Add tab-complete possibility and help subcommand

src/main/java/us/myles/ViaVersion/ViaVersionPlugin.java

@@ -5,7 +5,6 @@ import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.socket.SocketChannel;
-import lombok.Getter;
 import lombok.NonNull;
 import org.bukkit.Bukkit;
 import org.bukkit.entity.Player;
@@ -81,6 +80,7 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI, ViaVe
         Bukkit.getPluginManager().registerEvents(new UpdateListener(this), this);
 
         getCommand("viaversion").setExecutor(commandHandler = new ViaCommandHandler());
+        getCommand("viaversion").setTabCompleter(new ViaCommandHandler());
     }
 
     public void gatherProtocolVersion() {
@@ -286,15 +286,15 @@ public class ViaVersionPlugin extends JavaPlugin implements ViaVersionAPI, ViaVe
         return this.debug;
     }
 
+    public void setDebug(boolean value) {
+        this.debug = value;
+    }
+
     @Override
     public ViaVersionCommand getCommandHandler() {
         return commandHandler;
     }
 
-    public void setDebug(boolean value) {
-        this.debug = value;
-    }
-
     public boolean isCheckForUpdates() {
         return getConfig().getBoolean("checkforupdates", true);
     }

src/main/java/us/myles/ViaVersion/api/command/ViaSubCommand.java

@@ -1,9 +1,11 @@
 package us.myles.ViaVersion.api.command;
 
 import org.bukkit.command.CommandSender;
-import org.bukkit.entity.Player;
 import us.myles.ViaVersion.commands.ViaCommandHandler;
 
+import java.util.Collections;
+import java.util.List;
+
 public abstract class ViaSubCommand {
     /**
      * Subcommand name
@@ -31,6 +33,7 @@ public abstract class ViaSubCommand {
 
     /**
      * Permission, null for everyone
+     *
      * @return
      */
     public String permission() {
@@ -46,6 +49,17 @@ public abstract class ViaSubCommand {
      */
     public abstract boolean execute(CommandSender sender, String[] args);
 
+    /**
+     * Yay, possibility to implement tab-completion
+     *
+     * @param sender Command sender
+     * @param args   args
+     * @return tab complete possibilities
+     */
+    public List<String> onTabComplete(CommandSender sender, String[] args) {
+        return Collections.emptyList();
+    }
+
     public String color(String s) {
         return ViaCommandHandler.color(s);
     }

src/main/java/us/myles/ViaVersion/commands/ViaCommandHandler.java

@@ -6,6 +6,7 @@ import org.bukkit.ChatColor;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandExecutor;
 import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabCompleter;
 import us.myles.ViaVersion.api.ViaVersion;
 import us.myles.ViaVersion.api.command.ViaSubCommand;
 import us.myles.ViaVersion.api.command.ViaVersionCommand;
@@ -13,7 +14,7 @@ import us.myles.ViaVersion.commands.defaultsubs.*;
 
 import java.util.*;
 
-public class ViaCommandHandler implements ViaVersionCommand, CommandExecutor {
+public class ViaCommandHandler implements ViaVersionCommand, CommandExecutor, TabCompleter {
     private Map<String, ViaSubCommand> commandMap;
 
     public ViaCommandHandler() {
@@ -25,6 +26,14 @@ public class ViaCommandHandler implements ViaVersionCommand, CommandExecutor {
         }
     }
 
+    public static String color(String string) {
+        try {
+            string = ChatColor.translateAlternateColorCodes('&', string); //Dont replace all & with $ like we did before.
+        } catch (Exception ignored) {
+        }
+        return string;
+    }
+
     @Override
     public void registerSubCommand(@NonNull ViaSubCommand command) throws Exception {
         Validate.isTrue(command.name().matches("^[a-z0-9_-]{3,15}$"), command.name() + " is not a valid subcommand name");
@@ -69,6 +78,39 @@ public class ViaCommandHandler implements ViaVersionCommand, CommandExecutor {
         return result;
     }
 
+    @Override
+    public List<String> onTabComplete(CommandSender sender, Command command, String arg, String[] args) {
+        Set<ViaSubCommand> allowed = calculateAllowedCommands(sender);
+        List<String> output = new ArrayList<>();
+
+        //SubCommands tabcomplete
+        if (args.length == 1) {
+            if (!args[0].equals("")) {
+                for (ViaSubCommand sub : allowed)
+                    if (sub.name().toLowerCase().startsWith(args[0].toLowerCase()))
+                        output.add(sub.name());
+            } else {
+                for (ViaSubCommand sub : allowed)
+                    output.add(sub.name());
+            }
+        }
+        //Let the SubCommand handle it
+        else if (args.length >= 2) {
+            if (getSubCommand(args[0]) != null) {
+                ViaSubCommand sub = getSubCommand(args[0]);
+                if (!allowed.contains(sub))
+                    return output;
+
+                String[] subArgs = Arrays.copyOfRange(args, 1, args.length);
+
+                List<String> tab = sub.onTabComplete(sender, subArgs);
+                Collections.sort(tab);
+                return tab;
+            }
+        }
+        return output;
+    }
+
     public void showHelp(CommandSender sender) {
         Set<ViaSubCommand> allowed = calculateAllowedCommands(sender);
         if (allowed.size() == 0) {
@@ -94,20 +136,12 @@ public class ViaCommandHandler implements ViaVersionCommand, CommandExecutor {
         return permission == null || sender.hasPermission(permission);
     }
 
-
-    public static String color(String string) {
-        try {
-            string = ChatColor.translateAlternateColorCodes('&', string); //Dont replace all & with $ like we did before.
-        } catch (Exception ignored) {
-        }
-        return string;
-    }
-
     private void registerDefaults() throws Exception {
         registerSubCommand(new ListSubCmd());
         registerSubCommand(new DebugSubCmd());
         registerSubCommand(new DisplayLeaksSubCmd());
         registerSubCommand(new DontBugMeSubCmd());
         registerSubCommand(new AutoTeamSubCmd());
+        registerSubCommand(new HelpSubCmd());
     }
 }

src/main/java/us/myles/ViaVersion/commands/defaultsubs/HelpSubCmd.java

@@ -0,0 +1,27 @@
+package us.myles.ViaVersion.commands.defaultsubs;
+
+import org.bukkit.command.CommandSender;
+import us.myles.ViaVersion.ViaVersionPlugin;
+import us.myles.ViaVersion.api.ViaVersion;
+import us.myles.ViaVersion.api.command.ViaSubCommand;
+import us.myles.ViaVersion.commands.ViaCommandHandler;
+
+public class HelpSubCmd extends ViaSubCommand {
+    @Override
+    public String name() {
+        return "help";
+    }
+
+    @Override
+    public String description() {
+        return "You are looking at it right now!";
+    }
+
+    @Override
+    public boolean execute(CommandSender sender, String[] args) {
+        ViaVersionPlugin plugin = (ViaVersionPlugin) ViaVersion.getInstance();
+
+        ((ViaCommandHandler) plugin.getCommandHandler()).showHelp(sender);
+        return true;
+    }
+}