
 
-    public void disconnectUser(WebSocket conn, boolean closedByRemote) {
-        // TODO: notify clients and such if the connection was in fact closed by the remote. Also remove participant
-        synchronized (newUsers) {
-            newUsers.remove(conn);
-        }
-        synchronized (inGame) {
-            inGame.remove(conn);
-        }
-    }
-
     public boolean isUserConnected(WebSocket user) {
         return newUsers.contains(user) ||
                 readyToReconnect.containsKey(user) ||