Support Entity tagging

core/src/com/me/common/ecs/Engine.java

@@ -91,14 +91,22 @@ public class Engine {
     }
 
     /**
-     * Return the list of entities that are a part of the given group.
      * @param group the group to look up
-     * @return a list of entities
+     * @return the list of entities that are a part of the given group.
      */
     public Array<Entity> getEntitiesInGroup(String group) {
         return entityManager.getGroupEntities(group);
     }
 
+    /**
+     * @param tag the tag to look up
+     * @return the entity with the given tag, or null
+     */
+    public Entity getEntityByTag(String tag) {
+        return entityManager.getEntityByTag(tag);
+    }
+
+
     void addEntityGroup(Entity entity, String group) {
         entityManager.addEntityToGroup(entity, group);
     }
@@ -107,6 +115,14 @@ public class Engine {
         entityManager.removeEntityFromGroup(entity, group);
     }
 
+    void tagEntity(Entity entity, String tag) {
+        entityManager.tagEntity(entity, tag);
+    }
+
+    void removeEntityTag(Entity entity) {
+        entityManager.removeEntityTag(entity);
+    }
+
     void refreshEntity(Entity entity) {
         entityManager.queueRefresh(entity);
     }

core/src/com/me/common/ecs/Entity.java

@@ -18,6 +18,7 @@ public final class Entity {
     boolean removed;
 
     ObjectSet<String> groups;
+    String tag;
 
     private long uniqueId;
 
@@ -110,6 +111,22 @@ public final class Entity {
         return groups.contains(group);
     }
 
+    public String getTag() {
+        return tag;
+    }
+
+    public void setTag(String tag) {
+        engine.tagEntity(this, tag);
+    }
+
+    public void removeTag() {
+        engine.removeEntityTag(this);
+    }
+
+    public boolean hasTag(String tag) {
+        return tag.equals(this.tag);
+    }
+
     // Internal getComponent method accessed only by ComponentMapper
     Component getComponent(ComponentType type) {
         return engine.getEntityComponent(this, type);

core/src/com/me/common/ecs/EntityManager.java

@@ -12,6 +12,7 @@ final class EntityManager {
     private final Array<Entity> toRefresh;
 
     private final ObjectMap<String, Array<Entity>> groupEntities;
+    private final ObjectMap<String, Entity> taggedEntities;
 
     EntityManager(Engine engine) {
         this.engine = engine;
@@ -21,6 +22,7 @@ final class EntityManager {
         this.toRefresh = new Array<>(false, 16);
 
         this.groupEntities = new ObjectMap<>();
+        this.taggedEntities = new ObjectMap<>();
     }
 
     Array<Entity> getEntities() {
@@ -73,6 +75,25 @@ final class EntityManager {
         entity.groups.remove(group);
     }
 
+    Entity getEntityByTag(String tag) {
+        return taggedEntities.get(tag);
+    }
+
+    void tagEntity(Entity entity, String tag) {
+        Entity previouslyTagged = taggedEntities.put(tag, entity);
+        if (previouslyTagged != null) {
+            previouslyTagged.tag = null;
+        }
+        entity.tag = tag;
+    }
+
+    void removeEntityTag(Entity entity) {
+        if (entity.tag != null) {
+            taggedEntities.remove(entity.tag);
+            entity.tag = null;
+        }
+    }
+
     void queueRefresh(Entity entity) {
         toRefresh.add(entity);
     }
@@ -96,6 +117,8 @@ final class EntityManager {
                 getGroupEntities(group).removeValue(entity, true);
             }
             entity.groups.clear();
+
+            removeEntityTag(entity);
         }
     }