create negative material set for iterator

src/main/kotlin/xyz/alexcrea/cuanvil/group/ExcludeGroup.kt

@@ -6,7 +6,7 @@ import java.util.*
 class ExcludeGroup(name: String) : AbstractMaterialGroup(name) {
 
     override fun createDefaultSet(): MutableSet<NamespacedKey> {
-        return NegativeSet(HashSet())
+        return NegativeMaterialSet()
     }
 
     private var includedGroup: MutableSet<AbstractMaterialGroup> = HashSet()

src/main/kotlin/xyz/alexcrea/cuanvil/group/NegativeMaterialSet.kt

@@ -0,0 +1,22 @@
+package xyz.alexcrea.cuanvil.group
+
+import org.bukkit.NamespacedKey
+import xyz.alexcrea.cuanvil.util.MaterialUtil
+import xyz.alexcrea.cuanvil.util.NegativeSet
+
+class NegativeMaterialSet: NegativeSet<NamespacedKey>() {
+
+    override fun iterator(): MutableIterator<NamespacedKey> {
+        val materials = MaterialUtil.getMaterials()
+        materials.removeIf { negate.contains(it) }
+
+        return materials.iterator()
+    }
+
+    override fun isEmpty(): Boolean {
+        return negate.size >= MaterialUtil.getMaterialCount()
+    }
+
+    override val size get() = MaterialUtil.getMaterialCount() - negate.size
+
+}

src/main/kotlin/xyz/alexcrea/cuanvil/util/NegativeSet.kt

@@ -1,6 +1,6 @@
-package xyz.alexcrea.cuanvil.group
+package xyz.alexcrea.cuanvil.util
 
-class NegativeSet<T>(val negate: MutableSet<T>) : MutableSet<T> {
+open class NegativeSet<T>(val negate: MutableSet<T> = HashSet()) : MutableSet<T> {
 
     override fun iterator(): MutableIterator<T> {
         TODO("Not yet implemented") // can't be implemented I guess
@@ -15,7 +15,7 @@ class NegativeSet<T>(val negate: MutableSet<T>) : MutableSet<T> {
     }
 
     override fun addAll(elements: Collection<T>): Boolean {
-        return negate.removeAll(elements)
+        return negate.removeAll(elements.toSet())
     }
 
     override fun removeAll(elements: Collection<T>): Boolean {
@@ -34,7 +34,7 @@ class NegativeSet<T>(val negate: MutableSet<T>) : MutableSet<T> {
         TODO("Not yet implemented")
     }
 
-    override val size get() = TODO("Not yet implemented")
+    override val size: Int get() = TODO("Not yet implemented")
 
     override fun contains(element: T): Boolean {
         return !negate.contains(element)