/**
 * Compose a URI understood by the Push Notification Bridge from an APNs device token.
 * @param deviceID APNS device token.
 * @return string in format expected by the push notification bridge.
 */
-(NSString*)formatAsURI:(NSData*)deviceID {
    return [NSString stringWithFormat:@"apns://%@", [deviceID base64EncodedStringWithOptions:0]];
}

/**
 * Compose and send a subscription request to the Push Notification bridge
 * @param paths topic paths within the subscription request
 */
- (void)doPnSubscribe:(NSArray<NSString*> *)paths deviceToken:(NSData*)deviceToken {
    // Compose the JSON request from Obj-C literals
    NSString *const correlation = [[NSUUID UUID] UUIDString];
    PTDiffusionTopicSelector *const selector = [PTDiffusionTopicSelector topicSelectorWithAnyExpression:paths];
    NSDictionary *const request = 
        @{@"request": @{
           @"correlation": correlation,
           @"content": @{
              @"pnsub": @{
                @"destination": [self formatAsURI:deviceToken],
                @"topic": selector.description}
              }
           }};
    NSData *const requestData = [NSJSONSerialization dataWithJSONObject:request options:0 error:nil];

    // Send a message to `SERVICE_TOPIC`
    [_session.messaging sendWithTopicPath:SERVICE_TOPIC
                                    value:[[PTDiffusionContent alloc] initWithData:requestData]
                        completionHandler:^(NSError * _Nullable error)
                        {
                                if(error != nil) {
                                    NSLog(@"Send to topic %@ failed: %@", SERVICE_TOPIC, error);
                                }
                        }];
}
                    

import static java.util.UUID.randomUUID;

import java.io.PrintStream;

import org.json.JSONObject;
import org.json.JSONTokener;

import com.pushtechnology.diffusion.client.Diffusion;
import com.pushtechnology.diffusion.client.content.Content;
import com.pushtechnology.diffusion.client.features.Messaging;
import com.pushtechnology.diffusion.client.features.Messaging.MessageStream;
import com.pushtechnology.diffusion.client.features.Messaging.SendCallback;
import com.pushtechnology.diffusion.client.session.Session;
import com.pushtechnology.diffusion.client.types.ReceiveContext;

/**
 * An example of a client using the 'Messaging' feature to request the Push Notification Bridge
 * subscribe to a topic and relay updates to a GCM registration ID.
 *
 * @author Push Technology Limited
 * @since 5.9
 */
public class ClientSendingPushNotificationSubscription {

    private static final PrintStream OUT = System.out;

    private final String pushServiceTopicPath;
    private final Session session;
    private final Messaging messaging;
    private final MessageStream messageStream = new MessageStream.Default() {
        @Override
        public void onMessageReceived(String topicPath, Content content, ReceiveContext context) {
            final JSONObject response = (JSONObject) new JSONTokener(content.asString()).nextValue();
            final String correlation = response.getJSONObject("response").getString("correlation");

            OUT.printf("Received response with correlation '%s': %s", correlation, response);
        } };

    /**
     * Constructs message sending application.
     * @param pushServiceTopicPath topic path on which the Push Notification Bridgre is taking requests.
     */
    public ClientSendingPushNotificationSubscription(String pushServiceTopicPath) {
        this.pushServiceTopicPath = pushServiceTopicPath;
        this.session =
            Diffusion.sessions().principal("client").password("password")
                .open("ws://diffusion.example.com:80");
        this.messaging = session.feature(Messaging.class);
         messaging.addMessageStream(pushServiceTopicPath, messageStream);
    }

    /**
     * Close the session.
     */
    public void close() {
        messaging.removeMessageStream(messageStream);
        session.close();
    }

    /**
     * Compose & send a subscription request to the Push Notification Bridge.
     *
     * @param subscribedTopic topic to which the bridge subscribes.
     * @param gcmRegistrationID GCM registration ID to which the bridge relays updates.
     */
    public void requestPNSubscription(String gcmRegistrationID, String subscribedTopic) {
        // Compose the request
        final String gcmDestination = "gcm://" + gcmRegistrationID;
        final String correlation = randomUUID().toString();
        final JSONObject request = buildSubscriptionRequest(gcmDestination, subscribedTopic, correlation);

        // Send the request
        messaging.send(pushServiceTopicPath, request.toString(), new SendCallback.Default());
    }

    /**
     * Compose a subscription request.
     * <P>
     * @param destination The {@code gcm://} or {@code apns://} destination for any push notifications.
     * @param topic Diffusion topic subscribed-to by the Push Notification Bridge.
     * @param correlation value embedded in the response by the bridge relating it back to the request.
     * @return a complete request
     */
    private static JSONObject buildSubscriptionRequest(String destination, String topic, String correlation) {
        final JSONObject subObject = new JSONObject();
        subObject.put("destination", destination);
        subObject.put("topic", topic);

        final JSONObject contentObj = new JSONObject();
        contentObj.put("pnsub", subObject);

        final JSONObject requestObj = new JSONObject();
        requestObj.put("correlation", correlation);
        requestObj.put("content", contentObj);

        final JSONObject rootObject = new JSONObject();
        rootObject.put("request", requestObj);
        return rootObject;
    }
}