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 9c2589c7e0517f771b9ca06760273a0aecefb27d..7d2fee97f4d08eae245475c4b60c1a7ba46c840d 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -791,7 +791,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         chunkproviderserver.getLightEngine().setTaskPerBatch(worldserver.paperConfig().misc.lightQueueSize); // Paper - increase light queue size
         // 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
@@ -1710,11 +1710,14 @@ 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 - remember 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
         }
     }
 
@@ -1728,7 +1731,7 @@ 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 4bb29f86538552bb62125cc61210fd77b1ec671d..817193ca5fc15134d2985187bc2226ccbb4f0108 100644
--- a/src/main/java/net/minecraft/server/commands/DifficultyCommand.java
+++ b/src/main/java/net/minecraft/server/commands/DifficultyCommand.java
@@ -47,7 +47,7 @@ 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 - don't skip other difficulty-changing logic (fix upstream's fix)
             source.sendSuccess(Component.translatable("commands.difficulty.success", difficulty.getDisplayName()), true);
             return 0;
         }
diff --git a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
index e42df2956e2d852a5a4c8fdeda395a3efd32c44c..da83f111199a6b4c712a9bb8ab6f1d1b5c6ae77c 100644
--- a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
+++ b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
@@ -332,7 +332,7 @@ public class DedicatedServer extends MinecraftServer implements ServerInterface
 
     @Override
     public void forceDifficulty() {
-        this.setDifficulty(this.getProperties().difficulty, true);
+        // this.setDifficulty(this.getProperties().difficulty, true); // Paper - 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 29a03760f092a004a47e75120841d80e696b6c3d..be7d2275548936beade4aba02dc5b14fec95117a 100644
--- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
+++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
@@ -1144,7 +1144,7 @@ public class ServerPlayer extends Player {
                 this.isChangingDimension = true; // CraftBukkit - Set teleport invulnerability only if player changing worlds
 
                 this.connection.send(new ClientboundRespawnPacket(worldserver.dimensionTypeId(), worldserver.dimension(), BiomeManager.obfuscateSeed(worldserver.getSeed()), this.gameMode.getGameModeForPlayer(), this.gameMode.getPreviousGameModeForPlayer(), worldserver.isDebug(), worldserver.isFlat(), true, this.getLastDeathLocation()));
-                this.connection.send(new ClientboundChangeDifficultyPacket(this.level.getDifficulty(), this.level.getLevelData().isDifficultyLocked()));
+                this.connection.send(new ClientboundChangeDifficultyPacket(worldserver.getDifficulty(), this.level.getLevelData().isDifficultyLocked())); // Paper - fix difficulty sync issue
                 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 02b6cf65f6abedfd4933e4e64d254f190e061301..c59e90ba0de83eeda3719b6303bee9796b4a1af0 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -3498,7 +3498,7 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Tic
     public void handleChangeDifficulty(ServerboundChangeDifficultyPacket packet) {
         PacketUtils.ensureRunningOnSameThread(packet, this, this.player.getLevel());
         if (this.player.hasPermissions(2) || this.isSingleplayerOwner()) {
-            this.server.setDifficulty(packet.getDifficulty(), false);
+            // this.server.setDifficulty(packet.getDifficulty(), false); // Paper - 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 f0f2a5e94e0a4b143befa422fa99e68316f93d7f..99a9bf12f2e3e6ac5457da53f6f12118efce5d82 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -951,8 +951,8 @@ public final class CraftServer implements Server {
         org.spigotmc.SpigotConfig.init((File) 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)) {