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/***********************************************************************************************************************
 * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
 *
 * Licensed 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 eu.stratosphere.api.common;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * A PlanExecutor runs a plan. The specific implementation (such as the eu.stratosphere.client.LocalExecutor
 * and eu.stratosphere.client.RemoteExecutor) determines where and how to run the plan. 
 */
public abstract class PlanExecutor {

	private static final String LOCAL_EXECUTOR_CLASS = "eu.stratosphere.client.LocalExecutor";
	private static final String REMOTE_EXECUTOR_CLASS = "eu.stratosphere.client.RemoteExecutor";
	
	
	/**
	 * Execute the given plan and return the runtime in milliseconds.
	 * 
	 * @param plan The plan of the program to execute.
	 * @return The execution result, containing for example the net runtime of the program, and the accumulators.
	 * 
	 * @throws Exception Thrown, if job submission caused an exception.
	 */
	public abstract JobExecutionResult executePlan(Plan plan) throws Exception;
	
	
	/**
	 * Gets the programs execution plan in a JSON format.
	 * 
	 * @param plan The program to get the execution plan for.
	 * @return The execution plan, as a JSON string.
	 * 
	 * @throws Exception Thrown, if the executor could not connect to the compiler.
	 */
	public abstract String getOptimizerPlanAsJSON(Plan plan) throws Exception;
	
	
	/**
	 * Creates an executor that runs the plan locally in a multi-threaded environment.
	 * 
	 * @return A local executor.
	 * @see eu.stratosphere.client.LocalExecutor
	 */
	public static PlanExecutor createLocalExecutor() {
		Class leClass = loadExecutorClass(LOCAL_EXECUTOR_CLASS);
		
		try {
			return leClass.newInstance();
		}
		catch (Throwable t) {
			throw new RuntimeException("An error occurred while loading the local executor (" + LOCAL_EXECUTOR_CLASS + ").", t);
		}
	}

	/**
	 * Creates an executor that runs the plan on a remote environment. The remote executor is typically used
	 * to send the program to a cluster for execution.
	 * 
	 * @param hostname The address of the JobManager to send the program to.
	 * @param port The port of the JobManager to send the program to.
	 * @param jarFiles A list of jar files that contain the user-defined function (UDF) classes and all classes used
	 *                 from within the UDFs.
	 * @return A remote executor.
	 * @see eu.stratosphere.client.RemoteExecutor
	 */
	public static PlanExecutor createRemoteExecutor(String hostname, int port, String... jarFiles) {
		if (hostname == null) {
			throw new IllegalArgumentException("The hostname must not be null.");
		}
		if (port <= 0 || port > 0xffff) {
			throw new IllegalArgumentException("The port value is out of range.");
		}
		
		Class reClass = loadExecutorClass(REMOTE_EXECUTOR_CLASS);
		
		List files = (jarFiles == null || jarFiles.length == 0) ? Collections.emptyList() : Arrays.asList(jarFiles); 
		
		try {
			return reClass.getConstructor(String.class, int.class, List.class).newInstance(hostname, port, files);
		}
		catch (Throwable t) {
			throw new RuntimeException("An error occurred while loading the remote executor (" + REMOTE_EXECUTOR_CLASS + ").", t);
		}
	}
	
	private static final Class loadExecutorClass(String className) {
		try {
			Class leClass = Class.forName(className);
			return leClass.asSubclass(PlanExecutor.class);
		}
		catch (ClassNotFoundException cnfe) {
			throw new RuntimeException("Could not load the executor class (" + className + "). Do you have the 'stratosphere-clients' project in your dependencies?");
		}
		catch (Throwable t) {
			throw new RuntimeException("An error occurred while loading the executor (" + className + ").", t);
		}
	}
}