Keep track of shuffle-positions teleportees.

Introduces a means of "tracking" both the players and the boss itself
during the `shuffle-positions` ability for the sake of _not_ blocking
the teleport event(s) that could potentially be blocked otherwise.

Note that the change introduced in the PlayerTeleportEvent handler is
not strictly necessary. The final block of code _should_ always yield
the same result, as `shuffle-positions` _should_ be working solely on
positions that are all inside the arena region, but the out-of-bounds
check might be delayed, so we don't know for sure. It's just a safety
precaution, but it really shouldn't be necessary.

Fixes #792

src/main/java/com/garbagemule/MobArena/ArenaListener.java

@@ -93,6 +93,7 @@ import org.bukkit.material.Attachable;
 import org.bukkit.material.Bed;
 import org.bukkit.material.Door;
 import org.bukkit.material.Redstone;
+import org.bukkit.metadata.MetadataValue;
 import org.bukkit.potion.PotionEffect;
 import org.bukkit.potion.PotionEffectType;
 import org.bukkit.projectiles.ProjectileSource;
@@ -928,6 +929,11 @@ public class ArenaListener
         }
 
         if (isArenaMonster(event.getEntity())) {
+            for (MetadataValue metadata : event.getEntity().getMetadata("teleporting")) {
+                if (plugin.equals(metadata.getOwningPlugin())) {
+                    return;
+                }
+            }
             if (!monsterTeleport || !region.contains(event.getTo())) {
                 event.setCancelled(true);
             }
@@ -1328,6 +1334,13 @@ public class ArenaListener
             return TeleportResponse.ALLOW;
         }
 
+        // Same deal for players being teleported by shuffle-positions.
+        for (MetadataValue metadata : p.getMetadata("teleporting")) {
+            if (plugin.equals(metadata.getOwningPlugin())) {
+                return TeleportResponse.ALLOW;
+            }
+        }
+
         Location to = event.getTo();
         Location from = event.getFrom();
 

src/main/java/com/garbagemule/MobArena/waves/ability/core/ShufflePositions.java

@@ -6,6 +6,8 @@ import com.garbagemule.MobArena.waves.ability.Ability;
 import com.garbagemule.MobArena.waves.ability.AbilityInfo;
 import org.bukkit.Location;
 import org.bukkit.entity.LivingEntity;
+import org.bukkit.metadata.FixedMetadataValue;
+import org.bukkit.metadata.MetadataValue;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -30,6 +32,11 @@ public class ShufflePositions implements Ability
             locations.add(e.getLocation());
         }
 
+        // Keep track of teleportees
+        MetadataValue metadata = new FixedMetadataValue(arena.getPlugin(), true);
+        List<LivingEntity> teleportees = new ArrayList<>(entities);
+        teleportees.forEach(e -> e.setMetadata("teleporting", metadata));
+
         // Shuffle the entities list.
         Collections.shuffle(entities);
 
@@ -39,5 +46,8 @@ public class ShufflePositions implements Ability
         while (!entities.isEmpty() && !locations.isEmpty()) {
             entities.remove(0).teleport(locations.remove(0));
         }
+
+        // Remove teleportee metadata
+        teleportees.forEach(e -> e.removeMetadata("teleporting", arena.getPlugin()));
     }
 }