Changed item merging from full inventory copy to partial stacks copy

avoids copying itemstacks that are at max size, and cant be merged into anyway

src/main/java/gregtech/api/metatileentity/MetaTileEntity.java

@@ -22,6 +22,7 @@
 import gregtech.api.render.Textures;
 import gregtech.api.util.GTFluidUtils;
 import gregtech.api.util.GTUtility;
+import gregtech.api.util.InventoryUtils;
 import net.minecraft.block.Block;
 import net.minecraft.block.state.BlockFaceShape;
 import net.minecraft.client.renderer.texture.TextureAtlasSprite;
@@ -56,8 +57,6 @@
 import java.util.List;
 import java.util.function.Consumer;
 
-import static gregtech.api.util.InventoryUtils.simulateItemStackMerge;
-
 public abstract class MetaTileEntity implements ICoverable {
 
     public static final int DEFAULT_PAINTING_COLOR = 0xFFFFFF;
@@ -973,8 +972,14 @@ public static boolean addItemsToItemHandler(final IItemHandler handler,
                                                 final boolean simulate,
                                                 final List<ItemStack> items) {
         // determine if there is sufficient room to insert all items into the target inventory
-        final boolean canMerge = simulateItemStackMerge(items, handler);
-
+        boolean canMerge;
+        if (items.size() == 1) {
+            canMerge = ItemHandlerHelper.insertItemStacked(handler, items.get(0), true).isEmpty();
+        } else {
+            // merging 2 or more stacks may change the slots available for merging,
+            // needing full simulation of the state of the inventory after every merge
+            canMerge = InventoryUtils.simulateItemStackMerge(items, handler);
+        }
         // if we're not simulating and the merge should succeed, perform the merge.
         if (!simulate && canMerge)
             items.forEach(stack -> {

src/main/java/gregtech/api/util/InventoryUtils.java

@@ -43,6 +43,21 @@ public static List<ItemStack> deepCopy(final IItemHandler inventory,
             .collect(Collectors.toList());
     }
 
+    /**
+     * Creates a copy of the partial stacks in target inventory
+     *
+     * @param inventory the target inventory
+     * @return a copy of the partial stacks of the inventory.
+     */
+    public static List<ItemStack> copyPartialStacks(final IItemHandler inventory) {
+
+        return streamFrom(inventory)
+            .filter(not(ItemStack::isEmpty))
+            .filter(not(itemStack -> itemStack.getCount() == itemStack.getMaxStackSize()))
+            .map(ItemStack::copy)
+            .collect(Collectors.toList());
+    }
+
     /**
      * Determines whether all specified items will fit into a target inventory by
      * simulating merging like items into existing stacks, then checking if there
@@ -75,7 +90,7 @@ public static boolean simulateItemStackMerge(List<ItemStack> inputItems,
         itemStacks.sort(Comparator.comparingInt(ItemStack::getCount));
 
         // Deep copy the contents of the target inventory, skipping empty stacks
-        final List<ItemStack> inventoryStacks = deepCopy(inventory, false);
+        final List<ItemStack> inventoryStacks = copyPartialStacks(inventory);
 
         // Perform a merge of the ItemStacks
         mergeItemStacks(itemStacks, inventoryStacks);