Create OnlinePlayerMap.kt

src/main/kotlin/net/axay/kspigot/utils/OnlinePlayerMap.kt

@@ -0,0 +1,44 @@
+@file:Suppress("MemberVisibilityCanBePrivate")
+
+package net.axay.kspigot.utils
+
+import net.axay.kspigot.event.listen
+import org.bukkit.entity.Player
+import org.bukkit.event.player.PlayerQuitEvent
+import java.util.*
+
+object PlayerMapHolder {
+    internal val maps = HashSet<OnlinePlayerMap<*>>()
+
+    init {
+        listen<PlayerQuitEvent> { event ->
+            maps.removeIf {
+                if (it.internalMap.remove(event.player.uniqueId) != null) {
+                    it.internalMap.isEmpty()
+                } else false
+            }
+        }
+    }
+}
+
+/**
+ * A map where entries will be removed
+ * atomatically when a player leaves the server.
+ */
+class OnlinePlayerMap<V> {
+    val internalMap = HashMap<UUID, V>()
+
+    operator fun get(player: Player) = internalMap[player.uniqueId]
+
+    operator fun set(player: Player, value: V) {
+        if (internalMap.isEmpty())
+            PlayerMapHolder.maps += this
+        internalMap[player.uniqueId] = value
+    }
+
+    operator fun minusAssign(player: Player) {
+        internalMap -= player.uniqueId
+        if (internalMap.isEmpty())
+            PlayerMapHolder.maps -= this
+    }
+}