@Configuration
@IntegrationComponentScan
public class MqttConfiguration {

    private static final Logger log = LoggerFactory.getLogger(MqttConfiguration.class);

    @Value("${cloud-sdk.mqtt.inbound-topic: }")
    private String inboundTopic;

    @Resource
    private MqttPahoClientFactory mqttClientFactory;

    @Resource(name = ChannelName.INBOUND)
    private MessageChannel inboundChannel;


    /**
     * Clients of inbound message channels.
     * @return
     */
    @Bean
    public MqttPahoMessageDrivenChannelAdapter mqttInbound() {
        MqttPahoMessageDrivenChannelAdapter adapter = new MqttPahoMessageDrivenChannelAdapter(
                UUID.randomUUID().toString(), mqttClientFactory, inboundTopic.split(","));
        DefaultPahoMessageConverter converter = new DefaultPahoMessageConverter();
        // use byte types uniformly
        converter.setPayloadAsBytes(true);
        adapter.setConverter(converter);
        adapter.setQos(1);
        adapter.setOutputChannel(inboundChannel);
        return adapter;
    }

    /**
     * Clients of outbound message channels.
     * @return
     */
    @Bean
    @ServiceActivator(inputChannel = ChannelName.OUTBOUND)
    public MessageHandler mqttOutbound() {
        MqttPahoMessageHandler messageHandler = new MqttPahoMessageHandler(
                UUID.randomUUID().toString(), mqttClientFactory);
        DefaultPahoMessageConverter converter = new DefaultPahoMessageConverter();
        // use byte types uniformly
        converter.setPayloadAsBytes(true);

        messageHandler.setAsync(true);
        messageHandler.setDefaultQos(0);
        messageHandler.setConverter(converter);
        return messageHandler;
    }



    /**
     * Define a default channel to handle messages that have no effect.
     * @return
     */
    @Bean
    @ServiceActivator(inputChannel = ChannelName.DEFAULT)
    public MessageHandler defaultInboundHandler() {
        return message -> {
            log.info("The default channel does not handle messages." +
                    "\nTopic: " + message.getHeaders().get(MqttHeaders.RECEIVED_TOPIC) +
                    "\nPayload: " + message.getPayload() + "\n");
        };
    }
}

@Component
@MessagingGateway(defaultRequestChannel = ChannelName.OUTBOUND)
public interface IMqttMessageGateway {

    /**
     * Publish a message to a specific topic.
     * @param topic target
     * @param payload   message
     */
    void publish(@Header(MqttHeaders.TOPIC) String topic, byte[] payload);

    /**
     * Use a specific qos to push messages to a specific topic.
     * @param topic     target
     * @param payload   message
     * @param qos   qos
     */
    void publish(@Header(MqttHeaders.TOPIC) String topic, byte[] payload, @Header(MqttHeaders.QOS) int qos);
}