Add the ability to listen for replies to specific messages

javacord-api/src/main/java/org/javacord/api/event/message/MessageReplyEvent.java

@@ -0,0 +1,17 @@
+package org.javacord.api.event.message;
+
+import org.javacord.api.entity.message.Message;
+
+/**
+ * A message reply event.
+ */
+public interface MessageReplyEvent extends CertainMessageEvent {
+
+    /**
+     * Gets the message referenced by the message of this event.
+     *
+     * @return The message which was referenced.
+     */
+    Message getReferencedMessage();
+
+}

javacord-api/src/main/java/org/javacord/api/listener/message/MessageReplyListener.java

@@ -0,0 +1,25 @@
+package org.javacord.api.listener.message;
+
+import org.javacord.api.event.message.MessageReplyEvent;
+import org.javacord.api.listener.GloballyAttachableListener;
+import org.javacord.api.listener.ObjectAttachableListener;
+import org.javacord.api.listener.channel.TextChannelAttachableListener;
+import org.javacord.api.listener.server.ServerAttachableListener;
+import org.javacord.api.listener.user.UserAttachableListener;
+import org.javacord.api.listener.webhook.WebhookAttachableListener;
+
+/**
+ * This listener listens to message replies.
+ */
+@FunctionalInterface
+public interface MessageReplyListener extends ServerAttachableListener, UserAttachableListener,
+        WebhookAttachableListener, TextChannelAttachableListener, MessageAttachableListener,
+        GloballyAttachableListener, ObjectAttachableListener {
+
+    /**
+     * This method is called when a message is created which replies to another.
+     *
+     * @param event The event.
+     */
+    void onMessageReply(MessageReplyEvent event);
+}

javacord-core/src/main/java/org/javacord/core/event/message/MessageReplyEventImpl.java

@@ -0,0 +1,29 @@
+package org.javacord.core.event.message;
+
+import org.javacord.api.entity.message.Message;
+import org.javacord.api.event.message.MessageReplyEvent;
+
+/**
+ * The implementation of {@link MessageReplyEvent}.
+ */
+public class MessageReplyEventImpl extends CertainMessageEventImpl implements MessageReplyEvent {
+
+    private final Message referencedMessage;
+
+    /**
+     * Creates a new event instance.
+     *
+     * @param message The created message.
+     * @param referencedMessage The message which is being replied to.
+     */
+    public MessageReplyEventImpl(Message message, Message referencedMessage) {
+        super(message);
+        this.referencedMessage = referencedMessage;
+    }
+
+    @Override
+    public Message getReferencedMessage() {
+        return referencedMessage;
+    }
+
+}

javacord-core/src/main/java/org/javacord/core/util/handler/message/MessageCreateHandler.java

@@ -11,17 +11,23 @@
 import org.javacord.api.entity.message.MessageAuthor;
 import org.javacord.api.entity.message.MessageFlag;
 import org.javacord.api.entity.server.Server;
+import org.javacord.api.entity.user.User;
 import org.javacord.api.event.message.MessageCreateEvent;
+import org.javacord.api.event.message.MessageReplyEvent;
 import org.javacord.core.entity.channel.PrivateChannelImpl;
 import org.javacord.core.entity.channel.ServerThreadChannelImpl;
 import org.javacord.core.entity.user.MemberImpl;
 import org.javacord.core.entity.user.UserImpl;
 import org.javacord.core.event.message.MessageCreateEventImpl;
+import org.javacord.core.event.message.MessageReplyEventImpl;
 import org.javacord.core.util.event.DispatchQueueSelector;
 import org.javacord.core.util.gateway.PacketHandler;
 import org.javacord.core.util.logging.LoggerUtil;
 
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.Optional;
+import java.util.Set;
 
 /**
  * Handles the message create packet.
@@ -98,6 +104,27 @@ private void handle(TextChannel channel, JsonNode packet) {
                 author.asUser().orElse(null),
                 author.isWebhook() ? author.getId() : null,
                 event);
+
+        message.getReferencedMessage().ifPresent(referencedMessage -> {
+            MessageReplyEvent replyEvent = new MessageReplyEventImpl(message, referencedMessage);
+            Set<User> users = new HashSet<>();
+            referencedMessage.getUserAuthor().ifPresent(users::add);
+            message.getUserAuthor().ifPresent(users::add);
+
+            Set<Long> webhookIds =  new HashSet<>();
+            message.getAuthor().getWebhookId().ifPresent(webhookIds::add);
+            referencedMessage.getAuthor().getWebhookId().ifPresent(webhookIds::add);
+
+            api.getEventDispatcher().dispatchMessageReplyEvent(
+                    optionalServer.map(DispatchQueueSelector.class::cast).orElse(api),
+                    Collections.singleton(referencedMessage),
+                    optionalServer.map(Collections::singleton).orElse(null),
+                    Collections.singleton(message.getChannel()),
+                    users,
+                    webhookIds,
+                    replyEvent
+            );
+        });
     }
 
 }