custom-type.ex

defmodule Junk.SensibleDateTimeType do
  use Timex

  require Logger

  @behaviour Ecto.Type
  def type, do: :naive_datetime

  def load(%NaiveDateTime{} = value), do: value
  def load(_), do: :error

  def dump(%NaiveDateTime{} = naive_datetime) do
    {:ok, naive_datetime}
  end
  def dump(_), do: :error

  def cast(%NaiveDateTime{} = naive_datetime), do: naive_datetime
  def cast(string) when is_binary(string) do
    case Timex.parse(string, "{ISO:Extended}") do
      {:ok, datetime} -> {:ok, Timex.to_naive_datetime(datetime)}
      _ -> :error
    end
  end
end