package cz.cuni.amis.utils.collections;
   
   import java.util.ArrayList;
   import java.util.HashMap;
   import java.util.Map;
   
   /**
    * Translates one observable collection into another
    * @author ik
   */
  public abstract class TranslatedObservableCollection<T, U> extends ObservableList<T> {
  
      /**
       * Holds mapping between original objects and the translated one.
       */
      Map<Object, T> map = new HashMap<Object, T>();
  
      public TranslatedObservableCollection(ObservableCollection<U> col) {
          super(new ArrayList<T>());
  
          // listen for changes
          col.addCollectionListener(new ElementListener<U>() {
  
              @Override
              public void elementChanged(U elem, boolean added) {
                  if (added) {
                      insert(elem);
                  } else {
                      // remove element
                      T val = map.remove(getKeyForObj(elem));
                      remove(val);
                  }
              }
          });
  
          // import existing items
          for (U val : col) {
              insert(val);
          }
  
      }
  
      protected synchronized void insert(U elem) {
          if (map.containsKey(getKeyForObj(elem))) return; // will not insert already present item
      	T val = translate(elem);
          if (val != null) {
              map.put(getKeyForObj(elem), val);
              add(val);
          }
  
      }
  
      protected Object getKeyForObj(U elem) {
          return elem;
      }
  
      /**
       * Translates object from wrapped collection into this collection.
       * @param obj object to be translated
       * @return the translated object, null if the object shouldn't be added to the collection
       */
      protected abstract T translate(U obj);
  }