From 8355f3094813e85bd8ef28bff22d72d824361858 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Moritz=20B=C3=B6hme?= <mail@moritzboeh.me>
Date: Sun, 4 Aug 2024 13:56:50 +0200
Subject: [PATCH] feat: add server cache

---
 lib/todo/cache.ex        | 31 +++++++++++++++++++++++++++++++
 test/todo/cache_test.exs | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)
 create mode 100644 lib/todo/cache.ex
 create mode 100644 test/todo/cache_test.exs

diff --git a/lib/todo/cache.ex b/lib/todo/cache.ex
new file mode 100644
index 0000000..724b539
--- /dev/null
+++ b/lib/todo/cache.ex
@@ -0,0 +1,31 @@
+defmodule Todo.Cache do
+  use GenServer
+
+  @impl GenServer
+  def init(_init_args) do
+    {:ok, %{}}
+  end
+
+  @impl GenServer
+  def handle_call({:server_process, name}, _from, state) do
+    case Map.fetch(state, name) do
+      {:ok, process} ->
+        {:reply, process, state}
+
+      :error ->
+        new_process = Todo.Server.start()
+
+        new_state = Map.put(state, name, new_process)
+
+        {:reply, new_process, new_state}
+    end
+  end
+
+  def start() do
+    GenServer.start(__MODULE__, nil)
+  end
+
+  def server_process(pid, name) do
+    GenServer.call(pid, {:server_process, name})
+  end
+end
diff --git a/test/todo/cache_test.exs b/test/todo/cache_test.exs
new file mode 100644
index 0000000..e5a55ff
--- /dev/null
+++ b/test/todo/cache_test.exs
@@ -0,0 +1,36 @@
+defmodule Todo.TestCache do
+  use ExUnit.Case
+  alias Todo.Cache
+  alias Todo.Server
+
+  test "different names get different servers" do
+    {:ok, pid} = Cache.start()
+
+    {:ok, alice_server} = Cache.server_process(pid, "Alice")
+
+    {:ok, bob_server} = Cache.server_process(pid, "Bob")
+
+    assert alice_server != bob_server
+  end
+
+  test "same name gets same server" do
+    {:ok, pid} = Cache.start()
+
+    {:ok, alice_server} = Cache.server_process(pid, "Alice")
+
+    {:ok, alice_server2} = Cache.server_process(pid, "Alice")
+
+    assert alice_server == alice_server2
+  end
+
+  test "simple usage" do
+    {:ok, pid} = Cache.start()
+
+    {:ok, alice_server} = Cache.server_process(pid, "Alice")
+
+    Server.add(alice_server, %{date: ~D[2024-08-04], title: "Learn Elixir"})
+
+    assert [%{date: ~D[2024-08-04], title: "Learn Elixir"}] =
+             Server.entries(alice_server, ~D[2024-08-04])
+  end
+end