meta/lib/meta_web/controllers/user_registration_controller.ex

defmodule MetaWeb.UserRegistrationController do
  use MetaWeb, :controller

  alias Meta.Captcha
  alias Meta.Accounts
  alias Meta.Accounts.User
  alias MetaWeb.UserAuth

  defp is_registration_enabled?() do
    Application.get_env(:meta, :enable_registration)
  end

  def new(conn, _params) do
    changeset = Accounts.change_user_registration(%User{})
    {captcha_text, captcha_result} = Captcha.generate()

    with_notice = unless is_registration_enabled?() do
      conn
      |> put_flash(:error, "Registration is disabled for the time being.")
    else
      conn
    end

    with_notice
    |> assign(:captcha, captcha_text)
    |> put_session(:captcha, captcha_result)
    |> render("new.html", changeset: changeset)
  end

  def create(conn, %{"user" => user_params}) do
    unless is_registration_enabled?() do
      conn
      |> redirect(to: Routes.user_registration_path(conn, :new))
    else
      attrs = user_params
              |> Map.put("expected_captcha", get_session(conn, :captcha))

      case Accounts.register_user(attrs) do
        {:ok, user} ->
          {:ok, _} =
            Accounts.deliver_user_confirmation_instructions(
              user,
              &Routes.user_confirmation_url(conn, :confirm, &1)
            )

          conn
          |> put_flash(:info, "User created successfully.")
          |> UserAuth.log_in_user(user)

        {:error, %Ecto.Changeset{} = changeset} ->
          {captcha_text, captcha_result} = Captcha.generate()

          conn
          |> assign(:captcha, captcha_text)
          |> put_session(:captcha, captcha_result)
          |> render("new.html", changeset: changeset)
      end
    end
  end
end