When storage bus receive items, try to put them into existing slots first

src/main/kotlin/ru/dbotthepony/mc/otm/block/entity/storage/StorageBusBlockEntity.kt

@@ -1,6 +1,7 @@
 package ru.dbotthepony.mc.otm.block.entity.storage
 
 import it.unimi.dsi.fastutil.ints.Int2ObjectAVLTreeMap
+import it.unimi.dsi.fastutil.ints.IntArraySet
 import it.unimi.dsi.fastutil.longs.Long2ObjectAVLTreeMap
 import net.minecraft.core.BlockPos
 import net.minecraft.core.Direction
@@ -235,6 +236,38 @@ class StorageBusBlockEntity(blockPos: BlockPos, blockState: BlockState) : Matter
 			}
 		}
 
+		private inner class PrioritizedSlotIterator(tuple: TrackedTuple?) : Iterator<Int> {
+			private val tupleIndexes = IntArraySet()
+
+			init {
+				if (tuple != null) {
+					for (child in tuple.children) {
+						tupleIndexes.add(child.key)
+					}
+				}
+			}
+
+			private val seenIterator = tupleIndexes.iterator()
+			private val regularIterator = (0 until parent.slots).iterator()
+
+			override fun hasNext(): Boolean {
+				return seenIterator.hasNext() || regularIterator.hasNext()
+			}
+
+			override fun next(): Int {
+				if (seenIterator.hasNext())
+					return seenIterator.nextInt()
+
+				var value = regularIterator.nextInt()
+
+				while (tupleIndexes.remove(value)) {
+					value = regularIterator.nextInt()
+				}
+
+				return value
+			}
+		}
+
 		private var snapshot: EventsSnapshot? = null
 
 		override val storageType: StorageStackType<ItemStackWrapper>
@@ -435,7 +468,7 @@ class StorageBusBlockEntity(blockPos: BlockPos, blockState: BlockState) : Matter
 				leftover.count -= additional
 			}
 
-			for (slot in 0 until parent.slots) {
+			for (slot in PrioritizedSlotIterator(tuples[stack.key()])) {
 				val oldCount = leftover.count
 				leftover = ItemStackWrapper(parent.insertItem(slot, leftover.stack, simulate))