package au.gov.amsa.geo.distance;
   
   import java.util.ArrayList;
   import java.util.LinkedList;
   import java.util.List;
   
   import org.apache.log4j.Logger;
   
   import rx.Observable.Operator;
  import rx.Observer;
  import rx.Subscriber;
  import rx.observers.Subscribers;
  
  /**
   * Presizes the ArrayList returned by the given size parameter. This will save
   * some seconds in run time for large lists.
   */
  public class OperatorToObservableSizedList<T> implements Operator<List<T>, T> {
  
  	private static Logger log = Logger
  			.getLogger(OperatorToObservableSizedList.class);
  
  	private final int size;
  
  	public OperatorToObservableSizedList(int size) {
  		this.size = size;
  	}
  
  	@Override
  	public Subscriber<? super T> call(final Subscriber<? super List<T>> child) {
  		log.info("allocating list of size " + size);
  		final List<T> list;
  		if (size == 0)
  			list = new LinkedList<T>();
  		else
  			list = new ArrayList<T>(size);
  		log.info("allocated");
  		Subscriber<T> parent = Subscribers.from(new Observer<T>() {
  
  			@Override
  			public void onCompleted() {
  				child.onNext(list);
  				child.onCompleted();
  			}
  
  			@Override
  			public void onError(Throwable e) {
  				child.onError(e);
  			}
  
  			@Override
  			public void onNext(T t) {
  				list.add(t);
  			}
  		});
  		child.add(parent);
  		return parent;
  	}
  
  }