#4 describing how to implement custom channels and messages

src/Subscriber/Channel/ChannelMessageInterface.php

@@ -10,7 +10,31 @@
 /**
  * Channel data message.
  *
- * A channel uses the message to get (format) the data and send it to a subscriber via notification.
+ * A channel uses a message to get (format) the data and send it to a subscriber via notification.
+ *
+ * Message classes must implement this interface in order be sent via channel.
+ * Also, it must be tagged as 'app.subscriber.message' with the appropriate type.
+ *
+ * For example, a custom message serializes data to JSON:
+ *
+ *      final class JsonChannelMessage extends AbstractChannelMessage
+ *      {
+ *        public function getData(): string
+ *        {
+ *            return json_encode([
+ *              'order_num' => $this->getPaymentProcessing()->getOrder()->getExternalOrderId(),
+ *            ]);
+ *        }
+ *      }
+ *
+ *  In `config/services.yml` the custom channel:
+ *
+ *      services:
+ *        App\Subscriber\Channel\JsonChannelMessage:
+ *          tags:
+ *            - { name: 'app.subscriber.message', type: 'json' }
+ *
+ *  Then, the `json` custom message will be available in `subscriber:channels` command output.
  */
 interface ChannelMessageInterface
 {

src/Subscriber/Channel/NotificationChannelInterface.php

@@ -7,6 +7,35 @@
 use App\Subscriber\Exception\ChannelMessageException;
 use App\Subscriber\Exception\NotificationChannelException;
 
+/**
+ * Notification channel.
+ *
+ * Sends a notification message to a subscriber. A channel is transport for delivering the message.
+ *
+ * Custom channel, for example SMS notifications:
+ *
+ *      final class MyCustomSmsChannel implements NotificationChannelInterface
+ *      {
+ *          private readonly SmsTransport $sms;
+ *
+ *          // sms transport initialization, so on ...
+ *
+ *          public function send(ChannelMessageInterface $message, array $params): void
+ *          {
+ *              $this->sms->send($message->getData(), $params['phone_number']);
+ *          }
+ *      }
+ *
+ * In `config/services.yml` the custom channel:
+ *
+ *       services:
+ *         App\Subscriber\Channel\MyCustomSmsChannel:
+ *           tags:
+ *             - { name: 'app.subscriber.channel', type: 'sms' }
+ *
+ * Then, the `sms` custom channel will be available in `subscriber:channels` command output under `channels`.
+ * The adding subscriber command should be implemented too, in order to add subscribers.
+ */
 interface NotificationChannelInterface
 {
     /**