/*
 * 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.dataartisans;

import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.java.utils.ParameterTool;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumer082;
import org.apache.flink.streaming.util.serialization.SimpleStringSchema;

/**
 * Simple example on how to read with a Kafka consumer
 *
 * Note that the Kafka source is expecting the following parameters to be set
 *  - "bootstrap.servers" (comma separated list of kafka brokers)
 *  - "zookeeper.connect" (comma separated list of zookeeper servers)
 *  - "group.id" the id of the consumer group
 *  - "topic" the name of the topic to read data from.
 *
 * You can pass these required parameters using "--bootstrap.servers host:port,host1:port1 --zookeeper.connect host:port --topic testTopic"
 *
 * This is a valid input example:
 * 		--topic test --bootstrap.servers localhost:9092 --zookeeper.connect localhost:2181 --group.id myGroup
 *
 *
 */
public class ReadFromKafka {

	public static void main(String[] args) throws Exception {
		// create execution environment
		StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

		// parse user parameters
		ParameterTool parameterTool = ParameterTool.fromArgs(args);

		DataStream<String> messageStream = env.addSource(new FlinkKafkaConsumer082<>(parameterTool.getRequired("topic"), new SimpleStringSchema(), parameterTool.getProperties()));

		// print() will write the contents of the stream to the TaskManager's standard out stream
		// the rebelance call is causing a repartitioning of the data so that all machines
		// see the messages (for example in cases when "num kafka partitions" < "num flink operators"
		messageStream.rebalance().map(new MapFunction<String, String>() {
			private static final long serialVersionUID = -6867736771747690202L;

			@Override
			public String map(String value) throws Exception {
				return "Kafka and Flink says: " + value;
			}
		}).print();

		env.execute();
	}
}