From 7ba3b1cd4fa63d719db9a60792871b10679c8cfb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Moritz=20B=C3=B6hme?= <mail@moritzboeh.me>
Date: Wed, 7 Aug 2024 10:33:19 +0200
Subject: [PATCH] feat: extend supervision tree

---
 lib/todo/cache.ex           | 34 +++++++++++++---------------------
 lib/todo/database.ex        |  2 +-
 lib/todo/database_worker.ex |  2 +-
 lib/todo/server.ex          |  8 ++++++--
 4 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/lib/todo/cache.ex b/lib/todo/cache.ex
index 32b48c8..672966a 100644
--- a/lib/todo/cache.ex
+++ b/lib/todo/cache.ex
@@ -1,33 +1,25 @@
 defmodule Todo.Cache do
-  use GenServer
+  use DynamicSupervisor
 
-  @impl GenServer
-  def init(_init_args) do
+  def start_link(init_arg) do
     IO.puts("Starting #{__MODULE__}")
 
-    {:ok, %{}}
+    DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
   end
 
-  @impl GenServer
-  def handle_call({:server_process, name}, _from, state) do
-    case Map.fetch(state, name) do
-      {:ok, process} ->
-        {:reply, process, state}
+  @impl DynamicSupervisor
+  def init(_) do
+    DynamicSupervisor.init(strategy: :one_for_one)
+  end
 
-      :error ->
-        {:ok, new_process} = Todo.Server.start_link(name)
-
-        new_state = Map.put(state, name, new_process)
-
-        {:reply, new_process, new_state}
+  def server_process(todo_list_name) do
+    case start_child(todo_list_name) do
+      {:ok, pid} -> pid
+      {:error, {:already_started, pid}} -> pid
     end
   end
 
-  def start_link(_) do
-    GenServer.start_link(__MODULE__, nil, name: __MODULE__)
-  end
-
-  def server_process(name) do
-    GenServer.call(__MODULE__, {:server_process, name})
+  defp start_child(todo_list_name) do
+    DynamicSupervisor.start_child(__MODULE__, {Todo.Server, todo_list_name})
   end
 end
diff --git a/lib/todo/database.ex b/lib/todo/database.ex
index 9d67f38..f7112bb 100644
--- a/lib/todo/database.ex
+++ b/lib/todo/database.ex
@@ -45,6 +45,6 @@ defmodule Todo.Database do
   end
 
   defp choose_worker(key) do
-    :erlang.phash2(key, @pool_size)
+    :erlang.phash2(key, @pool_size) + 1
   end
 end
diff --git a/lib/todo/database_worker.ex b/lib/todo/database_worker.ex
index 8005d0c..1ffd956 100644
--- a/lib/todo/database_worker.ex
+++ b/lib/todo/database_worker.ex
@@ -44,7 +44,7 @@ defmodule Todo.DatabaseWorker do
         {:ok, contents} ->
           :erlang.binary_to_term(contents)
 
-        _ ->
+        {:error, :enoent} ->
           nil
       end
 
diff --git a/lib/todo/server.ex b/lib/todo/server.ex
index 21b0dba..15af6b1 100644
--- a/lib/todo/server.ex
+++ b/lib/todo/server.ex
@@ -1,8 +1,12 @@
 defmodule Todo.Server do
-  use GenServer
+  use GenServer, restart: :temporary
 
   def start_link(name) do
-    GenServer.start_link(__MODULE__, name)
+    GenServer.start_link(__MODULE__, name, name: via_tuple(name))
+  end
+
+  def via_tuple(name) do
+    Todo.ProcessRegistry.via_tuple({__MODULE__, name})
   end
 
   def add(pid, entry) do