Add API for custom chat completions like on Paper (#1232)

* Add API for custom chat completions like on Paper, renamed enum constant to match its function, NMS and wiki-vg

* add null and version checks

api/src/main/java/com/velocitypowered/api/proxy/Player.java

@@ -309,4 +309,33 @@ public interface Player extends
    * @return the player's client brand
    */
   @Nullable String getClientBrand();
+
+
+  /**
+   * Add custom chat completion suggestions shown to the player while typing a message.
+   *
+   * @param completions the completions to send
+   */
+  void addCustomChatCompletions(@NotNull Collection<String> completions);
+
+  /**
+   * Remove custom chat completion suggestions shown to the player while typing a message.
+   *
+   * <p>Online player names can't be removed with this method, it will only affect
+   * custom completions added by {@link #addCustomChatCompletions(Collection)}
+   * or {@link #setCustomChatCompletions(Collection)}.
+   *
+   * @param completions the completions to remove
+   */
+  void removeCustomChatCompletions(@NotNull Collection<String> completions);
+
+  /**
+   * Set the list of chat completion suggestions shown to the player while typing a message.
+   *
+   * <p>If completions were set previously, this method will remove them all
+   * and replace them with the provided completions.
+   *
+   * @param completions the completions to set
+   */
+  void setCustomChatCompletions(@NotNull Collection<String> completions);
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -69,6 +69,7 @@ import com.velocitypowered.proxy.protocol.packet.RemoveResourcePackPacket;
 import com.velocitypowered.proxy.protocol.packet.chat.ChatQueue;
 import com.velocitypowered.proxy.protocol.packet.chat.ChatType;
 import com.velocitypowered.proxy.protocol.packet.chat.ComponentHolder;
+import com.velocitypowered.proxy.protocol.packet.chat.PlayerChatCompletionPacket;
 import com.velocitypowered.proxy.protocol.packet.chat.builder.ChatBuilderFactory;
 import com.velocitypowered.proxy.protocol.packet.chat.legacy.LegacyChatPacket;
 import com.velocitypowered.proxy.protocol.packet.config.StartUpdatePacket;
@@ -961,6 +962,31 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
     this.clientBrand = clientBrand;
   }
 
+  @Override
+  public void addCustomChatCompletions(@NotNull Collection<String> completions) {
+    Preconditions.checkNotNull(completions, "completions");
+    this.sendCustomChatCompletionPacket(completions, PlayerChatCompletionPacket.Action.ADD);
+  }
+
+  @Override
+  public void removeCustomChatCompletions(@NotNull Collection<String> completions) {
+    Preconditions.checkNotNull(completions, "completions");
+    this.sendCustomChatCompletionPacket(completions, PlayerChatCompletionPacket.Action.REMOVE);
+  }
+
+  @Override
+  public void setCustomChatCompletions(@NotNull Collection<String> completions) {
+    Preconditions.checkNotNull(completions, "completions");
+    this.sendCustomChatCompletionPacket(completions, PlayerChatCompletionPacket.Action.SET);
+  }
+
+  private void sendCustomChatCompletionPacket(@NotNull Collection<String> completions,
+                                              PlayerChatCompletionPacket.Action action) {
+    if (connection.getProtocolVersion().noLessThan(ProtocolVersion.MINECRAFT_1_19_1)) {
+      connection.write(new PlayerChatCompletionPacket(completions.toArray(new String[0]), action));
+    }
+  }
+
   @Override
   public void spoofChatInput(String input) {
     Preconditions.checkArgument(input.length() <= LegacyChatPacket.MAX_SERVERBOUND_MESSAGE_LENGTH,

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/PlayerChatCompletionPacket.java

@@ -28,6 +28,13 @@ public class PlayerChatCompletionPacket implements MinecraftPacket {
   private String[] completions;
   private Action action;
 
+  public PlayerChatCompletionPacket() {
+  }
+
+  public PlayerChatCompletionPacket(String[] completions, Action action) {
+    this.completions = completions;
+    this.action = action;
+  }
 
   public String[] getCompletions() {
     return completions;
@@ -64,9 +71,9 @@ public class PlayerChatCompletionPacket implements MinecraftPacket {
     return handler.handle(this);
   }
 
-  enum Action {
+  public enum Action {
     ADD,
     REMOVE,
-    ALTER
+    SET
   }
 }