Update: Finished persistable todo server

chapter7/todo_cache/lib/todo/cache.ex

@@ -0,0 +1,33 @@
+defmodule Todo.Cache do
+  use GenServer
+
+  def start() do
+    GenServer.start(__MODULE__, nil)
+  end
+
+  def server_process(cache_pid, todo_list_name) do
+    GenServer.call(cache_pid, {:server_process, todo_list_name})
+  end
+
+  @impl true
+  def init(_) do
+    {:ok, %{}}
+  end
+
+  @impl true
+  def handle_call({:server_process, todo_list_name}, _, todo_servers) do
+    case Map.fetch(todo_servers, todo_list_name) do
+      {:ok, todo_server} ->
+        {:reply, todo_server, todo_servers}
+
+      :error ->
+        {:ok, new_todo_server} = Todo.Server.start()
+
+        {
+          :reply,
+          new_todo_server,
+          Map.put(todo_servers, todo_list_name, new_todo_server)
+        }
+    end
+  end
+end

chapter7/todo_cache/lib/todo/list.ex

@@ -0,0 +1,57 @@
+defmodule Todo.List do
+  defstruct auto_id: 1, entries: %{}
+
+  def new(entries \\ []) do
+    Enum.reduce(
+      entries,
+      %Todo.List{},
+      &add_entry(&2, &1)
+    )
+  end
+
+  def size(todo_list) do
+    Map.size(todo_list.entries)
+  end
+
+  def add_entry(todo_list, entry) do
+    entry = Map.put(entry, :id, todo_list.auto_id)
+
+    new_entries =
+      Map.put(
+        todo_list.entries,
+        todo_list.auto_id,
+        entry
+      )
+
+    %Todo.List{todo_list | entries: new_entries, auto_id: todo_list.auto_id + 1}
+  end
+
+  def entries(todo_list, date) do
+    todo_list.entries
+    |> Stream.filter(fn {_, entry} -> entry.date == date end)
+    |> Enum.map(fn {_, entry} -> entry end)
+  end
+
+  def update_entry(todo_list, %{} = new_entry) do
+    update_entry(todo_list, new_entry.id, fn _ -> new_entry end)
+  end
+
+  def update_entry(todo_list, entry_id, updater_fun) do
+    case Map.fetch(todo_list.entries, entry_id) do
+      :error ->
+        todo_list
+
+      {:ok, old_entry} ->
+        old_entry_id = old_entry.id
+        # Make sure that the result of the updater is a map and the
+        # id remains unchanged.
+        new_entry = %{id: ^old_entry_id} = updater_fun.(old_entry)
+        new_entries = Map.put(todo_list.entries, new_entry.id, new_entry)
+        %Todo.List{todo_list | entries: new_entries}
+    end
+  end
+
+  def delete_entry(todo_list, entry_id) do
+    %Todo.List{todo_list | entries: Map.delete(todo_list.entries, entry_id)}
+  end
+end

chapter7/todo_cache/lib/todo/server.ex

@@ -0,0 +1,48 @@
+defmodule Todo.Server do
+  use GenServer
+
+  def start do
+    GenServer.start(__MODULE__, nil)
+  end
+
+  def add_entry(pid, entry) do
+    GenServer.cast(pid, {:add_entry, entry})
+  end
+
+  def delete_entry(pid, entry_id) do
+    GenServer.cast(pid, {:delete_entry, entry_id})
+  end
+
+  def update_entry(pid, entry_id, updater_fun) do
+    GenServer.cast(pid, {:update_entry, entry_id, updater_fun})
+  end
+
+  def entries(pid, date) do
+    GenServer.call(pid, {:entries, date})
+  end
+
+  @impl true
+  def init(_) do
+    {:ok, Todo.List.new()}
+  end
+
+  @impl true
+  def handle_cast({:add_entry, entry}, state) do
+    {:noreply, Todo.List.add_entry(state, entry)}
+  end
+
+  @impl true
+  def handle_cast({:delete_entry, entry_id}, state) do
+    {:noreply, Todo.List.delete_entry(state, entry_id)}
+  end
+
+  @impl true
+  def handle_cast({:update_entry, entry_id, updater_fun}, state) do
+    {:noreply, Todo.List.update_entry(state, entry_id, updater_fun)}
+  end
+
+  @impl true
+  def handle_call({:entries, date}, _, state) do
+    {:reply, Todo.List.entries(state, date), state}
+  end
+end