elixir-todo-list/lib/todo/server.ex

defmodule Todo.Server do
  use GenServer

  def start_link(name) do
    GenServer.start_link(__MODULE__, name)
  end

  def add(pid, entry) do
    GenServer.cast(pid, {:add, entry})
  end

  def entries(pid, date) do
    GenServer.call(pid, {:entries, date})
  end

  def update(pid, id, update_fun) do
    GenServer.cast(pid, {:update, id, update_fun})
  end

  def delete(pid, id) do
    GenServer.cast(pid, {:delete, id})
  end

  @impl GenServer
  def init(name) do
    IO.puts("Starting #{__MODULE__} for #{name}.")

    {: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