Track emoji usage in messages and reactions

application/src/main/java/org/togetherjava/tjbot/features/Features.java

@@ -6,6 +6,7 @@
 import org.togetherjava.tjbot.config.FeatureBlacklist;
 import org.togetherjava.tjbot.config.FeatureBlacklistConfig;
 import org.togetherjava.tjbot.db.Database;
+import org.togetherjava.tjbot.features.analytics.EmojiTrackerListener;
 import org.togetherjava.tjbot.features.analytics.Metrics;
 import org.togetherjava.tjbot.features.basic.MemberCountDisplayRoutine;
 import org.togetherjava.tjbot.features.basic.PingCommand;
@@ -159,6 +160,7 @@ public static Collection<Feature> createFeatures(JDA jda, Database database, Con
         // Message receivers
         features.add(new TopHelpersMessageListener(database, config));
         features.add(new SuggestionsUpDownVoter(config, metrics));
+        features.add(new EmojiTrackerListener(metrics));
         features.add(new ScamBlocker(actionsStore, scamHistoryStore, config, metrics));
         features.add(new MediaOnlyChannelListener(config, metrics));
         features.add(new FileSharingMessageListener(config, metrics));

application/src/main/java/org/togetherjava/tjbot/features/analytics/EmojiTrackerListener.java

@@ -0,0 +1,57 @@
+package org.togetherjava.tjbot.features.analytics;
+
+import net.dv8tion.jda.api.entities.emoji.CustomEmoji;
+import net.dv8tion.jda.api.entities.emoji.Emoji;
+import net.dv8tion.jda.api.entities.emoji.EmojiUnion;
+import net.dv8tion.jda.api.events.message.MessageReceivedEvent;
+import net.dv8tion.jda.api.events.message.react.MessageReactionAddEvent;
+
+import org.togetherjava.tjbot.features.MessageReceiverAdapter;
+
+/**
+ * Listener that tracks custom emoji usage across all channels for analytics purposes.
+ * <p>
+ * Counts custom emojis used in messages and reactions so admins can see which emojis are unused and
+ * should be removed.
+ * <p>
+ * Custom emojis are tracked by their Discord ID (e.g. {@code emoji-custom-123456789}). Animated
+ * custom emojis are tracked separately (e.g. {@code emoji-custom-animated-123456789}).
+ */
+public final class EmojiTrackerListener extends MessageReceiverAdapter {
+    private final Metrics metrics;
+
+    /**
+     * Creates a new listener to track emoji usage across all channels.
+     *
+     * @param metrics to track emoji usage events
+     */
+    public EmojiTrackerListener(Metrics metrics) {
+        super();
+
+        this.metrics = metrics;
+    }
+
+    @Override
+    public void onMessageReceived(MessageReceivedEvent event) {
+        if (event.isWebhookMessage()) {
+            return;
+        }
+
+        event.getMessage().getMentions().getCustomEmojis().forEach(this::trackCustomEmoji);
+    }
+
+    @Override
+    public void onMessageReactionAdd(MessageReactionAddEvent event) {
+        EmojiUnion emoji = event.getEmoji();
+        if (emoji.getType() != Emoji.Type.CUSTOM) {
+            return;
+        }
+
+        trackCustomEmoji(emoji.asCustom());
+    }
+
+    private void trackCustomEmoji(CustomEmoji emoji) {
+        String prefix = emoji.isAnimated() ? "emoji-custom-animated-" : "emoji-custom-";
+        metrics.count(prefix + emoji.getIdLong());
+    }
+}