Add tab completion for commands and arguments

src/main/java/dansplugins/mailboxes/Mailboxes.java

@@ -8,15 +8,48 @@
 import dansplugins.mailboxes.services.*;
 import dansplugins.mailboxes.utils.*;
 
+import org.bukkit.Bukkit;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
 import org.bukkit.plugin.java.JavaPlugin;
 
 import java.io.File;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 public final class Mailboxes extends JavaPlugin {
     private final String pluginVersion = "v" + getDescription().getVersion();
 
+    // Config option names for tab completion (in camelCase to match config file)
+    private static final List<String> CONFIG_OPTIONS = Arrays.asList(
+        "debugMode",
+        "maxMessageIDNumber",
+        "maxMailboxIDNumber",
+        "preventSendingMessagesToSelf",
+        "assignmentAlertEnabled",
+        "unreadMessagesAlertEnabled",
+        "welcomeMessageEnabled",
+        "quotesEnabled",
+        "attachmentsEnabled",
+        "maxAttachmentStackSize"
+    );
+
+    // Boolean config options (stored in lowercase for case-insensitive comparison)
+    private static final Set<String> BOOLEAN_CONFIG_OPTIONS = new HashSet<>(Arrays.asList(
+        "debugmode",
+        "preventsendingmessagestoself",
+        "assignmentalertenabled",
+        "unreadmessagesalertenabled",
+        "welcomemessageenabled",
+        "quotesenabled",
+        "attachmentsenabled"
+    ));
+
     private final ConfigService configService = new ConfigService(this);
     private final Logger logger = new Logger(this);
     private final PersistentData persistentData = new PersistentData(logger);
@@ -82,4 +115,96 @@ public MailboxesAPI getAPI() {
     private boolean isVersionMismatched() {
         return !getConfig().getString("version").equalsIgnoreCase(getVersion());
     }
+
+    @Override
+    public List<String> onTabComplete(CommandSender sender, Command cmd, String label, String[] args) {
+        if (label.equalsIgnoreCase("mailboxes") || label.equalsIgnoreCase("m")) {
+            return getTabCompletions(sender, args);
+        }
+        return null;
+    }
+
+    private List<String> getTabCompletions(CommandSender sender, String[] args) {
+        if (args.length == 1) {
+            // Main subcommands
+            List<String> subcommands = Arrays.asList("help", "config", "list", "send", "open", "delete", "archive");
+            return filterCompletions(subcommands, args[0]);
+        }
+
+        if (args.length >= 2) {
+            String subcommand = args[0].toLowerCase();
+
+            switch (subcommand) {
+                case "config":
+                    return getConfigCompletions(args);
+                case "list":
+                    return getListCompletions(args);
+                case "send":
+                    return getSendCompletions(sender, args);
+            }
+        }
+
+        return new ArrayList<>();
+    }
+
+    private List<String> getConfigCompletions(String[] args) {
+        if (args.length == 2) {
+            // Config subcommands
+            return filterCompletions(Arrays.asList("show", "set"), args[1]);
+        }
+        if (args.length == 3 && args[1].equalsIgnoreCase("set")) {
+            // Config options
+            return filterCompletions(CONFIG_OPTIONS, args[2]);
+        }
+        if (args.length == 4 && args[1].equalsIgnoreCase("set")) {
+            // Suggest values based on the config option type
+            String option = args[2];
+            if (BOOLEAN_CONFIG_OPTIONS.contains(option.toLowerCase())) {
+                return filterCompletions(Arrays.asList("true", "false"), args[3]);
+            }
+        }
+        return new ArrayList<>();
+    }
+
+    private List<String> getListCompletions(String[] args) {
+        if (args.length == 2) {
+            return filterCompletions(Arrays.asList("active", "archived", "unread"), args[1]);
+        }
+        return new ArrayList<>();
+    }
+
+    private List<String> getSendCompletions(CommandSender sender, String[] args) {
+        if (args.length == 2) {
+            // Player names and -attach flag
+            List<String> completions = filterCompletions(
+                Bukkit.getOnlinePlayers().stream()
+                    .map(Player::getName)
+                    .collect(Collectors.toList()),
+                args[1]
+            );
+            // Also suggest -attach flag if user has permission
+            completions.addAll(getAttachFlagSuggestion(sender, args, args[1]));
+            return completions;
+        }
+        // Suggest -attach flag for subsequent positions if not already present
+        if (args.length >= 3) {
+            return getAttachFlagSuggestion(sender, args, args[args.length - 1]);
+        }
+        return new ArrayList<>();
+    }
+
+    private List<String> getAttachFlagSuggestion(CommandSender sender, String[] args, String input) {
+        // Check if -attach flag is already present
+        boolean hasAttachFlag = Arrays.stream(args).anyMatch(arg -> arg.equalsIgnoreCase("-attach"));
+        if (!hasAttachFlag && sender.hasPermission("mailboxes.send.attach")) {
+            return filterCompletions(Arrays.asList("-attach"), input);
+        }
+        return new ArrayList<>();
+    }
+
+    private List<String> filterCompletions(List<String> options, String input) {
+        return options.stream()
+            .filter(option -> option.toLowerCase().startsWith(input.toLowerCase()))
+            .collect(Collectors.toList());
+    }
 }