From cb99b184ede1f452ec820c48e6601d3458d86572 Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Thu, 28 May 2020 07:14:49 -0400
Subject: [PATCH] Allow plugins to mutate available commands sent to the
 client.

This is the first unstable API being introduced and is primarily to get feedback on the system.
---
 api/build.gradle                              |  1 +
 .../command/PlayerAvailableCommandsEvent.java | 37 +++++++++++++++++++
 .../backend/BackendPlaySessionHandler.java    |  7 +++-
 3 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 api/src/main/java/com/velocitypowered/api/event/command/PlayerAvailableCommandsEvent.java

diff --git a/api/build.gradle b/api/build.gradle
index b156d61fc..2680d18ce 100644
--- a/api/build.gradle
+++ b/api/build.gradle
@@ -26,6 +26,7 @@ dependencies {
     compile "org.slf4j:slf4j-api:${slf4jVersion}"
     compile 'com.google.inject:guice:4.2.2'
     compile "org.checkerframework:checker-qual:${checkerFrameworkVersion}"
+    compile 'com.mojang:brigadier:1.0.17'
 
     compile "org.spongepowered:configurate-hocon:${configurateVersion}"
     compile "org.spongepowered:configurate-yaml:${configurateVersion}"
diff --git a/api/src/main/java/com/velocitypowered/api/event/command/PlayerAvailableCommandsEvent.java b/api/src/main/java/com/velocitypowered/api/event/command/PlayerAvailableCommandsEvent.java
new file mode 100644
index 000000000..c60528c4c
--- /dev/null
+++ b/api/src/main/java/com/velocitypowered/api/event/command/PlayerAvailableCommandsEvent.java
@@ -0,0 +1,37 @@
+package com.velocitypowered.api.event.command;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.mojang.brigadier.tree.RootCommandNode;
+import com.velocitypowered.api.annotations.UnstableApi;
+import com.velocitypowered.api.proxy.Player;
+
+/**
+ * Allows plugins to modify the packet indicating commands available on the server to a
+ * Minecraft 1.13+ client.
+ */
+@UnstableApi
+public class PlayerAvailableCommandsEvent {
+
+  private final Player player;
+  private final RootCommandNode<?> rootNode;
+
+  /**
+   * Constructs an available commands event.
+   * @param player the targeted player
+   * @param rootNode the Brigadier root node
+   */
+  public PlayerAvailableCommandsEvent(Player player,
+      RootCommandNode<?> rootNode) {
+    this.player = checkNotNull(player, "player");
+    this.rootNode = checkNotNull(rootNode, "rootNode");
+  }
+
+  public Player getPlayer() {
+    return player;
+  }
+
+  public RootCommandNode<?> getRootNode() {
+    return rootNode;
+  }
+}
diff --git a/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java b/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java
index 747006dce..7bde50a23 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java
@@ -7,6 +7,7 @@ import com.mojang.brigadier.arguments.StringArgumentType;
 import com.mojang.brigadier.builder.LiteralArgumentBuilder;
 import com.mojang.brigadier.builder.RequiredArgumentBuilder;
 import com.mojang.brigadier.tree.LiteralCommandNode;
+import com.velocitypowered.api.event.command.PlayerAvailableCommandsEvent;
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.proxy.VelocityServer;
@@ -175,7 +176,11 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
           .build();
       commands.getRootNode().addChild(root);
     }
-    return false;
+
+    server.getEventManager().fire(
+        new PlayerAvailableCommandsEvent(serverConn.getPlayer(), commands.getRootNode()))
+        .thenAcceptAsync(event -> playerConnection.write(commands), playerConnection.eventLoop());
+    return true;
   }
 
   @Override