package votorola.g.web.gwt; // Copyright 2012, Michael Allan.  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Votorola Software"), to deal in the Votorola Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicence, and/or sell copies of the Votorola Software, and to permit persons to whom the Votorola Software is furnished to do so, subject to the following conditions: The preceding copyright notice and this permission notice shall be included in all copies or substantial portions of the Votorola Software. THE VOTOROLA SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE VOTOROLA SOFTWARE OR THE USE OR OTHER DEALINGS IN THE VOTOROLA SOFTWARE.

import com.google.gwt.jsonp.client.JsonpRequest;
import com.google.gwt.user.client.rpc.AsyncCallback;


/** A callback wrapper that uses an atomizer to enforce non-overlapping JSONP
  * request/response exchanges.
  */
public final class AtomicAsyncCallback<T,R> implements AsyncCallback<T>
{


    /** Partially creates an AtomicAsyncCallback for {@linkplain #init(JsonpRequest) init}
      * to finish.
      *
      *     @param atomizer the exchange atomizer to use.
      *     @param callback the callback to guard.
      */
    public static <T,R> AtomicAsyncCallback<T,R> wrap( final JSONPAtomizer<R> atomizer,
      final AsyncCallback<T> callback )
    {
        return new AtomicAsyncCallback<T,R>( atomizer, callback );
    }



    private AtomicAsyncCallback( JSONPAtomizer<R> _atomizer, AsyncCallback<T> _callback )
    {
        atomizer = _atomizer;
        callback = _callback;
    }



    /** Completes the creation of this callback.  Call once only.  If the specified
      * request completes before another is issued on the same atomizer, then one of
      * {@linkplain #onFailure(Throwable) onFailure} or {@linkplain #onSuccess onSuccess}
      * is called.  Otherwise the request is abandoned.
      */
    public void init( JsonpRequest<R> _request )
    {
        request = _request;
        atomizer.setPendingRequest( request );
    }



   // - A s y n c - C a l l b a c k ------------------------------------------------------


    public void onFailure( final Throwable x )
    {
        assert request != null: "init was called";
        if( request != atomizer.pendingRequest() ) return;

        atomizer.clearPendingRequest( request );
        callback.onFailure( x );
    }



    public void onSuccess( final T result )
    {
        assert request != null: "init was called";
        if( request != atomizer.pendingRequest() ) return;

        atomizer.clearPendingRequest( request );
        callback.onSuccess( result );
    }



//// P r i v a t e ///////////////////////////////////////////////////////////////////////


    private final JSONPAtomizer<R> atomizer;



    private final AsyncCallback<T> callback;



    private JsonpRequest<R> request; // final when initialized


}