From 1550e896a072869fdd966d511ebc68d1b408ae50 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Moritz=20B=C3=B6hme?= <mail@moritzboeh.me>
Date: Wed, 7 Aug 2024 00:48:49 +0200
Subject: [PATCH] feat: add database workers

---
 lib/todo/database.ex        |  50 ++++++++++++++++++++++++------------
 lib/todo/database_worker.ex |  48 ++++++++++++++++++++++++++++++++++
 persist/a                   | Bin 0 -> 198 bytes
 3 files changed, 81 insertions(+), 17 deletions(-)
 create mode 100644 lib/todo/database_worker.ex
 create mode 100644 persist/a

diff --git a/lib/todo/database.ex b/lib/todo/database.ex
index 07862fd..b67dfb8 100644
--- a/lib/todo/database.ex
+++ b/lib/todo/database.ex
@@ -1,7 +1,9 @@
 defmodule Todo.Database do
+  alias Todo.DatabaseWorker
   use GenServer
 
   @db_folder "./persist"
+  @num_of_workers 3
 
   def start do
     GenServer.start(__MODULE__, nil, name: __MODULE__)
@@ -19,33 +21,47 @@ defmodule Todo.Database do
   def init(_) do
     File.mkdir_p!(@db_folder)
 
-    {:ok, nil}
+    {:ok, nil, {:continue, :init}}
   end
 
   @impl GenServer
-  def handle_cast({:store, key, data}, state) do
-    key
-    |> file_name()
-    |> File.write!(:erlang.term_to_binary(data))
+  def handle_continue(:init, nil) do
+    File.mkdir_p!(@db_folder)
 
-    {:noreply, state}
+    workers =
+      0..(@num_of_workers - 1)
+      |> Enum.map(fn i ->
+        {:ok, pid} = Todo.DatabaseWorker.start(@db_folder)
+        {i, pid}
+      end)
+      |> Map.new()
+
+    IO.inspect(workers)
+    {:noreply, workers}
   end
 
   @impl GenServer
-  def handle_call({:get, key}, _, state) do
+  def handle_cast({:store, key, data}, workers) do
+    workers
+    |> get_worker(key)
+    |> DatabaseWorker.store(key, data)
+
+    {:noreply, workers}
+  end
+
+  @impl GenServer
+  def handle_call({:get, key}, _, workers) do
     data =
-      case File.read(file_name(key)) do
-        {:ok, contents} ->
-          :erlang.binary_to_term(contents)
+      workers
+      |> get_worker(key)
+      |> DatabaseWorker.get(key)
 
-        _ ->
-          nil
-      end
-
-    {:reply, data, state}
+    {:reply, data, workers}
   end
 
-  def file_name(key) do
-    Path.join(@db_folder, to_string(key))
+  defp choose_worker(workers, key) do
+    id = :erlang.phash2(key, @num_of_workers)
+
+    Map.fetch!(workers, id)
   end
 end
diff --git a/lib/todo/database_worker.ex b/lib/todo/database_worker.ex
new file mode 100644
index 0000000..8a2e265
--- /dev/null
+++ b/lib/todo/database_worker.ex
@@ -0,0 +1,48 @@
+defmodule Todo.DatabaseWorker do
+  use GenServer
+
+  def start(db_folder) do
+    GenServer.start(__MODULE__, db_folder)
+  end
+
+  def store(pid, key, data) do
+    GenServer.cast(pid, {:store, key, data})
+  end
+
+  def get(pid, key) do
+    GenServer.call(pid, {:get, key})
+  end
+
+  @impl GenServer
+  def init(db_folder) do
+    {:ok, db_folder}
+  end
+
+  @impl GenServer
+  def handle_cast({:store, key, data}, db_folder) do
+    {db_folder, key}
+    |> file_name()
+    |> File.write!(:erlang.term_to_binary(data))
+
+    {:noreply, db_folder}
+  end
+
+  @impl GenServer
+  def handle_call({:get, key}, _, db_folder) do
+    data =
+      case File.read(file_name({db_folder, key})) do
+        {:ok, contents} ->
+          :erlang.binary_to_term(contents)
+
+        _ ->
+          nil
+      end
+
+    {:reply, data, db_folder}
+  end
+
+  def file_name({db_folder, key}) do
+    Path.join(db_folder, to_string(key))
+  end
+
+end
diff --git a/persist/a b/persist/a
new file mode 100644
index 0000000000000000000000000000000000000000..dca63f37477f53429f5e68755f2497b2cc76cffd
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