From 805b24208115cfbe72cbb636f667debc9e6283d2 Mon Sep 17 00:00:00 2001
From: Marco Milanesi <kpanic@gmail.com>
Date: Sun, 14 Apr 2019 14:57:04 +0200
Subject: [PATCH 1/2] Introduce :ets in the worker

---
 lib/forecastr/cache/worker.ex | 38 ++++++++++++++++++++++++-----------
 test/forecastr_test.exs       |  9 +++++----
 2 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/lib/forecastr/cache/worker.ex b/lib/forecastr/cache/worker.ex
index aed5e1d..a7f3d7b 100644
--- a/lib/forecastr/cache/worker.ex
+++ b/lib/forecastr/cache/worker.ex
@@ -5,8 +5,8 @@ defmodule Forecastr.Cache.Worker do
 
   # Client API
   @spec start_link(Keyword.t()) :: {:ok, pid()}
-  def start_link(opts) do
-    GenServer.start_link(__MODULE__, %{}, opts)
+  def start_link([name: worker_name] = opts) do
+    GenServer.start_link(__MODULE__, %{name: worker_name, timer_ref: nil}, opts)
   end
 
   @spec get(atom(), String.t()) :: map() | nil
@@ -21,27 +21,41 @@ defmodule Forecastr.Cache.Worker do
   end
 
   # Server callbacks
-  def init(state) do
+  def init(%{name: worker_name} = state) do
+    ^worker_name = :ets.new(worker_name, [:named_table])
     {:ok, state}
   end
 
-  def handle_call({:get, query}, _from, state) do
-    entry = Map.get(state, query)
+  def handle_call({:get, query}, _from, %{name: worker_name} = state) do
+    entry =
+      case :ets.lookup(worker_name, query) do
+        [] -> nil
+        [{_key, value}] -> value
+      end
+
     {:reply, entry, state}
   end
 
-  def handle_call({:set, query, response, options}, _from, state) do
-    state = Map.put(state, query, response)
-    purge_cache(query, options)
-    {:reply, :ok, state}
+  def handle_call(
+        {:set, query, response, options},
+        _from,
+        %{name: worker_name, timer_ref: timer_ref} = state
+      ) do
+    true = :ets.insert(worker_name, {query, response})
+    timer_ref = schedule_purge_cache(query, timer_ref, options)
+    {:reply, :ok, %{state | timer_ref: timer_ref}}
   end
 
-  def purge_cache(query, ttl: minutes) do
-    # Purge every N minutes
+  def schedule_purge_cache(query, nil = _timer_ref, ttl: minutes),
+    do: Process.send_after(self(), {:purge_cache, query}, minutes)
+
+  def schedule_purge_cache(query, timer_ref, ttl: minutes) do
+    Process.cancel_timer(timer_ref)
     Process.send_after(self(), {:purge_cache, query}, minutes)
   end
 
   def handle_info({:purge_cache, query}, state) do
-    {:noreply, Map.delete(state, query)}
+    true = :ets.delete_object(Keyword.get(state, :name), query)
+    {:noreply, state}
   end
 end
diff --git a/test/forecastr_test.exs b/test/forecastr_test.exs
index a49dfc8..e5ca18c 100644
--- a/test/forecastr_test.exs
+++ b/test/forecastr_test.exs
@@ -59,17 +59,18 @@ defmodule ForecastrTest do
   test "Forecastr.forecast cache correctly :today" do
     Application.put_env(:forecastr, :backend, OWMBackendToday)
     assert {:ok, _response} = Forecastr.forecast(:today, "Wonderland")
-    state = :sys.get_state(Forecastr.Cache.Today)
 
-    assert %{"wonderland" => today_weather()} == state
+    [state] = :ets.tab2list(Forecastr.Cache.Today)
+
+    assert {"wonderland", today_weather()} == state
   end
 
   test "Forecastr.forecast cache correctly :in_five_days" do
     Application.put_env(:forecastr, :backend, OWMBackendFiveDays)
     assert {:ok, _response} = Forecastr.forecast(:in_five_days, "Wonderland")
-    state = :sys.get_state(Forecastr.Cache.InFiveDays)
+    [state] = :ets.tab2list(Forecastr.Cache.InFiveDays)
 
-    assert %{"wonderland" => five_days_weather()} == state
+    assert {"wonderland", five_days_weather()} == state
   end
 
   test "Forecastr.forecast hits the cache when it's pre-warmed for today" do

From d28e07320d845834929c48d725fa2a1fcd886c7b Mon Sep 17 00:00:00 2001
From: Marco Milanesi <kpanic@gmail.com>
Date: Sun, 14 Apr 2019 15:03:39 +0200
Subject: [PATCH 2/2] Address credo issue

---
 lib/forecastr/renderer/png.ex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/forecastr/renderer/png.ex b/lib/forecastr/renderer/png.ex
index f1a4c08..d8179cd 100644
--- a/lib/forecastr/renderer/png.ex
+++ b/lib/forecastr/renderer/png.ex
@@ -14,7 +14,7 @@ defmodule Forecastr.Renderer.PNG do
   Render a map coming from the backend (OWM API currently)
   """
   @spec render(map()) :: {:ok, map()}
-  def render(map = %{"name" => city_name}) do
+  def render(%{"name" => city_name} = map) do
     map
     |> Forecastr.Renderer.ASCII.render(:png)
     |> render_png(city_name)