feat: provides repeated event protection

lib/tower.ex

@@ -426,11 +426,20 @@ defmodule Tower do
     :logger.compare_levels(level1, level2) in [:gt, :eq]
   end
 
-  defp report_event(%Event{} = event) do
-    reporters()
-    |> Enum.each(fn reporter ->
-      report_event(reporter, event)
-    end)
+  defp report_event(%Event{similarity_id: similarity_id} = event) do
+    Tower.Protection.seen(similarity_id)
+
+    Tower.Protection.get(similarity_id)
+    |> case do
+      1 ->
+        reporters()
+        |> Enum.each(fn reporter ->
+          report_event(reporter, event)
+        end)
+
+      amount ->
+        IO.puts("Ignoring repeated event with similarity_id=#{similarity_id}. Seen #{amount} times.")
+    end
   end
 
   defp report_event(reporter, %Event{reason: %ReportEventError{reporter: reporter}}) do

lib/tower/application.ex

@@ -9,7 +9,8 @@ defmodule Tower.Application do
   def start(_type, _args) do
     Supervisor.start_link(
       [
-        {Task.Supervisor, name: Tower.TaskSupervisor}
+        {Task.Supervisor, name: Tower.TaskSupervisor},
+        Tower.Protection
       ],
       strategy: :one_for_one,
       name: Tower.Supervisor

lib/tower/protection.ex

@@ -0,0 +1,27 @@
+defmodule Tower.Protection do
+  use Agent
+
+  @empty_state %{}
+
+  def start_link(_initial_value) do
+    Agent.start_link(fn -> @empty_state end, name: __MODULE__)
+  end
+
+  def get(key) do
+    Agent.get(__MODULE__, fn state -> Map.get(state, key) end)
+  end
+
+  def seen(key) do
+    Agent.update(
+      __MODULE__,
+      fn state ->
+        {_, new_state} =
+          Map.get_and_update(state, key, fn current_value ->
+            {current_value, (current_value || 0) + 1}
+          end)
+
+        new_state
+      end
+    )
+  end
+end

test/tower_test.exs

@@ -554,7 +554,7 @@ defmodule TowerTest do
 
   test "protects reporters from repeated events" do
     capture_log(fn ->
-      for _ <- 1..2 do
+      for _ <- 1..10 do
         in_unlinked_process(fn ->
           1 / 0
         end)
@@ -573,12 +573,6 @@ defmodule TowerTest do
           kind: :error,
           reason: %RuntimeError{message: "something else"}
         },
-        %{
-          similarity_id: similarity_id,
-          level: :error,
-          kind: :error,
-          reason: %ArithmeticError{message: "bad argument in arithmetic expression"}
-        },
         %{
           similarity_id: similarity_id,
           level: :error,