fix: ViewerEngine#untrack impl

Author: Tofaa2

api/src/main/java/me/tofaa/entitylib/ve/ViewerEngine.java

@@ -25,21 +25,56 @@ public class ViewerEngine {
     private final Set<WrapperEntity> tracked;
     private final ViewerEngineListener listener;
     private Executor executor;
+    private boolean enabled = false;
 
+    /**
+     * Creates an instance of ViewerEngine
+     * It is recommended to specify explicitly the Executor that should be used.
+     */
     public ViewerEngine() {
+        this(Executors.newSingleThreadExecutor());
+    }
+
+    /**
+     * Creates an instance of ViewerEngine with a specific executor. Depending on your rules one thread might not be enough
+     * @param executor The executor that is used to process entity tracking.
+     */
+    public ViewerEngine(Executor executor) {
         this.globalRules = new CopyOnWriteArrayList<>();
         this.tracked = Collections.newSetFromMap(new WeakHashMap<>());
-        this.executor = Executors.newSingleThreadExecutor();
+        this.executor = executor;
         this.listener = new ViewerEngineListener(this);
     }
 
+    /**
+     * Enables this viewer engine.
+     * Registers a viewer engine listener to handle tracking
+     */
     public void enable() {
+        if (enabled) {
+            return;
+        }
+        enabled = true;
         EntityLib.getApi().getPacketEvents().getEventManager().registerListener(listener);
     }
+
+
+    /**
+     * Disables this viewer engine.
+     * Unregisters the viewer engine listener that handles tracking.
+     */
     public void disable() {
+        if (!enabled) {
+            return;
+        }
+        enabled = false;
         EntityLib.getApi().getPacketEvents().getEventManager().unregisterListener(listener);
     }
 
+    /**
+     * Refreshes and updates every tracked by this viewer engine entities viewers to see if they follow the spawning rules.
+     * If they do not they will no longer see the entity;
+     */
     public void refresh() {
         getTracked0().forEach(entity -> {
             for (UUID viewer : entity.getViewers()) {
@@ -58,19 +93,40 @@ public void setExecutor(Executor executor) {
         this.executor = executor;
     }
 
+    /**
+     * Tells this ViewerEngine to begin tracking a specific {@link WrapperEntity}
+     * @param entity the entity to begin tracking.
+     */
     public void track(@NotNull WrapperEntity entity) {
         tracked.add(entity);
     }
 
+    /**
+     * Tells this ViewerEngine to stop tracking a specific {@link WrapperEntity}
+     * @param entity the entity to stop tracking.
+     */
+    public void untrack(@NotNull WrapperEntity entity) {
+        tracked.remove(entity);
+    }
+
     public void clearTracked() {
         tracked.clear();
     }
 
+    /**
+     * Checks if a viewer/user validates every viewer rule handled by this viewer engine or not.
+     * @param user The user to check
+     * @param entity The entity that is getting its own viewer rules checked as well as the global defined one with {@link ViewerEngine#addViewerRule(ViewerRule)}
+     * @return true if the user passed and did not fail any rules, false otherwise
+     */
     public boolean canSpawnFor(User user, WrapperEntity entity) {
         if (entity.getViewerRules().stream().anyMatch(rule -> rule.shouldSee(user))) return true;
         return globalRules.stream().anyMatch(rule -> rule.shouldSee(user));
     }
 
+    /**
+     * Same as {@link ViewerEngine#canSpawnFor(User, WrapperEntity)} but with UUID instead of User
+     */
     public boolean canSpawnFor(UUID userId, WrapperEntity entity) {
         User user = EntityLib.getApi().getPacketEvents().getProtocolManager().getUser(
                 EntityLib.getApi().getPacketEvents().getProtocolManager().getChannel(userId)
@@ -79,6 +135,9 @@ public boolean canSpawnFor(UUID userId, WrapperEntity entity) {
         return canSpawnFor(user, entity);
     }
 
+    /**
+     * @return An unmodifiable view of the entities that are being tracked.
+     */
     public @UnmodifiableView Collection<WrapperEntity> getTracked() {
         return Collections.unmodifiableCollection(tracked);
     }