import org.apache.kafka.clients.consumer.ConsumerConfig
import org.apache.kafka.common.serialization.StringDeserializer
import org.slf4j.LoggerFactory
import org.springframework.context.annotation.Bean
import org.springframework.stereotype.Component
import reactor.core.publisher.Mono
import reactor.core.scheduler.Schedulers
import reactor.kafka.receiver.KafkaReceiver
import reactor.kafka.receiver.ReceiverOptions
import reactor.kafka.receiver.ReceiverRecord
import reactor.kotlin.core.publisher.toMono
import reactor.util.retry.Retry
import java.time.Duration
import java.util.*
@Component
class KafkaProcessor {
    private val logger = LoggerFactory.getLogger(javaClass)
    private val consumerProps = hashMapOf(
        ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG to StringDeserializer::javaClass,
        ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG to StringDeserializer::javaClass,
        ConsumerConfig.GROUP_ID_CONFIG to "groupId",
        ConsumerConfig.AUTO_OFFSET_RESET_CONFIG to "earliest",
        ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG to "localhost:9092"
    private val receiverOptions = ReceiverOptions.create<String, String>(consumerProps)
        .subscription(Collections.singleton("some-topic"))
        .commitInterval(Duration.ofSeconds(1))
        .commitBatchSize(1000)
        .maxCommitAttempts(1)
    private val kafkaReceiver: KafkaReceiver<String, String> = KafkaReceiver.create(receiverOptions)
    @Bean
    fun processKafkaMessages(): Unit {
        kafkaReceiver.receive()
            .groupBy { m -> m.receiverOffset().topicPartition() }
            .flatMap { partitionFlux ->
                partitionFlux.publishOn(Schedulers.elastic())
                    .concatMap { receiverRecord ->
                        processRecord(receiverRecord)
                            .map { it.receiverOffset().acknowledge() }
            .retryWhen(
                Retry.backoff(3, Duration.ofSeconds(1))
                    .maxBackoff(Duration.ofSeconds(3))
                    .doBeforeRetry { rs ->
                        logger.warn("Retrying: ${rs.totalRetries() + 1}/3 due to ${rs.failure()}")
                    .onRetryExhaustedThrow { _, u ->
                        logger.error("All ${u.totalRetries() + 1} attempts failed with the last exception: ${u.failure()}")
                        u.failure()
            .subscribe()
    private fun processRecord(record: ReceiverRecord<String, String>): Mono<ReceiverRecord<String, String>> {
        return record.toMono()