Add _IslamicMabimsLunar calendar class for MABIMS crescent visibility criteria

holidays/calendars/__init__.py

@@ -18,7 +18,7 @@
 from holidays.calendars.gregorian import GREGORIAN_CALENDAR
 from holidays.calendars.hebrew import _HebrewLunisolar
 from holidays.calendars.hindu import _CustomHinduHolidays, _HinduLunisolar
-from holidays.calendars.islamic import _CustomIslamicHolidays, _IslamicLunar
+from holidays.calendars.islamic import _CustomIslamicHolidays, _IslamicLunar, _IslamicMabimsLunar
 from holidays.calendars.julian import JULIAN_CALENDAR
 from holidays.calendars.julian_revised import JULIAN_REVISED_CALENDAR
 from holidays.calendars.mongolian import _CustomMongolianHolidays, _MongolianLunisolar

holidays/calendars/islamic.py

@@ -998,6 +998,9 @@ class _IslamicLunar:
         2077: (OCT, 27),
     }
 
+    EID_AL_FITR_DATES_CONFIRMED_YEARS = (2001, 2026)
+    EID_AL_ADHA_DATES_CONFIRMED_YEARS = (2001, 2026)
+
     EID_AL_FITR_DATES = {
         1925: (APR, 24),
         1926: (APR, 14),
@@ -4264,3 +4267,79 @@ def tasua_dates(self, year: int) -> Iterable[tuple[date, bool]]:
 
 class _CustomIslamicHolidays(_CustomCalendar, _IslamicLunar):
     pass
+
+
+class _IslamicMabimsLunar(_CustomCalendar, _IslamicLunar):
+    """Islamic calendar based on MABIMS crescent visibility criteria.
+
+    Used by Brunei Darussalam, Indonesia, Malaysia, and Singapore.
+    Dates primarily follow Singapore's MUIS (Majlis Ugama Islam Singapura)
+    astronomical calculations (Hisab) based on the MABIMS 2021 criteria:
+    - Moon altitude >= 3 degrees
+    - Moon elongation >= 6.4 degrees
+
+    References:
+        * <https://www.muis.gov.sg/resources/islamic-calendar/>
+        * <https://www.muslim.sg/articles/ramadan-countdown-unity-in-diversity>
+    """
+
+    EID_AL_FITR_DATES_CONFIRMED_YEARS = (2001, 2026)
+    EID_AL_ADHA_DATES_CONFIRMED_YEARS = (2001, 2026)
+
+    EID_AL_FITR_DATES = {
+        2001: (DEC, 16),
+        2002: (DEC, 6),
+        2003: (NOV, 25),
+        2004: (NOV, 14),
+        2005: (NOV, 3),
+        2006: (OCT, 24),
+        2007: (OCT, 13),
+        2008: (OCT, 1),
+        2009: (SEP, 20),
+        2010: (SEP, 10),
+        2011: (AUG, 30),
+        2012: (AUG, 19),
+        2013: (AUG, 8),
+        2014: (JUL, 28),
+        2015: (JUL, 17),
+        2016: (JUL, 6),
+        2017: (JUN, 25),
+        2018: (JUN, 15),
+        2019: (JUN, 5),
+        2020: (MAY, 24),
+        2021: (MAY, 13),
+        2022: (MAY, 3),
+        2023: (APR, 22),
+        2024: (APR, 10),
+        2025: (MAR, 31),
+        2026: (MAR, 21),
+    }
+
+    EID_AL_ADHA_DATES = {
+        2001: (MAR, 6),
+        2002: (FEB, 23),
+        2003: (FEB, 12),
+        2004: (FEB, 1),
+        2005: (JAN, 21),
+        2006: ((JAN, 10), (DEC, 31)),
+        2007: (DEC, 20),
+        2008: (DEC, 8),
+        2009: (NOV, 27),
+        2010: (NOV, 17),
+        2011: (NOV, 6),
+        2012: (OCT, 26),
+        2013: (OCT, 15),
+        2014: (OCT, 5),
+        2015: (SEP, 24),
+        2016: (SEP, 12),
+        2017: (SEP, 1),
+        2018: (AUG, 22),
+        2019: (AUG, 11),
+        2020: (JUL, 31),
+        2021: (JUL, 20),
+        2022: (JUL, 10),
+        2023: (JUN, 29),
+        2024: (JUN, 17),
+        2025: (JUN, 7),
+        2026: (MAY, 27),
+    }

tests/calendars/test_islamic.py

@@ -0,0 +1,79 @@
+#  holidays
+#  --------
+#  A fast, efficient Python library for generating country, province and state
+#  specific sets of holidays on the fly. It aims to make determining whether a
+#  specific date is a holiday as fast and flexible as possible.
+#
+#  Authors: Vacanza Team and individual contributors (see CONTRIBUTORS file)
+#           dr-prodigy <dr.prodigy.github@gmail.com> (c) 2017-2023
+#           ryanss <ryanssdev@icloud.com> (c) 2014-2017
+#  Website: https://github.com/vacanza/holidays
+#  License: MIT (see LICENSE file)
+
+import unittest
+from datetime import date
+
+from holidays.calendars.gregorian import FEB, MAR, APR, MAY, JUN, JUL, OCT, NOV, DEC
+from holidays.calendars.islamic import _IslamicMabimsLunar
+
+
+class TestIslamicMabimsLunar(unittest.TestCase):
+    def setUp(self) -> None:
+        super().setUp()
+        self.calendar = _IslamicMabimsLunar()
+
+    def test_eid_al_fitr_dates(self):
+        eid_al_fitr_dates = {
+            2001: date(2001, DEC, 16),
+            2002: date(2002, DEC, 6),
+            2003: date(2003, NOV, 25),
+            2006: date(2006, OCT, 24),
+            2019: date(2019, JUN, 5),
+            2022: date(2022, MAY, 3),
+            2023: date(2023, APR, 22),
+            2024: date(2024, APR, 10),
+            2025: date(2025, MAR, 31),
+            2026: date(2026, MAR, 21),
+        }
+        for year, expected_date in eid_al_fitr_dates.items():
+            dates = {dt: is_estimated for dt, is_estimated in self.calendar.eid_al_fitr_dates(year)}
+            self.assertIn(expected_date, dates)
+            self.assertFalse(dates[expected_date], f"Eid al-Fitr {year} should be confirmed, not estimated")
+
+    def test_eid_al_adha_dates(self):
+        eid_al_adha_dates = {
+            2001: date(2001, MAR, 6),
+            2002: date(2002, FEB, 23),
+            2006: date(2006, DEC, 31),
+            2010: date(2010, NOV, 17),
+            2014: date(2014, OCT, 5),
+            2022: date(2022, JUL, 10),
+            2023: date(2023, JUN, 29),
+            2024: date(2024, JUN, 17),
+            2025: date(2025, JUN, 7),
+            2026: date(2026, MAY, 27),
+        }
+        for year, expected_date in eid_al_adha_dates.items():
+            dates = {dt: is_estimated for dt, is_estimated in self.calendar.eid_al_adha_dates(year)}
+            self.assertIn(expected_date, dates)
+            self.assertFalse(dates[expected_date], f"Eid al-Adha {year} should be confirmed, not estimated")
+
+    def test_eid_al_adha_2006_dual_date(self):
+        """2006 has two Eid al-Adha dates - Jan 10 and Dec 31."""
+        dates = {dt for dt, _ in self.calendar.eid_al_adha_dates(2006)}
+        self.assertIn(date(2006, 1, 10), dates)
+        self.assertIn(date(2006, 12, 31), dates)
+
+    def test_fallback_to_base_outside_range(self):
+        """Years outside 2001-2026 should fall back to base _IslamicLunar dates."""
+        dates_1990 = list(self.calendar.eid_al_fitr_dates(1990))
+        dates_2030 = list(self.calendar.eid_al_fitr_dates(2030))
+        self.assertTrue(len(dates_1990) > 0)
+        self.assertTrue(len(dates_2030) > 0)
+        # Outside confirmed range should be estimated
+        for _, is_estimated in dates_1990:
+            self.assertTrue(is_estimated)
+
+
+if __name__ == "__main__":
+    unittest.main()