feat: implement rate limit solution

This commit slows down the processing of event queues for the sole
purpose of preventing Discord API endpoint saturation as well as to
avoid the global Discord API Gateway rate limiter.

Moreover, it removes a few 'static' keywords that should not be there.

application/src/main/java/org/togetherjava/tjbot/features/dynamicvc/DynamicVoiceListener.java

@@ -7,6 +7,8 @@
 import net.dv8tion.jda.api.events.guild.voice.GuildVoiceUpdateEvent;
 import org.apache.commons.lang3.tuple.Pair;
 import org.jetbrains.annotations.NotNull;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import org.togetherjava.tjbot.config.Config;
 import org.togetherjava.tjbot.features.VoiceReceiverAdapter;
@@ -19,6 +21,8 @@
 import java.util.Optional;
 import java.util.Queue;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executor;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Predicate;
 import java.util.regex.Matcher;
@@ -41,14 +45,22 @@
  */
 public class DynamicVoiceListener extends VoiceReceiverAdapter {
 
+    private final Logger logger = LoggerFactory.getLogger(DynamicVoiceListener.class);
+
     private final Map<String, Predicate<String>> channelPredicates = new HashMap<>();
     private static final Pattern channelTopicPattern = Pattern.compile("(\\s+\\d+)$");
 
     /** Map of event queues for each channel topic. */
-    private static final Map<String, Queue<GuildVoiceUpdateEvent>> eventQueues = new HashMap<>();
+    private final Map<String, Queue<GuildVoiceUpdateEvent>> eventQueues = new HashMap<>();
 
     /** Map to track if an event queue is currently being processed for each channel topic. */
-    private static final Map<String, AtomicBoolean> activeQueuesMap = new HashMap<>();
+    private final Map<String, AtomicBoolean> activeQueuesMap = new HashMap<>();
+
+    /** Boolean to track if events from all queues should be handled at a slower rate. */
+    private final AtomicBoolean slowmode = new AtomicBoolean(false);
+    private final Executor eventQueueExecutor =
+            CompletableFuture.delayedExecutor(1L, TimeUnit.SECONDS);
+    private static final int SLOWMODE_THRESHOLD = 5;
 
     /**
      * Initializes a new {@link DynamicVoiceListener} with the specified configuration.
@@ -85,11 +97,19 @@ private void insertEventToQueue(GuildVoiceUpdateEvent event, String channelTopic
         }
 
         eventQueue.add(event);
+        slowmode.set(eventQueue.size() >= SLOWMODE_THRESHOLD);
 
         if (activeQueuesMap.get(channelTopic).get()) {
             return;
         }
 
+        if (slowmode.get()) {
+            logger.info("Running with slowmode");
+            CompletableFuture.runAsync(() -> processEventFromQueue(channelTopic),
+                    eventQueueExecutor);
+            return;
+        }
+
         processEventFromQueue(channelTopic);
     }