Hopefully the right transfer stack code 🤞

src/main/java/de/ellpeck/actuallyadditions/common/container/DrillContainer.java

@@ -7,6 +7,7 @@ import net.minecraft.entity.player.PlayerEntity;
 import net.minecraft.entity.player.PlayerInventory;
 import net.minecraft.inventory.container.ClickType;
 import net.minecraft.inventory.container.Container;
+import net.minecraft.inventory.container.Slot;
 import net.minecraft.item.ItemStack;
 import net.minecraft.network.PacketBuffer;
 import net.minecraftforge.items.ItemStackHandler;
@@ -60,6 +61,7 @@ public class DrillContainer extends Container {
     @Nonnull
     @Override
     public ItemStack slotClick(int slotId, int dragType, @Nonnull ClickType clickTypeIn, @Nonnull PlayerEntity player) {
+        // Don't let the user pickup, throw or swap the drill, any drill
         if ((clickTypeIn == ClickType.SWAP || clickTypeIn == ClickType.THROW || clickTypeIn == ClickType.PICKUP)
                 && slotId >= 0
                 && slotId <= this.inventorySlots.size()
@@ -70,6 +72,31 @@ public class DrillContainer extends Container {
         return super.slotClick(slotId, dragType, clickTypeIn, player);
     }
 
+    @Override
+    public ItemStack transferStackInSlot(PlayerEntity playerIn, int index) {
+        Slot fromSlot = this.inventorySlots.get(index);
+
+        if (fromSlot == null || !fromSlot.getHasStack()) {
+            return ItemStack.EMPTY;
+        }
+
+        ItemStack fromStack = fromSlot.getStack();
+
+        // Moves items from the Drill to the players inventory
+        if (index > ContainerHelper.PLAYER_INVENTORY_END_SLOT) {
+            if (!this.mergeItemStack(fromStack, 0, ContainerHelper.PLAYER_INVENTORY_END_SLOT, false)) {
+                return ItemStack.EMPTY;
+            }
+        } else {
+            // Moves the item from the players inventory to the drill
+            if (!this.mergeItemStack(fromStack, ContainerHelper.PLAYER_INVENTORY_END_SLOT + 1, ContainerHelper.PLAYER_INVENTORY_END_SLOT + 6, false)) {
+                return ItemStack.EMPTY;
+            }
+        }
+
+        return fromStack;
+    }
+
     @Override
     public void onContainerClosed(@Nonnull PlayerEntity playerIn) {
         super.onContainerClosed(playerIn);

src/main/java/de/ellpeck/actuallyadditions/common/container/package-info.java

@@ -0,0 +1,7 @@
+@ParametersAreNonnullByDefault
+@MethodsReturnNonnullByDefault
+package de.ellpeck.actuallyadditions.common.container;
+
+import mcp.MethodsReturnNonnullByDefault;
+
+import javax.annotation.ParametersAreNonnullByDefault;

src/main/java/de/ellpeck/actuallyadditions/common/utilities/ContainerHelper.java

@@ -1,7 +1,9 @@
 package de.ellpeck.actuallyadditions.common.utilities;
 
 import net.minecraft.inventory.container.Slot;
+import net.minecraft.item.ItemStack;
 import net.minecraftforge.items.IItemHandler;
+import net.minecraftforge.items.ItemStackHandler;
 import net.minecraftforge.items.SlotItemHandler;
 
 import java.util.function.Consumer;
@@ -10,6 +12,20 @@ public class ContainerHelper {
     public static final int DEFAULT_SLOTS_X = 8;
     public static final int SLOT_SPACING = 18;
 
+    /**
+     * This value assumes you have used the {@link ContainerHelper#setupPlayerInventory(IItemHandler, int, int, int, Consumer)}
+     * method to generate your inventories slots. Do not use if otherwise
+     */
+    public static final int PLAYER_INVENTORY_END_SLOT = 35;
+
+    /**
+     *
+     * @param handler   the inventory handler (should always be the players)
+     * @param index     the starting index, should always be 0 logically. If otherwise, do not use {@link ContainerHelper#PLAYER_INVENTORY_END_SLOT}
+     * @param x         x offset for the inventory, for a full width inventory, this is typically 8
+     * @param y         y offset for the inventory, no default sorry
+     * @param consumer  Typically a containers the Containers#addSlot(Slot) method
+     */
     public static void setupPlayerInventory(IItemHandler handler, int index, int x, int y, Consumer<Slot> consumer) {
         // Build the players inventory first, building from bottom to top, right to left. The (i>0) magic handles the
         // space between the hotbar inventory and the players remaining inventory.
@@ -22,4 +38,10 @@ public class ContainerHelper {
         }
     }
 
+    public static ItemStackHandler getHandlerFromItem(ItemStack itemStack, String key, int size) {
+        ItemStackHandler handler = new ItemStackHandler(size);
+        handler.deserializeNBT(itemStack.getOrCreateChildTag(key));
+        return handler;
+    }
+
 }