defmodule Tox do
  @moduledoc """
  Some structs and functions to work with dates, times, durations, periods, and
  intervals.
  """

  @typedoc """
  Units related to dates and times.
  """
  @type unit ::
          :year
          | :month
          | :week
          | :day
          | :hour
          | :minute
          | :second
          | :microsecond

  @typedoc """
  An amount of time with a specified unit e.g. `{second: 500}`.
  """
  @type duration :: {unit(), integer()}

  @typedoc """
  Boundaries specifies whether the start and end of an interval are included or
  excluded.

  * `:open`: start and end are excluded
  * `:closed`: start and end are included
  * `:left_open`: start is excluded and end is included
  * `:right_open`: start is included and end is excluded
  """
  @type boundaries :: :closed | :left_open | :right_open | :open

  @doc false
  @spec days_per_week :: integer()
  def days_per_week, do: 7

  @doc false
  @spec week(Calendar.date()) :: {Calendar.year(), non_neg_integer()}
  def week(%{calendar: Calendar.ISO, year: year, month: month, day: day}) do
    :calendar.iso_week_number({year, month, day})
  end
end