/*

  * Licensed to the Apache Software Foundation (ASF) under one

  * or more contributor license agreements.  See the NOTICE file

  * distributed with this work for additional information

  * regarding copyright ownership.  The ASF licenses this file

  * to you under the Apache License, Version 2.0 (the

  * "License"); you may not use this file except in compliance

  * with the License.  You may obtain a copy of the License at

  *

  *     http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.giraph.jython;

 import org.apache.giraph.graph.AbstractComputation;

 import org.apache.giraph.graph.GraphType;

 import org.apache.giraph.graph.Language;

 import org.apache.giraph.graph.Vertex;

 import org.apache.giraph.jython.wrappers.JythonWritableWrapper;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import org.python.core.PyObject;

 import com.google.common.base.Preconditions;

 import java.io.IOException;

 /**

  * The {@link org.apache.giraph.graph.Computation} class for using

  * Jython with Giraph. This class implements the Giraph necessary

  * interfaces but it actually holds a reference to the

  * {@link JythonComputation} which does the real work.

  *

  * The two classes are linked and together they allow us to coerce Jython types

  * to Writables.

  *

  * @param <I> Vertex ID

  * @param <V> Vertex value

  * @param <E> Edge value

  * @param <M1> Incoming message value

  * @param <M2> Outgoing message value

  */

 public class JythonGiraphComputation<I extends WritableComparable,

     V extends Writable, E extends Writable, M1 extends Writable,

     M2 extends Writable>

     extends AbstractComputation<I, V, E, M1, M2> {

   /** The user's computation class */

   private final JythonComputation jythonComputation;

   /**

    * Constructor

    *

    * @param jythonComputation the user's Jython computation

    */

   public JythonGiraphComputation(JythonComputation jythonComputation) {

     this.jythonComputation = jythonComputation;

   }

   @Override public void compute(Vertex<I, V, E> vertex, Iterable<M1> messages)

     throws IOException {

     jythonComputation.compute(vertex, messages);

   }

   /**

    * Wrap a vertex id in a {@link WritableComparable} wrapper if necessary

    *

    * @param object data to wrap

    * @return writable value

    */

   public WritableComparable wrapIdIfNecessary(Object object) {

     return wrapIfNecessary(object, GraphType.VERTEX_ID);

   }

   /**

    * Wrap a user value (IVEMM) in a {@link Writable} wrapper if necessary

    *

    * @param object data to wrap

    * @param graphType type of data (IVEMM)

    * @param <W> writable type

    * @return writable value

    */

   public <W extends Writable> W

   wrapIfNecessary(Object object, GraphType graphType) {

     if (graphType.interfaceClass().isInstance(object)) {

       return (W) object;

     }

     if (getConf().getValueLanguages().get(graphType) == Language.JYTHON &&

         getConf().getValueNeedsWrappers().get(graphType)) {

       Preconditions.checkArgument(object instanceof PyObject);

       return (W) new JythonWritableWrapper((PyObject) object);

     } else {

       return (W) object;

     }

   }

 }