defimpl Timex.Protocol, for: NaiveDateTime do
  @moduledoc """
  This module implements Timex functionality for NaiveDateTime
  """
  alias Timex.{Types, Duration}
  import Timex.Macros

  @epoch_seconds :calendar.datetime_to_gregorian_seconds({{1970, 1, 1}, {0, 0, 0}})

  @spec now() :: NaiveDateTime.t()
  def now() do
    Timex.to_naive_datetime(Timex.from_unix(:os.system_time(), :native))
  end

  @spec to_julian(NaiveDateTime.t()) :: float
  def to_julian(%NaiveDateTime{:year => y, :month => m, :day => d}) do
    Timex.Calendar.Julian.julian_date(y, m, d)
  end

  @spec to_gregorian_seconds(NaiveDateTime.t()) :: non_neg_integer
  def to_gregorian_seconds(date), do: to_seconds(date, :zero)

  @spec to_gregorian_microseconds(NaiveDateTime.t()) :: non_neg_integer
  def to_gregorian_microseconds(%NaiveDateTime{microsecond: {us, _}} = date) do
    s = to_seconds(date, :zero)
    s * (1_000 * 1_000) + us
  end

  @spec to_unix(NaiveDateTime.t()) :: non_neg_integer
  def to_unix(date), do: trunc(to_seconds(date, :epoch))

  @spec to_date(NaiveDateTime.t()) :: Date.t()
  def to_date(date), do: NaiveDateTime.to_date(date)

  @spec to_datetime(NaiveDateTime.t(), timezone :: Types.valid_timezone()) ::
          DateTime.t() | {:error, term}
  def to_datetime(%NaiveDateTime{:microsecond => {us, precision}} = d, timezone) do
    {date, {h, mm, s}} = NaiveDateTime.to_erl(d)
    Timex.DateTime.Helpers.construct({date, {h, mm, s, us}}, precision, timezone)
  end

  @spec to_naive_datetime(NaiveDateTime.t()) :: NaiveDateTime.t()
  def to_naive_datetime(%NaiveDateTime{} = date), do: date

  @spec to_erl(NaiveDateTime.t()) :: Types.datetime()
  def to_erl(%NaiveDateTime{} = d), do: NaiveDateTime.to_erl(d)

  @spec century(NaiveDateTime.t()) :: non_neg_integer
  def century(%NaiveDateTime{:year => year}), do: Timex.century(year)

  @spec is_leap?(NaiveDateTime.t()) :: boolean
  def is_leap?(%NaiveDateTime{year: year}), do: :calendar.is_leap_year(year)

  @spec beginning_of_day(NaiveDateTime.t()) :: NaiveDateTime.t()
  def beginning_of_day(%NaiveDateTime{:microsecond => {_, precision}} = datetime) do
    %{datetime | :hour => 0, :minute => 0, :second => 0, :microsecond => {0, precision}}
  end

  @spec end_of_day(NaiveDateTime.t()) :: NaiveDateTime.t()
  def end_of_day(%NaiveDateTime{microsecond: {_, precision}} = datetime) do
    if precision > 0 do
      us = Timex.DateTime.Helpers.to_precision(999_999, precision)
      %{datetime | :hour => 23, :minute => 59, :second => 59, :microsecond => {us, precision}}
    else
      %{datetime | :hour => 23, :minute => 59, :second => 59, :microsecond => {0, 0}}
    end
  end

  @spec beginning_of_week(NaiveDateTime.t(), Types.weekstart()) :: NaiveDateTime.t()
  def beginning_of_week(%NaiveDateTime{} = date, weekstart) do
    case Timex.days_to_beginning_of_week(date, weekstart) do
      {:error, _} = err ->
        err

      days ->
        beginning_of_day(shift(date, days: -days))
    end
  end

  @spec end_of_week(NaiveDateTime.t(), Types.weekstart()) :: NaiveDateTime.t()
  def end_of_week(%NaiveDateTime{} = date, weekstart) do
    case Timex.days_to_end_of_week(date, weekstart) do
      {:error, _} = err ->
        err

      days_to_end ->
        end_of_day(shift(date, days: days_to_end))
    end
  end

  @spec beginning_of_year(NaiveDateTime.t()) :: NaiveDateTime.t()
  def beginning_of_year(%NaiveDateTime{:year => y}) do
    {:ok, nd} = NaiveDateTime.new(y, 1, 1, 0, 0, 0)
    nd
  end

  @spec end_of_year(NaiveDateTime.t()) :: NaiveDateTime.t()
  def end_of_year(%NaiveDateTime{microsecond: {_, precision}} = date) do
    if precision > 0 do
      us = Timex.DateTime.Helpers.to_precision(999_999, precision)

      %{
        date
        | :month => 12,
          :day => 31,
          :hour => 23,
          :minute => 59,
          :second => 59,
          :microsecond => {us, precision}
      }
    else
      %{
        date
        | :month => 12,
          :day => 31,
          :hour => 23,
          :minute => 59,
          :second => 59,
          :microsecond => {0, 0}
      }
    end
  end

  @spec beginning_of_quarter(NaiveDateTime.t()) :: NaiveDateTime.t()
  def beginning_of_quarter(%NaiveDateTime{month: month} = date) do
    month = 1 + 3 * (Timex.quarter(month) - 1)
    beginning_of_month(%{date | :month => month, :day => 1})
  end

  @spec end_of_quarter(NaiveDateTime.t()) :: NaiveDateTime.t()
  def end_of_quarter(%NaiveDateTime{month: month} = date) do
    month = 3 * Timex.quarter(month)
    end_of_month(%{date | :month => month, :day => 1})
  end

  @spec beginning_of_month(NaiveDateTime.t()) :: NaiveDateTime.t()
  def beginning_of_month(%NaiveDateTime{microsecond: {_, precision}} = datetime),
    do: %{
      datetime
      | :day => 1,
        :hour => 0,
        :minute => 0,
        :second => 0,
        :microsecond => {0, precision}
    }

  @spec end_of_month(NaiveDateTime.t()) :: NaiveDateTime.t()
  def end_of_month(%NaiveDateTime{microsecond: {_, precision}} = date) do
    if precision > 0 do
      us = Timex.DateTime.Helpers.to_precision(999_999, precision)

      %{
        date
        | :day => days_in_month(date),
          :hour => 23,
          :minute => 59,
          :second => 59,
          :microsecond => {us, precision}
      }
    else
      %{
        date
        | :day => days_in_month(date),
          :hour => 23,
          :minute => 59,
          :second => 59,
          :microsecond => {0, 0}
      }
    end
  end

  @spec quarter(NaiveDateTime.t()) :: 1..4
  def quarter(%NaiveDateTime{month: month}), do: Timex.quarter(month)

  def days_in_month(%NaiveDateTime{:year => y, :month => m}), do: Timex.days_in_month(y, m)

  def week_of_month(%NaiveDateTime{:year => y, :month => m, :day => d}),
    do: Timex.week_of_month(y, m, d)

  def weekday(%NaiveDateTime{:year => y, :month => m, :day => d}),
    do: :calendar.day_of_the_week({y, m, d})

  def day(%NaiveDateTime{} = date) do
    {:ok, nd} = NaiveDateTime.new(date.year, 1, 1, 0, 0, 0)
    1 + Timex.diff(date, nd, :days)
  end

  def is_valid?(%NaiveDateTime{
        :year => y,
        :month => m,
        :day => d,
        :hour => h,
        :minute => min,
        :second => sec
      }) do
    :calendar.valid_date({y, m, d}) and Timex.is_valid_time?({h, min, sec})
  end

  def iso_week(%NaiveDateTime{:year => y, :month => m, :day => d}),
    do: Timex.iso_week(y, m, d)

  def from_iso_day(%NaiveDateTime{year: year} = date, day) when is_day_of_year(day) do
    {year, month, day_of_month} = Timex.Helpers.iso_day_to_date_tuple(year, day)
    %{date | :year => year, :month => month, :day => day_of_month}
  end

  @spec set(NaiveDateTime.t(), list({atom(), term})) :: NaiveDateTime.t() | {:error, term}
  def set(%NaiveDateTime{} = date, options) do
    validate? = Keyword.get(options, :validate, true)

    Enum.reduce(options, date, fn
      _option, {:error, _} = err ->
        err

      option, result ->
        case option do
          {:validate, _} ->
            result

          {:datetime, {{y, m, d}, {h, min, sec}}} ->
            if validate? do
              %{
                result
                | :year => Timex.normalize(:year, y),
                  :month => Timex.normalize(:month, m),
                  :day => Timex.normalize(:day, {y, m, d}),
                  :hour => Timex.normalize(:hour, h),
                  :minute => Timex.normalize(:minute, min),
                  :second => Timex.normalize(:second, sec)
              }
            else
              %{
                result
                | :year => y,
                  :month => m,
                  :day => d,
                  :hour => h,
                  :minute => min,
                  :second => sec
              }
            end

          {:date, {y, m, d}} ->
            if validate? do
              {yn, mn, dn} = Timex.normalize(:date, {y, m, d})
              %{result | :year => yn, :month => mn, :day => dn}
            else
              %{result | :year => y, :month => m, :day => d}
            end

          {:date, %Date{} = d} ->
            Timex.set(result, date: {d.year, d.month, d.day})

          {:time, {h, m, s}} ->
            if validate? do
              %{
                result
                | :hour => Timex.normalize(:hour, h),
                  :minute => Timex.normalize(:minute, m),
                  :second => Timex.normalize(:second, s)
              }
            else
              %{result | :hour => h, :minute => m, :second => s}
            end

          {:time, {h, m, s, ms}} ->
            if validate? do
              %{
                result
                | :hour => Timex.normalize(:hour, h),
                  :minute => Timex.normalize(:minute, m),
                  :second => Timex.normalize(:second, s),
                  :microsecond => Timex.normalize(:microsecond, ms)
              }
            else
              %{result | :hour => h, :minute => m, :second => s, :microsecond => ms}
            end

          {:time, %Time{} = t} ->
            Timex.set(result, time: {t.hour, t.minute, t.second, t.microsecond})

          {:day, d} ->
            if validate? do
              %{result | :day => Timex.normalize(:day, {result.year, result.month, d})}
            else
              %{result | :day => d}
            end

          {name, val} when name in [:year, :month, :hour, :minute, :second, :microsecond] ->
            if validate? do
              Map.put(result, name, Timex.normalize(name, val))
            else
              Map.put(result, name, val)
            end

          {name, _} when name in [:timezone] ->
            result

          {option_name, _} ->
            {:error, {:bad_option, option_name}}
        end
    end)
  end

  @spec shift(NaiveDateTime.t(), list({atom(), term})) :: NaiveDateTime.t() | {:error, term}
  def shift(%NaiveDateTime{} = datetime, shifts) when is_list(shifts) do
    apply_shifts(datetime, shifts)
  end

  defp apply_shifts(datetime, []),
    do: datetime

  defp apply_shifts(datetime, [{:duration, %Duration{} = duration} | rest]) do
    duration_microseconds = Duration.to_microseconds(duration)
    shifted = shift_by(datetime, duration_microseconds, :microseconds)
    apply_shifts(shifted, rest)
  end

  defp apply_shifts(datetime, [{unit, 0} | rest]) when is_atom(unit),
    do: apply_shifts(datetime, rest)

  defp apply_shifts(datetime, [{unit, value} | rest]) when is_atom(unit) and is_integer(value) do
    shifted = shift_by(datetime, value, unit)
    apply_shifts(shifted, rest)
  end

  defp apply_shifts({:error, _} = err, _),
    do: err

  defp shift_by(%NaiveDateTime{:year => y} = datetime, value, :years) do
    shifted = %{datetime | :year => y + value}
    # If a plain shift of the year fails, then it likely falls on a leap day,
    # so set the day to the last day of that month
    case :calendar.valid_date({shifted.year, shifted.month, shifted.day}) do
      false ->
        last_day = :calendar.last_day_of_the_month(shifted.year, shifted.month)

        cond do
          shifted.day <= last_day ->
            shifted

          :else ->
            %{shifted | :day => last_day}
        end

      true ->
        shifted
    end
  end

  defp shift_by(%NaiveDateTime{:year => year, :month => month} = datetime, value, :months) do
    m = month + value

    shifted =
      cond do
        m > 0 ->
          years = div(m - 1, 12)
          month = rem(m - 1, 12) + 1
          %{datetime | :year => year + years, :month => month}

        m <= 0 ->
          years = div(m, 12) - 1
          month = 12 + rem(m, 12)
          %{datetime | :year => year + years, :month => month}
      end

    # If the shift fails, it's because it's a high day number, and the month
    # shifted to does not have that many days. This will be handled by always
    # shifting to the last day of the month shifted to.
    case :calendar.valid_date({shifted.year, shifted.month, shifted.day}) do
      false ->
        last_day = :calendar.last_day_of_the_month(shifted.year, shifted.month)

        cond do
          shifted.day <= last_day ->
            shifted

          :else ->
            %{shifted | :day => last_day}
        end

      true ->
        shifted
    end
  end

  defp shift_by(datetime, value, :weeks),
    do: shift_by(datetime, value * 60 * 60 * 24 * 7 * 1_000_000, :microseconds)

  defp shift_by(datetime, value, :days),
    do: shift_by(datetime, value * 60 * 60 * 24 * 1_000_000, :microseconds)

  defp shift_by(datetime, value, :hours),
    do: shift_by(datetime, value * 60 * 60 * 1_000_000, :microseconds)

  defp shift_by(datetime, value, :minutes),
    do: shift_by(datetime, value * 60 * 1_000_000, :microseconds)

  defp shift_by(datetime, value, :seconds),
    do: shift_by(datetime, value * 1_000_000, :microseconds)

  defp shift_by(datetime, value, :milliseconds),
    do: shift_by(datetime, value * 1_000, :microseconds)

  defp shift_by(
         %NaiveDateTime{microsecond: {current_microseconds, current_precision}} = datetime,
         value,
         :microseconds
       ) do
    microseconds_from_zero =
      :calendar.datetime_to_gregorian_seconds({
        {datetime.year, datetime.month, datetime.day},
        {datetime.hour, datetime.minute, datetime.second}
      }) * 1_000_000 + current_microseconds + value

    if microseconds_from_zero < 0 do
      {:error, :shift_to_invalid_date}
    else
      seconds_from_zero = div(microseconds_from_zero, 1_000_000)
      rem_microseconds = rem(microseconds_from_zero, 1_000_000)
      us = Timex.DateTime.Helpers.to_precision(rem_microseconds, current_precision)

      seconds_from_zero
      |> :calendar.gregorian_seconds_to_datetime()
      |> Timex.to_naive_datetime()
      |> Map.put(:microsecond, {us, current_precision})
    end
  end

  defp shift_by(_datetime, _value, units),
    do: {:error, {:unknown_shift_unit, units}}

  defp to_seconds(
         %NaiveDateTime{year: y, month: m, day: d, hour: h, minute: mm, second: s},
         :zero
       ) do
    :calendar.datetime_to_gregorian_seconds({{y, m, d}, {h, mm, s}})
  end

  defp to_seconds(
         %NaiveDateTime{year: y, month: m, day: d, hour: h, minute: mm, second: s},
         :epoch
       ) do
    :calendar.datetime_to_gregorian_seconds({{y, m, d}, {h, mm, s}}) - @epoch_seconds
  end
end