From 8f0b13ec33df520d05fd8d44616bd4d6a8b84652 Mon Sep 17 00:00:00 2001
From: Mustafa Turan <mustafaturan.net@gmail.com>
Date: Mon, 28 May 2018 00:16:41 -0700
Subject: [PATCH] Log empty topic listeners to prevent unnecessary ets inserts
 Add missing tests for existence check

---
 CHANGELOG.md                                 |  3 ++-
 lib/event_bus/services/notification.ex       | 11 ++++++++---
 test/event_bus/managers/observation_test.exs |  7 +++++++
 test/event_bus/managers/store_test.exs       |  7 +++++++
 test/event_bus/managers/topic_test.exs       |  7 +++++++
 5 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index be80cbe..3e134db 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [1.3.X]
 
-
+- Log empty topic listeners
+- Add missing tests for existence check
 - Update time spent calculation for EventSource block
 - Remove support for system event tracing (Updated the wiki to create wrapper for system event tracing)
 
diff --git a/lib/event_bus/services/notification.ex b/lib/event_bus/services/notification.ex
index 62a4fa0..326d73a 100644
--- a/lib/event_bus/services/notification.ex
+++ b/lib/event_bus/services/notification.ex
@@ -11,10 +11,15 @@ defmodule EventBus.Service.Notification do
   @spec notify(Event.t()) :: no_return()
   def notify(%Event{id: id, topic: topic} = event) do
     listeners = Subscription.subscribers(topic)
-    :ok = Store.create(event)
-    :ok = Observation.create({listeners, topic, id})
 
-    notify_listeners(listeners, {topic, id})
+    if listeners == [] do
+      Logger.log(@logging_level, "Topic :#{topic} listener set is empty!")
+    else
+      :ok = Store.create(event)
+      :ok = Observation.create({listeners, topic, id})
+
+      notify_listeners(listeners, {topic, id})
+    end
   end
 
   @spec notify_listeners(list(), tuple()) :: no_return()
diff --git a/test/event_bus/managers/observation_test.exs b/test/event_bus/managers/observation_test.exs
index 3757b9a..6da1e78 100644
--- a/test/event_bus/managers/observation_test.exs
+++ b/test/event_bus/managers/observation_test.exs
@@ -15,6 +15,13 @@ defmodule EventBus.Manager.ObservationTest do
     :ok
   end
 
+  test "exist?" do
+    topic = :metrics_received_1
+    Observation.register_topic(topic)
+
+    assert Observation.exist?(topic)
+  end
+
   test "register_topic" do
     assert :ok == Observation.register_topic(:metrics_destroyed)
   end
diff --git a/test/event_bus/managers/store_test.exs b/test/event_bus/managers/store_test.exs
index a831ace..29cfa20 100644
--- a/test/event_bus/managers/store_test.exs
+++ b/test/event_bus/managers/store_test.exs
@@ -15,6 +15,13 @@ defmodule EventBus.Manager.StoreTest do
     :ok
   end
 
+  test "exist?" do
+    topic = :metrics_received_1
+    Store.register_topic(topic)
+
+    assert Store.exist?(topic)
+  end
+
   test "register_topic" do
     assert :ok == Store.register_topic(@topic)
   end
diff --git a/test/event_bus/managers/topic_test.exs b/test/event_bus/managers/topic_test.exs
index ea27ef6..f7b25ac 100644
--- a/test/event_bus/managers/topic_test.exs
+++ b/test/event_bus/managers/topic_test.exs
@@ -13,6 +13,13 @@ defmodule EventBus.Manager.TopicTest do
     :ok
   end
 
+  test "exist?" do
+    topic = :metrics_received_1
+    Topic.register(topic)
+
+    assert Topic.exist?(topic)
+  end
+
   test "register_topic" do
     assert :ok == Topic.register(:t1)
   end