   end
 
   @doc false
-  def naive_datetime_to_iso8601(year, month, day, hour, minute, second, microsecond, format \\ :extended) do
-    date_to_string(year, month, day, format) <> "T" <> time_to_string(hour, minute, second, microsecond, format)
-  end
-
-  @doc false
-  def datetime_to_iso8601(year, month, day, hour, minute, second, microsecond,
-                          time_zone, _zone_abbr, utc_offset, std_offset, format \\ :extended) do
-    date_to_string(year, month, day, format) <> "T" <>
+  def naive_datetime_to_iso8601(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second,
+        microsecond,
+        format \\ :extended
+      ) do
+    date_to_string(year, month, day, format) <>
+      "T" <> time_to_string(hour, minute, second, microsecond, format)
+  end
+
+  @doc false
+  def datetime_to_iso8601(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second,
+        microsecond,
+        time_zone,
+        _zone_abbr,
+        utc_offset,
+        std_offset,
+        format \\ :extended
+      ) do
+    date_to_string(year, month, day, format) <>
+      "T" <>
       time_to_string(hour, minute, second, microsecond, format) <>
       offset_to_string(utc_offset, std_offset, time_zone, format)
   end

  defp days_before_month(12), do: 334

  defp leap_day_offset(_year, month) when month < 3, do: 0
  defp leap_day_offset(year, _month) do
    if leap_year?(year), do: 1, else: 0
  end

  def add_day_fraction_to_iso_days({days, {parts, ppd}}, add, ppd) do
    normalize_iso_days(days, parts + add, ppd)
  end

  def add_day_fraction_to_iso_days({days, {parts, ppd}}, add, add_ppd) do
    parts = parts * add_ppd
    add = add * ppd
