Add API events system

api/src/main/java/us/ajg0702/queue/api/AjQueueAPI.java

@@ -1,5 +1,6 @@
 package us.ajg0702.queue.api;
 
+import us.ajg0702.queue.api.events.utils.EventReceiver;
 import us.ajg0702.queue.api.premium.Logic;
 import us.ajg0702.queue.api.premium.LogicGetter;
 import us.ajg0702.queue.api.spigot.AjQueueSpigotAPI;
@@ -114,5 +115,7 @@ public abstract class AjQueueAPI {
      */
     public abstract void shutdown();
 
+    public abstract <E> void listen(Class<E> event, EventReceiver<E> handler);
+
     public abstract ExecutorService getServersUpdateExecutor();
 }

api/src/main/java/us/ajg0702/queue/api/events/Cancellable.java

@@ -0,0 +1,15 @@
+package us.ajg0702.queue.api.events;
+
+public interface Cancellable {
+    /**
+     * Whether this event is canceled.
+     * @return True if canceled. False if not.
+     */
+    boolean isCancelled();
+
+    /**
+     * Allows you to cancel or un-cancel this event
+     * @param cancelled True to cancel the event, false to un-cancel
+     */
+    void setCancelled(boolean cancelled);
+}

api/src/main/java/us/ajg0702/queue/api/events/Event.java

@@ -0,0 +1,4 @@
+package us.ajg0702.queue.api.events;
+
+public interface Event {
+}

api/src/main/java/us/ajg0702/queue/api/events/PositionChangeEvent.java

@@ -0,0 +1,51 @@
+package us.ajg0702.queue.api.events;
+
+import org.jetbrains.annotations.Nullable;
+import us.ajg0702.queue.api.players.AdaptedPlayer;
+import us.ajg0702.queue.api.players.QueuePlayer;
+import us.ajg0702.queue.api.queues.QueueServer;
+
+/**
+ * Called when someone is added or removed from a queue that the player is in, causing the player's position to change
+ */
+public class PositionChangeEvent implements Event {
+    private final QueuePlayer player;
+    private final int position;
+
+    public PositionChangeEvent(QueuePlayer player) {
+        this.player = player;
+        position = player.getPosition();
+    }
+
+    /**
+     * Gets the QueuePlayer object that represents this player
+     * @return the QueuePlayer object
+     */
+    public QueuePlayer getQueuePlayer() {
+        return player;
+    }
+
+    /**
+     * Gets the AdaptedPlayer that this event is about. May return null!
+     * @return The AdaptedPlayer that this event is about. Returns null if the player is offline.
+     */
+    public @Nullable AdaptedPlayer getPlayer() {
+        return player.getPlayer();
+    }
+
+    /**
+     * Gets the player's new position in the queue
+     * @return The player's new position. 1 being 1st, 2 being 2nd, etc
+     */
+    public int getPosition() {
+        return position;
+    }
+
+    /**
+     * Gets the queue that this event is from
+     * @return The QueueServer that the player is in that their position changed
+     */
+    public QueueServer getQueue() {
+        return player.getQueueServer();
+    }
+}

api/src/main/java/us/ajg0702/queue/api/events/PreQueueEvent.java

@@ -0,0 +1,45 @@
+package us.ajg0702.queue.api.events;
+
+import us.ajg0702.queue.api.players.AdaptedPlayer;
+import us.ajg0702.queue.api.queues.QueueServer;
+
+/**
+ * Called after all checks are made, right before a player is actually added to the queue.
+ * If canceled, the player will not be added to the queue.
+ * If you cancel this event, it is up to you to send a message telling the player why they were not added to the queue.
+ */
+public class PreQueueEvent implements Event, Cancellable {
+    private final AdaptedPlayer player;
+    private final QueueServer target;
+
+    private boolean cancelled = false;
+
+    public PreQueueEvent(AdaptedPlayer player, QueueServer target) {
+        this.player = player;
+        this.target = target;
+    }
+
+    /**
+     * Gets the player that is joining the queue
+     * @return
+     */
+    public AdaptedPlayer getPlayer() {
+        return player;
+    }
+
+    /**
+     * Gets the target QueueServer that the player is trying to queue for
+     * @return The QueueServer that the player is trying to queue for
+     */
+    public QueueServer getTarget() {
+        return target;
+    }
+
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    public void setCancelled(boolean cancelled) {
+        this.cancelled = cancelled;
+    }
+}

api/src/main/java/us/ajg0702/queue/api/events/SuccessfulSendEvent.java

@@ -0,0 +1,34 @@
+package us.ajg0702.queue.api.events;
+
+import us.ajg0702.queue.api.players.AdaptedPlayer;
+import us.ajg0702.queue.api.players.QueuePlayer;
+import us.ajg0702.queue.api.server.AdaptedServer;
+
+/**
+ * Called after a player is successfully sent to a server.
+ */
+public class SuccessfulSendEvent implements Event {
+    private final QueuePlayer player;
+    private final AdaptedServer server;
+
+    public SuccessfulSendEvent(QueuePlayer player, AdaptedServer server) {
+        this.player = player;
+        this.server = server;
+    }
+
+    /**
+     * Gets the player that was sent
+     * @return the player that was sent
+     */
+    public AdaptedPlayer getPlayer() {
+        return player.getPlayer();
+    }
+
+    /**
+     * Gets the server that the player was sent to
+     * @return The server that the player was sent to
+     */
+    public AdaptedServer getServer() {
+        return server;
+    }
+}

api/src/main/java/us/ajg0702/queue/api/events/utils/EventReceiver.java

@@ -0,0 +1,6 @@
+package us.ajg0702.queue.api.events.utils;
+
+@FunctionalInterface
+public interface EventReceiver<E> {
+    void execute(E event);
+}

api/src/main/java/us/ajg0702/queue/api/players/AdaptedPlayer.java

@@ -55,6 +55,12 @@ public interface AdaptedPlayer extends Handle, Audience {
      */
     String getServerName();
 
+    /**
+     * Gets the server that the player is currently connected to
+     * @return The server that the player is currently connected to.
+     */
+    AdaptedServer getCurrentServer();
+
     /**
      * Gets the player's unique id (UUID)
      * @return The player's uuid