validate_meta.exs

# I wont use it anymore, but it sounded like a nice way to
# validate map fields with a dedicated schema

defmodule M do
  @spec validate_meta(changeset :: Ecto.Changeset.t()) ::
          Ecto.Changeset.t()
  defp validate_meta(%Ecto.Changeset{valid?: false} = changeset), do: changeset

  defp validate_meta(changeset) do
    params = changeset |> get_change(:meta)

    schema = %{
      upload_id: :string,
      asset_id: :string,
      playback_id: :string,
      title: :string
    }

    changeset_meta =
      {%{}, schema}
      |> cast(params, Map.keys(schema))
      |> validate_required([:upload_id])

    with {:ok, _} <- apply_action(changeset_meta, :validate_meta) do
      changeset
    else
      {:error, %Ecto.Changeset{} = changeset_meta} ->
        changeset_meta.errors
        |> Enum.reduce(changeset, fn {field, {msg, meta}}, changeset ->
          changeset |> add_error(:meta, "#{field} #{msg}", meta)
        end)
    end
  end
end