[EXPERIMENTAL] Add "player swaps items" event for #1329

Should be replaced whenever Spigot adds an event

src/main/java/net/aufdemrand/denizen/Denizen.java

@@ -680,6 +680,7 @@ public void onEnable() {
             ScriptEvent.registerScriptEvent(new PlayerSprintScriptEvent());
             ScriptEvent.registerScriptEvent(new PlayerStatisticIncrementsScriptEvent());
             ScriptEvent.registerScriptEvent(new PlayerStepsOnScriptEvent());
+            ScriptEvent.registerScriptEvent(new PlayerSwapsItemsScriptEvent());
             ScriptEvent.registerScriptEvent(new PlayerTakesFromFurnaceScriptEvent());
             ScriptEvent.registerScriptEvent(new PlayerThrowsEggScriptEvent());
             ScriptEvent.registerScriptEvent(new PlayerUsesPortalScriptEvent());

src/main/java/net/aufdemrand/denizen/events/player/PlayerSwapsItemsScriptEvent.java

@@ -0,0 +1,52 @@
+package net.aufdemrand.denizen.events.player;
+
+import net.aufdemrand.denizen.BukkitScriptEntryData;
+import net.aufdemrand.denizen.events.BukkitScriptEvent;
+import net.aufdemrand.denizen.objects.dPlayer;
+import net.aufdemrand.denizencore.scripts.ScriptEntryData;
+import net.aufdemrand.denizencore.scripts.containers.ScriptContainer;
+import net.aufdemrand.denizencore.utilities.CoreUtilities;
+
+public class PlayerSwapsItemsScriptEvent extends BukkitScriptEvent {
+
+    // <--[event]
+    // @Events
+    // player swaps items
+    //
+    // @Regex ^on player swaps items$
+    //
+    // @Warning This event is a prototype and may change drastically in the future.
+    //
+    // @Cancellable true
+    //
+    // @Triggers when a player swaps the items in their main and offhand.
+    //
+    // -->
+
+    public PlayerSwapsItemsScriptEvent() {
+        instance = this;
+    }
+
+    public static PlayerSwapsItemsScriptEvent instance;
+    public dPlayer player;
+
+    @Override
+    public boolean couldMatch(ScriptContainer scriptContainer, String s) {
+        return CoreUtilities.toLowerCase(s).startsWith("player swaps items");
+    }
+
+    @Override
+    public boolean matches(ScriptContainer scriptContainer, String s) {
+        return true;
+    }
+
+    @Override
+    public String getName() {
+        return "PlayerSwapsItems";
+    }
+
+    @Override
+    public ScriptEntryData getScriptEntryData() {
+        return new BukkitScriptEntryData(player, null);
+    }
+}

src/main/java/net/aufdemrand/denizen/utilities/packets/intercept/DenizenPacketListener.java

@@ -1,5 +1,6 @@
 package net.aufdemrand.denizen.utilities.packets.intercept;
 
+import net.aufdemrand.denizen.events.player.PlayerSwapsItemsScriptEvent;
 import net.aufdemrand.denizen.events.player.ResourcePackStatusScriptEvent;
 import net.aufdemrand.denizen.objects.dPlayer;
 import net.aufdemrand.denizen.utilities.DenizenAPI;
@@ -80,6 +81,20 @@ public void run() {
         super.a(packet);
     }
 
+    @Override
+    public void a(PacketPlayInBlockDig packet) {
+        if (packet.c() == PacketPlayInBlockDig.EnumPlayerDigType.SWAP_HELD_ITEMS) {
+            // Run async to allow cancellation
+            PlayerSwapsItemsScriptEvent event = PlayerSwapsItemsScriptEvent.instance;
+            event.player = dPlayer.mirrorBukkitPlayer(player.getBukkitEntity());
+            event.fire();
+            if (event.cancelled) {
+                return;
+            }
+        }
+        super.a(packet);
+    }
+
     // For compatibility with other plugins using Reflection weirdly...
     @Override
     public void sendPacket(Packet packet) {