package org.webslinger.lang;

 import java.util.Collection;

 import java.util.Map;

 import java.util.concurrent.atomic.AtomicReference;

 public abstract class AtomicCollection<T> {

     private final AtomicReference<Collection<T>> ref;

     protected AtomicCollection(Collection<T> initial) {

         ref = new AtomicReference<Collection<T>>(initial);

     }

     protected abstract Collection<T> copyCollection(Collection<T> old);

     public Collection<T> collection() {

         return ref.get();

     }

     public boolean add(T value) {

         Collection<T> oldCollection, newCollection;

         boolean wasAdded;

         do {

             oldCollection = ref.get();

             newCollection = copyCollection(oldCollection);

             wasAdded = newCollection.add(value);

         } while (!ref.compareAndSet(oldCollection, newCollection));

         return wasAdded;

     }

     public boolean remove(T value) {

         Collection<T> oldCollection, newCollection;

         boolean wasRemoved;

         do {

             oldCollection = ref.get();

             newCollection = copyCollection(oldCollection);

             wasRemoved = newCollection.remove(value);

         } while (!ref.compareAndSet(oldCollection, newCollection));

         return wasRemoved;

     }

 }