From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 28 Jun 2020 03:59:10 -0400
Subject: [PATCH] Fix Per World Difficulty / Remembering Difficulty

Fixes per world difficulty with /difficulty command and also
makes it so that the server keeps the last difficulty used instead
of restoring the server.properties every single load.

diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 2575129d1647eda4acb1ce4f19619f42257cb6f8..f5a2645afc64f3ba9ee21e6442697d6eb2fabb13 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -830,7 +830,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         worldloadlistener.stop();
         // CraftBukkit start
         // this.updateMobSpawningFlags();
-        worldserver.setSpawnSettings(this.isSpawningMonsters(), this.isSpawningAnimals());
+        worldserver.setSpawnSettings(worldserver.serverLevelData.getDifficulty() != Difficulty.PEACEFUL && ((DedicatedServer) this).settings.getProperties().spawnMonsters, this.isSpawningAnimals()); // Paper - per level difficulty (from setDifficulty(ServerLevel, Difficulty, boolean))
 
         this.forceTicks = false;
         // CraftBukkit end
@@ -1826,11 +1826,14 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         }
     }
 
-    public void setDifficulty(Difficulty difficulty, boolean forceUpdate) {
-        if (forceUpdate || !this.worldData.isDifficultyLocked()) {
-            this.worldData.setDifficulty(this.worldData.isHardcore() ? Difficulty.HARD : difficulty);
-            this.updateMobSpawningFlags();
-            this.getPlayerList().getPlayers().forEach(this::sendDifficultyUpdate);
+    // Paper start - per level difficulty
+    public void setDifficulty(ServerLevel level, Difficulty difficulty, boolean forceUpdate) {
+        PrimaryLevelData worldData = level.serverLevelData;
+        if (forceUpdate || !worldData.isDifficultyLocked()) {
+            worldData.setDifficulty(worldData.isHardcore() ? Difficulty.HARD : difficulty);
+            level.setSpawnSettings(worldData.getDifficulty() != Difficulty.PEACEFUL && ((DedicatedServer) this).settings.getProperties().spawnMonsters, this.isSpawningAnimals());
+            // this.getPlayerList().getPlayers().forEach(this::sendDifficultyUpdate);
+            // Paper end - per level difficulty
         }
     }
 
@@ -1844,7 +1847,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         while (iterator.hasNext()) {
             ServerLevel worldserver = (ServerLevel) iterator.next();
 
-            worldserver.setSpawnSettings(this.isSpawningMonsters(), this.isSpawningAnimals());
+            worldserver.setSpawnSettings(worldserver.serverLevelData.getDifficulty() != Difficulty.PEACEFUL && ((DedicatedServer) this).settings.getProperties().spawnMonsters, this.isSpawningAnimals()); // Paper - per level difficulty (from setDifficulty(ServerLevel, Difficulty, boolean))
         }
 
     }
diff --git a/src/main/java/net/minecraft/server/commands/DifficultyCommand.java b/src/main/java/net/minecraft/server/commands/DifficultyCommand.java
index 997a96a21440ae72696d68f8031ece4ba487d3ef..3d8584929cee000ae7df10c5bd94f35820e70294 100644
--- a/src/main/java/net/minecraft/server/commands/DifficultyCommand.java
+++ b/src/main/java/net/minecraft/server/commands/DifficultyCommand.java
@@ -49,7 +49,7 @@ public class DifficultyCommand {
         if (worldServer.getDifficulty() == difficulty) { // CraftBukkit
             throw DifficultyCommand.ERROR_ALREADY_DIFFICULT.create(difficulty.getKey());
         } else {
-            worldServer.serverLevelData.setDifficulty(difficulty); // CraftBukkit
+            minecraftserver.setDifficulty(worldServer, difficulty, true); // Paper - per level difficulty; don't skip other difficulty-changing logic (fix upstream's fix)
             source.sendSuccess(() -> {
                 return Component.translatable("commands.difficulty.success", difficulty.getDisplayName());
             }, true);
diff --git a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
index 539a8ddfcf660bf824325516c88cf91f4a32a746..1bc8217cf1df95edadd57e18a91885808d31cb93 100644
--- a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
+++ b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
@@ -346,7 +346,7 @@ public class DedicatedServer extends MinecraftServer implements ServerInterface
 
     @Override
     public void forceDifficulty() {
-        this.setDifficulty(this.getProperties().difficulty, true);
+        // this.setDifficulty(this.getProperties().difficulty, true); // Paper - per level difficulty; Don't overwrite level.dat's difficulty, keep current
     }
 
     @Override
diff --git a/src/main/java/net/minecraft/server/level/ServerPlayer.java b/src/main/java/net/minecraft/server/level/ServerPlayer.java
index bf6c81300d29c445a1012d1159866547c202d135..e6a24484ef11a1d815a85126aec221547479f7d3 100644
--- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
+++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
@@ -1238,7 +1238,7 @@ public class ServerPlayer extends Player {
                 this.isChangingDimension = true; // CraftBukkit - Set teleport invulnerability only if player changing worlds
 
                 this.connection.send(new ClientboundRespawnPacket(this.createCommonSpawnInfo(worldserver), (byte) 3));
-                this.connection.send(new ClientboundChangeDifficultyPacket(this.level().getDifficulty(), this.level().getLevelData().isDifficultyLocked()));
+                this.connection.send(new ClientboundChangeDifficultyPacket(worldserver.getDifficulty(), this.level().getLevelData().isDifficultyLocked())); // Paper - per level difficulty
                 PlayerList playerlist = this.server.getPlayerList();
 
                 playerlist.sendPlayerPermissionLevel(this);
diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index c265889aa577c87706d658145954e95e0dc2a713..856f91450e746ff4d8b1105db6e87c8d8aa8168a 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -3242,7 +3242,7 @@ public class ServerGamePacketListenerImpl extends ServerCommonPacketListenerImpl
     public void handleChangeDifficulty(ServerboundChangeDifficultyPacket packet) {
         PacketUtils.ensureRunningOnSameThread(packet, this, this.player.serverLevel());
         if (this.player.hasPermissions(2) || this.isSingleplayerOwner()) {
-            this.server.setDifficulty(packet.getDifficulty(), false);
+            // this.server.setDifficulty(packet.getDifficulty(), false); // Paper - per level difficulty; don't allow clients to change this
         }
     }
 
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 91b8fefc2c97c1f487bde1559d4ccf76795ca954..3e4cde7825634c4949312e44f19b03cc96c4aaa3 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -985,8 +985,8 @@ public final class CraftServer implements Server {
         org.spigotmc.SpigotConfig.init((File) this.console.options.valueOf("spigot-settings")); // Spigot
         this.console.paperConfigurations.reloadConfigs(this.console);
         for (ServerLevel world : this.console.getAllLevels()) {
-            world.serverLevelData.setDifficulty(config.difficulty);
-            world.setSpawnSettings(config.spawnMonsters, config.spawnAnimals);
+            // world.serverLevelData.setDifficulty(config.difficulty); // Paper - per level difficulty
+            world.setSpawnSettings(world.serverLevelData.getDifficulty() != Difficulty.PEACEFUL && config.spawnMonsters, config.spawnAnimals); // Paper - per level difficulty (from MinecraftServer#setDifficulty(ServerLevel, Difficulty, boolean))
 
             for (SpawnCategory spawnCategory : SpawnCategory.values()) {
                 if (CraftSpawnCategory.isValidForLimits(spawnCategory)) {
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index 77395861f528b0443db84bf882351c7f5ccfd3ba..680733c3ccf8ff27478d43b3dfab6028cec5c829 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -1188,7 +1188,7 @@ public class CraftWorld extends CraftRegionAccessor implements World {
 
     @Override
     public void setDifficulty(Difficulty difficulty) {
-        this.getHandle().serverLevelData.setDifficulty(net.minecraft.world.Difficulty.byId(difficulty.getValue()));
+        this.getHandle().getServer().setDifficulty(this.getHandle(), net.minecraft.world.Difficulty.byId(difficulty.getValue()), true); // Paper - per level difficulty; don't skip other difficulty-changing logic
     }
 
     @Override