snip_form_backend.ex

  # sample mount
  # @impl true
  # def mount(params, _session, socket) do
  #   context = %{
  #     params: params,
  #     lang: "en"
  #   }
  #   initial_form_state = get_initial_form_state(socket.assigns)
  #   {:ok,
  #    socket
  #    |> assign(
  #      context: context,
  #      form_state: initial_form_state,
  #      saved_form_state: nil,
  #      form_changeset: get_form_changeset(initial_form_state, %{}),
  #    )}
  # end

  def handle_event("save", %{"form_data" => incoming_data}, socket) do
    get_form_changeset(socket.assigns.form_state, incoming_data)
    |> Ecto.Changeset.apply_action(:update)
    |> case do
      {:ok, form_state_with_changes_applied} ->
        form_state_with_changes_applied |> MavuUtils.log("form_state_with_changes_applied", :info)

        form_state = get_initial_form_state(socket.assigns)

        {:noreply,
         Phoenix.LiveView.assign(socket,
           saved_form_state: form_state_with_changes_applied,
           form_state: form_state,
           form_changeset: get_form_changeset(form_state, socket.assigns[:context])
         )}

      {:error, %Ecto.Changeset{} = changeset_with_errors} ->
        {:noreply, Phoenix.LiveView.assign(socket, form_changeset: changeset_with_errors)}
    end
  end

  @impl true
  def handle_event("validate", %{"form_data" => incoming_data} = _msg, socket) do
    incoming_data |> MavuUtils.log("mwuits-debug 2021-08-30_10:16 ", :info)

    validated_changeset =
      get_form_changeset(socket.assigns.form_state, incoming_data)
      |> Map.put(:action, :validate)
      |> MavuUtils.log("mwuits-debug 2021-08-30_10:09 B ", :info)

    {:noreply, assign(socket, form_changeset: validated_changeset)}
  end

  def get_form_changeset(initial_data, changes, _context \\ %{}) do
    types =
      ~w(keyword)a
      |> Enum.map(&{&1, :string})
      |> Map.new()

    schemaless_rec = {initial_data, types}

    Ecto.Changeset.cast(schemaless_rec, changes, Map.keys(types), empty_values: [])
    |> Ecto.Changeset.validate_length(:keyword, max: 10)
    |> Ecto.Changeset.validate_format(:keyword, ~r/^[a-z_ -.]*$/,
      message: "only lowercase alpha allowed"
    )
  end

  def get_initial_form_state(_assigns) do
    %{
      keyword: "foo"
    }
  end