Changeable Max Stack Size for Items and Inventory

src/main/java/ch/njol/skript/expressions/ExprMaxStack.java

@@ -18,35 +18,131 @@
  */
 package ch.njol.skript.expressions;
 
+import ch.njol.skript.Skript;
 import ch.njol.skript.aliases.ItemType;
+import ch.njol.skript.classes.Changer.ChangeMode;
 import ch.njol.skript.doc.Description;
 import ch.njol.skript.doc.Examples;
 import ch.njol.skript.doc.Name;
+import ch.njol.skript.doc.RequiredPlugins;
 import ch.njol.skript.doc.Since;
 import ch.njol.skript.expressions.base.SimplePropertyExpression;
+import ch.njol.util.Math2;
+import ch.njol.util.coll.CollectionUtils;
+import org.bukkit.Bukkit;
+import org.bukkit.event.Event;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.meta.ItemMeta;
+import org.jetbrains.annotations.Nullable;
 
-/**
- * @author joeuguce99
- */
 @Name("Maximum Stack Size")
-@Description("The maximum stack size of the specified material, e.g. 64 for torches, 16 for buckets, and 1 for swords.")
-@Examples("send \"You can only pick up %max stack size of player's tool% of %type of (player's tool)%\" to player")
-@Since("2.1")
-public class ExprMaxStack extends SimplePropertyExpression<ItemType, Long> {
+@Description({
+	"The maximum stack size of an item (e.g. 64 for torches, 16 for buckets, and 1 for swords), or of an inventory to have items to stack up to.",
+	"Since MC 1.20.5 onwards, the maximum stack size of items can be changed (any integer from 1 to 99), and the said item can be stacked up to the set value, up to the maximum stack size of an inventory."
+})
+@Examples({
+	"send \"You can only pick up %max stack size of player's tool% of %type of (player's tool)%\" to player",
+	"",
+	"set the maximum stack size of inventory of all players to 16",
+	"",
+	"add 8 to the maximum stack size of player's tool",
+	"",
+	"reset the maximum stack size of {_gui}"
+})
+@Since("2.1, INSERT VERSION (changeable, inventory support)")
+@RequiredPlugins("Spigot 1.20.5+ (changeable item max stack size)")
+public class ExprMaxStack extends SimplePropertyExpression<Object, Integer> {
 
 	static {
-		register(ExprMaxStack.class, Long.class, "max[imum] stack[[ ]size]", "itemtype");
+		register(ExprMaxStack.class, Integer.class, "max[imum] stack[[ ]size]", "itemtypes/inventories");
+	}
+
+	private static final boolean CHANGEABLE_ITEM_STACK_SIZE = Skript.methodExists(ItemMeta.class, "setMaxStackSize", Integer.class);
+
+	@Override
+	@Nullable
+	public Integer convert(Object source) {
+		if (source instanceof ItemType) {
+			return ((ItemType) source).getRandom().getMaxStackSize();
+		} else if (source instanceof Inventory) {
+			return (((Inventory) source).getMaxStackSize());
+		} else {
+			// Invalid source -- return null
+			return null;
+		}
 	}
-
-	@SuppressWarnings("null")
+
+	@Override
+	@Nullable
+	public Class<?>[] acceptChange(ChangeMode mode) {
+		switch (mode) {
+            case ADD:
+			case DELETE:
+            case REMOVE:
+			case RESET:
+			case SET:
+				if (!CHANGEABLE_ITEM_STACK_SIZE && ItemType.class.isAssignableFrom(getExpr().getReturnType())) {
+					Skript.error("Changers for maximum stack size of items requires Minecraft 1.20.5 or newer");
+					return null;
+				}
+				return CollectionUtils.array(Integer.class);
+			default:
+				return null;
+        }
+	}
+
 	@Override
-	public Long convert(final ItemType i) {
-		return (long) i.getRandom().getMaxStackSize();
+	public void change(Event event, @Nullable Object[] delta, ChangeMode mode) {
+		for (Object source : getExpr().getArray(event)) {
+			Integer change = null;
+			if (mode != ChangeMode.DELETE && mode != ChangeMode.RESET)
+				change = (int) delta[0];
+			if (source instanceof ItemType) {
+				if (!CHANGEABLE_ITEM_STACK_SIZE)
+					continue;
+				ItemType itemType = ((ItemType) source);
+				int size = itemType.getRandom().getMaxStackSize();
+                switch (mode) {
+                    case ADD:
+						size += change;
+                        break;
+                    case SET:
+						size = change;
+						break;
+                    case REMOVE:
+						size -= change;
+                        break;
+                }
+				ItemMeta meta = itemType.getItemMeta();
+				// Minecraft only accepts stack size from 1 to 99
+				meta.setMaxStackSize(change != null ? Math2.fit(1, size, 99) : null);
+				itemType.setItemMeta(meta);
+			} else if (source instanceof Inventory) {
+				Inventory inv = ((Inventory) source);
+				int size = inv.getMaxStackSize();
+				switch (mode) {
+					case ADD:
+						size += change;
+						break;
+					case SET:
+						size = change;
+						break;
+					case REMOVE:
+						size -= change;
+						break;
+					case DELETE:
+					case RESET:
+						size = Bukkit.createInventory(null, inv.getType()).getMaxStackSize();
+						break;
+				}
+				inv.setMaxStackSize(size);
+			}
+		}
 	}
 
 	@Override
-	public Class<? extends Long> getReturnType() {
-		return Long.class;
+	public Class<? extends Integer> getReturnType() {
+		return Integer.class;
 	}
 
 	@Override

src/test/skript/tests/syntaxes/expressions/ExprMaxStack.sk

@@ -2,3 +2,49 @@ test "max stack":
 	assert max stack size of diamond sword is 1 with "diamond sword max stack size failed"
 	assert max stack size of bucket is 16 with "bucket max stack size failed"
 	assert max stack size of dirt is 64 with "dirt max stack size failed"
+
+test "max stack override - itemtype" when running minecraft "1.20.5":
+	set {_item} to diamond
+	set max stack size of {_item} to 32
+	assert max stack size of {_item} is 32 with "diamond should have max stack size of 32"
+	add 2 to max stack size of {_item}
+	assert max stack size of {_item} is 34 with "diamond should have max stack size of 34"
+	remove 4 from max stack size of {_item}
+	assert max stack size of {_item} is 30 with "diamond should have max stack size of 30"
+	reset max stack size of {_item}
+	assert max stack size of {_item} is 64 with "diamond should have max stack size of 64"
+
+	set {_item} to bucket
+	set max stack size of {_item} to 24
+	assert max stack size of {_item} is 24 with "bucket should have max stack size of 24"
+	add 2 to max stack size of {_item}
+	assert max stack size of {_item} is 26 with "bucket should have max stack size of 26"
+	remove 4 from max stack size of {_item}
+	assert max stack size of {_item} is 22 with "bucket should have max stack size of 22"
+	reset max stack size of {_item}
+	assert max stack size of {_item} is 16 with "bucket should have max stack size of 16"
+
+	set {_item} to diamond sword
+	set max stack size of {_item} to 16
+	assert max stack size of {_item} is 16 with "diamond sword should have max stack size of 16"
+	add 2 to max stack size of {_item}
+	assert max stack size of {_item} is 18 with "diamond sword should have max stack size of 18"
+	remove 4 from max stack size of {_item}
+	assert max stack size of {_item} is 14 with "diamond sword should have max stack size of 14"
+	reset max stack size of {_item}
+	assert max stack size of {_item} is 1 with "diamond sword should have max stack size of 1"
+
+test "max stack override - inventory":
+	set {_default} to 99 # 1.20.5 and newer
+	if running below minecraft "1.20.5":
+		set {_default} to 64
+	set {_inv} to a new chest inventory with 1 rows
+	assert max stack size of {_inv} is {_default} with "inventory should have max stack size of %{_default}%"
+	set max stack size of {_inv} to 32
+	assert max stack size of {_inv} is 32 with "inventory should have max stack size of 32"
+	add 2 to max stack size of {_inv}
+	assert max stack size of {_inv} is 34 with "inventory should have max stack size of 34"
+	remove 4 from max stack size of {_inv}
+	assert max stack size of {_inv} is 30 with "inventory should have max stack size of 30"
+	reset max stack size of {_inv}
+	assert max stack size of {_inv} is {_default} with "inventory should have factory max stack size of %{_default}%"