defmodule Timex.Time do

  @million 1_000_000

  Enum.each [usecs: @million, msecs: 1_000], fn {type, coef} ->
    def to_usecs(value, unquote(type)), do: value * @million / unquote(coef)
    def to_msecs(value, unquote(type)), do: value * 1000 / unquote(coef)
    def to_secs(value, unquote(type)),  do: value / unquote(coef)
    def to_mins(value, unquote(type)),  do: value / unquote(coef) / 60
    def to_hours(value, unquote(type)), do: value / unquote(coef) / 3600
    def to_days(value, unquote(type)),  do: value / unquote(coef) / (3600 * 24)
    def to_weeks(value, unquote(type)), do: value / unquote(coef) / (3600 * 24 * 7)
  end

  Enum.each [secs: 1, mins: 60, hours: 3600, days: 3600 * 24, weeks: 3600 * 24 * 7], fn {type, coef} ->
    def unquote(type)(value), do: value * unquote(coef)
    def to_usecs(value, unquote(type)), do: value * unquote(coef) * @million
    def to_msecs(value, unquote(type)), do: value * unquote(coef) * 1000
    def to_secs(value, unquote(type)),  do: value * unquote(coef)
    def to_mins(value, unquote(type)),  do: value * unquote(coef) / 60
    def to_hours(value, unquote(type)), do: value * unquote(coef) / 3600
    def to_days(value, unquote(type)),  do: value * unquote(coef) / (3600 * 24)
    def to_weeks(value, unquote(type)), do: value * unquote(coef) / (3600 * 24 * 7)
  end


  Enum.each [:to_usecs, :to_msecs, :to_secs, :to_mins, :to_hours, :to_days, :to_weeks], fn name ->
    def unquote(name)({hours, minutes, seconds}, :hms), do: unquote(name)(hours * 3600 + minutes * 60 + seconds, :secs)
  end

  @doc """
  Converts an hour between 0..24 to {1..12, :am/:pm}

  ## Examples

    iex> to_12hour_clock(23)
    {11, :pm}

  """
  def to_12hour_clock(hour) when hour in 0..24 do
    case hour do
      hour when hour > 12       -> {hour - 12, :pm}
      hour when hour in [0, 12] -> {12, :pm}
      hour when hour < 12       -> {hour, :am}
    end
  end
  @doc """
  Converts an hour between 1..12 in either am or pm, to value between 0..24

  ## Examples

    iex> to_24hour_clock(7, :pm)
    19

  """
  def to_24hour_clock(hour, am_or_pm) when hour in 1..12 and am_or_pm in [:am, :AM, :pm, :PM] do
    case am_or_pm do
      :am -> hour
      :pm -> hour + 12
    end
  end

  def from(value, :usecs) do
    { sec, micro } = mdivmod(value)
    { mega, sec }  = mdivmod(sec)
    { mega, sec, micro }
  end

  def from(value, :msecs) do
    #micro = value * 1000
    { sec, micro } = divmod(value, 1000)
    { mega, sec }  = mdivmod(sec)
    { mega, sec, micro }
  end

  def from(value, :secs) do
    # trunc ...
    { sec, micro } = mdivmod(value)
    { mega, sec }  = mdivmod(sec)
    { mega, sec, micro }
  end

  def to_usecs({mega, sec, micro}), do: (mega * @million + sec) * @million + micro
  def to_msecs({mega, sec, micro}), do: (mega * @million + sec) * 1000 + micro / 1000
  def to_secs({mega, sec, micro}),  do: mega * @million + sec + micro / @million
  def to_mins(timestamp),           do: to_secs(timestamp) / 60
  def to_hours(timestamp),          do: to_secs(timestamp) / 3600
  def to_days(timestamp),           do: to_secs(timestamp) / (3600 * 24)
  def to_weeks(timestamp),          do: to_secs(timestamp) / (3600 * 24 * 7)

  def to_timestamp(value, :usecs) do
    { secs, microsecs } = mdivmod(value)
    { megasecs, secs }  = mdivmod(secs)
    {megasecs, secs, microsecs}
  end
  def to_timestamp(value, :msecs) do
    { secs, microsecs } = divmod(value, 1000)
    { megasecs, secs }  = mdivmod(secs)
    {megasecs, secs, microsecs}
  end
  def to_timestamp(value, :secs) do
    secs      = trunc(value)
    microsecs = trunc((value - secs) * @million)
    { megasecs, secs } = mdivmod(secs)
    {megasecs, secs, microsecs}
  end
  def to_timestamp(value, :mins),  do: to_timestamp(value * 60, :secs)
  def to_timestamp(value, :hours), do: to_timestamp(value * 3600, :secs)
  def to_timestamp(value, :days),  do: to_timestamp(value * 3600 * 24, :secs)
  def to_timestamp(value, :weeks), do: to_timestamp(value * 3600 * 24 * 7, :secs)
  def to_timestamp(value, :hms),   do: to_timestamp(to_secs(value, :hms), :secs)

  def add({mega1,sec1,micro1}, {mega2,sec2,micro2}) do
    normalize { mega1+mega2, sec1+sec2, micro1+micro2 }
  end

  def sub({mega1,sec1,micro1}, {mega2,sec2,micro2}) do
    normalize { mega1-mega2, sec1-sec2, micro1-micro2 }
  end

  def scale({mega, secs, micro}, coef) do
    normalize { mega*coef, secs*coef, micro*coef }
  end

  def invert({mega, sec, micro}) do
    { -mega, -sec, -micro }
  end

  def abs(timestamp={mega, sec, micro}) do
    cond do
      mega != 0 -> value = mega
      sec != 0  -> value = sec
      true      -> value = micro
    end

    if value < 0 do
      invert(timestamp)
    else
      timestamp
    end
  end

  @doc """
  Return a timestamp representing a time lapse of length 0.

    Time.convert(Time.zero, :sec)
    #=> 0

  Can be useful for operations on collections of timestamps. For instance,

    Enum.reduce timestamps, Time.zero, Time.add(&1, &2)

  """
  def zero, do: {0, 0, 0}

  @doc """
  Convert timestamp in the form { megasecs, seconds, microsecs } to the
  specified time units.

  Supported units: microseconds (:usec), milliseconds (:msec), seconds (:sec),
  minutes (:min), hours (:hour), days (:day), or weeks (:week).
  """
  def convert(timestamp, type \\ :timestamp)
  def convert(timestamp, :timestamp), do: timestamp
  def convert(timestamp, :usecs), do: to_secs(timestamp) * 1000000
  def convert(timestamp, :msecs), do: to_secs(timestamp) * 1000
  def convert(timestamp, :secs),  do: to_secs(timestamp)
  def convert(timestamp, :mins),  do: to_secs(timestamp) / 60
  def convert(timestamp, :hours), do: to_secs(timestamp) / 3600
  def convert(timestamp, :days),  do: to_secs(timestamp) / (3600 * 24)
  def convert(timestamp, :weeks), do: to_secs(timestamp) / (3600 * 24 * 7)

  @doc """
  Return time interval since the first day of year 0 to Epoch.
  """
  def epoch(type \\ :timestamp)

  def epoch(:timestamp) do
    seconds = :calendar.datetime_to_gregorian_seconds({ {1970,1,1}, {0,0,0} })
    { mega, sec } = mdivmod(seconds)
    { mega, sec, 0 }
  end

  def epoch(type) do
    convert(epoch, type)
  end

  @doc """
  Time interval since Epoch.

  The argument is an atom indicating the type of time units to return (see
  convert/2 for supported values).

  When the argument is omitted, the return value's format is { megasecs, seconds, microsecs }.
  """
  def now(type \\ :timestamp)

  def now(:timestamp) do
    :os.timestamp
  end

  def now(type) do
    convert(now, type)
  end

  @doc """
  Time interval between timestamp and now. If timestamp is after now in time, the
  return value will be negative.

  The second argument is an atom indicating the type of time units to return:
  microseconds (:usec), milliseconds (:msec), seconds (:sec), minutes (:min),
  or hours (:hour).

  When the second argument is omitted, the return value's format is { megasecs,
  seconds, microsecs }.
  """
  def elapsed(timestamp, type \\ :timestamp)

  def elapsed(timestamp, type) do
    diff(now, timestamp, type)
  end

  @doc """
  Time interval between two timestamps. If the first timestamp comes before the
  second one in time, the return value will be negative.

  The third argument is an atom indicating the type of time units to return:
  microseconds (:usec), milliseconds (:msec), seconds (:sec), minutes (:min),
  or hours (:hour).

  When the third argument is omitted, the return value's format is { megasecs,
  seconds, microsecs }.
  """
  def diff(t1, t2, type \\ :timestamp)

  def diff({mega1,secs1,micro1}, {mega2,secs2,micro2}, :timestamp) do
    # TODO: normalize the result
    {mega1 - mega2, secs1 - secs2, micro1 - micro2}
  end

  def diff(t1, t2, type) do
    convert(diff(t1, t2), type)
  end

  def measure(fun) do
    measure_result(:timer.tc(fun))
  end

  def measure(fun, args) do
    measure_result(:timer.tc(fun, args))
  end

  def measure(module, fun, args) do
    measure_result(:timer.tc(module, fun, args))
  end

  defp measure_result({micro, ret}) do
    { to_timestamp(micro, :usec), ret }
  end

  defp normalize({mega, sec, micro}) do
    # TODO: check for negative values
    if micro >= @million do
      { sec, micro } = mdivmod(sec, micro)
    end

    if sec >= @million do
      { mega, sec } = mdivmod(mega, sec)
    end

    { mega, sec, micro }
  end

  defp divmod(a, b) do
    { div(a, b), rem(a, b) }
  end

  defp divmod(initial, a, b) do
    { initial + div(a, b), rem(a, b) }
  end

  defp mdivmod(a) do
    divmod(a, 1_000_000)
  end

  defp mdivmod(initial, a) do
    divmod(initial, a, 1_000_000)
  end
end