/*
    * 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;
      }
    }
 }