server - update view count on threads

lib/myapp/data/reply.ex

@@ -44,7 +44,7 @@ defmodule MyApp.Data.Reply do
     thread_id = Map.get(reply, :thread_id)
     user_id = Map.get(reply, :user_id)
     query = from t in Data.Thread, where: t.id == ^thread_id,
-      update: [set: [last_reply_id: ^user_id], inc: [reply_count: 1]]
+      update: [set: [last_reply_id: ^user_id, updated_at: ^DateTime.utc_now], inc: [reply_count: 1]]
 
     case Repo.update_all(query, []) do
       nil -> {:error, "update thread error"}

lib/myapp/data/thread.ex

@@ -110,6 +110,14 @@ defmodule MyApp.Data.Thread do
     end
   end
 
+  # this doesn't update the 'updated_at' field which is what we want
+  def update_view_count(thread_id) do
+    query = from t in Data.Thread,
+      update: [inc: [view_count: 1]],
+      where: t.id == ^thread_id
+    Repo.update_all(query, [])
+  end
+
   # TODO: delete thread
 
   defp process_user_update(thread, _params) when is_nil(thread), do: {:error, "Invalid thread"}

lib/myapp/view_counter.ex

@@ -0,0 +1,20 @@
+defmodule MyApp.ViewCounter do
+  alias MyApp.Data
+
+  # cache end points for 5 minutes based on the browser fingerprint
+
+  @spec thread_view_count(String.t, integer) :: {:error, String.t} | {any, boolean}
+  def thread_view_count(fingerprint, thread_id) do
+
+    key = "#{fingerprint}:#{thread_id}"
+
+    case Cachex.get(:myapp, key) do
+      {:ok, _} -> {:error, "Already viewed."}
+      {:missing, _} ->
+        {1, nil} = Data.Thread.update_view_count(thread_id)
+        Cachex.set(:myapp, key, true, ttl: :timer.minutes(5))
+    end
+
+  end
+
+end

lib/myapp_web/controllers/thread_controller.ex

@@ -50,7 +50,14 @@ defmodule MyAppWeb.ThreadController do
   @spec get(map, map) :: any
   def get(conn, params) do
 
-    {output, status} = params["id"]
+    fingerprint = get_req_header(conn, "fp")
+    thread_id = params["id"]
+
+    spawn fn ->
+      MyApp.ViewCounter.thread_view_count(fingerprint, thread_id)
+    end
+
+    {output, status} = thread_id
       |> Data.Thread.get
       |> Response.put_resp