import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.clients.producer.ProducerRecord;

import java.time.Instant;
import java.util.Properties;

public class KafkaProducerApp {

    public static final String STRING_SERIALIZER = "org.apache.kafka.common.serialization.StringSerializer";
    public static final String TOPIC = "my-topic";

    public static void main(String[] args) {
        Properties props = new Properties();

        // These are the 3 required properties.
        // 1. Cluster membership: partition leaders, etc
        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092, BROKER-1:9092, BROKER-2:9093");

        // 2. How keys and values are serialized.
        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, STRING_SERIALIZER);
        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, STRING_SERIALIZER);

        KafkaProducer<String, String> myProducer = new KafkaProducer<String, String>(props);

        try {
            for (int i = 0; i < 100; i++) {
                Instant ts = Instant.now();
                Double ss = ts.toEpochMilli() + ts.getNano() / 1E9;
                ProducerRecord myMessage = new ProducerRecord(TOPIC, String.format("%3d : %09.3f", i, ss));
                myProducer.send(myMessage); // Best practice: wrap in try..catch.
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            myProducer.close();
        }
    }

    public static void createMessagesExample() {
        // Message with only the required properties.
        ProducerRecord myMessage = new ProducerRecord(
                TOPIC, // Topic to which the record will be sent.
                "My Message 1" // Message content, matching the serializer type for value
        );

        // Non-matching type: runtime exception
        // ProducerRecord myBadMessage = new ProducerRecord(TOPIC, 3.14159);

        ProducerRecord myPartitionedMessage = new ProducerRecord(
                TOPIC, // String Topic
                1,  // Integer Partition
                "My Message 1" // String Message
        );

        ProducerRecord myKeyedMessage = new ProducerRecord(
                TOPIC, // String Topic
                "Course-001",  // K key
                "My Message 1" // String Message
        );

        // Adding optional properties
        ProducerRecord msg3 = new ProducerRecord(
                TOPIC, // String Topic
                1, // Integer Partition
                124535353325L, // Long timestamp, added in Kafka 0.10.
                "Course-001", // K key: basis to determine partitioning strategy. Don't use blank or NULL.
                // Key may contain additional message information, but adds overhead, depends on serializer.
                "My Message 1" // V value
        );
        // The actual TS being send with the message is defined in server.properties:
        // log.message.timestamp.type = [CreateTime, LogAppendTime]
        // - CreateTime: producer-set timestamp is used
        // - LogAppendtime: broker-set to the time when the message is appended to the commit log. Overrides the producet-set one.
    }
}