Implement potential selector in monoliths

src/main/java/emu/nebula/game/tower/StarTowerManager.java

@@ -14,6 +14,7 @@ import lombok.Getter;
 public class StarTowerManager extends PlayerManager implements GameDatabaseObject {
     @Id
     private int uid;
+    private int lastBuildId;
     
     private transient StarTowerInstance instance;
     
@@ -29,6 +30,10 @@ public class StarTowerManager extends PlayerManager implements GameDatabaseObjec
         this.save();
     }
     
+    public int getNextBuildId() {
+        return ++this.lastBuildId;
+    }
+    
     public StarTowerInstance apply(StarTowerApplyReq req) {
         // Sanity checks
         var data = GameData.getStarTowerDataTable().get(req.getId());
@@ -48,4 +53,14 @@ public class StarTowerManager extends PlayerManager implements GameDatabaseObjec
         // Success
         return this.instance;
     }
+
+    public StarTowerInstance giveUp() {
+        var instance = this.instance;
+        
+        if (instance != null) {
+            this.instance = null;
+        }
+        
+        return instance;
+    }
 }