defp validate_end_date(changeset) do
  validate_change(changeset, :end_date, fn :end_date, end_date ->
    {:ok, current_date} = DateTime.now("Etc/UTC")
    case DateTime.compare(end_date, current_date) do
      :lt ->
        [end_date: "cannot be in the past"]
      _ ->
        []
    end
  end)
end

defp validate_start_price(changeset) do
  validate_change(changeset, :start_price, fn :start_price, start_price ->
    cond do
      start_price < 100 ->
        [start_price: "cannot be less than $1"]
      true ->
        []
    end
  end)
end

defp forbid_start_price_update(changeset) do
  validate_change(changeset, :start_price, fn :start_price, _start_price ->
    [start_price: "cannot be modified"]
  end)
end

defp forbid_end_date_update(changeset) do
  validate_change(changeset, :end_date, fn :end_date, _end_date ->
    [end_date: "cannot be modified"]
  end)
end