Implement basic slash commands support

src/main/java/wtf/beatrice/hidekobot/HidekoBot.java

@@ -7,7 +7,9 @@ import net.dv8tion.jda.api.entities.Activity;
 import net.dv8tion.jda.api.requests.GatewayIntent;
 import wtf.beatrice.hidekobot.listeners.MessageListener;
 import wtf.beatrice.hidekobot.listeners.MessageLogger;
+import wtf.beatrice.hidekobot.listeners.SlashCommandListener;
 import wtf.beatrice.hidekobot.utils.Logger;
+import wtf.beatrice.hidekobot.utils.SlashCommandsUtil;
 
 import javax.security.auth.login.LoginException;
 import java.util.ArrayList;
@@ -18,7 +20,7 @@ public class HidekoBot
 {
     private static String botToken;
     private static String standardInviteLink =
-            "https://discord.com/oauth2/authorize?client_id=%userid%&scope=bot&permissions=8";
+            "https://discord.com/oauth2/authorize?client_id=%userid%&scope=bot+applications.commands&permissions=8";
     private static String botUserId;
     private static final String version = "0.0.1"; // we should probably find a way to make this consistent with Maven
 
@@ -66,6 +68,10 @@ public class HidekoBot
 
         // register listeners
         jda.addEventListener(new MessageListener());
+        jda.addEventListener(new SlashCommandListener());
+
+        // update slash commands
+        SlashCommandsUtil.updateSlashCommands(jda);
 
         // set the bot's status
         jda.getPresence().setStatus(OnlineStatus.ONLINE);

src/main/java/wtf/beatrice/hidekobot/listeners/SlashCommandListener.java

@@ -0,0 +1,19 @@
+package wtf.beatrice.hidekobot.listeners;
+
+import net.dv8tion.jda.api.events.interaction.command.SlashCommandInteractionEvent;
+import net.dv8tion.jda.api.hooks.ListenerAdapter;
+import org.jetbrains.annotations.NotNull;
+
+public class SlashCommandListener extends ListenerAdapter
+{
+
+    @Override
+    public void onSlashCommandInteraction(@NotNull SlashCommandInteractionEvent event)
+    {
+        if(event.getName().equals("ping"))
+        {
+            event.reply("Pong!").queue();
+        }
+
+    }
+}

src/main/java/wtf/beatrice/hidekobot/utils/SlashCommandsUtil.java

@@ -0,0 +1,91 @@
+package wtf.beatrice.hidekobot.utils;
+
+import net.dv8tion.jda.api.JDA;
+import net.dv8tion.jda.api.interactions.commands.Command;
+import net.dv8tion.jda.api.interactions.commands.build.CommandData;
+import net.dv8tion.jda.api.interactions.commands.build.Commands;
+import wtf.beatrice.hidekobot.listeners.MessageListener;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class SlashCommandsUtil
+{
+
+    private static final Logger logger = new Logger(MessageListener.class);
+
+    static List<CommandData> allCommands = new ArrayList<>()
+    {{
+        add(Commands.slash("ping", "Test if the bot is responsive."));
+    }};
+
+    public static void updateSlashCommands(JDA jdaInstance)
+    {
+        List<CommandData> toAdd = new ArrayList<>();
+        List<Command> toDelete = new ArrayList<>();
+
+        List<Command> registeredCommands = jdaInstance.retrieveCommands().complete();
+
+        // for each command that we have already registered...
+        for(Command currRegCmd : registeredCommands)
+        {
+            // queue it for removal.
+            boolean toRemove = true;
+
+            // iterate through all "recognized" commands
+            for(CommandData cmdData : allCommands)
+            {
+                // if we find the same command...
+                if(cmdData.getName().equals(currRegCmd.getName()))
+                {
+                    // then don't remove it
+                    toRemove = false;
+                    // and quit the loop since we found it.
+                    break;
+                }
+            }
+
+            // if no match was found, queue this command for removal.
+            if(toRemove) toDelete.add(currRegCmd);
+
+        }
+
+        // for each "recognized" valid command
+        for(CommandData currCmdData : allCommands)
+        {
+            // queue it for registration.
+            boolean toRegister = true;
+
+            // iterate through all already registered commands.
+            for(Command cmd : registeredCommands)
+            {
+                // if this command was already registered...
+                if(cmd.getName().equals(currCmdData.getName()))
+                {
+                    // flag that we don't need to register it
+                    toRegister = false;
+                    // and quit the loop since we found a match.
+                    break;
+                }
+            }
+
+            // if no match was found, queue this command for registration.
+            if(toRegister) toAdd.add(currCmdData);
+        }
+
+        logger.log("Found " + registeredCommands.size() + " commands.");
+
+        // remove all commands queued for removal.
+        for(Command cmd : toDelete)
+        {
+            jdaInstance.deleteCommandById(cmd.getId()).queue();
+        }
+
+        logger.log("Deleted " + toDelete.size() + " commands.");
+
+        // register all new commands.
+        jdaInstance.updateCommands().addCommands(toAdd).queue();
+        logger.log("Registered " + toAdd.size() + " new commands.");
+
+    }
+}