Protect invisible player from town add tab completes. (#5873)

* Protect invisible player from town add tab completes.

Closes #5872.

* Fix build.

* Actually fix build.

* Catch similar issue with /ta checkperm, fix up method in ResidentUtil
that was doing something...

src/com/palmergames/bukkit/towny/command/BaseCommand.java

@@ -24,6 +24,7 @@
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.stream.Collectors;
 
 public class BaseCommand implements TabCompleter{
 
@@ -207,6 +208,24 @@ public static List<String> getResidentsWithoutTownStartingWith(String str) {
 		else 
 			return Collections.emptyList();
 	}
+
+	/**
+	 * Returns a list of residents which are online and have no town, and can be seen by the sender.
+	 * 
+	 * @param arg the string to check if the resident's name starts with.
+	 * @return the residents names or an empty list.
+	 */
+	public List<String> getVisibleResidentsForPlayerWithoutTownsStartingWith(String arg, CommandSender sender) {
+		if (!(sender instanceof Player player))
+			return getResidentsWithoutTownStartingWith(arg);
+		List<String> residents = getOnlinePlayersWithoutTown().stream()
+			.filter(res -> player.canSee(res.getPlayer()))
+			.map(res -> res.getName())
+			.collect(Collectors.toCollection(ArrayList::new));
+		return !residents.isEmpty()
+			? NameUtil.filterByStart(residents, arg)
+			: Collections.emptyList();
+	}
 
 	/**
 	 * Parses the given string into a boolean choice.

src/com/palmergames/bukkit/towny/command/TownCommand.java

@@ -379,7 +379,7 @@ public List<String> onTabComplete(CommandSender sender, Command command, String
 					break;
 				case "add":
 					if (args.length == 2)
-						return getResidentsWithoutTownStartingWith(args[1]);
+						return getVisibleResidentsForPlayerWithoutTownsStartingWith(args[1], sender);
 					break;
 				case "kick":
 					if (args.length == 2)
@@ -419,7 +419,7 @@ public List<String> onTabComplete(CommandSender sender, Command command, String
 												.collect(Collectors.toList());
 									} catch (TownyException ignore) {}
 								} else {
-									return getResidentsWithoutTownStartingWith(args[1]);
+									return getVisibleResidentsForPlayerWithoutTownsStartingWith(args[1], sender);
 								}
 							}
 						case 3:

src/com/palmergames/bukkit/towny/command/TownyAdminCommand.java

@@ -356,7 +356,7 @@ else if (args.length > 2 && TownyCommandAddonAPI.hasCommand(CommandType.TOWNYADM
 				break;
 			case "checkperm":
 				if (args.length == 2)
-					return NameUtil.filterByStart(BukkitTools.getOnlinePlayers()
+					return NameUtil.filterByStart(BukkitTools.getVisibleOnlinePlayers(sender)
 						.stream()
 						.map(Player::getName)
 						.collect(Collectors.toList()), args[1]);

src/com/palmergames/bukkit/towny/utils/ResidentUtil.java

@@ -53,23 +53,9 @@ public class ResidentUtil {
 	 * @return - List of residents that can actually be seen.
 	 */
 	public static List<Resident> getOnlineResidentsViewable(Player viewer, ResidentList residentList) {
-
-		List<Resident> onlineResidents = new ArrayList<>();
-		for (Player player : BukkitTools.getOnlinePlayers()) {
-			if (player != null) {
-				/*
-				 * Loop town/nation resident list
-				 */
-				for (Resident resident : residentList.getResidents()) {
-					if (resident.getName().equalsIgnoreCase(player.getName()))
-						if ((viewer == null) || (viewer.canSee(BukkitTools.getPlayerExact(resident.getName())))) {
-							onlineResidents.add(resident);
-						}
-				}
-			}
-		}
-
-		return onlineResidents;
+		return residentList.getResidents().stream()
+			.filter(res -> viewer != null ?  res.isOnline() && viewer.canSee(res.getPlayer()) : res.isOnline())
+			.collect(Collectors.toList());
 	}
 
 	/**

src/com/palmergames/bukkit/util/BukkitTools.java

@@ -9,6 +9,7 @@
 import org.bukkit.OfflinePlayer;
 import org.bukkit.Server;
 import org.bukkit.World;
+import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Entity;
 import org.bukkit.entity.Player;
 import org.bukkit.plugin.PluginManager;
@@ -95,6 +96,15 @@ public static Player getPlayer(UUID playerUUID) {
 		return server.getPlayer(playerUUID);
 	}
 
+	public static Collection<? extends Player> getVisibleOnlinePlayers(CommandSender sender) {
+		if (!(sender instanceof Player player))
+			return Bukkit.getOnlinePlayers();
+
+		return Bukkit.getOnlinePlayers().stream()
+			.filter(p -> player.canSee(p))
+			.collect(Collectors.toCollection(ArrayList::new));
+	}
+
 	/**
 	 * Tests if this player is online.
 	 *