Add time states for PlayerItemHeldEvent and hotbar slot

src/main/java/ch/njol/skript/classes/data/BukkitEventValues.java

@@ -107,6 +107,7 @@
 import org.bukkit.event.player.PlayerItemBreakEvent;
 import org.bukkit.event.player.PlayerItemConsumeEvent;
 import org.bukkit.event.player.PlayerItemDamageEvent;
+import org.bukkit.event.player.PlayerItemHeldEvent;
 import org.bukkit.event.player.PlayerItemMendEvent;
 import org.bukkit.event.player.PlayerMoveEvent;
 import org.bukkit.event.player.PlayerPickupArrowEvent;
@@ -1650,6 +1651,22 @@ public Location get(LootGenerateEvent event) {
 			}, EventValues.TIME_NOW);
 		}
 
+    // PlayerItemHeldEvent
+		EventValues.registerEventValue(PlayerItemHeldEvent.class, Slot.class, new Getter<Slot, PlayerItemHeldEvent>() {
+			@Override
+			@Nullable
+			public Slot get(PlayerItemHeldEvent event) {
+				return new InventorySlot(event.getPlayer().getInventory(), event.getNewSlot());
+			}
+		}, EventValues.TIME_NOW);
+		EventValues.registerEventValue(PlayerItemHeldEvent.class, Slot.class, new Getter<Slot, PlayerItemHeldEvent>() {
+			@Override
+			@Nullable
+			public Slot get(PlayerItemHeldEvent event) {
+				return new InventorySlot(event.getPlayer().getInventory(), event.getPreviousSlot());
+			}
+		}, EventValues.TIME_PAST);
+
 		// PlayerPickupArrowEvent
 		// This event value is restricted to MC 1.14+ due to an API change which has the return type changed
 		// which throws a NoSuchMethodError if used in a 1.13 server.

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

@@ -20,70 +20,116 @@
 
 import org.bukkit.entity.Player;
 import org.bukkit.event.Event;
+import org.bukkit.event.player.PlayerItemHeldEvent;
 import org.bukkit.inventory.PlayerInventory;
 import org.eclipse.jdt.annotation.Nullable;
 
-import ch.njol.skript.classes.Changer;
+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.Since;
-import ch.njol.skript.expressions.base.SimplePropertyExpression;
+import ch.njol.skript.expressions.base.PropertyExpression;
+import ch.njol.skript.lang.Expression;
+import ch.njol.skript.lang.SkriptParser.ParseResult;
+import ch.njol.skript.registrations.EventValues;
+import ch.njol.skript.util.Getter;
 import ch.njol.skript.util.slot.InventorySlot;
 import ch.njol.skript.util.slot.Slot;
+import ch.njol.util.Kleenean;
 
 @Name("Hotbar Slot")
-@Description({"The currently selected hotbar <a href='./classes.html#slot'>slot</a>. To retrieve its number use <a href='#ExprSlotIndex'>Slot Index</a> expression."})
-@Examples({"message \"%player's current hotbar slot%\"",
-            "set player's selected hotbar slot to slot 4 of player",
-			"send \"index of player's current hotbar slot = 1\" # second slot from the left"})
+@Description({
+	"The currently selected hotbar <a href='./classes.html#slot'>slot</a>.",
+	"To retrieve its number use <a href='#ExprSlotIndex'>Slot Index</a> expression.",
+	"Use future and past tense to grab the previous slot in an item change event, see example."
+})
+@Examples({
+	"message \"%player's current hotbar slot%\"",
+	"set player's selected hotbar slot to slot 4 of player",
+	"",
+	"send \"index of player's current hotbar slot = 1\" # second slot from the left",
+	"",
+	"on item held change:",
+		"\tif the selected hotbar slot was a diamond:",
+			"\t\tset the currently selected hotbar slot to slot 5 of player"
+})
 @Since("2.2-dev36")
-public class ExprHotbarSlot extends SimplePropertyExpression<Player, Slot> {
+public class ExprHotbarSlot extends PropertyExpression<Player, Slot> {
 
 	static {
-		register(ExprHotbarSlot.class, Slot.class, "[([currently] selected|current)] hotbar slot", "players");
+		registerDefault(ExprHotbarSlot.class, Slot.class, "[the] [([current:currently] selected|current:current)] hotbar slot[s]", "players");
 	}
-
-	@Override
-	@Nullable
-	public Slot convert(Player p) {
-		PlayerInventory invi = p.getInventory();
-		assert invi != null;
-		return new InventorySlot(invi, invi.getHeldItemSlot());
-	}
-
+
+	// This exists because time states should not register when the 'currently' tag of the syntax is present.
+	private boolean current;
+
 	@Override
-	protected String getPropertyName() {
-		return "hotbar slot";
+	@SuppressWarnings("unchecked")
+	public boolean init(Expression<?>[] exprs, int matchedPattern, Kleenean isDelayed, ParseResult parseResult) {
+		setExpr((Expression<? extends Player>) exprs[0]);
+		current = parseResult.hasTag("current");
+		return true;
 	}
-	
+
 	@Override
-	public Class<? extends Slot> getReturnType() {
-		return Slot.class;
+	protected Slot[] get(Event event, Player[] source) {
+		return get(source, new Getter<Slot, Player>() {
+			@Override
+			@Nullable
+			public Slot get(Player player) {
+				int time = getTime();
+				PlayerInventory inventory = player.getInventory();
+				if (event instanceof PlayerItemHeldEvent && time != EventValues.TIME_NOW) {
+					PlayerItemHeldEvent switchEvent = (PlayerItemHeldEvent) event;
+					if (time == EventValues.TIME_FUTURE)
+						return new InventorySlot(inventory, switchEvent.getNewSlot());
+					if (time == EventValues.TIME_PAST)
+						return new InventorySlot(inventory, switchEvent.getPreviousSlot());
+				}
+				return new InventorySlot(inventory, inventory.getHeldItemSlot());
+			}
+		});
 	}
-	
+
 	@Override
 	@Nullable
-	public Class<?>[] acceptChange(Changer.ChangeMode mode) {
-		if (mode == Changer.ChangeMode.SET)
+	public Class<?>[] acceptChange(ChangeMode mode) {
+		if (mode == ChangeMode.SET)
 			return new Class[] {Slot.class};
 		return null;
 	}
-	
+
 	@Override
-	public void change(Event e, @Nullable Object[] delta, Changer.ChangeMode mode) {
+	public void change(Event event, @Nullable Object[] delta, ChangeMode mode) {
 		assert delta != null;
 		Slot slot = (Slot) delta[0];
 		if (!(slot instanceof InventorySlot))
 			return; // Only inventory slots can be hotbar slots
-		
+
 		int index = ((InventorySlot) slot).getIndex();
 		if (index > 8) // Only slots in hotbar can be current hotbar slot
 			return;
-
-		for (Player p : getExpr().getArray(e)) {
-			p.getInventory().setHeldItemSlot(index);
-		}
+
+		for (Player player : getExpr().getArray(event))
+			player.getInventory().setHeldItemSlot(index);
 	}
-
+
+	@Override
+	public boolean setTime(int time) {
+		if (current)
+			return super.setTime(time);
+		return super.setTime(time, getExpr(), PlayerItemHeldEvent.class);
+	}
+
+	@Override
+	public Class<? extends Slot> getReturnType() {
+		return Slot.class;
+	}
+
+	@Override
+	public String toString(@Nullable Event event, boolean debug) {
+		return "hotbar slot of " + getExpr().toString(event, debug);
+	}
+
 }