Spam detection

src/main/java/net/javadiscord/javabot2/Bot.java

@@ -9,11 +9,17 @@
 import com.zaxxer.hikari.HikariDataSource;
 import net.javadiscord.javabot2.command.SlashCommandListener;
 import net.javadiscord.javabot2.config.BotConfig;
+import net.javadiscord.javabot2.systems.moderation.SpamListener;
+import net.javadiscord.javabot2.systems.moderation.MessageCache;
 import org.javacord.api.DiscordApi;
 import org.javacord.api.DiscordApiBuilder;
 import org.javacord.api.entity.intent.Intent;
+import org.javacord.api.entity.message.Message;
+import org.javacord.api.entity.message.MessageAuthor;
 
 import java.nio.file.Path;
+import java.util.LinkedList;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 
@@ -46,6 +52,11 @@ public class Bot {
 	 */
 	public static ScheduledExecutorService asyncPool;
 
+	/**
+	 * The message cache.
+	 */
+	public static ConcurrentHashMap<MessageAuthor, LinkedList<Message>> messageCache;
+
 	// Hide constructor.
 	private Bot() {}
 
@@ -60,8 +71,12 @@ public static void main(String[] args) {
 				.setToken(config.getSystems().getDiscordBotToken())
 				.setAllIntentsExcept(Intent.GUILD_MESSAGE_TYPING, Intent.GUILD_PRESENCES, Intent.GUILD_VOICE_STATES)
 				.login().join();
+
+		initListeners(api);
+
 		config.loadGuilds(api.getServers()); // Once we've logged in, load all guild config files.
 		config.flush(); // Flush to save any new config files that are generated for new guilds.
+
 		SlashCommandListener commandListener = new SlashCommandListener(
 				api,
 				args.length > 0 && args[0].equalsIgnoreCase("--register-commands"),
@@ -70,6 +85,18 @@ public static void main(String[] args) {
 		api.addSlashCommandCreateListener(commandListener);
 	}
 
+	/**
+	 * Initializes and adds all listeners to the API.
+	 * @param api the API
+	 */
+	private static void initListeners(DiscordApi api) {
+		MessageCache cache = new MessageCache();
+		messageCache = cache.getCache();
+
+		api.addMessageCreateListener(new SpamListener());
+		api.addMessageCreateListener(cache);
+	}
+
 	/**
 	 * Initializes all the basic data sources that are needed by the bot's other
 	 * capabilities. This should be called <strong>before</strong> logging in

src/main/java/net/javadiscord/javabot2/config/guild/ModerationConfig.java

@@ -16,6 +16,31 @@ public class ModerationConfig extends GuildConfigItem {
 	 */
 	private long staffRoleId;
 
+	/**
+	 * The amount of seconds to be looked into the past to determine if a user is spamming.
+	 */
+	private int pastMessageCountBeforeDurationInSeconds;
+
+	/**
+	 * The amount of messages to be sent within {@link #pastMessageCountBeforeDurationInSeconds}.
+	 */
+	private int messageSpamAmount;
+
+	/**
+	 * The amount of messages to be cached for each user.
+	 */
+	private int cachedMessagesPerUser;
+
+	/**
+	 * The frequency of cleaning up the cached messages. Amount in minutes.
+	 */
+	private int cachedMessageCleanupFrequency;
+
+	/**
+	 * The amount of minutes for removing this cached messages.
+	 */
+	private int amountOfMinutesForRemoval;
+
 	public Role getStaffRole() {
 		return this.getGuild().getRoleById(staffRoleId).orElseThrow();
 	}

src/main/java/net/javadiscord/javabot2/systems/moderation/MessageCache.java

@@ -0,0 +1,82 @@
+package net.javadiscord.javabot2.systems.moderation;
+
+import net.javadiscord.javabot2.Bot;
+import org.javacord.api.entity.message.Message;
+import org.javacord.api.entity.message.MessageAuthor;
+import org.javacord.api.event.message.MessageCreateEvent;
+import org.javacord.api.listener.message.MessageCreateListener;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.LinkedList;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Caches incoming messages and cleans it out when needed.
+ */
+public class MessageCache implements MessageCreateListener {
+
+	private final ConcurrentHashMap<MessageAuthor, Instant> lastModifications;
+	private final ConcurrentHashMap<MessageAuthor, LinkedList<Message>> cache;
+
+    /**
+     * Creates the cache.
+     */
+	public MessageCache() {
+		lastModifications = new ConcurrentHashMap<>();
+		cache = new ConcurrentHashMap<>();
+        // TODO config
+		Bot.asyncPool.scheduleAtFixedRate(this::clean, -1, -1, TimeUnit.MINUTES);
+	}
+
+	@Override
+	public void onMessageCreate(MessageCreateEvent event) {
+		if (!event.getMessageAuthor().isYourself()) {
+			add(event.getMessage());
+		}
+	}
+
+	/**
+	 * Removes all Map entries which have not been modified within the last 10 minutes.
+	 */
+	private void clean() {
+		lastModifications.forEach((messageAuthor, instant) -> {
+			// if last modification is older than n minutes
+            // TODO config
+			if (instant.isAfter(Instant.now().minus(Duration.ofMinutes(-1)))) {
+				cache.remove(messageAuthor);
+				lastModifications.remove(messageAuthor);
+			}
+		});
+	}
+
+	/**
+	 * Add the message either as a new Map entry or to the existing list per user.
+	 * Also removes if the amount of messages per user is over a certain treshold.
+	 * @param msg the message to be added
+	 */
+	private void add(Message msg) {
+		if (cache.containsKey(msg.getAuthor())) {
+			LinkedList<Message> msgList = cache.get(msg.getAuthor());
+			msgList.offer(msg);
+			lastModifications.replace(msg.getAuthor(), Instant.now());
+
+			// TODO config
+			if (msgList.size() >= -1) {
+				msgList.poll();
+			}
+
+		} else {
+			LinkedList<Message> messages = new LinkedList<>();
+			messages.add(msg);
+			cache.put(msg.getAuthor(), messages);
+			lastModifications.put(msg.getAuthor(), Instant.now());
+		}
+	}
+
+	public ConcurrentHashMap<MessageAuthor, LinkedList<Message>> getCache() {
+		return cache;
+	}
+}
+

src/main/java/net/javadiscord/javabot2/systems/moderation/SpamListener.java

@@ -0,0 +1,34 @@
+package net.javadiscord.javabot2.systems.moderation;
+
+import net.javadiscord.javabot2.Bot;
+import org.javacord.api.event.message.MessageCreateEvent;
+import org.javacord.api.listener.message.MessageCreateListener;
+
+import java.time.Duration;
+import java.time.Instant;
+
+/**
+ * Listens for spam using the {@link MessageCache}.
+ */
+public class SpamListener implements MessageCreateListener {
+
+	@Override
+	public void onMessageCreate(MessageCreateEvent event) {
+		if (!event.getMessageAuthor().isYourself() && Bot.messageCache.containsKey(event.getMessageAuthor())) {
+			int amountOfMessages = (int) Bot.messageCache.get(event.getMessageAuthor())
+					.stream()
+					//TODO get time from config
+					.filter(msg -> msg.getCreationTimestamp().isAfter(Instant.now().minus(Duration.ofSeconds(-1))))
+					.count();
+
+			//TODO get amount from config
+			if (amountOfMessages >= -1) {
+				//TODO spam detected
+				// placeholder for checkstyle not to complain.
+				// should be replaced with a warn + purge which is not implemented yet
+				event.deleteMessage("spam");
+			}
+		}
+	}
+
+}