Improve the way player uuid data is saved/stored. Add a warning message to catch ip forwarding issues

common/src/main/java/me/lucko/luckperms/common/api/delegates/model/ApiStorage.java

@@ -254,7 +254,7 @@ public class ApiStorage implements me.lucko.luckperms.api.Storage {
     public CompletableFuture<Boolean> saveUUIDData(@Nonnull String username, @Nonnull UUID uuid) {
         Objects.requireNonNull(username, "username");
         Objects.requireNonNull(uuid, "uuid");
-        return this.handle.noBuffer().saveUUIDData(uuid, checkUsername(username))
+        return this.handle.noBuffer().savePlayerData(uuid, checkUsername(username))
                 .thenApply(r -> true)
                 .exceptionally(consumeExceptionToFalse());
     }
@@ -263,13 +263,13 @@ public class ApiStorage implements me.lucko.luckperms.api.Storage {
     @Override
     public CompletableFuture<UUID> getUUID(@Nonnull String username) {
         Objects.requireNonNull(username, "username");
-        return this.handle.noBuffer().getUUID(checkUsername(username));
+        return this.handle.noBuffer().getPlayerUuid(checkUsername(username));
     }
 
     @Nonnull
     @Override
     public CompletableFuture<String> getName(@Nonnull UUID uuid) {
         Objects.requireNonNull(uuid, "uuid");
-        return this.handle.noBuffer().getName(uuid);
+        return this.handle.noBuffer().getPlayerName(uuid);
     }
 }

common/src/main/java/me/lucko/luckperms/common/commands/group/GroupListMembers.java

@@ -92,7 +92,7 @@ public class GroupListMembers extends SubCommand<Group> {
         if (!matchedUsers.isEmpty()) {
             LoadingCache<UUID, String> uuidLookups = Caffeine.newBuilder()
                     .build(u -> {
-                        String s = plugin.getStorage().getName(u).join();
+                        String s = plugin.getStorage().getPlayerName(u).join();
                         if (s == null || s.isEmpty() || s.equals("null")) {
                             s = u.toString();
                         }

common/src/main/java/me/lucko/luckperms/common/commands/log/LogRecent.java

@@ -86,7 +86,7 @@ public class LogRecent extends SubCommand<Log> {
                 }
             }
 
-            uuid = plugin.getStorage().getUUID(target.toLowerCase()).join();
+            uuid = plugin.getStorage().getPlayerUuid(target.toLowerCase()).join();
             if (uuid == null) {
                 if (!plugin.getConfiguration().get(ConfigKeys.USE_SERVER_UUID_CACHE)) {
                     Message.USER_NOT_FOUND.send(sender, target);

common/src/main/java/me/lucko/luckperms/common/commands/log/LogUserHistory.java

@@ -81,7 +81,7 @@ public class LogUserHistory extends SubCommand<Log> {
                 }
             }
 
-            uuid = plugin.getStorage().getUUID(target.toLowerCase()).join();
+            uuid = plugin.getStorage().getPlayerUuid(target.toLowerCase()).join();
             if (uuid == null) {
                 if (!plugin.getConfiguration().get(ConfigKeys.USE_SERVER_UUID_CACHE)) {
                     Message.USER_NOT_FOUND.send(sender, target);

common/src/main/java/me/lucko/luckperms/common/commands/misc/SearchCommand.java

@@ -86,7 +86,7 @@ public class SearchCommand extends SingleCommand {
         if (!matchedUsers.isEmpty()) {
             LoadingCache<UUID, String> uuidLookups = Caffeine.newBuilder()
                     .build(u -> {
-                        String s = plugin.getStorage().getName(u).join();
+                        String s = plugin.getStorage().getPlayerName(u).join();
                         if (s == null || s.isEmpty() || s.equals("null")) {
                             s = u.toString();
                         }

common/src/main/java/me/lucko/luckperms/common/commands/user/UserClone.java

@@ -73,7 +73,7 @@ public class UserClone extends SubCommand<User> {
                 }
             }
 
-            uuid = plugin.getStorage().getUUID(target.toLowerCase()).join();
+            uuid = plugin.getStorage().getPlayerUuid(target.toLowerCase()).join();
             if (uuid == null) {
                 if (!plugin.getConfiguration().get(ConfigKeys.USE_SERVER_UUID_CACHE)) {
                     Message.USER_NOT_FOUND.send(sender, target);

common/src/main/java/me/lucko/luckperms/common/commands/user/UserInfo.java

@@ -67,6 +67,7 @@ public class UserInfo extends SubCommand<User> {
         Message.USER_INFO_GENERAL.send(sender,
                 user.getName().orElse("Unknown"),
                 user.getUuid(),
+                user.getUuid().version() == 4 ? "&2mojang" : "&8offline",
                 status.asString(plugin.getLocaleManager()),
                 user.getPrimaryGroup().getValue()
         );

common/src/main/java/me/lucko/luckperms/common/commands/user/UserMainCommand.java

@@ -96,7 +96,7 @@ public class UserMainCommand extends MainCommand<User, UserIdentifier> {
                 }
             }
 
-            uuid = plugin.getStorage().getUUID(target.toLowerCase()).join();
+            uuid = plugin.getStorage().getPlayerUuid(target.toLowerCase()).join();
             if (uuid == null) {
                 if (!plugin.getConfiguration().get(ConfigKeys.USE_SERVER_UUID_CACHE)) {
                     Message.USER_NOT_FOUND.send(sender, target);
@@ -111,7 +111,7 @@ public class UserMainCommand extends MainCommand<User, UserIdentifier> {
             }
         }
 
-        String name = plugin.getStorage().getName(uuid).join();
+        String name = plugin.getStorage().getPlayerName(uuid).join();
         return UserIdentifier.of(uuid, name);
     }
 

common/src/main/java/me/lucko/luckperms/common/event/EventFactory.java

@@ -72,8 +72,8 @@ import me.lucko.luckperms.common.event.impl.EventUserFirstLogin;
 import me.lucko.luckperms.common.event.impl.EventUserLoad;
 import me.lucko.luckperms.common.event.impl.EventUserLoginProcess;
 import me.lucko.luckperms.common.event.impl.EventUserPromote;
-import me.lucko.luckperms.common.event.model.EntitySender;
+import me.lucko.luckperms.common.event.model.EntitySourceImpl;
-import me.lucko.luckperms.common.event.model.SourceEntity;
+import me.lucko.luckperms.common.event.model.SenderEntity;
 import me.lucko.luckperms.common.model.Group;
 import me.lucko.luckperms.common.model.PermissionHolder;
 import me.lucko.luckperms.common.model.Track;
@@ -268,12 +268,12 @@ public final class EventFactory {
     }
 
     public void handleUserDemote(User user, Track track, String from, String to, Sender source) {
-        EventUserDemote event = new EventUserDemote(track.getApiDelegate(), new ApiUser(user), from, to, new SourceEntity(new EntitySender(source)));
+        EventUserDemote event = new EventUserDemote(track.getApiDelegate(), new ApiUser(user), from, to, new EntitySourceImpl(new SenderEntity(source)));
         fireEventAsync(event);
     }
 
     public void handleUserPromote(User user, Track track, String from, String to, Sender source) {
-        EventUserPromote event = new EventUserPromote(track.getApiDelegate(), new ApiUser(user), from, to, new SourceEntity(new EntitySender(source)));
+        EventUserPromote event = new EventUserPromote(track.getApiDelegate(), new ApiUser(user), from, to, new EntitySourceImpl(new SenderEntity(source)));
         fireEventAsync(event);
     }
 

common/src/main/java/me/lucko/luckperms/common/event/impl/EventLogNotify.java

@@ -29,7 +29,7 @@ import me.lucko.luckperms.api.Entity;
 import me.lucko.luckperms.api.LogEntry;
 import me.lucko.luckperms.api.event.log.LogNotifyEvent;
 import me.lucko.luckperms.common.event.AbstractEvent;
-import me.lucko.luckperms.common.event.model.EntitySender;
+import me.lucko.luckperms.common.event.model.SenderEntity;
 import me.lucko.luckperms.common.sender.Sender;
 
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -56,7 +56,7 @@ public class EventLogNotify extends AbstractEvent implements LogNotifyEvent {
     @Override
     public synchronized Entity getNotifiable() {
         if (this.notifiable == null) {
-            this.notifiable = new EntitySender(this.sender);
+            this.notifiable = new SenderEntity(this.sender);
         }
         return this.notifiable;
     }

common/src/main/java/me/lucko/luckperms/common/event/model/EntitySourceImpl.java

@@ -30,10 +30,10 @@ import me.lucko.luckperms.api.event.source.EntitySource;
 
 import javax.annotation.Nonnull;
 
-public class SourceEntity implements EntitySource {
+public class EntitySourceImpl implements EntitySource {
     private final Entity entity;
 
-    public SourceEntity(Entity entity) {
+    public EntitySourceImpl(Entity entity) {
         this.entity = entity;
     }
 
@@ -51,6 +51,6 @@ public class SourceEntity implements EntitySource {
 
     @Override
     public String toString() {
-        return "Sender(type=ENTITY, entity=" + this.entity + ")";
+        return "Source(type=ENTITY, entity=" + this.entity + ")";
     }
 }

common/src/main/java/me/lucko/luckperms/common/event/model/SenderEntity.java

@@ -33,10 +33,10 @@ import java.util.UUID;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
-public class EntitySender implements Entity {
+public class SenderEntity implements Entity {
     private final Sender sender;
 
-    public EntitySender(Sender sender) {
+    public SenderEntity(Sender sender) {
         this.sender = sender;
     }
 
@@ -67,6 +67,6 @@ public class EntitySender implements Entity {
 
     @Override
     public String toString() {
-        return "Sender(type=" + getType() + ", sender=" + this.sender + ")";
+        return "SenderEntity(type=" + getType() + ", sender=" + this.sender + ")";
     }
 }

common/src/main/java/me/lucko/luckperms/common/event/model/UnknownSource.java

@@ -29,10 +29,10 @@ import me.lucko.luckperms.api.event.source.Source;
 
 import javax.annotation.Nonnull;
 
-public final class SourceUnknown implements Source {
+public final class UnknownSource implements Source {
-    private static final Source INSTANCE = new SourceUnknown();
+    private static final Source INSTANCE = new UnknownSource();
 
-    private SourceUnknown() {
+    private UnknownSource() {
 
     }
 

common/src/main/java/me/lucko/luckperms/common/listener/AbstractConnectionListener.java

@@ -29,6 +29,7 @@ import me.lucko.luckperms.common.assignments.AssignmentRule;
 import me.lucko.luckperms.common.config.ConfigKeys;
 import me.lucko.luckperms.common.model.User;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
 
 import java.util.Set;
 import java.util.UUID;
@@ -61,11 +62,16 @@ public abstract class AbstractConnectionListener implements ConnectionListener {
         this.plugin.getUserManager().getHouseKeeper().registerUsage(u);
 
         // save uuid data.
-        String name = this.plugin.getStorage().noBuffer().getName(u).join();
+        PlayerSaveResult saveResult = this.plugin.getStorage().savePlayerData(u, username).join();
-        if (name == null) {
+        if (saveResult.includes(PlayerSaveResult.Status.CLEAN_INSERT)) {
             this.plugin.getEventFactory().handleUserFirstLogin(u, username);
         }
-        this.plugin.getStorage().noBuffer().saveUUIDData(u, username);
+
+        if (saveResult.includes(PlayerSaveResult.Status.OTHER_UUIDS_PRESENT_FOR_USERNAME)) {
+            this.plugin.getLogger().warn("LuckPerms already has data for player '" + username + "' - but this data is stored under a different uuid.");
+            this.plugin.getLogger().warn("'" + username + "' has previously used the unique ids " + saveResult.getOtherUuids() + " but is now connecting with '" + u + "'");
+            this.plugin.getLogger().warn("This is usually because the server is not authenticating correctly. If you're using BungeeCord, please ensure that IP-Forwarding is setup correctly!");
+        }
 
         User user = this.plugin.getStorage().noBuffer().loadUser(u, username).join();
         if (user == null) {

common/src/main/java/me/lucko/luckperms/common/locale/message/Message.java

@@ -309,7 +309,7 @@ public enum Message {
 
     USER_INFO_GENERAL(
             "{PREFIX}&b&l> &bUser Info: &f{}" + "\n" +
-            "{PREFIX}&f- &3UUID: &f{}" + "\n" +
+            "{PREFIX}&f- &3UUID: &f{} &7(type: {}&7)" + "\n" +
             "{PREFIX}&f- &3Status: {}" + "\n" +
             "{PREFIX}&f- &3Primary Group: &f{}",
             false

common/src/main/java/me/lucko/luckperms/common/storage/AbstractStorage.java

@@ -290,17 +290,17 @@ public class AbstractStorage implements Storage {
     }
 
     @Override
-    public CompletableFuture<Void> saveUUIDData(UUID uuid, String username) {
+    public CompletableFuture<PlayerSaveResult> savePlayerData(UUID uuid, String username) {
-        return makeFuture(() -> this.dao.saveUUIDData(uuid, username));
+        return makeFuture(() -> this.dao.savePlayerData(uuid, username));
     }
 
     @Override
-    public CompletableFuture<UUID> getUUID(String username) {
+    public CompletableFuture<UUID> getPlayerUuid(String username) {
-        return makeFuture(() -> this.dao.getUUID(username));
+        return makeFuture(() -> this.dao.getPlayerUuid(username));
     }
 
     @Override
-    public CompletableFuture<String> getName(UUID uuid) {
+    public CompletableFuture<String> getPlayerName(UUID uuid) {
-        return makeFuture(() -> this.dao.getName(uuid));
+        return makeFuture(() -> this.dao.getPlayerName(uuid));
     }
 }

common/src/main/java/me/lucko/luckperms/common/storage/PlayerSaveResult.java

@@ -0,0 +1,194 @@
+/*
+ * This file is part of LuckPerms, licensed under the MIT License.
+ *
+ *  Copyright (c) lucko (Luck) <luck@lucko.me>
+ *  Copyright (c) contributors
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining a copy
+ *  of this software and associated documentation files (the "Software"), to deal
+ *  in the Software without restriction, including without limitation the rights
+ *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *  copies of the Software, and to permit persons to whom the Software is
+ *  furnished to do so, subject to the following conditions:
+ *
+ *  The above copyright notice and this permission notice shall be included in all
+ *  copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ *  SOFTWARE.
+ */
+
+package me.lucko.luckperms.common.storage;
+
+import com.google.common.collect.ImmutableSet;
+
+import java.util.Arrays;
+import java.util.EnumSet;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * Represents the result to a player history save operation
+ */
+public final class PlayerSaveResult {
+    private static final PlayerSaveResult CLEAN_INSERT = new PlayerSaveResult(Status.CLEAN_INSERT);
+    private static final PlayerSaveResult NO_CHANGE = new PlayerSaveResult(Status.NO_CHANGE);
+
+    public static PlayerSaveResult cleanInsert() {
+        return CLEAN_INSERT;
+    }
+
+    public static PlayerSaveResult noChange() {
+        return NO_CHANGE;
+    }
+
+    public static PlayerSaveResult usernameUpdated(String oldUsername) {
+        return new PlayerSaveResult(oldUsername, null, Status.USERNAME_UPDATED);
+    }
+
+    public static PlayerSaveResult determineBaseResult(String username, String oldUsername) {
+        PlayerSaveResult result;
+        if (oldUsername == null) {
+            result = PlayerSaveResult.cleanInsert();
+        } else if (oldUsername.equalsIgnoreCase(username)) {
+            result = PlayerSaveResult.noChange();
+        } else {
+            result = PlayerSaveResult.usernameUpdated(oldUsername);
+        }
+        return result;
+    }
+
+    private final Set<Status> status;
+    @Nullable private final String oldUsername;
+    @Nullable private final Set<UUID> otherUuids;
+
+    private PlayerSaveResult(EnumSet<Status> status, @Nullable String oldUsername, @Nullable Set<UUID> otherUuids) {
+        this.status = ImmutableSet.copyOf(status);
+        this.oldUsername = oldUsername;
+        this.otherUuids = otherUuids;
+    }
+
+    private PlayerSaveResult(@Nullable String oldUsername, @Nullable Set<UUID> otherUuids, Status... status) {
+        this(EnumSet.copyOf(Arrays.asList(status)), oldUsername, otherUuids);
+    }
+
+    private PlayerSaveResult(Status... status) {
+        this(null, null, status);
+    }
+
+    /**
+     * Returns a new {@link PlayerSaveResult} with the {@link Status#OTHER_UUIDS_PRESENT_FOR_USERNAME}
+     * status attached to the state of this result.
+     *
+     * @param otherUuids the other uuids
+     * @return a new result
+     */
+    public PlayerSaveResult withOtherUuidsPresent(@Nonnull Set<UUID> otherUuids) {
+        EnumSet<Status> status = EnumSet.copyOf(this.status);
+        status.add(Status.OTHER_UUIDS_PRESENT_FOR_USERNAME);
+        return new PlayerSaveResult(status, this.oldUsername, ImmutableSet.copyOf(otherUuids));
+    }
+
+    /**
+     * Gets the status returned by the operation
+     *
+     * @return the status
+     */
+    public Set<Status> getStatus() {
+        return this.status;
+    }
+
+    /**
+     * Gets if the result includes a certain status code.
+     *
+     * @param status the status to check for
+     * @return if the result includes the status
+     */
+    public boolean includes(Status status) {
+        return this.status.contains(status);
+    }
+
+    /**
+     * Gets the old username involved in the result
+     *
+     * @return the old username
+     * @see Status#USERNAME_UPDATED
+     */
+    @Nullable
+    public String getOldUsername() {
+        return this.oldUsername;
+    }
+
+    /**
+     * Gets the other uuids involved in the result
+     *
+     * @return the other uuids
+     * @see Status#OTHER_UUIDS_PRESENT_FOR_USERNAME
+     */
+    @Nullable
+    public Set<UUID> getOtherUuids() {
+        return this.otherUuids;
+    }
+
+    @Override
+    public boolean equals(Object that) {
+        if (this == that) return true;
+        if (that == null || getClass() != that.getClass()) return false;
+        PlayerSaveResult result = (PlayerSaveResult) that;
+        return Objects.equals(this.status, result.status) &&
+                Objects.equals(this.oldUsername, result.oldUsername) &&
+                Objects.equals(this.otherUuids, result.otherUuids);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(this.status, this.oldUsername, this.otherUuids);
+    }
+
+    /**
+     * The various states the result can take
+     */
+    public enum Status {
+
+        /**
+         * There was no existing data saved for either the uuid or username
+         */
+        CLEAN_INSERT,
+
+        /**
+         * There was existing data for the player, no change was needed.
+         */
+        NO_CHANGE,
+
+        /**
+         * There was already a record for the UUID saved, but it was for a different username.
+         *
+         * <p>This is normal, players are able to change their usernames.</p>
+         */
+        USERNAME_UPDATED,
+
+        /**
+         * There was already a record for the username saved, but it was under a different uuid.
+         *
+         * <p>This is a bit of a cause for concern. It's possible that "player1" has changed
+         * their username to "player2", and "player3" has changed their username to "player1".
+         * If the original "player1" doesn't join after changing their name, this conflict could
+         * occur.</p>
+         *
+         * <p>However, what's more likely is that the server is not setup to authenticate
+         * correctly. Usually this is a problem with BungeeCord "ip-forwarding", but could be
+         * that the user of the plugin is running a network off a shared database with one
+         * server in online mode and another in offline mode.</p>
+         */
+        OTHER_UUIDS_PRESENT_FOR_USERNAME,
+    }
+}

common/src/main/java/me/lucko/luckperms/common/storage/Storage.java

@@ -99,9 +99,9 @@ public interface Storage {
 
     CompletableFuture<Void> deleteTrack(Track track, DeletionCause cause);
 
-    CompletableFuture<Void> saveUUIDData(UUID uuid, String username);
+    CompletableFuture<PlayerSaveResult> savePlayerData(UUID uuid, String username);
 
-    CompletableFuture<UUID> getUUID(String username);
+    CompletableFuture<UUID> getPlayerUuid(String username);
 
-    CompletableFuture<String> getName(UUID uuid);
+    CompletableFuture<String> getPlayerName(UUID uuid);
 }

common/src/main/java/me/lucko/luckperms/common/storage/dao/AbstractDao.java

@@ -33,6 +33,7 @@ import me.lucko.luckperms.common.model.Group;
 import me.lucko.luckperms.common.model.Track;
 import me.lucko.luckperms.common.model.User;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
 
 import java.util.Collections;
 import java.util.List;
@@ -105,12 +106,12 @@ public abstract class AbstractDao {
 
     public abstract void deleteTrack(Track track) throws Exception;
 
-    public abstract void saveUUIDData(UUID uuid, String username) throws Exception;
+    public abstract PlayerSaveResult savePlayerData(UUID uuid, String username) throws Exception;
 
     @Nullable
-    public abstract UUID getUUID(String username) throws Exception;
+    public abstract UUID getPlayerUuid(String username) throws Exception;
 
     @Nullable
-    public abstract String getName(UUID uuid) throws Exception;
+    public abstract String getPlayerName(UUID uuid) throws Exception;
 
 }

common/src/main/java/me/lucko/luckperms/common/storage/dao/SplitStorageDao.java

@@ -35,6 +35,7 @@ import me.lucko.luckperms.common.model.Group;
 import me.lucko.luckperms.common.model.Track;
 import me.lucko.luckperms.common.model.User;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
 import me.lucko.luckperms.common.storage.SplitStorageType;
 import me.lucko.luckperms.common.storage.StorageType;
 
@@ -191,17 +192,17 @@ public class SplitStorageDao extends AbstractDao {
     }
 
     @Override
-    public void saveUUIDData(UUID uuid, String username) throws Exception {
+    public PlayerSaveResult savePlayerData(UUID uuid, String username) throws Exception {
-        this.backing.get(this.types.get(SplitStorageType.UUID)).saveUUIDData(uuid, username);
+        return this.backing.get(this.types.get(SplitStorageType.UUID)).savePlayerData(uuid, username);
     }
 
     @Override
-    public UUID getUUID(String username) throws Exception {
+    public UUID getPlayerUuid(String username) throws Exception {
-        return this.backing.get(this.types.get(SplitStorageType.UUID)).getUUID(username);
+        return this.backing.get(this.types.get(SplitStorageType.UUID)).getPlayerUuid(username);
     }
 
     @Override
-    public String getName(UUID uuid) throws Exception {
+    public String getPlayerName(UUID uuid) throws Exception {
-        return this.backing.get(this.types.get(SplitStorageType.UUID)).getName(uuid);
+        return this.backing.get(this.types.get(SplitStorageType.UUID)).getPlayerName(uuid);
     }
 }

common/src/main/java/me/lucko/luckperms/common/storage/dao/file/ConfigurateDao.java

@@ -47,6 +47,7 @@ import me.lucko.luckperms.common.node.NodeHeldPermission;
 import me.lucko.luckperms.common.node.NodeModel;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
 import me.lucko.luckperms.common.references.UserIdentifier;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
 import me.lucko.luckperms.common.storage.dao.AbstractDao;
 import me.lucko.luckperms.common.utils.ImmutableCollectors;
 import me.lucko.luckperms.common.utils.Uuids;
@@ -670,17 +671,17 @@ public abstract class ConfigurateDao extends AbstractDao {
     }
 
     @Override
-    public void saveUUIDData(UUID uuid, String username) {
+    public PlayerSaveResult savePlayerData(UUID uuid, String username) {
-        this.uuidCache.addMapping(uuid, username);
+        return this.uuidCache.addMapping(uuid, username);
     }
 
     @Override
-    public UUID getUUID(String username) {
+    public UUID getPlayerUuid(String username) {
-        return this.uuidCache.lookup(username);
+        return this.uuidCache.lookupUuid(username);
     }
 
     @Override
-    public String getName(UUID uuid) {
+    public String getPlayerName(UUID uuid) {
         return this.uuidCache.lookupUsername(uuid);
     }
 

common/src/main/java/me/lucko/luckperms/common/storage/dao/file/FileUuidCache.java

@@ -26,9 +26,12 @@
 package me.lucko.luckperms.common.storage.dao.file;
 
 import com.google.common.base.Splitter;
-import com.google.common.collect.Maps;
+import com.google.common.collect.Iterables;
+import com.google.common.collect.Multimaps;
+import com.google.common.collect.SetMultimap;
 
-import me.lucko.luckperms.common.utils.DateUtil;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
+import me.lucko.luckperms.common.utils.Uuids;
 
 import java.io.BufferedReader;
 import java.io.BufferedWriter;
@@ -36,19 +39,60 @@ import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Map;
+import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
 
 import javax.annotation.Nullable;
 
 public class FileUuidCache {
-    private static final Splitter KV_SPLIT = Splitter.on('=').omitEmptyStrings();
+    private static final Splitter KV_SPLIT = Splitter.on(':').omitEmptyStrings();
-    private static final Splitter TIME_SPLIT = Splitter.on('|').omitEmptyStrings();
+    private static final Splitter LEGACY_KV_SPLIT = Splitter.on('=').omitEmptyStrings();
+    private static final Splitter LEGACY_TIME_SPLIT = Splitter.on('|').omitEmptyStrings();
 
-    // the map for lookups
+    // the lookup map
-    private final Map<String, Map.Entry<UUID, Long>> lookupMap = new ConcurrentHashMap<>();
+    private final LookupMap lookupMap = new LookupMap();
+
+    private static final class LookupMap extends ConcurrentHashMap<UUID, String> {
+        private final SetMultimap<String, UUID> reverse = Multimaps.newSetMultimap(new ConcurrentHashMap<>(), ConcurrentHashMap::newKeySet);
+
+        @Override
+        public String put(UUID key, String value) {
+            String existing = super.put(key, value);
+
+            // check if we need to remove a reverse entry which has been replaced
+            // existing might be null
+            if (!value.equalsIgnoreCase(existing)) {
+                if (existing != null) {
+                    this.reverse.remove(existing.toLowerCase(), key);
+                }
+            }
+
+            this.reverse.put(value.toLowerCase(), key);
+            return existing;
+        }
+
+        @Override
+        public String remove(Object k) {
+            UUID key = (UUID) k;
+            String username = super.remove(key);
+            if (username != null) {
+                this.reverse.remove(username.toLowerCase(), key);
+            }
+            return username;
+        }
+
+        public String lookupUsername(UUID uuid) {
+            return super.get(uuid);
+        }
+
+        public Set<UUID> lookupUuid(String name) {
+            return this.reverse.get(name.toLowerCase());
+        }
+    }
 
     /**
      * Adds a mapping to the cache
@@ -56,8 +100,25 @@ public class FileUuidCache {
      * @param uuid the uuid of the player
      * @param username the username of the player
      */
-    public void addMapping(UUID uuid, String username) {
+    public PlayerSaveResult addMapping(UUID uuid, String username) {
-        this.lookupMap.put(username.toLowerCase(), Maps.immutableEntry(uuid, DateUtil.unixSecondsNow()));
+        // perform the insert
+        String oldUsername = this.lookupMap.put(uuid, username);
+
+        PlayerSaveResult result = PlayerSaveResult.determineBaseResult(username, oldUsername);
+
+        Set<UUID> conflicting = new HashSet<>(this.lookupMap.lookupUuid(username));
+        conflicting.remove(uuid);
+
+        if (!conflicting.isEmpty()) {
+            // remove the mappings for conflicting uuids
+            for (UUID conflict : conflicting) {
+                this.lookupMap.remove(conflict);
+            }
+
+            result = result.withOtherUuidsPresent(conflicting);
+        }
+
+        return result;
     }
 
     /**
@@ -67,9 +128,9 @@ public class FileUuidCache {
      * @return a uuid, or null
      */
     @Nullable
-    public UUID lookup(String username) {
+    public UUID lookupUuid(String username) {
-        Map.Entry<UUID, Long> ret = this.lookupMap.get(username.toLowerCase());
+        Set<UUID> uuids = this.lookupMap.lookupUuid(username);
-        return ret == null ? null : ret.getKey();
+        return Iterables.getFirst(uuids, null);
     }
 
     /**
@@ -79,23 +140,46 @@ public class FileUuidCache {
      * @return a username, or null
      */
     public String lookupUsername(UUID uuid) {
-        String username = null;
+        return this.lookupMap.lookupUsername(uuid);
-        Long time = Long.MIN_VALUE;
-
-        for (Map.Entry<String, Map.Entry<UUID, Long>> ent : this.lookupMap.entrySet()) {
-            if (!ent.getValue().getKey().equals(uuid)) {
-                continue;
     }
 
-            Long t = ent.getValue().getValue();
+    private void loadEntry(String entry) {
+        if (entry.contains(":")) {
+            // new format
+            Iterator<String> parts = KV_SPLIT.split(entry).iterator();
 
-            if (t > time) {
+            if (!parts.hasNext()) return;
-                time = t;
+            String uuidPart = parts.next();
-                username = ent.getKey();
+
-            }
+            if (!parts.hasNext()) return;
+            String usernamePart = parts.next();
+
+            UUID uuid = Uuids.fromString(uuidPart);
+            if (uuid == null) return;
+
+            this.lookupMap.put(uuid, usernamePart);
+        } else if (entry.contains("=")) {
+            // old format
+            Iterator<String> parts = LEGACY_KV_SPLIT.split(entry).iterator();
+
+            if (!parts.hasNext()) return;
+            String usernamePart = parts.next();
+
+            if (!parts.hasNext()) return;
+            String uuidPart = parts.next();
+
+            // contains a time
+            if (uuidPart.contains("|")) {
+                Iterator<String> valueParts = LEGACY_TIME_SPLIT.split(uuidPart).iterator();
+                if (!valueParts.hasNext()) return;
+                uuidPart = valueParts.next();
             }
 
-        return username;
+            UUID uuid = Uuids.fromString(uuidPart);
+            if (uuid == null) return;
+
+            this.lookupMap.put(uuid, usernamePart);
+        }
     }
 
     public void load(File file) {
@@ -104,61 +188,14 @@ public class FileUuidCache {
         }
 
         try (BufferedReader reader = Files.newBufferedReader(file.toPath(), StandardCharsets.UTF_8)) {
-
             String entry;
             while ((entry = reader.readLine()) != null) {
                 entry = entry.trim();
                 if (entry.isEmpty() || entry.startsWith("#")) {
                     continue;
                 }
-
+                loadEntry(entry);
-                Iterator<String> parts = KV_SPLIT.split(entry).iterator();
-
-                if (!parts.hasNext()) continue;
-                String key = parts.next();
-
-                if (!parts.hasNext()) continue;
-                String value = parts.next();
-
-                UUID uid;
-                Long t;
-
-                // contains a time (backwards compat)
-                if (value.contains("|")) {
-                    // try to split and extract the time element from the end.
-                    Iterator<String> valueParts = TIME_SPLIT.split(value).iterator();
-
-                    if (!valueParts.hasNext()) continue;
-                    String uuid = valueParts.next();
-
-                    if (!valueParts.hasNext()) continue;
-                    String time = valueParts.next();
-
-                    try {
-                        uid = UUID.fromString(uuid);
-                    } catch (IllegalArgumentException e) {
-                        continue;
             }
-
-                    try {
-                        t = Long.parseLong(time);
-                    } catch (NumberFormatException e) {
-                        continue;
-                    }
-                } else {
-                    // just parse from the value
-                    try {
-                        uid = UUID.fromString(value);
-                    } catch (IllegalArgumentException e) {
-                        continue;
-                    }
-
-                    t = 0L;
-                }
-
-                this.lookupMap.put(key, Maps.immutableEntry(uid, t));
-            }
-
         } catch (IOException e) {
             e.printStackTrace();
         }
@@ -168,13 +205,11 @@ public class FileUuidCache {
         try (BufferedWriter writer = Files.newBufferedWriter(file.toPath(), StandardCharsets.UTF_8)) {
             writer.write("# LuckPerms UUID lookup cache");
             writer.newLine();
-
+            for (Map.Entry<UUID, String> ent : this.lookupMap.entrySet()) {
-            for (Map.Entry<String, Map.Entry<UUID, Long>> ent : this.lookupMap.entrySet()) {
+                String out = ent.getKey() + ":" + ent.getValue();
-                String out = ent.getKey() + "=" + ent.getValue().getKey().toString() + "|" + ent.getValue().getValue().toString();
                 writer.write(out);
                 writer.newLine();
             }
-
             writer.flush();
         } catch (IOException e) {
             e.printStackTrace();

common/src/main/java/me/lucko/luckperms/common/storage/dao/mongodb/MongoDao.java

@@ -34,6 +34,7 @@ import com.mongodb.ServerAddress;
 import com.mongodb.client.MongoCollection;
 import com.mongodb.client.MongoCursor;
 import com.mongodb.client.MongoDatabase;
+import com.mongodb.client.model.Filters;
 import com.mongodb.client.model.UpdateOptions;
 
 import me.lucko.luckperms.api.HeldPermission;
@@ -56,6 +57,7 @@ import me.lucko.luckperms.common.node.NodeHeldPermission;
 import me.lucko.luckperms.common.node.NodeModel;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
 import me.lucko.luckperms.common.references.UserIdentifier;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
 import me.lucko.luckperms.common.storage.StorageCredentials;
 import me.lucko.luckperms.common.storage.dao.AbstractDao;
 
@@ -569,29 +571,53 @@ public class MongoDao extends AbstractDao {
     }
 
     @Override
-    public void saveUUIDData(UUID uuid, String username) {
+    public PlayerSaveResult savePlayerData(UUID uuid, String username) {
+        username = username.toLowerCase();
         MongoCollection<Document> c = this.database.getCollection(this.prefix + "uuid");
-        c.replaceOne(new Document("_id", uuid), new Document("_id", uuid).append("name", username.toLowerCase()), new UpdateOptions().upsert(true));
+
+        // find any existing mapping
+        String oldUsername = getPlayerName(uuid);
+
+        // do the insert
+        if (!username.equalsIgnoreCase(oldUsername)) {
+            c.replaceOne(new Document("_id", uuid), new Document("_id", uuid).append("name", username), new UpdateOptions().upsert(true));
+        }
+
+        PlayerSaveResult result = PlayerSaveResult.determineBaseResult(username, oldUsername);
+
+        Set<UUID> conflicting = new HashSet<>();
+        try (MongoCursor<Document> cursor = c.find(new Document("name", username)).iterator()) {
+            if (cursor.hasNext()) {
+                conflicting.add(cursor.next().get("_id", UUID.class));
+            }
+        }
+        conflicting.remove(uuid);
+
+        if (!conflicting.isEmpty()) {
+            // remove the mappings for conflicting uuids
+            c.deleteMany(Filters.and(conflicting.stream().map(u -> Filters.eq("_id", u)).collect(Collectors.toList())));
+            result = result.withOtherUuidsPresent(conflicting);
+        }
+
+        return result;
     }
 
     @Override
-    public UUID getUUID(String username) {
+    public UUID getPlayerUuid(String username) {
         MongoCollection<Document> c = this.database.getCollection(this.prefix + "uuid");
-        try (MongoCursor<Document> cursor = c.find(new Document("name", username.toLowerCase())).iterator()) {
+        Document doc = c.find(new Document("name", username.toLowerCase())).first();
-            if (cursor.hasNext()) {
+        if (doc != null) {
-                return cursor.next().get("_id", UUID.class);
+            return doc.get("_id", UUID.class);
-            }
         }
         return null;
     }
 
     @Override
-    public String getName(UUID uuid) {
+    public String getPlayerName(UUID uuid) {
         MongoCollection<Document> c = this.database.getCollection(this.prefix + "uuid");
-        try (MongoCursor<Document> cursor = c.find(new Document("_id", uuid)).iterator()) {
+        Document doc = c.find(new Document("_id", uuid)).first();
-            if (cursor.hasNext()) {
+        if (doc != null) {
-                return cursor.next().get("name", String.class);
+            return doc.get("name", String.class);
-            }
         }
         return null;
     }

common/src/main/java/me/lucko/luckperms/common/storage/dao/sql/SqlDao.java

@@ -46,6 +46,7 @@ import me.lucko.luckperms.common.node.NodeHeldPermission;
 import me.lucko.luckperms.common.node.NodeModel;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
 import me.lucko.luckperms.common.references.UserIdentifier;
+import me.lucko.luckperms.common.storage.PlayerSaveResult;
 import me.lucko.luckperms.common.storage.dao.AbstractDao;
 import me.lucko.luckperms.common.storage.dao.sql.connection.AbstractConnectionFactory;
 import me.lucko.luckperms.common.storage.dao.sql.connection.file.SQLiteConnectionFactory;
@@ -68,8 +69,6 @@ import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.UUID;
-import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -83,14 +82,15 @@ public class SqlDao extends AbstractDao {
     private static final String USER_PERMISSIONS_SELECT_DISTINCT = "SELECT DISTINCT uuid FROM {prefix}user_permissions";
     private static final String USER_PERMISSIONS_SELECT_PERMISSION = "SELECT uuid, value, server, world, expiry, contexts FROM {prefix}user_permissions WHERE permission=?";
 
-    private static final String PLAYER_SELECT = "SELECT username, primary_group FROM {prefix}players WHERE uuid=?";
+    private static final String PLAYER_SELECT_UUID_BY_USERNAME = "SELECT uuid FROM {prefix}players WHERE username=? LIMIT 1";
-    private static final String PLAYER_SELECT_UUID = "SELECT uuid FROM {prefix}players WHERE username=? LIMIT 1";
+    private static final String PLAYER_SELECT_USERNAME_BY_UUID = "SELECT username FROM {prefix}players WHERE uuid=? LIMIT 1";
-    private static final String PLAYER_SELECT_USERNAME = "SELECT username FROM {prefix}players WHERE uuid=? LIMIT 1";
+    private static final String PLAYER_UPDATE_USERNAME_FOR_UUID = "UPDATE {prefix}players SET username=? WHERE uuid=?";
-    private static final String PLAYER_SELECT_PRIMARY_GROUP = "SELECT primary_group FROM {prefix}players WHERE uuid=? LIMIT 1";
     private static final String PLAYER_INSERT = "INSERT INTO {prefix}players VALUES(?, ?, ?)";
-    private static final String PLAYER_UPDATE = "UPDATE {prefix}players SET username=? WHERE uuid=?";
+    private static final String PLAYER_SELECT_ALL_UUIDS_BY_USERNAME = "SELECT uuid FROM {prefix}players WHERE username=? AND NOT uuid=?";
-    private static final String PLAYER_DELETE = "DELETE FROM {prefix}players WHERE username=? AND NOT uuid=?";
+    private static final String PLAYER_DELETE_ALL_UUIDS_BY_USERNAME = "DELETE FROM {prefix}players WHERE username=? AND NOT uuid=?";
-    private static final String PLAYER_UPDATE_PRIMARY_GROUP = "UPDATE {prefix}players SET primary_group=? WHERE uuid=?";
+    private static final String PLAYER_SELECT_BY_UUID = "SELECT username, primary_group FROM {prefix}players WHERE uuid=?";
+    private static final String PLAYER_SELECT_PRIMARY_GROUP_BY_UUID = "SELECT primary_group FROM {prefix}players WHERE uuid=? LIMIT 1";
+    private static final String PLAYER_UPDATE_PRIMARY_GROUP_BY_UUID = "UPDATE {prefix}players SET primary_group=? WHERE uuid=?";
 
     private static final String GROUP_PERMISSIONS_SELECT = "SELECT permission, value, server, world, expiry, contexts FROM {prefix}group_permissions WHERE name=?";
     private static final String GROUP_PERMISSIONS_DELETE = "DELETE FROM {prefix}group_permissions WHERE name=?";
@@ -295,8 +295,8 @@ public class SqlDao extends AbstractDao {
         user.getIoLock().lock();
         try {
             List<NodeModel> data = new ArrayList<>();
-            AtomicReference<String> primaryGroup = new AtomicReference<>(null);
+            String primaryGroup = null;
-            AtomicReference<String> userName = new AtomicReference<>(null);
+            String userName = null;
 
             // Collect user permissions
             try (Connection c = this.provider.getConnection()) {
@@ -319,27 +319,26 @@ public class SqlDao extends AbstractDao {
 
             // Collect user meta (username & primary group)
             try (Connection c = this.provider.getConnection()) {
-                try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT))) {
+                try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_BY_UUID))) {
                     ps.setString(1, user.getUuid().toString());
 
                     try (ResultSet rs = ps.executeQuery()) {
                         if (rs.next()) {
-                            userName.set(rs.getString("username"));
+                            userName = rs.getString("username");
-                            primaryGroup.set(rs.getString("primary_group"));
+                            primaryGroup = rs.getString("primary_group");
                         }
                     }
                 }
             }
 
             // update username & primary group
-            String pg = primaryGroup.get();
+            if (primaryGroup == null) {
-            if (pg == null) {
+                primaryGroup = NodeFactory.DEFAULT_GROUP_NAME;
-                pg = NodeFactory.DEFAULT_GROUP_NAME;
             }
-            user.getPrimaryGroup().setStoredValue(pg);
+            user.getPrimaryGroup().setStoredValue(primaryGroup);
 
             // Update their username to what was in the storage if the one in the local instance is null
-            user.setName(userName.get(), true);
+            user.setName(userName, true);
 
             // If the user has any data in storage
             if (!data.isEmpty()) {
@@ -378,7 +377,7 @@ public class SqlDao extends AbstractDao {
                         ps.setString(1, user.getUuid().toString());
                         ps.execute();
                     }
-                    try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_UPDATE_PRIMARY_GROUP))) {
+                    try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_UPDATE_PRIMARY_GROUP_BY_UUID))) {
                         ps.setString(1, NodeFactory.DEFAULT_GROUP_NAME);
                         ps.setString(2, user.getUuid().toString());
                         ps.execute();
@@ -453,7 +452,7 @@ public class SqlDao extends AbstractDao {
             try (Connection c = this.provider.getConnection()) {
                 boolean hasPrimaryGroupSaved;
 
-                try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_PRIMARY_GROUP))) {
+                try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_PRIMARY_GROUP_BY_UUID))) {
                     ps.setString(1, user.getUuid().toString());
                     try (ResultSet rs = ps.executeQuery()) {
                         hasPrimaryGroupSaved = rs.next();
@@ -462,7 +461,7 @@ public class SqlDao extends AbstractDao {
 
                 if (hasPrimaryGroupSaved) {
                     // update
-                    try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_UPDATE_PRIMARY_GROUP))) {
+                    try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_UPDATE_PRIMARY_GROUP_BY_UUID))) {
                         ps.setString(1, user.getPrimaryGroup().getStoredValue().orElse(NodeFactory.DEFAULT_GROUP_NAME));
                         ps.setString(2, user.getUuid().toString());
                         ps.execute();
@@ -772,24 +771,23 @@ public class SqlDao extends AbstractDao {
         Track track = this.plugin.getTrackManager().getOrMake(name);
         track.getIoLock().lock();
         try {
-            AtomicBoolean exists = new AtomicBoolean(false);
+            boolean exists = false;
-            AtomicReference<String> groups = new AtomicReference<>(null);
+            String groups = null;
-
             try (Connection c = this.provider.getConnection()) {
                 try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(TRACK_SELECT))) {
                     ps.setString(1, track.getName());
                     try (ResultSet rs = ps.executeQuery()) {
                         if (rs.next()) {
-                            exists.set(true);
+                            exists = true;
-                            groups.set(rs.getString("groups"));
+                            groups = rs.getString("groups");
                         }
                     }
                 }
             }
 
-            if (exists.get()) {
+            if (exists) {
                 // Track exists, let's load.
-                track.setGroups(this.gson.fromJson(groups.get(), LIST_STRING_TYPE));
+                track.setGroups(this.gson.fromJson(groups, LIST_STRING_TYPE));
             } else {
                 String json = this.gson.toJson(track.getGroups());
                 try (Connection c = this.provider.getConnection()) {
@@ -813,14 +811,13 @@ public class SqlDao extends AbstractDao {
             track.getIoLock().lock();
         }
         try {
-            AtomicReference<String> groups = new AtomicReference<>(null);
+            String groups;
-
             try (Connection c = this.provider.getConnection()) {
                 try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(TRACK_SELECT))) {
                     ps.setString(1, name);
                     try (ResultSet rs = ps.executeQuery()) {
                         if (rs.next()) {
-                            groups.set(rs.getString("groups"));
+                            groups = rs.getString("groups");
                         } else {
                             return Optional.empty();
                         }
@@ -833,7 +830,7 @@ public class SqlDao extends AbstractDao {
                 track.getIoLock().lock();
             }
 
-            track.setGroups(this.gson.fromJson(groups.get(), LIST_STRING_TYPE));
+            track.setGroups(this.gson.fromJson(groups, LIST_STRING_TYPE));
             return Optional.of(track);
 
         } finally {
@@ -911,49 +908,25 @@ public class SqlDao extends AbstractDao {
     }
 
     @Override
-    public void saveUUIDData(UUID uuid, String username) throws SQLException {
+    public PlayerSaveResult savePlayerData(UUID uuid, String username) throws SQLException {
-        final String u = username.toLowerCase();
+        username = username.toLowerCase();
-        AtomicReference<String> remoteUserName = new AtomicReference<>(null);
 
-        // cleanup any old values
+        // find any existing mapping
+        String oldUsername = getPlayerName(uuid);
+
+        // do the insert
+        if (!username.equalsIgnoreCase(oldUsername)) {
             try (Connection c = this.provider.getConnection()) {
-            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_DELETE))) {
+                if (oldUsername != null) {
-                ps.setString(1, u);
+                    try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_UPDATE_USERNAME_FOR_UUID))) {
+                        ps.setString(1, username);
                         ps.setString(2, uuid.toString());
                         ps.execute();
                     }
-        }
-
-        try (Connection c = this.provider.getConnection()) {
-            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_USERNAME))) {
-                ps.setString(1, uuid.toString());
-                try (ResultSet rs = ps.executeQuery()) {
-                    if (rs.next()) {
-                        remoteUserName.set(rs.getString("username"));
-                    }
-                }
-            }
-        }
-
-        if (remoteUserName.get() != null) {
-            // the value is already correct
-            if (remoteUserName.get().equals(u)) {
-                return;
-            }
-
-            try (Connection c = this.provider.getConnection()) {
-                try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_UPDATE))) {
-                    ps.setString(1, u);
-                    ps.setString(2, uuid.toString());
-                    ps.execute();
-                }
-            }
                 } else {
-            // first time we've seen this uuid
-            try (Connection c = this.provider.getConnection()) {
                     try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_INSERT))) {
                         ps.setString(1, uuid.toString());
-                    ps.setString(2, u);
+                        ps.setString(2, username);
                         ps.setString(3, NodeFactory.DEFAULT_GROUP_NAME);
                         ps.execute();
                     }
@@ -961,41 +934,65 @@ public class SqlDao extends AbstractDao {
             }
         }
 
-    @Override
+        PlayerSaveResult result = PlayerSaveResult.determineBaseResult(username, oldUsername);
-    public UUID getUUID(String username) throws SQLException {
-        final String u = username.toLowerCase();
-        final AtomicReference<UUID> uuid = new AtomicReference<>(null);
 
+        Set<UUID> conflicting = new HashSet<>();
         try (Connection c = this.provider.getConnection()) {
-            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_UUID))) {
+            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_ALL_UUIDS_BY_USERNAME))) {
-                ps.setString(1, u);
+                ps.setString(1, username);
+                ps.setString(2, uuid.toString());
+                try (ResultSet rs = ps.executeQuery()) {
+                    while (rs.next()) {
+                        conflicting.add(UUID.fromString(rs.getString("uuid")));
+                    }
+                }
+            }
+        }
+
+        if (!conflicting.isEmpty()) {
+            // remove the mappings for conflicting uuids
+            try (Connection c = this.provider.getConnection()) {
+                try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_DELETE_ALL_UUIDS_BY_USERNAME))) {
+                    ps.setString(1, username);
+                    ps.setString(2, uuid.toString());
+                    ps.execute();
+                }
+            }
+            result = result.withOtherUuidsPresent(conflicting);
+        }
+
+        return result;
+    }
+
+    @Override
+    public UUID getPlayerUuid(String username) throws SQLException {
+        username = username.toLowerCase();
+        try (Connection c = this.provider.getConnection()) {
+            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_UUID_BY_USERNAME))) {
+                ps.setString(1, username);
                 try (ResultSet rs = ps.executeQuery()) {
                     if (rs.next()) {
-                        uuid.set(UUID.fromString(rs.getString("uuid")));
+                        return UUID.fromString(rs.getString("uuid"));
                     }
                 }
             }
         }
-
+        return null;
-        return uuid.get();
     }
 
     @Override
-    public String getName(UUID uuid) throws SQLException {
+    public String getPlayerName(UUID uuid) throws SQLException {
-        final AtomicReference<String> name = new AtomicReference<>(null);
-
         try (Connection c = this.provider.getConnection()) {
-            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_USERNAME))) {
+            try (PreparedStatement ps = c.prepareStatement(this.prefix.apply(PLAYER_SELECT_USERNAME_BY_UUID))) {
                 ps.setString(1, uuid.toString());
                 try (ResultSet rs = ps.executeQuery()) {
                     if (rs.next()) {
-                        name.set(rs.getString("username"));
+                        return rs.getString("username");
                     }
                 }
             }
         }
-
+        return null;
-        return name.get();
     }
 
     /**

common/src/main/java/me/lucko/luckperms/common/utils/Uuids.java

@@ -41,7 +41,7 @@ public final class Uuids {
     public static final Predicate<String> PREDICATE = s -> parseNullable(s) != null;
 
     @Nullable
-    private static UUID fromString(String s) {
+    public static UUID fromString(String s) {
         try {
             return UUID.fromString(s);
         } catch (IllegalArgumentException e) {