defmodule Farmbot.TimeUtils do
  @moduledoc "Helper functions for working with time."

  def format_time(%DateTime{} = dt) do
    "#{format_num(dt.month)}/#{format_num(dt.day)}/#{dt.year} " <>
      "at #{format_num(dt.hour)}:#{format_num(dt.minute)}"
  end

  defp format_num(num), do: :io_lib.format('~2..0B', [num]) |> to_string

  # returns midnight of today
  @spec build_epoch(DateTime.t) :: DateTime.t
  def build_epoch(time) do
    tz = Farmbot.Asset.fbos_config().timezone
    n  = Timex.Timezone.convert(time, tz)
    Timex.shift(n, hours: -n.hour, seconds: -n.second, minutes: -n.minute)
  end

  @doc """
  Compares a datetime with another.
  • -1 -- the first date comes before the second one
  • 0  -- both arguments represent the same date when coalesced to the same
    timezone.
  • 1  -- the first date comes after the second one

  Returns :gt if the first datetime is later than the second and :lt for vice
  versa. If the two datetimes are equal :eq is returned.
  """
  def compare_datetimes(left, right) do
    case Timex.compare(left, right, :seconds) do
      -1 -> :lt
      0 -> :eq
      1 -> :gt
    end
  end
end