feat: add database workers

lib/todo/cache.ex

@@ -3,6 +3,7 @@ defmodule Todo.Cache do
 
   @impl GenServer
   def init(_init_args) do
+    Todo.Database.start()
     {:ok, %{}}
   end
 
@@ -13,7 +14,7 @@ defmodule Todo.Cache do
         {:reply, process, state}
 
       :error ->
-        new_process = Todo.Server.start()
+        {:ok, new_process} = Todo.Server.start(name)
 
         new_state = Map.put(state, name, new_process)
 

lib/todo/database.ex

@@ -0,0 +1,67 @@
+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__)
+  end
+
+  def store(key, data) do
+    GenServer.cast(__MODULE__, {:store, key, data})
+  end
+
+  def get(key) do
+    GenServer.call(__MODULE__, {:get, key})
+  end
+
+  @impl GenServer
+  def init(_) do
+    File.mkdir_p!(@db_folder)
+
+    {:ok, nil, {:continue, :init}}
+  end
+
+  @impl GenServer
+  def handle_continue(:init, nil) do
+    File.mkdir_p!(@db_folder)
+
+    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_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 =
+      workers
+      |> get_worker(key)
+      |> DatabaseWorker.get(key)
+
+    {:reply, data, workers}
+  end
+
+  defp choose_worker(workers, key) do
+    id = :erlang.phash2(key, @num_of_workers)
+
+    Map.fetch!(workers, id)
+  end
+end

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

lib/todo/server.ex

@@ -1,52 +1,8 @@
 defmodule Todo.Server do
   use GenServer
 
-  @impl GenServer
+  def start(name) do
-  def init(%_{} = todo_list) do
+    GenServer.start(__MODULE__, name)
-    {:ok, todo_list}
-  end
-
-  @impl GenServer
-  def init(entries) do
-    {:ok, Todo.List.new(entries)}
-  end
-
-  @impl GenServer
-  def handle_call({:entries, date}, _from, todo_list) do
-    entries = Todo.List.entries(todo_list, date)
-
-    {:reply, entries, todo_list}
-  end
-
-  @impl GenServer
-  def handle_cast({:add, entry}, todo_list) do
-    new_todo_list = Todo.List.add(todo_list, entry)
-
-    {:noreply, new_todo_list}
-  end
-
-  @impl GenServer
-  def handle_cast({:update, id, update_fun}, todo_list) do
-    new_todo_list = Todo.List.update(todo_list, id, update_fun)
-
-    {:noreply, new_todo_list}
-  end
-
-  @impl GenServer
-  def handle_cast({:delete, id}, todo_list) do
-    new_todo_list = Todo.List.delete(todo_list, id)
-
-    {:noreply, new_todo_list}
-  end
-
-  def start(entries \\ [])
-
-  def start(%_{} = todo_list) do
-    GenServer.start(__MODULE__, todo_list)
-  end
-
-  def start(entries) do
-    GenServer.start(__MODULE__, entries)
   end
 
   def add(pid, entry) do
@@ -64,4 +20,46 @@ defmodule Todo.Server do
   def delete(pid, id) do
     GenServer.cast(pid, {:delete, id})
   end
+
+  @impl GenServer
+  def init(name) do
+    {:ok, {name, nil}, {:continue, :init}}
+  end
+
+  @impl GenServer
+  def handle_continue(:init, {name, nil}) do
+    todo_list = Todo.Database.get(name) || Todo.List.new()
+    {:noreply, {name, todo_list}}
+  end
+
+  @impl GenServer
+  def handle_call({:entries, date}, _from, {name, todo_list}) do
+    entries = Todo.List.entries(todo_list, date)
+
+    {:reply, entries, {name, todo_list}}
+  end
+
+  @impl GenServer
+  def handle_cast({:add, entry}, {name, todo_list}) do
+    new_todo_list = Todo.List.add(todo_list, entry)
+    Todo.Database.store(name, new_todo_list)
+
+    {:noreply, {name, new_todo_list}}
+  end
+
+  @impl GenServer
+  def handle_cast({:update, id, update_fun}, {name, todo_list}) do
+    new_todo_list = Todo.List.update(todo_list, id, update_fun)
+    Todo.Database.store(name, new_todo_list)
+
+    {:noreply, {name, new_todo_list}}
+  end
+
+  @impl GenServer
+  def handle_cast({:delete, id}, {name, todo_list}) do
+    new_todo_list = Todo.List.delete(todo_list, id)
+    Todo.Database.store(name, new_todo_list)
+
+    {:noreply, {name, new_todo_list}}
+  end
 end