More consolidation of nth/last-wday functionality

- Remove _get_last_weekday_of_month and replaced it with
  _get_nth_weekday_of_month() and avoid making multiple calls to the calendar
  module when both '#' and 'L' syntax are used at the same time.
- Updated unittests for get_last_weekday_of_month() to instead simply call
  _get_nth_weekday_of_month()[-1].
- Create unit test for new function.

Note that _get_nth_weekday_of_month() is a good candidate for caching as
repeated calls to calendar add up over time, especially when evaluating
multiple cron expressions concurrently.

2 files changed, 33 insertions, 32 deletions

diff --git a/src/croniter/croniter.py b/src/croniter/croniter.py
index 17e883d..45ccaf1 100644
--- a/src/croniter/croniter.py
+++ b/src/croniter/croniter.py
@@ -394,19 +394,14 @@ class croniter(object):
 
             candidates = []
             for wday, nth in nth_weekday_of_month.items():
-                c = None
-                if nth != {"l"}:
-                    w = (wday + 6) % 7
-                    c = calendar.Calendar(w).monthdayscalendar(d.year, d.month)
-                    if c[0][0] == 0:
-                        c.pop(0)
+                c = self._get_nth_weekday_of_month(d.year, d.month, wday)
                 for n in nth:
                     if n == "l":
-                        candidate = self._get_last_weekday_of_month(d.year, d.month, wday)
+                        candidate = c[-1]
                     elif len(c) < n:
                         continue
                     else:
-                        candidate = c[n - 1][0]
+                        candidate = c[n - 1]
                     if (
                         (is_prev and candidate <= d.day) or
                         (not is_prev and d.day <= candidate)
@@ -548,21 +543,15 @@ class croniter(object):
         return (candidate - x - range_val)
 
     @staticmethod
-    def _get_last_weekday_of_month(year, month, day_of_week):
-        """ Given the year/month of timestamp, determine the last day of the
-        month which is a particular day of the week.  Calendar week starts on
-        Sunday, to match cron's day_of_week convention.
+    def _get_nth_weekday_of_month(year, month, day_of_week):
+        """ For a given year/month return a list of days in nth-day-of-month order.
+        The last weekday of the month is always [-1].
         """
-        # How expensive is this?  Easily cache by (year, month, dow)
-        day_of_week = int(day_of_week)
-        cal = calendar.Calendar(6).monthdayscalendar(year, month)
-        week = -1
-        while True:
-            day = cal[week][day_of_week]
-            if day == 0:    # 0 means absent / different month
-                week -= 1
-            else:
-                return day
+        w = (day_of_week + 6) % 7
+        c = calendar.Calendar(w).monthdayscalendar(year, month)
+        if c[0][0] == 0:
+            c.pop(0)
+        return tuple(i[0] for i in c)
 
     def is_leap(self, year):
         if year % 400 == 0 or (year % 4 == 0 and year % 100 != 0):
diff --git a/src/croniter/tests/test_croniter.py b/src/croniter/tests/test_croniter.py
index c171983..1083b62 100755
--- a/src/croniter/tests/test_croniter.py
+++ b/src/croniter/tests/test_croniter.py
@@ -1103,19 +1103,31 @@ class CroniterTest(base.TestCase):
             '2020-03-29T02:01:00+02:00',
             '2020-03-29T03:01:00+02:00'])
 
-    def test_wdom_core_simple(self):
-        f = croniter._get_last_weekday_of_month
+
+    def test_nth_wday_simple(self):
+        f = lambda y,m,w: croniter._get_nth_weekday_of_month(y,m,w)
+        sun, mon, tue, wed, thu, fri, sat = range(7)
+
+        self.assertEqual(f(2000, 1, mon), (3, 10, 17, 24, 31))
+        self.assertEqual(f(2000, 2, tue), (1, 8, 15, 22, 29)) # Leap year
+        self.assertEqual(f(2000, 3, wed), (1, 8, 15, 22, 29))
+        self.assertEqual(f(2000, 4, thu), (6, 13, 20, 27))
+        self.assertEqual(f(2000, 2, fri), (4, 11, 18, 25))
+        self.assertEqual(f(2000, 2, sat), (5, 12, 19, 26))
+
+    def test_nth_as_last_wday_simple(self):
+        f = lambda y,m,w: croniter._get_nth_weekday_of_month(y,m,w)[-1]
         sun, mon, tue, wed, thu, fri, sat = range(7)
-        self.assertEqual(f(2021, 3, sun), 28)
-        self.assertEqual(f(2035, 12, sat), 29)
-        self.assertEqual(f(2000, 1, fri), 28)
-        self.assertEqual(f(2014, 8, mon), 25)
-        self.assertEqual(f(2022, 2, tue), 22)
-        self.assertEqual(f(1999, 10, wed), 27)
-        self.assertEqual(f(2005, 7, thu), 28)
+        self.assertEqual(f(2000, 2, tue), 29)
+        self.assertEqual(f(2000, 2, sun), 27)
+        self.assertEqual(f(2000, 2, mon), 28)
+        self.assertEqual(f(2000, 2, wed), 23)
+        self.assertEqual(f(2000, 2, thu), 24)
+        self.assertEqual(f(2000, 2, fri), 25)
+        self.assertEqual(f(2000, 2, sat), 26)
 
     def test_wdom_core_leap_year(self):
-        f = croniter._get_last_weekday_of_month
+        f = lambda y,m,w: croniter._get_nth_weekday_of_month(y,m,w)[-1]
         sun, mon, tue, wed, thu, fri, sat = range(7)
         self.assertEqual(f(2000, 2, tue), 29)
         self.assertEqual(f(2000, 2, sun), 27)