/**
 * 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 com.datatorrent.api;

import org.apache.hadoop.conf.Configuration;

/**
 * Interface to be implemented for Java based streaming application declaration.
 * <p>
 * An application is the top level DAG with external configuration for
 * application master / engine settings, application specific properties or
 * overrides for individual operators in the DAG. <br>
 * Application launchers (CLI) use the interface to identify application DAGs
 * within jar files and supply the configuration upon instantiation.
 * <p>
 * Operator properties in the DAG can be configured externally. When an
 * application is launched from the CLI, any settings in dt-site.xml would
 * override property values in the DAG. It is therefore possible to have
 * defaults in the DAG code and supply environment/launch context specific
 * settings through the configuration.
 *
 * @since 0.3.2
 */
public interface StreamingApplication
{
  /**
   * Prefix used in configuration keys.
   */
  String APEX_PREFIX = "apex.";

  /**
   * Legacy prefix, to be removed in future release,
   * when all code dependencies are upgraded.
   */
  @Deprecated
  String DT_PREFIX = "dt.";
  /**
   * Launch mode for the application.
   * Used in the client to set configuration depending on how the DAG is executed.
   */
  String ENVIRONMENT = DT_PREFIX + "environment";

  /**
   * Streaming Application code would be executing in one of these environments.
   * ENVIRONMENT key in conf is set to LOCAL when the application is running in local mode.
   * It's set to CLUSTER when the application is running in distributed mode.
   */
  enum Environment
  {
    LOCAL,
    CLUSTER
  }

  /**
   * <p>populateDAG.</p>
   */
  void populateDAG(DAG dag, Configuration conf);

}