Introduce a "modular" /velocity command.

proxy/src/main/java/com/velocitypowered/proxy/command/VelocityCommand.java

@@ -1,5 +1,7 @@
 package com.velocitypowered.proxy.command;
 
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import com.velocitypowered.api.command.Command;
 import com.velocitypowered.api.command.CommandSource;
 import com.velocitypowered.api.permission.Tristate;
@@ -10,9 +12,74 @@ import net.kyori.text.format.TextColor;
 import net.kyori.text.format.TextDecoration;
 import org.checkerframework.checker.nullness.qual.NonNull;
 
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.stream.Collectors;
+
 public class VelocityCommand implements Command {
+    private final Map<String, Command> subcommands = ImmutableMap.<String, Command>builder()
+            .put("version", Info.INSTANCE)
+            .build();
+
+    private void usage(CommandSource source) {
+        String commandText = "/velocity <" + String.join("|", subcommands.keySet()) + ">";
+        source.sendMessage(TextComponent.of(commandText, TextColor.RED));
+    }
+
     @Override
     public void execute(CommandSource source, String[] args) {
+        if (args.length == 0) {
+            usage(source);
+            return;
+        }
+
+        Command command = subcommands.get(args[0].toLowerCase(Locale.US));
+        if (command == null) {
+            usage(source);
+            return;
+        }
+        command.execute(source, Arrays.copyOfRange(args, 1, args.length));
+    }
+
+    @Override
+    public List<String> suggest(@NonNull CommandSource source, @NonNull String[] currentArgs) {
+        if (currentArgs.length == 0) {
+            return ImmutableList.copyOf(subcommands.keySet());
+        }
+
+        if (currentArgs.length == 1) {
+            return subcommands.keySet().stream()
+                    .filter(name -> name.regionMatches(true, 0, currentArgs[0], 0, currentArgs[0].length()))
+                    .collect(Collectors.toList());
+        }
+
+        Command command = subcommands.get(currentArgs[0].toLowerCase(Locale.US));
+        if (command == null) {
+            return ImmutableList.of();
+        }
+        return command.suggest(source, Arrays.copyOfRange(currentArgs, 1, currentArgs.length));
+    }
+
+    @Override
+    public boolean hasPermission(@NonNull CommandSource source, @NonNull String[] args) {
+        if (args.length == 0) {
+            return true;
+        }
+        Command command = subcommands.get(args[0].toLowerCase(Locale.US));
+        if (command == null) {
+            return true;
+        }
+        return command.hasPermission(source, Arrays.copyOfRange(args, 1, args.length));
+    }
+
+    private static class Info implements Command {
+        static final Info INSTANCE = new Info();
+        private Info() {}
+
+        @Override
+        public void execute(@NonNull CommandSource source, @NonNull String[] args) {
             String implVersion = VelocityServer.class.getPackage().getImplementationVersion();
             TextComponent velocity = TextComponent.builder("Velocity ")
                     .decoration(TextDecoration.BOLD, true)
@@ -44,3 +111,4 @@ public class VelocityCommand implements Command {
             return source.getPermissionValue("velocity.command.info") != Tristate.FALSE;
         }
     }
+}