Add DifficultyChangeEvent (#3525)

src/main/java/net/minecraftforge/common/ForgeHooks.java

@@ -89,12 +89,14 @@ import net.minecraft.util.text.TextFormatting;
 import net.minecraft.util.text.event.ClickEvent;
 import net.minecraft.world.IBlockAccess;
 import net.minecraft.world.World;
+import net.minecraft.world.EnumDifficulty;
 import net.minecraft.world.GameType;
 import net.minecraft.world.storage.loot.LootEntry;
 import net.minecraft.world.storage.loot.LootTable;
 import net.minecraft.world.storage.loot.conditions.LootCondition;
 import net.minecraftforge.common.util.BlockSnapshot;
 import net.minecraftforge.event.AnvilUpdateEvent;
+import net.minecraftforge.event.DifficultyChangeEvent;
 import net.minecraftforge.event.ForgeEventFactory;
 import net.minecraftforge.event.ServerChatEvent;
 import net.minecraftforge.event.entity.EntityTravelToDimensionEvent;
@@ -510,6 +512,11 @@ public class ForgeHooks
         }
         return false;
     }
+    
+    public static void onDifficultyChange(EnumDifficulty difficulty, EnumDifficulty oldDifficulty)
+    {
+        MinecraftForge.EVENT_BUS.post(new DifficultyChangeEvent(difficulty, oldDifficulty));
+    }
 
     //Optifine Helper Functions u.u, these are here specifically for Optifine
     //Note: When using Optifine, these methods are invoked using reflection, which

src/main/java/net/minecraftforge/event/DifficultyChangeEvent.java

@@ -0,0 +1,62 @@
+/*
+ * Minecraft Forge
+ * Copyright (c) 2016.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation version 2.1
+ * of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+package net.minecraftforge.event;
+
+import javax.annotation.Nonnull;
+
+import net.minecraft.world.EnumDifficulty;
+import net.minecraftforge.common.ForgeHooks;
+import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.fml.common.eventhandler.Cancelable;
+import net.minecraftforge.fml.common.eventhandler.Event;
+import net.minecraftforge.fml.common.eventhandler.Event.HasResult;
+
+/**
+ * DifficultyChangeEvent is fired when difficulty is changing. <br>
+ * <br>
+ * This event is fired via the {@link ForgeHooks#onDifficultyChange(EnumDifficulty, EnumDifficulty)}.<br>
+ * <br>
+ * This event is not {@link Cancelable}.<br>
+ * <br>
+ * This event does not have a result. {@link HasResult}<br>
+ * <br>
+ * This event is fired on the {@link MinecraftForge#EVENT_BUS}.
+ **/
+public class DifficultyChangeEvent extends Event
+{
+    private final EnumDifficulty difficulty;
+    private final EnumDifficulty oldDifficulty;
+
+    public DifficultyChangeEvent(EnumDifficulty difficulty, EnumDifficulty oldDifficulty)
+    {
+        this.difficulty = difficulty;
+        this.oldDifficulty = oldDifficulty;
+    }
+
+    public EnumDifficulty getDifficulty()
+    {
+        return difficulty;
+    }
+
+    public EnumDifficulty getOldDifficulty()
+    {
+        return oldDifficulty;
+    }
+}