MatteryContainer now save only non empty itemstacks

src/main/kotlin/ru/dbotthepony/mc/otm/container/MatteryContainer.kt

@@ -1,5 +1,6 @@
 package ru.dbotthepony.mc.otm.container
 
+import it.unimi.dsi.fastutil.ints.IntAVLTreeSet
 import net.minecraft.world.item.ItemStack
 import net.minecraft.nbt.CompoundTag
 import net.minecraft.nbt.ListTag
@@ -9,6 +10,7 @@ import kotlin.jvm.JvmOverloads
 import net.minecraft.world.entity.player.Player
 import net.minecraft.world.level.block.entity.BlockEntity
 import ru.dbotthepony.mc.otm.core.ifHas
+import ru.dbotthepony.mc.otm.core.set
 import java.util.*
 
 @Suppress("UNUSED")
@@ -59,7 +61,7 @@ open class MatteryContainer(val watcher: Runnable, private val size: Int) : Cont
 		setChanged()
 	}
 
-	fun deserializeNBT(tag: ListTag?) {
+	private fun deserializeNBT(tag: ListTag?) {
 		Arrays.fill(slots, ItemStack.EMPTY)
 
 		if (tag == null) {
@@ -67,9 +69,40 @@ open class MatteryContainer(val watcher: Runnable, private val size: Int) : Cont
 			return
 		}
 
+		var isIndexed = true
+
+		for (i in 0 until tag.size.coerceAtMost(size)) {
+			if (!(tag[i] as CompoundTag).contains("slotIndex")) {
+				isIndexed = false
+				break
+			}
+		}
+
+		if (isIndexed) {
+			val freeSlots = IntAVLTreeSet()
+
+			for (i in 0 until size)
+				freeSlots.add(i)
+
+			for (i in 0 until tag.size.coerceAtMost(size)) {
+				val nbt = tag[i] as CompoundTag
+				var slotID = nbt.getInt("slotIndex")
+
+				if (freeSlots.remove(slotID)) {
+					slots[slotID] = ItemStack.of(nbt)
+				} else if (freeSlots.isEmpty()) {
+					break
+				} else {
+					slotID = freeSlots.firstInt()
+					freeSlots.remove(slotID)
+					slots[slotID] = ItemStack.of(nbt)
+				}
+			}
+		} else {
 			for (i in 0 until tag.size.coerceAtMost(size)) {
 				slots[i] = ItemStack.of(tag[i] as CompoundTag)
 			}
+		}
 
 		setChanged()
 	}
@@ -91,8 +124,12 @@ open class MatteryContainer(val watcher: Runnable, private val size: Int) : Cont
 
 	fun serializeNBT(): ListTag {
 		return ListTag().also {
-			for (i in 0 until size) {
+			for ((i, item) in slots.withIndex()) {
-				it.add(this[i].serializeNBT())
+				if (!item.isEmpty) {
+					it.add(item.serializeNBT().also {
+						it["slotIndex"] = i
+					})
+				}
 			}
 		}
 	}