moment

defmodule Moment do
  defstruct year: 2014, month: 0, day: 0,
            hour: 0, minute: 0, second: 0,
            nanosecond: 0, offset: 0

  @doc """
  Returns an instance of Moment in Universal Time.
  """
  def utcnow() do
    now = :os.timestamp

    {{ year, month, day }, { hour, minute, second }} = :calendar.now_to_universal_time(now)
    { _megasecond, _second, microsecond } = now

    %Moment{year: year, month: month, day: day,
            hour: hour, minute: minute, second: second,
            nanosecond: microsecond * 1000, offset: 0}
  end

  @doc """
  Returns an instance of Moment in local time.
  """
  def now() do
    now = :os.timestamp

    {{ year, month, day }, { hour, minute, second }} = :calendar.now_to_local_time(now)
    { _megasecond, _second, microsecond } = now

    offset = calc_offset(now)

    %Moment{year: year, month: month, day: day,
            hour: hour, minute: minute, second: second,
            nanosecond: microsecond * 1000, offset: offset}
  end

  @doc """
  year
  """
  def year(moment) do
    moment.year
  end

  @doc """
  quarter, in 1..4
  """
  def quarter(moment) do
    div(moment.month - 1, 3) + 1
  end

  @doc """
  month, in 1..12
  """
  def month(moment) do
    moment.month
  end

  @doc """
  day, in 1..31
  """
  def day(moment) do
    moment.day
  end

  @doc """
  hour, in 0..23
  """
  def hour(moment) do
    moment.hour
  end

  @doc """
  minute, in 0..59
  """
  def minute(moment) do
    moment.minute
  end

  @doc """
  second, in 0..59
  """
  def second(moment) do
    moment.second
  end

  @doc """
  millisecond, in 0..999
  """
  def millisecond(moment) do
    div(moment.nanosecond, 1_000_000)
  end

  @doc """
  microsecond, in 0..999
  """
  def microsecond(moment) do
    rem(div(moment.nanosecond, 1_000), 1000)
  end

  @doc """
  nanosecond, in 0..999
  """
  def nanosecond(moment) do
    rem(moment.nanosecond, 1000)
  end

  @doc """
  Format moment as an iso8601 string.
  """
  def to_iso_string(moment) do
    Moment.Formatter.format(moment, "YYYY-MM-DDTHH:mm:ss.SSSZ")
  end

  @doc """
  Format moment according to format string.
  """
  def format(moment, format_str) do
    Moment.Formatter.format(moment, format_str)
  end

  @doc """
  Parse the moment string according to format string.

  Returns `{:ok, moment}` in case of success,
  `{:error, reason}` otherwise.
  """
  def parse(moment_str, format_str) do
    Moment.Parser.parse(moment_str, format_str)
  end

  @doc """
  Parse the moment string according to format string.

  Fails with a `RuntimeError` if the moment cannot be parsed.
  """
  def parse!(moment_str, format_str) do
    Moment.Parser.parse!(moment_str, format_str)
  end


  # Private
  # -------

  defp calc_offset(now) do
    local = now
    |> :calendar.now_to_local_time
    |> :calendar.datetime_to_gregorian_seconds

    universal = now
    |> :calendar.now_to_universal_time
    |> :calendar.datetime_to_gregorian_seconds

    div(local, 60) - div(universal, 60)
  end
end