public ItemStack transferStackInSlot(EntityPlayer player, int slotIndex)
    {
        ItemStack itemstack = null;
        Slot slot = (Slot) this.inventorySlots.get(slotIndex);

        if (slot != null && slot.getHasStack()) {
            ItemStack itemstack1 = slot.getStack();
            itemstack = itemstack1.copy();

            // If item is in TileEntity inventory
            if (slotIndex >= INPUT_CONCRETE_1 && slotIndex <= INPUT_MODIFIER_2 && slotIndex < INV_START) {
                // try to place in player inventory / action bar
                if (!this.mergeItemStack(itemstack1, INV_START, HOTBAR_END + 1, false)) {
                    return null;
                }
                slot.onSlotChange(itemstack1, itemstack);
            }
            // Item is in player inventory, try to place in GUI
            else if (slotIndex < HOTBAR_END) {
                // if it's concrete put in Concrete slot
                //   if (itemstack1.isItemEqual(new ItemStack(ModBlocks.concrete))) {
                if (BlockTableRecipes.isCraftableBlock(itemstack1)) {
                    if (!this.mergeItemStack(itemstack1, INPUT_CONCRETE_1, INPUT_CONCRETE_1 + 1, false)) {
                        return null;
                    }
                }
                // if it is a recipe material, place in the Modifier input slot
                else if (BlockTableRecipes.isMaterial(itemstack1)) {
                    if (!this.mergeItemStack(itemstack1, INPUT_MODIFIER_2, INPUT_MODIFIER_2 + 1, false)) {
                        return null;
                    }
                }
                // item in player's inventory, but not in action bar
                else if (slotIndex >= INV_START && slotIndex < HOTBAR_START) {
                    // place in action bar
                    if (!this.mergeItemStack(itemstack1, HOTBAR_START, HOTBAR_END + 1, false)) {
                        return null;
                    }
                }
                // item in action bar - place in player inventory
                else if (slotIndex >= HOTBAR_START && slotIndex < HOTBAR_END + 1 && !this.mergeItemStack(itemstack1, INV_START, HOTBAR_START, false)) {
                    return null;
                }
            }
            // In one of the slots; try to place in player inventory / action bar
            else if (slotIndex >= INPUT_CONCRETE_1 && slotIndex <= INPUT_MODIFIER_2 && !this.mergeItemStack(itemstack1, INV_START, HOTBAR_END + 1, false)) {
                return null;
            }
            if (itemstack1.stackSize == 0) {
                slot.putStack((ItemStack) null);
            } else {
                slot.onSlotChanged();
            }
            if (itemstack1.stackSize == itemstack.stackSize) {
                return null;
            }
            slot.onPickupFromSlot(player, itemstack1);
        }
        return itemstack;
    }