/*
    * 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.Language;
  import org.apache.giraph.jython.factories.JythonComputationFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.python.core.Py;
  import org.python.core.PyObject;
  import org.python.util.PythonInterpreter;
  
  import static org.apache.giraph.conf.GiraphConstants.COMPUTATION_FACTORY_CLASS;
  import static org.apache.giraph.conf.GiraphConstants.COMPUTATION_LANGUAGE;
  
  /**
   * Helpers for running jobs with Jython.
   */
  public class JythonUtils {
    /**
     * The Jython interpreter. Cached here for fast access. We use a singleton
     * for this so that we can parse all of the Jython scripts once at startup
     * and then have their data loaded for the rest of the job.
     */
    private static final PythonInterpreter INTERPRETER =
        new PythonInterpreter();
  
    /** Don't construct */
    private JythonUtils() { }
  
    /**
     * Get Jython interpreter
     *
     * @return interpreter
     */
    public static PythonInterpreter getInterpreter() {
      return INTERPRETER;
    }
  
    /**
     * Sets up the Configuration for using Jython
     *
     * @param conf Configuration to se
     * @param klassName Class name of Jython Computation
     */
    public static void init(Configuration conf, String klassName) {
      COMPUTATION_LANGUAGE.set(conf, Language.JYTHON);
      COMPUTATION_FACTORY_CLASS.set(conf, JythonComputationFactory.class);
      JythonOptions.JYTHON_COMPUTATION_CLASS_NAME.set(conf, klassName);
    }
  
    /**
     * Instantiate new instance of the Jython class
     *
     * @param className Jython class name
     * @return new instance of class
     */
    public static PyObject newInstance(String className) {
      PyObject pyClass = JythonUtils.getInterpreter().get(className);
      PyObject pyObject = pyClass.__call__();
      return pyObject;
    }
  
    /**
     * Instantiate new instance of the Jython class
     *
     * @param <T> Jython type
     * @param className Jython class name
     * @param klass Java interface Class
     * @return new instance of class
     */
    public static <T> T newInstance(String className, Class<? extends T> klass) {
      PyObject pyObject = newInstance(className);
      Object object = pyObject.__tojava__(klass);
      if (Py.NoConversion.equals(object)) {
        throw new IllegalArgumentException("Cannot coerce Jython class " +
            className + " to Java type " + klass.getSimpleName());
      } else {
        return (T) object;
      }
    }
  }