From 9fb0fba82133d71ba3a22b8dacf730e6570b370c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonatan=20M=C3=A4nnchen?= <jonatan@maennchen.ch>
Date: Tue, 4 Aug 2020 20:03:55 +0200
Subject: [PATCH 01/15] DateHelper DateTime Support

---
 lib/crontab/date_helper.ex        | 268 +++++++++++++++++++++++++++---
 test/crontab/date_helper_test.exs |   2 +-
 2 files changed, 244 insertions(+), 26 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index bbf4c47..fdc45aa 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -3,10 +3,12 @@ defmodule Crontab.DateHelper do
 
   @type unit :: :year | :month | :day | :hour | :minute | :second | :microsecond
 
+  @type date :: NaiveDateTime.t() | DateTime.t()
+
   @units [
     {:year, {nil, nil}},
     {:month, {1, 12}},
-    {:day, {1, :end_onf_month}},
+    {:day, {1, :end_of_month}},
     {:hour, {0, 23}},
     {:minute, {0, 59}},
     {:second, {0, 59}},
@@ -21,8 +23,11 @@ defmodule Crontab.DateHelper do
       iex> Crontab.DateHelper.beginning_of(~N[2016-03-14 01:45:45.123], :year)
       ~N[2016-01-01 00:00:00]
 
+      iex> Crontab.DateHelper.beginning_of(~U[2016-03-14 01:45:45.123Z], :year)
+      ~U[2016-01-01 00:00:00Z]
+
   """
-  @spec beginning_of(NaiveDateTime.t(), unit) :: NaiveDateTime.t()
+  @spec beginning_of(date, unit :: unit) :: date when date: date
   def beginning_of(date, unit) do
     _beginning_of(date, proceeding_units(unit))
   end
@@ -35,16 +40,28 @@ defmodule Crontab.DateHelper do
       iex> Crontab.DateHelper.end_of(~N[2016-03-14 01:45:45.123], :year)
       ~N[2016-12-31 23:59:59.999999]
 
+      iex> Crontab.DateHelper.end_of(~U[2016-03-14 01:45:45.123Z], :year)
+      ~U[2016-12-31 23:59:59.999999Z]
+
   """
-  @spec end_of(NaiveDateTime.t(), unit) :: NaiveDateTime.t()
+  @spec end_of(date, unit :: unit) :: date when date: date
   def end_of(date, unit) do
     _end_of(date, proceeding_units(unit))
   end
 
   @doc """
-  Find the last occurrence of weekday in month.
+  Find last occurrence of weekday in month
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.last_weekday(~N[2016-03-14 01:45:45.123], 6)
+      26
+
+      iex> Crontab.DateHelper.last_weekday(~U[2016-03-14 01:45:45.123Z], 6)
+      26
+
   """
-  @spec last_weekday(NaiveDateTime.t(), Calendar.day_of_week()) :: Calendar.day()
+  @spec last_weekday(date :: date, day_of_week :: Calendar.day_of_week()) :: Calendar.day()
   def last_weekday(date, weekday) do
     date
     |> end_of(:month)
@@ -52,9 +69,19 @@ defmodule Crontab.DateHelper do
   end
 
   @doc """
-  Find the nth weekday of month.
+  Find nth weekday of month
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.nth_weekday(~N[2016-03-14 01:45:45.123], 6, 2)
+      12
+
+      iex> Crontab.DateHelper.nth_weekday(~U[2016-03-14 01:45:45.123Z], 6, 2)
+      12
+
   """
-  @spec nth_weekday(NaiveDateTime.t(), Calendar.day_of_week(), integer) :: Calendar.day()
+  @spec nth_weekday(date :: date, weekday :: Calendar.day_of_week(), n :: pos_integer) ::
+          Calendar.day()
   def nth_weekday(date, weekday, n) do
     date
     |> beginning_of(:month)
@@ -62,7 +89,16 @@ defmodule Crontab.DateHelper do
   end
 
   @doc """
-  Find the last occurrence of weekday in month.
+  Find last occurrence of weekday in month
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.last_weekday_of_month(~N[2016-03-14 01:45:45.123])
+      31
+
+      iex> Crontab.DateHelper.last_weekday_of_month(~U[2016-03-14 01:45:45.123Z])
+      31
+
   """
   @spec last_weekday_of_month(NaiveDateTime.t()) :: Calendar.day()
   def last_weekday_of_month(date) do
@@ -70,9 +106,18 @@ defmodule Crontab.DateHelper do
   end
 
   @doc """
-  Find the next occurrence of weekday relative to date.
+  Find next occurrence of weekday relative to date
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.next_weekday_to(~N[2016-03-14 01:45:45.123])
+      14
+
+      iex> Crontab.DateHelper.next_weekday_to(~U[2016-03-14 01:45:45.123Z])
+      14
+
   """
-  @spec next_weekday_to(NaiveDateTime.t()) :: Calendar.day()
+  @spec next_weekday_to(date :: date) :: Calendar.day()
   def next_weekday_to(date = %NaiveDateTime{year: year, month: month, day: day}) do
     weekday = :calendar.day_of_the_week(year, month, day)
     next_day = NaiveDateTime.add(date, 1, :day)
@@ -87,8 +132,36 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  @spec inc_year(NaiveDateTime.t()) :: NaiveDateTime.t()
-  def inc_year(date) do
+  def next_weekday_to(date = %DateTime{year: year, month: month, day: day}) do
+    weekday = :calendar.day_of_the_week(year, month, day)
+    # FIXME: How to correct date with tz?
+    next_day = DateTime.add(date, 1, :day)
+    # FIXME: How to correct date with tz?
+    previous_day = DateTime.add(date, -1, :day)
+
+    cond do
+      weekday == 7 && next_day.month == date.month -> next_day.day
+      weekday == 7 -> DateTime.add(date, -2, :day).day
+      weekday == 6 && previous_day.month == date.month -> previous_day.day
+      weekday == 6 -> DateTime.add(date, 2, :day).day
+      true -> date.day
+    end
+  end
+
+  @doc """
+  Increment Year
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.inc_year(~N[2016-03-14 01:45:45.123])
+      ~N[2017-03-15 01:45:45.123]
+
+      iex> Crontab.DateHelper.inc_year(~U[2016-03-14 01:45:45.123Z])
+      ~U[2017-03-15 01:45:45.123Z]
+
+  """
+  @spec inc_year(date) :: date when date: date
+  def inc_year(date = %NaiveDateTime{}) do
     leap_year? =
       date
       |> NaiveDateTime.to_date()
@@ -101,8 +174,35 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  @spec dec_year(NaiveDateTime.t()) :: NaiveDateTime.t()
-  def dec_year(date) do
+  def inc_year(date = %DateTime{}) do
+    leap_year? =
+      date
+      |> DateTime.to_date()
+      |> Date.leap_year?()
+
+    if leap_year? do
+      # FIXME: How to correct date with tz?
+      DateTime.add(date, 366, :day)
+    else
+      # FIXME: How to correct date with tz?
+      DateTime.add(date, 365, :day)
+    end
+  end
+
+  @doc """
+  Decrement Year
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.dec_year(~N[2016-03-14 01:45:45.123])
+      ~N[2015-03-14 01:45:45.123]
+
+      iex> Crontab.DateHelper.dec_year(~U[2016-03-14 01:45:45.123Z])
+      ~U[2015-03-14 01:45:45.123Z]
+
+  """
+  @spec dec_year(date) :: date when date: date
+  def dec_year(date = %NaiveDateTime{}) do
     leap_year? =
       date
       |> NaiveDateTime.to_date()
@@ -115,7 +215,34 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  @spec inc_month(NaiveDateTime.t()) :: NaiveDateTime.t()
+  def dec_year(date = %DateTime{}) do
+    leap_year? =
+      date
+      |> DateTime.to_date()
+      |> Date.leap_year?()
+
+    if leap_year? do
+      # FIXME: How to correct date with tz?
+      DateTime.add(date, -366, :day)
+    else
+      # FIXME: How to correct date with tz?
+      DateTime.add(date, -365, :day)
+    end
+  end
+
+  @doc """
+  Increment Month
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.inc_month(~N[2016-03-14 01:45:45.123])
+      ~N[2016-04-01 01:45:45.123]
+
+      iex> Crontab.DateHelper.inc_month(~U[2016-03-14 01:45:45.123Z])
+      ~U[2016-04-01 01:45:45.123Z]
+
+  """
+  @spec inc_month(date) :: date when date: date
   def inc_month(date = %NaiveDateTime{day: day}) do
     days =
       date
@@ -125,25 +252,69 @@ defmodule Crontab.DateHelper do
     NaiveDateTime.add(date, days + 1 - day, :day)
   end
 
-  @spec dec_month(NaiveDateTime.t()) :: NaiveDateTime.t()
-  def dec_month(date) do
+  def inc_month(date = %DateTime{day: day}) do
     days =
+      date
+      |> DateTime.to_date()
+      |> Date.days_in_month()
+
+    # FIXME: How to correct date with tz?
+    DateTime.add(date, days + 1 - day, :day)
+  end
+
+  @doc """
+  Decrement Month
+
+  ### Examples:
+
+      iex> Crontab.DateHelper.dec_month(~N[2016-03-14 01:45:45.123])
+      ~N[2016-02-14 01:45:45.123]
+
+      iex> Crontab.DateHelper.dec_month(~U[2016-03-14 01:45:45.123Z])
+      ~U[2016-02-14 01:45:45.123Z]
+
+      iex> Crontab.DateHelper.dec_month(~N[2011-05-31 23:59:59])
+      ~N[2011-04-30 23:59:59]
+
+  """
+  @spec dec_month(date) :: date when date: date
+  def dec_month(date = %NaiveDateTime{day: day}) do
+    days_in_last_month =
       date
       |> NaiveDateTime.to_date()
+      |> day_in_last_month
+      |> Date.days_in_month()
+
+    NaiveDateTime.add(date, -(day + max(days_in_last_month - day, 0)), :day)
+  end
+
+  def dec_month(date = %DateTime{day: day}) do
+    days_in_last_month =
+      date
+      |> DateTime.to_date()
+      |> day_in_last_month
       |> Date.days_in_month()
 
-    NaiveDateTime.add(date, -days, :day)
+    # FIXME: How to correct date with tz?
+    DateTime.add(date, -(day + max(days_in_last_month - day, 0)), :day)
   end
 
-  @spec _beginning_of(NaiveDateTime.t(), [{unit, {any, any}}]) :: NaiveDateTime.t()
+  defp day_in_last_month(start_date), do: day_in_last_month(start_date, start_date)
+
+  defp day_in_last_month(date = %Date{month: month}, start_date = %Date{month: month}),
+    do: date |> Date.add(-1) |> day_in_last_month(start_date)
+
+  defp day_in_last_month(date, _start_date), do: date
+
+  @spec _beginning_of(date, [{unit, {any, any}}]) :: date when date: date
   defp _beginning_of(date, [{unit, {lower, _}} | tail]) do
     _beginning_of(Map.put(date, unit, lower), tail)
   end
 
   defp _beginning_of(date, []), do: date
 
-  @spec _end_of(NaiveDateTime.t(), [{unit, {any, any}}]) :: NaiveDateTime.t()
-  defp _end_of(date, [{unit, {_, :end_onf_month}} | tail]) do
+  @spec _end_of(date, [{unit, {any, any}}]) :: date when date: date
+  defp _end_of(date = %NaiveDateTime{}, [{unit, {_, :end_of_month}} | tail]) do
     upper =
       date
       |> NaiveDateTime.to_date()
@@ -152,6 +323,16 @@ defmodule Crontab.DateHelper do
     _end_of(Map.put(date, unit, upper), tail)
   end
 
+  defp _end_of(date = %DateTime{}, [{unit, {_, :end_of_month}} | tail]) do
+    upper =
+      date
+      |> DateTime.to_date()
+      |> Date.days_in_month()
+
+    # FIXME: How to correct date with tz?
+    _end_of(Map.put(date, unit, upper), tail)
+  end
+
   defp _end_of(date, [{unit, {_, upper}} | tail]) do
     _end_of(Map.put(date, unit, upper), tail)
   end
@@ -165,7 +346,7 @@ defmodule Crontab.DateHelper do
       |> Enum.reduce([], fn {key, value}, acc ->
         cond do
           Enum.count(acc) > 0 ->
-            Enum.concat(acc, [{key, value}])
+            [{key, value} | acc]
 
           key == unit ->
             [{key, value}]
@@ -174,14 +355,20 @@ defmodule Crontab.DateHelper do
             []
         end
       end)
+      |> Enum.reverse()
 
     units
   end
 
-  @spec nth_weekday(NaiveDateTime.t(), Calendar.day_of_week(), :start) :: boolean
+  @spec nth_weekday(date :: date, weekday :: Calendar.day_of_week(), position :: :start) ::
+          boolean
   defp nth_weekday(date = %NaiveDateTime{}, _, 0, :start),
     do: NaiveDateTime.add(date, -1, :day).day
 
+  # FIXME: How to correct date with tz?
+  defp nth_weekday(date = %DateTime{}, _, 0, :start),
+    do: DateTime.add(date, -1, :day).day
+
   defp nth_weekday(date = %NaiveDateTime{year: year, month: month, day: day}, weekday, n, :start) do
     if :calendar.day_of_the_week(year, month, day) == weekday do
       nth_weekday(NaiveDateTime.add(date, 1, :day), weekday, n - 1, :start)
@@ -190,7 +377,17 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  @spec last_weekday_of_month(NaiveDateTime.t(), :end) :: Calendar.day()
+  defp nth_weekday(date = %DateTime{year: year, month: month, day: day}, weekday, n, :start) do
+    if :calendar.day_of_the_week(year, month, day) == weekday do
+      # FIXME: How to correct date with tz?
+      nth_weekday(DateTime.add(date, 1, :day), weekday, n - 1, :start)
+    else
+      # FIXME: How to correct date with tz?
+      nth_weekday(DateTime.add(date, 1, :day), weekday, n, :start)
+    end
+  end
+
+  @spec last_weekday_of_month(date :: date(), position :: :end) :: Calendar.day()
   defp last_weekday_of_month(date = %NaiveDateTime{year: year, month: month, day: day}, :end) do
     weekday = :calendar.day_of_the_week(year, month, day)
 
@@ -201,7 +398,19 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  @spec last_weekday(NaiveDateTime.t(), non_neg_integer, :end) :: Calendar.day()
+  defp last_weekday_of_month(date = %DateTime{year: year, month: month, day: day}, :end) do
+    weekday = :calendar.day_of_the_week(year, month, day)
+
+    if weekday > 5 do
+      # FIXME: How to correct date with tz?
+      last_weekday_of_month(DateTime.add(date, -1, :day), :end)
+    else
+      day
+    end
+  end
+
+  @spec last_weekday(date :: date, weekday :: Calendar.day_of_week(), position :: :end) ::
+          Calendar.day()
   defp last_weekday(date = %NaiveDateTime{year: year, month: month, day: day}, weekday, :end) do
     if :calendar.day_of_the_week(year, month, day) == weekday do
       day
@@ -209,4 +418,13 @@ defmodule Crontab.DateHelper do
       last_weekday(NaiveDateTime.add(date, -1, :day), weekday, :end)
     end
   end
+
+  defp last_weekday(date = %DateTime{year: year, month: month, day: day}, weekday, :end) do
+    if :calendar.day_of_the_week(year, month, day) == weekday do
+      day
+    else
+      # FIXME: How to correct date with tz?
+      last_weekday(DateTime.add(date, -1, :day), weekday, :end)
+    end
+  end
 end
diff --git a/test/crontab/date_helper_test.exs b/test/crontab/date_helper_test.exs
index f1bfe44..f6eb7bc 100644
--- a/test/crontab/date_helper_test.exs
+++ b/test/crontab/date_helper_test.exs
@@ -6,7 +6,7 @@ defmodule Crontab.DateHelperTest do
   doctest Crontab.DateHelper
 
   describe "inc_month/1" do
-    test "does not jump obver month" do
+    test "does not jump over month" do
       assert Crontab.DateHelper.inc_month(~N[2019-05-31 23:00:00]) == ~N[2019-06-01 23:00:00]
     end
   end

From 939315520cc13fd66e9c2c4fde7041724ece6664 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Sun, 11 Feb 2024 20:42:36 +0800
Subject: [PATCH 02/15] Add mix_test_watch as dev dep

---
 mix.exs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mix.exs b/mix.exs
index 59014c5..a5fe4a7 100644
--- a/mix.exs
+++ b/mix.exs
@@ -43,7 +43,8 @@ defmodule Crontab.Mixfile do
       {:ex_doc, ">= 0.0.0", only: :dev, runtime: false},
       {:excoveralls, "~> 0.5", only: [:test], runtime: false},
       {:dialyxir, "~> 1.0", only: [:dev], runtime: false},
-      {:credo, "~> 1.0", only: [:dev], runtime: false}
+      {:credo, "~> 1.0", only: [:dev], runtime: false},
+      {:mix_test_watch, "~> 1.1", only: [:dev, :test], runtime: false}
     ]
   end
 

From 5a556d8f8a152b4ee7fc101690c23c0b0ecb91f7 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Sun, 11 Feb 2024 21:33:00 +0800
Subject: [PATCH 03/15] Simplify date_helper with extracted add/3 and
 days_in_year/1

---
 lib/crontab/date_checker.ex |  16 +--
 lib/crontab/date_helper.ex  | 198 +++++++-----------------------------
 2 files changed, 43 insertions(+), 171 deletions(-)

diff --git a/lib/crontab/date_checker.ex b/lib/crontab/date_checker.ex
index 3d4df08..ef0a4c2 100644
--- a/lib/crontab/date_checker.ex
+++ b/lib/crontab/date_checker.ex
@@ -7,8 +7,6 @@ defmodule Crontab.DateChecker do
 
   alias Crontab.DateHelper
 
-  @type date :: NaiveDateTime.t() | DateTime.t()
-
   @doc """
   Check a condition list against a given date.
 
@@ -27,7 +25,8 @@ defmodule Crontab.DateChecker do
       true
 
   """
-  @spec matches_date?(cron_expression :: CronExpression.t(), date :: date) :: boolean | no_return
+  @spec matches_date?(cron_expression :: CronExpression.t(), date :: DateHelper.date()) ::
+          boolean | no_return
   def matches_date?(cron_expression_or_condition_list, date)
 
   def matches_date?(%CronExpression{reboot: true}, _),
@@ -39,7 +38,10 @@ defmodule Crontab.DateChecker do
     |> matches_date?(execution_date)
   end
 
-  @spec matches_date?(condition_list :: CronExpression.condition_list(), date :: date) :: boolean
+  @spec matches_date?(
+          condition_list :: CronExpression.condition_list(),
+          date :: DateHelper.date()
+        ) :: boolean
   def matches_date?([], _), do: true
 
   def matches_date?([{interval, conditions} | tail], execution_date) do
@@ -61,7 +63,7 @@ defmodule Crontab.DateChecker do
   @spec matches_date?(
           interval :: CronExpression.interval(),
           condition_list :: CronExpression.condition_list(),
-          date :: date
+          date :: DateHelper.date()
         ) :: boolean
   def matches_date?(_, [:* | _], _), do: true
   def matches_date?(_, [], _), do: false
@@ -80,7 +82,7 @@ defmodule Crontab.DateChecker do
           interval :: CronExpression.interval(),
           values :: [CronExpression.time_unit()],
           condition :: CronExpression.value(),
-          date :: date
+          date :: DateHelper.date()
         ) :: boolean
   defp matches_specific_date?(_, [], _, _), do: false
   defp matches_specific_date?(_, _, :*, _), do: true
@@ -171,7 +173,7 @@ defmodule Crontab.DateChecker do
     end
   end
 
-  @spec get_interval_value(interval :: CronExpression.interval(), date :: date) :: [
+  @spec get_interval_value(interval :: CronExpression.interval(), date :: DateHelper.date()) :: [
           CronExpression.time_unit()
         ]
   defp get_interval_value(:second, %{second: second}), do: [second]
diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index fdc45aa..c3d4dd1 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -100,10 +100,8 @@ defmodule Crontab.DateHelper do
       31
 
   """
-  @spec last_weekday_of_month(NaiveDateTime.t()) :: Calendar.day()
-  def last_weekday_of_month(date) do
-    last_weekday_of_month(end_of(date, :month), :end)
-  end
+  @spec last_weekday_of_month(date :: date()) :: Calendar.day()
+  def last_weekday_of_month(date), do: last_weekday_of_month(end_of(date, :month), :end)
 
   @doc """
   Find next occurrence of weekday relative to date
@@ -118,32 +116,16 @@ defmodule Crontab.DateHelper do
 
   """
   @spec next_weekday_to(date :: date) :: Calendar.day()
-  def next_weekday_to(date = %NaiveDateTime{year: year, month: month, day: day}) do
-    weekday = :calendar.day_of_the_week(year, month, day)
-    next_day = NaiveDateTime.add(date, 1, :day)
-    previous_day = NaiveDateTime.add(date, -1, :day)
-
-    cond do
-      weekday == 7 && next_day.month == date.month -> next_day.day
-      weekday == 7 -> NaiveDateTime.add(date, -2, :day).day
-      weekday == 6 && previous_day.month == date.month -> previous_day.day
-      weekday == 6 -> NaiveDateTime.add(date, 2, :day).day
-      true -> date.day
-    end
-  end
-
-  def next_weekday_to(date = %DateTime{year: year, month: month, day: day}) do
+  def next_weekday_to(date = %{year: year, month: month, day: day}) do
     weekday = :calendar.day_of_the_week(year, month, day)
-    # FIXME: How to correct date with tz?
-    next_day = DateTime.add(date, 1, :day)
-    # FIXME: How to correct date with tz?
-    previous_day = DateTime.add(date, -1, :day)
+    next_day = add(date, 1, :day)
+    previous_day = add(date, -1, :day)
 
     cond do
       weekday == 7 && next_day.month == date.month -> next_day.day
-      weekday == 7 -> DateTime.add(date, -2, :day).day
+      weekday == 7 -> add(date, -2, :day).day
       weekday == 6 && previous_day.month == date.month -> previous_day.day
-      weekday == 6 -> DateTime.add(date, 2, :day).day
+      weekday == 6 -> add(date, 2, :day).day
       true -> date.day
     end
   end
@@ -161,33 +143,7 @@ defmodule Crontab.DateHelper do
 
   """
   @spec inc_year(date) :: date when date: date
-  def inc_year(date = %NaiveDateTime{}) do
-    leap_year? =
-      date
-      |> NaiveDateTime.to_date()
-      |> Date.leap_year?()
-
-    if leap_year? do
-      NaiveDateTime.add(date, 366, :day)
-    else
-      NaiveDateTime.add(date, 365, :day)
-    end
-  end
-
-  def inc_year(date = %DateTime{}) do
-    leap_year? =
-      date
-      |> DateTime.to_date()
-      |> Date.leap_year?()
-
-    if leap_year? do
-      # FIXME: How to correct date with tz?
-      DateTime.add(date, 366, :day)
-    else
-      # FIXME: How to correct date with tz?
-      DateTime.add(date, 365, :day)
-    end
-  end
+  def inc_year(date), do: add(date, days_in_year(date), :day)
 
   @doc """
   Decrement Year
@@ -202,33 +158,7 @@ defmodule Crontab.DateHelper do
 
   """
   @spec dec_year(date) :: date when date: date
-  def dec_year(date = %NaiveDateTime{}) do
-    leap_year? =
-      date
-      |> NaiveDateTime.to_date()
-      |> Date.leap_year?()
-
-    if leap_year? do
-      NaiveDateTime.add(date, -366, :day)
-    else
-      NaiveDateTime.add(date, -365, :day)
-    end
-  end
-
-  def dec_year(date = %DateTime{}) do
-    leap_year? =
-      date
-      |> DateTime.to_date()
-      |> Date.leap_year?()
-
-    if leap_year? do
-      # FIXME: How to correct date with tz?
-      DateTime.add(date, -366, :day)
-    else
-      # FIXME: How to correct date with tz?
-      DateTime.add(date, -365, :day)
-    end
-  end
+  def dec_year(date), do: add(date, -days_in_year(date), :day)
 
   @doc """
   Increment Month
@@ -243,23 +173,12 @@ defmodule Crontab.DateHelper do
 
   """
   @spec inc_month(date) :: date when date: date
-  def inc_month(date = %NaiveDateTime{day: day}) do
-    days =
-      date
-      |> NaiveDateTime.to_date()
-      |> Date.days_in_month()
-
-    NaiveDateTime.add(date, days + 1 - day, :day)
-  end
-
-  def inc_month(date = %DateTime{day: day}) do
+  def inc_month(date = %{year: year, month: month, day: day}) do
     days =
-      date
-      |> DateTime.to_date()
+      Date.new!(year, month, day)
       |> Date.days_in_month()
 
-    # FIXME: How to correct date with tz?
-    DateTime.add(date, days + 1 - day, :day)
+    add(date, days + 1 - day, :day)
   end
 
   @doc """
@@ -278,25 +197,13 @@ defmodule Crontab.DateHelper do
 
   """
   @spec dec_month(date) :: date when date: date
-  def dec_month(date = %NaiveDateTime{day: day}) do
-    days_in_last_month =
-      date
-      |> NaiveDateTime.to_date()
-      |> day_in_last_month
-      |> Date.days_in_month()
-
-    NaiveDateTime.add(date, -(day + max(days_in_last_month - day, 0)), :day)
-  end
-
-  def dec_month(date = %DateTime{day: day}) do
+  def dec_month(date = %{year: year, month: month, day: day}) do
     days_in_last_month =
-      date
-      |> DateTime.to_date()
+      Date.new!(year, month, day)
       |> day_in_last_month
       |> Date.days_in_month()
 
-    # FIXME: How to correct date with tz?
-    DateTime.add(date, -(day + max(days_in_last_month - day, 0)), :day)
+    add(date, -(day + max(days_in_last_month - day, 0)), :day)
   end
 
   defp day_in_last_month(start_date), do: day_in_last_month(start_date, start_date)
@@ -314,22 +221,11 @@ defmodule Crontab.DateHelper do
   defp _beginning_of(date, []), do: date
 
   @spec _end_of(date, [{unit, {any, any}}]) :: date when date: date
-  defp _end_of(date = %NaiveDateTime{}, [{unit, {_, :end_of_month}} | tail]) do
-    upper =
-      date
-      |> NaiveDateTime.to_date()
-      |> Date.days_in_month()
-
-    _end_of(Map.put(date, unit, upper), tail)
-  end
-
-  defp _end_of(date = %DateTime{}, [{unit, {_, :end_of_month}} | tail]) do
+  defp _end_of(date = %{year: year, month: month, day: day}, [{unit, {_, :end_of_month}} | tail]) do
     upper =
-      date
-      |> DateTime.to_date()
+      Date.new!(year, month, day)
       |> Date.days_in_month()
 
-    # FIXME: How to correct date with tz?
     _end_of(Map.put(date, unit, upper), tail)
   end
 
@@ -362,48 +258,19 @@ defmodule Crontab.DateHelper do
 
   @spec nth_weekday(date :: date, weekday :: Calendar.day_of_week(), position :: :start) ::
           boolean
-  defp nth_weekday(date = %NaiveDateTime{}, _, 0, :start),
-    do: NaiveDateTime.add(date, -1, :day).day
-
-  # FIXME: How to correct date with tz?
-  defp nth_weekday(date = %DateTime{}, _, 0, :start),
-    do: DateTime.add(date, -1, :day).day
-
-  defp nth_weekday(date = %NaiveDateTime{year: year, month: month, day: day}, weekday, n, :start) do
-    if :calendar.day_of_the_week(year, month, day) == weekday do
-      nth_weekday(NaiveDateTime.add(date, 1, :day), weekday, n - 1, :start)
-    else
-      nth_weekday(NaiveDateTime.add(date, 1, :day), weekday, n, :start)
-    end
-  end
+  defp nth_weekday(date, _, 0, :start), do: add(date, -1, :day).day
 
-  defp nth_weekday(date = %DateTime{year: year, month: month, day: day}, weekday, n, :start) do
-    if :calendar.day_of_the_week(year, month, day) == weekday do
-      # FIXME: How to correct date with tz?
-      nth_weekday(DateTime.add(date, 1, :day), weekday, n - 1, :start)
-    else
-      # FIXME: How to correct date with tz?
-      nth_weekday(DateTime.add(date, 1, :day), weekday, n, :start)
-    end
+  defp nth_weekday(date = %{year: year, month: month, day: day}, weekday, n, :start) do
+    modifier = if :calendar.day_of_the_week(year, month, day) == weekday, do: n - 1, else: n
+    nth_weekday(add(date, 1, :day), weekday, modifier, :start)
   end
 
   @spec last_weekday_of_month(date :: date(), position :: :end) :: Calendar.day()
-  defp last_weekday_of_month(date = %NaiveDateTime{year: year, month: month, day: day}, :end) do
-    weekday = :calendar.day_of_the_week(year, month, day)
-
-    if weekday > 5 do
-      last_weekday_of_month(NaiveDateTime.add(date, -1, :day), :end)
-    else
-      day
-    end
-  end
-
-  defp last_weekday_of_month(date = %DateTime{year: year, month: month, day: day}, :end) do
+  defp last_weekday_of_month(date = %{year: year, month: month, day: day}, :end) do
     weekday = :calendar.day_of_the_week(year, month, day)
 
     if weekday > 5 do
-      # FIXME: How to correct date with tz?
-      last_weekday_of_month(DateTime.add(date, -1, :day), :end)
+      last_weekday_of_month(add(date, -1, :day), :end)
     else
       day
     end
@@ -411,20 +278,23 @@ defmodule Crontab.DateHelper do
 
   @spec last_weekday(date :: date, weekday :: Calendar.day_of_week(), position :: :end) ::
           Calendar.day()
-  defp last_weekday(date = %NaiveDateTime{year: year, month: month, day: day}, weekday, :end) do
+  defp last_weekday(date = %{year: year, month: month, day: day}, weekday, :end) do
     if :calendar.day_of_the_week(year, month, day) == weekday do
       day
     else
-      last_weekday(NaiveDateTime.add(date, -1, :day), weekday, :end)
+      last_weekday(add(date, -1, :day), weekday, :end)
     end
   end
 
-  defp last_weekday(date = %DateTime{year: year, month: month, day: day}, weekday, :end) do
-    if :calendar.day_of_the_week(year, month, day) == weekday do
-      day
-    else
-      # FIXME: How to correct date with tz?
-      last_weekday(DateTime.add(date, -1, :day), weekday, :end)
+  defp add(datetime = %DateTime{}, amt, unit), do: DateTime.add(datetime, amt, unit)
+  defp add(datetime = %NaiveDateTime{}, amt, unit), do: NaiveDateTime.add(datetime, amt, unit)
+
+  defp days_in_year(%{year: year}) do
+    Date.new!(year, 1, 1)
+    |> Date.leap_year?()
+    |> case do
+      true -> 366
+      false -> 365
     end
   end
 end

From fe2920eb98e495358eeb262b1d52cbde3b921e05 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Mon, 12 Feb 2024 23:25:15 +0800
Subject: [PATCH 04/15] Handle daylight savings start and end calculations

---
 lib/crontab/date_helper.ex        | 37 ++++++++++++++++--
 mix.exs                           |  4 +-
 test/crontab/date_helper_test.exs | 63 ++++++++++++++++++++++++++++++-
 3 files changed, 99 insertions(+), 5 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index c3d4dd1..f2d98d6 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -1,4 +1,6 @@
 defmodule Crontab.DateHelper do
+  use Private
+
   @moduledoc false
 
   @type unit :: :year | :month | :day | :hour | :minute | :second | :microsecond
@@ -286,9 +288,6 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  defp add(datetime = %DateTime{}, amt, unit), do: DateTime.add(datetime, amt, unit)
-  defp add(datetime = %NaiveDateTime{}, amt, unit), do: NaiveDateTime.add(datetime, amt, unit)
-
   defp days_in_year(%{year: year}) do
     Date.new!(year, 1, 1)
     |> Date.leap_year?()
@@ -297,4 +296,36 @@ defmodule Crontab.DateHelper do
       false -> 365
     end
   end
+
+  private do
+    def add(datetime = %NaiveDateTime{}, amt, unit), do: NaiveDateTime.add(datetime, amt, unit)
+
+    def add(datetime = %DateTime{}, amt, unit) do
+      candidate = DateTime.add(datetime, amt, unit)
+      adjustment = datetime.std_offset - candidate.std_offset
+      adjusted = DateTime.add(candidate, adjustment, :second)
+
+      case adjusted.std_offset == candidate.std_offset do
+        false ->
+          candidate
+
+        true ->
+          adj_plus_1h = DateTime.add(adjusted, 1, :hour)
+
+          case adj_plus_1h.std_offset == adjusted.std_offset do
+            true ->
+              adjusted
+
+            _ ->
+              # the one hour at end of daylight savings with ambiguous timezone
+              # return datetime with the standard (not daylight savings) timezone
+              %DateTime{
+                adjusted
+                | std_offset: adj_plus_1h.std_offset,
+                  zone_abbr: adj_plus_1h.zone_abbr
+              }
+          end
+      end
+    end
+  end
 end
diff --git a/mix.exs b/mix.exs
index a5fe4a7..627b4ff 100644
--- a/mix.exs
+++ b/mix.exs
@@ -44,7 +44,9 @@ defmodule Crontab.Mixfile do
       {:excoveralls, "~> 0.5", only: [:test], runtime: false},
       {:dialyxir, "~> 1.0", only: [:dev], runtime: false},
       {:credo, "~> 1.0", only: [:dev], runtime: false},
-      {:mix_test_watch, "~> 1.1", only: [:dev, :test], runtime: false}
+      {:mix_test_watch, "~> 1.1", only: [:dev, :test], runtime: false},
+      {:private, "~> 0.1", only: [:dev, :test], runtime: false},
+      {:tz, "~> 0.26", only: [:dev, :test]}
     ]
   end
 
diff --git a/test/crontab/date_helper_test.exs b/test/crontab/date_helper_test.exs
index f6eb7bc..b1e3d92 100644
--- a/test/crontab/date_helper_test.exs
+++ b/test/crontab/date_helper_test.exs
@@ -4,10 +4,71 @@ defmodule Crontab.DateHelperTest do
   use ExUnit.Case, async: true
 
   doctest Crontab.DateHelper
+  alias Crontab.DateHelper
 
   describe "inc_month/1" do
     test "does not jump over month" do
-      assert Crontab.DateHelper.inc_month(~N[2019-05-31 23:00:00]) == ~N[2019-06-01 23:00:00]
+      assert DateHelper.inc_month(~N[2019-05-31 23:00:00]) == ~N[2019-06-01 23:00:00]
+    end
+  end
+
+  describe "add/3 on NaiveDateTime" do
+    test "one day to day before NY DST starts" do
+      date = ~N[2024-03-09 12:34:56]
+      assert DateHelper.add(date, 1, :day) == ~N[2024-03-10 12:34:56]
+    end
+  end
+
+  describe "add/3 on DateTime UTC" do
+    test "one day to day before NY DST starts" do
+      date = ~U[2024-03-09 12:34:56Z]
+      assert DateHelper.add(date, 1, :day) == ~U[2024-03-10 12:34:56Z]
+    end
+  end
+
+  describe "add/3 on DateTime NYT" do
+    test "one day to day before NY DST starts" do
+      day_before = DateTime.from_naive!(~N[2024-03-09 12:34:56], "America/New_York")
+      expected = DateTime.from_naive!(~N[2024-03-10 12:34:56], "America/New_York")
+
+      assert DateHelper.add(day_before, 1, :day) == expected
+    end
+
+    test "one day to day before NY DST ends" do
+      day_before = DateTime.from_naive!(~N[2024-11-02 12:34:56], "America/New_York")
+      expected = DateTime.from_naive!(~N[2024-11-03 12:34:56], "America/New_York")
+
+      assert DateHelper.add(day_before, 1, :day) == expected
+    end
+
+    for {unit, time} <- [{:second, ~T[03:00:00]}, {:minute, ~T[03:00:59]}, {:hour, ~T[03:59:59]}] do
+      test "one #{unit} to one second before NY DST starts" do
+        one_sec_before = DateTime.from_naive!(~N[2024-03-10 01:59:59], "America/New_York")
+        expected = DateTime.new!(~D[2024-03-10], unquote(Macro.escape(time)), "America/New_York")
+
+        assert DateHelper.add(one_sec_before, 1, unquote(unit)) == expected
+      end
+    end
+
+    # , {:minute, ~T[01:00:59]}, {:hour, ~T[01:59:59]}] do
+    for {unit, hour, minute, second} <- [{:second, 1, 0, 0}, {:minute, 1, 0, 59}, {:hour, 1, 59, 59}] do
+      test "one #{unit} to one second before NY DST ends" do
+        one_sec_before = DateTime.from_naive!(~N[2024-11-03 00:59:59], "America/New_York")
+
+        # 'cos 1:00:00 to 1:59:00 can be represented as timezones for EDT and EST,
+        # so "work backwards" by getting the EST time from 2:00 onwards then minus 1 hour
+        two_plus = Time.new!(unquote(hour) + 1, unquote(minute), unquote(second))
+
+        expected =
+          DateTime.new!(~D[2024-11-03], two_plus, "America/New_York")
+          |> DateTime.add(-1, :hour)
+
+        assert DateHelper.add(one_sec_before, 1, unquote(unit)) == expected
+      end
+    end
+
+    setup do
+      Calendar.put_time_zone_database(Tz.TimeZoneDatabase)
     end
   end
 end

From 22b21bd25cabf6f82ee52640f5a4045443c38bf5 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Mon, 12 Feb 2024 23:38:08 +0800
Subject: [PATCH 05/15] Fix formatting issues

---
 test/crontab/date_helper_test.exs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/test/crontab/date_helper_test.exs b/test/crontab/date_helper_test.exs
index b1e3d92..dc2c014 100644
--- a/test/crontab/date_helper_test.exs
+++ b/test/crontab/date_helper_test.exs
@@ -51,7 +51,11 @@ defmodule Crontab.DateHelperTest do
     end
 
     # , {:minute, ~T[01:00:59]}, {:hour, ~T[01:59:59]}] do
-    for {unit, hour, minute, second} <- [{:second, 1, 0, 0}, {:minute, 1, 0, 59}, {:hour, 1, 59, 59}] do
+    for {unit, hour, minute, second} <- [
+          {:second, 1, 0, 0},
+          {:minute, 1, 0, 59},
+          {:hour, 1, 59, 59}
+        ] do
       test "one #{unit} to one second before NY DST ends" do
         one_sec_before = DateTime.from_naive!(~N[2024-11-03 00:59:59], "America/New_York")
 

From b71ead253ffb822785c6256e5158556a437b9327 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 00:08:03 +0800
Subject: [PATCH 06/15] Use DateTime.from_naive/2 to determine ambiguity

---
 lib/crontab/date_helper.ex        | 19 ++++---------------
 test/crontab/date_helper_test.exs |  1 -
 2 files changed, 4 insertions(+), 16 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index f2d98d6..1c3ecee 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -309,21 +309,10 @@ defmodule Crontab.DateHelper do
         false ->
           candidate
 
-        true ->
-          adj_plus_1h = DateTime.add(adjusted, 1, :hour)
-
-          case adj_plus_1h.std_offset == adjusted.std_offset do
-            true ->
-              adjusted
-
-            _ ->
-              # the one hour at end of daylight savings with ambiguous timezone
-              # return datetime with the standard (not daylight savings) timezone
-              %DateTime{
-                adjusted
-                | std_offset: adj_plus_1h.std_offset,
-                  zone_abbr: adj_plus_1h.zone_abbr
-              }
+        _ ->
+          case DateTime.from_naive(DateTime.to_naive(adjusted), adjusted.time_zone) do
+            {:ambiguous, _, target} -> target
+            {:ok, target} -> target
           end
       end
     end
diff --git a/test/crontab/date_helper_test.exs b/test/crontab/date_helper_test.exs
index dc2c014..93694ad 100644
--- a/test/crontab/date_helper_test.exs
+++ b/test/crontab/date_helper_test.exs
@@ -50,7 +50,6 @@ defmodule Crontab.DateHelperTest do
       end
     end
 
-    # , {:minute, ~T[01:00:59]}, {:hour, ~T[01:59:59]}] do
     for {unit, hour, minute, second} <- [
           {:second, 1, 0, 0},
           {:minute, 1, 0, 59},

From 1fbaaf98dffbd174de29c8e913967e956191d224 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 00:11:10 +0800
Subject: [PATCH 07/15] Remove private as dep

---
 lib/crontab/date_helper.ex | 31 ++++++++++++++-----------------
 mix.exs                    |  1 -
 2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index 1c3ecee..b5f3a8c 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -1,6 +1,4 @@
 defmodule Crontab.DateHelper do
-  use Private
-
   @moduledoc false
 
   @type unit :: :year | :month | :day | :hour | :minute | :second | :microsecond
@@ -297,24 +295,23 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  private do
-    def add(datetime = %NaiveDateTime{}, amt, unit), do: NaiveDateTime.add(datetime, amt, unit)
+  @doc false
+  def add(datetime = %NaiveDateTime{}, amt, unit), do: NaiveDateTime.add(datetime, amt, unit)
 
-    def add(datetime = %DateTime{}, amt, unit) do
-      candidate = DateTime.add(datetime, amt, unit)
-      adjustment = datetime.std_offset - candidate.std_offset
-      adjusted = DateTime.add(candidate, adjustment, :second)
+  def add(datetime = %DateTime{}, amt, unit) do
+    candidate = DateTime.add(datetime, amt, unit)
+    adjustment = datetime.std_offset - candidate.std_offset
+    adjusted = DateTime.add(candidate, adjustment, :second)
 
-      case adjusted.std_offset == candidate.std_offset do
-        false ->
-          candidate
+    case adjusted.std_offset == candidate.std_offset do
+      false ->
+        candidate
 
-        _ ->
-          case DateTime.from_naive(DateTime.to_naive(adjusted), adjusted.time_zone) do
-            {:ambiguous, _, target} -> target
-            {:ok, target} -> target
-          end
-      end
+      _ ->
+        case DateTime.from_naive(DateTime.to_naive(adjusted), adjusted.time_zone) do
+          {:ambiguous, _, target} -> target
+          {:ok, target} -> target
+        end
     end
   end
 end
diff --git a/mix.exs b/mix.exs
index 627b4ff..5ed6d02 100644
--- a/mix.exs
+++ b/mix.exs
@@ -45,7 +45,6 @@ defmodule Crontab.Mixfile do
       {:dialyxir, "~> 1.0", only: [:dev], runtime: false},
       {:credo, "~> 1.0", only: [:dev], runtime: false},
       {:mix_test_watch, "~> 1.1", only: [:dev, :test], runtime: false},
-      {:private, "~> 0.1", only: [:dev, :test], runtime: false},
       {:tz, "~> 0.26", only: [:dev, :test]}
     ]
   end

From 7d4a869d8e92b4f98f2e3b505057df265d7d119f Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 00:16:36 +0800
Subject: [PATCH 08/15] Reinstate date type in DateChecker

---
 lib/crontab/date_checker.ex | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/crontab/date_checker.ex b/lib/crontab/date_checker.ex
index ef0a4c2..8e85819 100644
--- a/lib/crontab/date_checker.ex
+++ b/lib/crontab/date_checker.ex
@@ -7,6 +7,8 @@ defmodule Crontab.DateChecker do
 
   alias Crontab.DateHelper
 
+  @type date :: NaiveDateTime.t() | DateTime.t()
+
   @doc """
   Check a condition list against a given date.
 

From 3fbafe8e0aa9f4684006e51e52bde8e63bdcc933 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 12:57:32 +0800
Subject: [PATCH 09/15] Replace all DateHelper.date with DateChecker.date in
 date_checker

---
 lib/crontab/date_checker.ex | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/crontab/date_checker.ex b/lib/crontab/date_checker.ex
index 8e85819..e87990c 100644
--- a/lib/crontab/date_checker.ex
+++ b/lib/crontab/date_checker.ex
@@ -27,7 +27,7 @@ defmodule Crontab.DateChecker do
       true
 
   """
-  @spec matches_date?(cron_expression :: CronExpression.t(), date :: DateHelper.date()) ::
+  @spec matches_date?(cron_expression :: CronExpression.t(), date :: date) ::
           boolean | no_return
   def matches_date?(cron_expression_or_condition_list, date)
 
@@ -42,7 +42,7 @@ defmodule Crontab.DateChecker do
 
   @spec matches_date?(
           condition_list :: CronExpression.condition_list(),
-          date :: DateHelper.date()
+          date :: date
         ) :: boolean
   def matches_date?([], _), do: true
 
@@ -65,7 +65,7 @@ defmodule Crontab.DateChecker do
   @spec matches_date?(
           interval :: CronExpression.interval(),
           condition_list :: CronExpression.condition_list(),
-          date :: DateHelper.date()
+          date :: date
         ) :: boolean
   def matches_date?(_, [:* | _], _), do: true
   def matches_date?(_, [], _), do: false
@@ -84,7 +84,7 @@ defmodule Crontab.DateChecker do
           interval :: CronExpression.interval(),
           values :: [CronExpression.time_unit()],
           condition :: CronExpression.value(),
-          date :: DateHelper.date()
+          date :: date
         ) :: boolean
   defp matches_specific_date?(_, [], _, _), do: false
   defp matches_specific_date?(_, _, :*, _), do: true
@@ -175,7 +175,7 @@ defmodule Crontab.DateChecker do
     end
   end
 
-  @spec get_interval_value(interval :: CronExpression.interval(), date :: DateHelper.date()) :: [
+  @spec get_interval_value(interval :: CronExpression.interval(), date :: date) :: [
           CronExpression.time_unit()
         ]
   defp get_interval_value(:second, %{second: second}), do: [second]

From 76552ed1808d0731be4c1b86169f4003e67a8c43 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 13:28:07 +0800
Subject: [PATCH 10/15] Change to using if, instead of case, in
 date_helper.add/3

---
 lib/crontab/date_helper.ex | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index b5f3a8c..96bdc79 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -303,15 +303,13 @@ defmodule Crontab.DateHelper do
     adjustment = datetime.std_offset - candidate.std_offset
     adjusted = DateTime.add(candidate, adjustment, :second)
 
-    case adjusted.std_offset == candidate.std_offset do
-      false ->
+    if adjusted.std_offset != candidate.std_offset do
         candidate
-
-      _ ->
-        case DateTime.from_naive(DateTime.to_naive(adjusted), adjusted.time_zone) do
-          {:ambiguous, _, target} -> target
-          {:ok, target} -> target
-        end
+    else
+      case DateTime.from_naive(DateTime.to_naive(adjusted), adjusted.time_zone) do
+        {:ambiguous, _, target} -> target
+        {:ok, target} -> target
+      end
     end
   end
 end

From 238aafcddf1ce8b6ffe3b624bb75098176bf676a Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 14:11:52 +0800
Subject: [PATCH 11/15] Fix inc_year/1 and dec_year/1 in date_helper

---
 lib/crontab/date_helper.ex        | 35 ++++++++++++--------
 test/crontab/date_helper_test.exs | 54 +++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+), 14 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index 96bdc79..f29fb9a 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -136,14 +136,22 @@ defmodule Crontab.DateHelper do
   ### Examples:
 
       iex> Crontab.DateHelper.inc_year(~N[2016-03-14 01:45:45.123])
-      ~N[2017-03-15 01:45:45.123]
+      ~N[2017-03-14 01:45:45.123]
 
       iex> Crontab.DateHelper.inc_year(~U[2016-03-14 01:45:45.123Z])
-      ~U[2017-03-15 01:45:45.123Z]
+      ~U[2017-03-14 01:45:45.123Z]
 
   """
   @spec inc_year(date) :: date when date: date
-  def inc_year(date), do: add(date, days_in_year(date), :day)
+  def inc_year(date = %{month: 2, day: 29}), do: add(date, 365, :day)
+
+  def inc_year(date = %{month: month}) do
+    candidate = add(date, 365, :day)
+    date_leap_year_before_mar? = Date.leap_year?(date) and month < 3
+    candidate_leap_year_after_feb? = Date.leap_year?(candidate) and month > 2
+    adjustment = if candidate_leap_year_after_feb? or date_leap_year_before_mar?, do: 1, else: 0
+    add(candidate, adjustment, :day)
+  end
 
   @doc """
   Decrement Year
@@ -158,7 +166,15 @@ defmodule Crontab.DateHelper do
 
   """
   @spec dec_year(date) :: date when date: date
-  def dec_year(date), do: add(date, -days_in_year(date), :day)
+  def dec_year(date = %{month: 2, day: 29}), do: add(date, -366, :day)
+
+  def dec_year(date = %{month: month}) do
+    candidate = add(date, -365, :day)
+    date_leap_year_after_mar? = Date.leap_year?(date) and month > 2
+    candidate_leap_year_before_feb? = Date.leap_year?(candidate) and month < 3
+    adjustment = if date_leap_year_after_mar? or candidate_leap_year_before_feb?, do: -1, else: 0
+    add(candidate, adjustment, :day)
+  end
 
   @doc """
   Increment Month
@@ -286,15 +302,6 @@ defmodule Crontab.DateHelper do
     end
   end
 
-  defp days_in_year(%{year: year}) do
-    Date.new!(year, 1, 1)
-    |> Date.leap_year?()
-    |> case do
-      true -> 366
-      false -> 365
-    end
-  end
-
   @doc false
   def add(datetime = %NaiveDateTime{}, amt, unit), do: NaiveDateTime.add(datetime, amt, unit)
 
@@ -304,7 +311,7 @@ defmodule Crontab.DateHelper do
     adjusted = DateTime.add(candidate, adjustment, :second)
 
     if adjusted.std_offset != candidate.std_offset do
-        candidate
+      candidate
     else
       case DateTime.from_naive(DateTime.to_naive(adjusted), adjusted.time_zone) do
         {:ambiguous, _, target} -> target
diff --git a/test/crontab/date_helper_test.exs b/test/crontab/date_helper_test.exs
index 93694ad..58eed24 100644
--- a/test/crontab/date_helper_test.exs
+++ b/test/crontab/date_helper_test.exs
@@ -12,6 +12,60 @@ defmodule Crontab.DateHelperTest do
     end
   end
 
+  describe "dec_year/1" do
+    test "non-leap year back to leap year at end feb" do
+      given = ~N[2025-02-28 00:00:00]
+      assert DateHelper.dec_year(given) == ~N[2024-02-28 00:00:00]
+    end
+
+    test "leap year back to non-leap year at end feb" do
+      given = ~N[2024-02-29 00:00:00]
+      assert DateHelper.dec_year(given) == ~N[2023-02-28 00:00:00]
+    end
+
+    test "non-leap year back to leap year at start mar" do
+      given = ~N[2025-03-01 00:00:00]
+      assert DateHelper.dec_year(given) == ~N[2024-03-01 00:00:00]
+    end
+
+    test "leap year back to non-leap year at start mar" do
+      given = ~N[2024-03-01 00:00:00]
+      assert DateHelper.dec_year(given) == ~N[2023-03-01 00:00:00]
+    end
+
+    test "non-leap year back to non-leap year" do
+      given = ~N[2026-03-01 00:00:00]
+      assert DateHelper.dec_year(given) == ~N[2025-03-01 00:00:00]
+    end
+  end
+
+  describe "inc_year/1" do
+    test "non-leap year to leap year at end feb" do
+      given = ~N[2023-02-28 00:00:00]
+      assert DateHelper.inc_year(given) == ~N[2024-02-28 00:00:00]
+    end
+
+    test "leap year to non-leap year at end feb" do
+      given = ~N[2024-02-29 00:00:00]
+      assert DateHelper.inc_year(given) == ~N[2025-02-28 00:00:00]
+    end
+
+    test "non-leap year to leap year at start mar" do
+      given = ~N[2023-03-01 00:00:00]
+      assert DateHelper.inc_year(given) == ~N[2024-03-01 00:00:00]
+    end
+
+    test "leap year to non-leap year at start mar" do
+      given = ~N[2024-03-01 00:00:00]
+      assert DateHelper.inc_year(given) == ~N[2025-03-01 00:00:00]
+    end
+
+    test "non-leap year to non-leap year" do
+      given = ~N[2025-03-01 00:00:00]
+      assert DateHelper.inc_year(given) == ~N[2026-03-01 00:00:00]
+    end
+  end
+
   describe "add/3 on NaiveDateTime" do
     test "one day to day before NY DST starts" do
       date = ~N[2024-03-09 12:34:56]

From d669fa22beb6e9f251ae4c0c03adfe8d8769c66a Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 14:15:18 +0800
Subject: [PATCH 12/15] Move time zone database setup to config.exs

---
 config/config.exs                 | 3 +++
 test/crontab/date_helper_test.exs | 4 ----
 2 files changed, 3 insertions(+), 4 deletions(-)
 create mode 100644 config/config.exs

diff --git a/config/config.exs b/config/config.exs
new file mode 100644
index 0000000..8a05082
--- /dev/null
+++ b/config/config.exs
@@ -0,0 +1,3 @@
+import Config
+
+config :elixir, :time_zone_database, Tz.TimeZoneDatabase
diff --git a/test/crontab/date_helper_test.exs b/test/crontab/date_helper_test.exs
index 58eed24..e91b4f2 100644
--- a/test/crontab/date_helper_test.exs
+++ b/test/crontab/date_helper_test.exs
@@ -123,9 +123,5 @@ defmodule Crontab.DateHelperTest do
         assert DateHelper.add(one_sec_before, 1, unquote(unit)) == expected
       end
     end
-
-    setup do
-      Calendar.put_time_zone_database(Tz.TimeZoneDatabase)
-    end
   end
 end

From f6b023157ce8c4eadc5204a45fad218ad816219c Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 14:19:31 +0800
Subject: [PATCH 13/15] Replace all :calendar.day_of_the_week with
 Date.day_of_week in date_helper

---
 lib/crontab/date_helper.ex | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index f29fb9a..295e385 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -116,8 +116,8 @@ defmodule Crontab.DateHelper do
 
   """
   @spec next_weekday_to(date :: date) :: Calendar.day()
-  def next_weekday_to(date = %{year: year, month: month, day: day}) do
-    weekday = :calendar.day_of_the_week(year, month, day)
+  def next_weekday_to(date) do
+    weekday = Date.day_of_week(date)
     next_day = add(date, 1, :day)
     previous_day = add(date, -1, :day)
 
@@ -276,16 +276,14 @@ defmodule Crontab.DateHelper do
           boolean
   defp nth_weekday(date, _, 0, :start), do: add(date, -1, :day).day
 
-  defp nth_weekday(date = %{year: year, month: month, day: day}, weekday, n, :start) do
-    modifier = if :calendar.day_of_the_week(year, month, day) == weekday, do: n - 1, else: n
+  defp nth_weekday(date, weekday, n, :start) do
+    modifier = if Date.day_of_week(date) == weekday, do: n - 1, else: n
     nth_weekday(add(date, 1, :day), weekday, modifier, :start)
   end
 
   @spec last_weekday_of_month(date :: date(), position :: :end) :: Calendar.day()
-  defp last_weekday_of_month(date = %{year: year, month: month, day: day}, :end) do
-    weekday = :calendar.day_of_the_week(year, month, day)
-
-    if weekday > 5 do
+  defp last_weekday_of_month(date = %{day: day}, :end) do
+    if Date.day_of_week(date) > 5 do
       last_weekday_of_month(add(date, -1, :day), :end)
     else
       day
@@ -294,8 +292,8 @@ defmodule Crontab.DateHelper do
 
   @spec last_weekday(date :: date, weekday :: Calendar.day_of_week(), position :: :end) ::
           Calendar.day()
-  defp last_weekday(date = %{year: year, month: month, day: day}, weekday, :end) do
-    if :calendar.day_of_the_week(year, month, day) == weekday do
+  defp last_weekday(date = %{day: day}, weekday, :end) do
+    if Date.day_of_week(date) == weekday do
       day
     else
       last_weekday(add(date, -1, :day), weekday, :end)

From fed56e91d6fb6290c43c6c14bfa5d60ed3bac856 Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 14:33:15 +0800
Subject: [PATCH 14/15] Simplify DateHelper.dec_month/1

---
 lib/crontab/date_helper.ex | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index 295e385..97b23d8 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -214,20 +214,12 @@ defmodule Crontab.DateHelper do
   """
   @spec dec_month(date) :: date when date: date
   def dec_month(date = %{year: year, month: month, day: day}) do
-    days_in_last_month =
-      Date.new!(year, month, day)
-      |> day_in_last_month
-      |> Date.days_in_month()
-
+    days_in_last_month = Date.new!(year, month, 1) |> Date.add(-1) |> Date.days_in_month()
     add(date, -(day + max(days_in_last_month - day, 0)), :day)
   end
 
-  defp day_in_last_month(start_date), do: day_in_last_month(start_date, start_date)
-
-  defp day_in_last_month(date = %Date{month: month}, start_date = %Date{month: month}),
-    do: date |> Date.add(-1) |> day_in_last_month(start_date)
-
-  defp day_in_last_month(date, _start_date), do: date
+  # defp day_in_last_month(%{year: year, month: month}),
+  # do: Date.new!(year, month, 1) |> Date.add(-1)
 
   @spec _beginning_of(date, [{unit, {any, any}}]) :: date when date: date
   defp _beginning_of(date, [{unit, {lower, _}} | tail]) do

From 733cc1ba75865a08dc284e343c79aa49a3abdc2f Mon Sep 17 00:00:00 2001
From: shaolang <shaolang@ymail.com>
Date: Tue, 13 Feb 2024 14:51:57 +0800
Subject: [PATCH 15/15] Address lingering issues from code review

---
 lib/crontab/date_helper.ex | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/lib/crontab/date_helper.ex b/lib/crontab/date_helper.ex
index 97b23d8..2834b74 100644
--- a/lib/crontab/date_helper.ex
+++ b/lib/crontab/date_helper.ex
@@ -218,9 +218,6 @@ defmodule Crontab.DateHelper do
     add(date, -(day + max(days_in_last_month - day, 0)), :day)
   end
 
-  # defp day_in_last_month(%{year: year, month: month}),
-  # do: Date.new!(year, month, 1) |> Date.add(-1)
-
   @spec _beginning_of(date, [{unit, {any, any}}]) :: date when date: date
   defp _beginning_of(date, [{unit, {lower, _}} | tail]) do
     _beginning_of(Map.put(date, unit, lower), tail)
@@ -229,11 +226,8 @@ defmodule Crontab.DateHelper do
   defp _beginning_of(date, []), do: date
 
   @spec _end_of(date, [{unit, {any, any}}]) :: date when date: date
-  defp _end_of(date = %{year: year, month: month, day: day}, [{unit, {_, :end_of_month}} | tail]) do
-    upper =
-      Date.new!(year, month, day)
-      |> Date.days_in_month()
-
+  defp _end_of(date, [{unit, {_, :end_of_month}} | tail]) do
+    upper = Date.days_in_month(date)
     _end_of(Map.put(date, unit, upper), tail)
   end