Update

src/main/java/systems/brn/plasticgun/lib/Util.java

@@ -1,5 +1,7 @@
 package systems.brn.plasticgun.lib;
 
+import net.minecraft.entity.player.PlayerInventory;
+import net.minecraft.inventory.Inventory;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.server.network.ServerPlayerEntity;
@@ -28,4 +30,71 @@ public class Util {
         }
         return ItemStack.EMPTY;
     }
+
+    public static int canInsertItemIntoInventory(Inventory inventory, ItemStack itemStack) {
+        // Get the player's inventory
+        int maxInsert = 0;
+
+        if (inventory instanceof PlayerInventory playerInventory) {
+            // Iterate through the slots in the player's inventory
+            for (int i = 0; i < playerInventory.main.size(); i++) {
+                ItemStack slotStack = playerInventory.main.get(i);
+                maxInsert = canInsertToStack(slotStack, itemStack, maxInsert);
+            }
+        } else {
+            for (int i = 0; i < inventory.size(); i++) {
+                ItemStack slotStack = inventory.getStack(i);
+                maxInsert = canInsertToStack(slotStack, itemStack, maxInsert);
+            }
+        }
+
+        return maxInsert; // Return the maximum insertion count
+    }
+
+    public static int canInsertToStack(ItemStack stack1, ItemStack stack2, int maxInsert) {
+        if (stack1.isEmpty() || ItemStack.areItemsEqual(stack1, stack2)) {
+            int remainingSpace = stack1.isEmpty() ? stack2.getMaxCount() : stack1.getMaxCount() - stack1.getCount();
+            maxInsert += remainingSpace;
+            // If the maximum insertion count is greater than or equal to the item count, return the item count
+            if (maxInsert >= stack2.getCount()) {
+                return stack2.getCount();
+            }
+        }
+        return maxInsert;
+    }
+
+    public static boolean canCombine(ItemStack stack1, ItemStack stack2) {
+        return !stack1.isEmpty() && stack1.getItem() == stack2.getItem() && ItemStack.areItemsAndComponentsEqual(stack1, stack2);
+    }
+
+    public static ItemStack insertStackIntoInventory(Inventory inventory, ItemStack stack) {
+        // First, try to merge with existing stacks
+        for (int i = 0; i < inventory.size(); i++) {
+            ItemStack slotStack = inventory.getStack(i);
+            if (canCombine(slotStack, stack)) {
+                int transferAmount = Math.min(stack.getCount(), slotStack.getMaxCount() - slotStack.getCount());
+                if (transferAmount > 0) {
+                    slotStack.increment(transferAmount);
+                    stack.decrement(transferAmount);
+                    inventory.markDirty();
+                    if (stack.isEmpty()) {
+                        return ItemStack.EMPTY;
+                    }
+                }
+            }
+        }
+
+        // Next, try to find an empty slot
+        for (int i = 0; i < inventory.size(); i++) {
+            ItemStack slotStack = inventory.getStack(i);
+            if (slotStack.isEmpty()) {
+                inventory.setStack(i, stack.copy());
+                stack.setCount(0);
+                inventory.markDirty();
+                return ItemStack.EMPTY;
+            }
+        }
+
+        return stack;
+    }
 }