1 files changed, 49 insertions, 0 deletions
diff --git a/src/main/scala/xyz/driver/core/messaging/CreateOnDemand.scala b/src/main/scala/xyz/driver/core/messaging/CreateOnDemand.scala
new file mode 100644
index 0000000..1af5308
--- /dev/null
+++ b/src/main/scala/xyz/driver/core/messaging/CreateOnDemand.scala
@@ -0,0 +1,49 @@
+package xyz.driver.core
+package messaging
+
+import java.util.concurrent.ConcurrentHashMap
+
+import scala.async.Async.{async, await}
+import scala.concurrent.Future
+
+/** Utility mixin that will ensure that topics and subscriptions exist before
+  * attempting to read or write from or to them.
+  */
+trait CreateOnDemand extends Bus {
+
+  /** Create the given topic. This operation is idempotent and is expected to succeed if the topic
+    * already exists.
+    */
+  def createTopic(topic: Topic[_]): Future[Unit]
+
+  /** Create the given subscription. This operation is idempotent and is expected to succeed if the subscription
+    * already exists.
+    */
+  def createSubscription(topic: Topic[_], config: SubscriptionConfig): Future[Unit]
+
+  private val createdTopics        = new ConcurrentHashMap[Topic[_], Future[Unit]]
+  private val createdSubscriptions = new ConcurrentHashMap[(Topic[_], SubscriptionConfig), Future[Unit]]
+
+  private def ensureTopic(topic: Topic[_]) =
+    createdTopics.computeIfAbsent(topic, t => createTopic(t))
+
+  private def ensureSubscription(topic: Topic[_], config: SubscriptionConfig) =
+    createdSubscriptions.computeIfAbsent(topic -> config, {
+      case (t, c) => createSubscription(t, c)
+    })
+
+  abstract override def publishMessages[A](topic: Topic[A], messages: Seq[A]): Future[Unit] = async {
+    await(ensureTopic(topic))
+    await(super.publishMessages(topic, messages))
+  }
+
+  abstract override def fetchMessages[A](
+      topic: Topic[A],
+      config: SubscriptionConfig,
+      maxMessages: Int): Future[Seq[Message[A]]] = async {
+    await(ensureTopic(topic))
+    await(ensureSubscription(topic, config))
+    await(super.fetchMessages(topic, config, maxMessages))
+  }
+
+}