feat: add Morrow.fromordinal

morrow/constants.mojo

@@ -1,7 +1,12 @@
-from ._py import py_dt_datetime
-
 # todo: hardcode for tmp
 alias _MAX_TIMESTAMP: Int = 32503737600
 alias MAX_TIMESTAMP = _MAX_TIMESTAMP
 alias MAX_TIMESTAMP_MS = MAX_TIMESTAMP * 1000
 alias MAX_TIMESTAMP_US = MAX_TIMESTAMP * 1_000_000
+
+alias _DAYS_IN_MONTH = VariadicList[Int](
+    -1, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+)
+alias _DAYS_BEFORE_MONTH = VariadicList[Int](
+    -1, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
+)  # -1 is a placeholder for indexing purposes.

morrow/morrow.mojo

@@ -1,9 +1,15 @@
 from ._py import py_dt_datetime
-from .util import normalize_timestamp, num2str, _ymd2ord
+from .util import normalize_timestamp, num2str, _ymd2ord, _days_before_year
 from ._libc import c_gettimeofday, c_localtime, c_gmtime, c_strptime
 from ._libc import CTimeval, CTm
 from .timezone import TimeZone
 from .timedelta import TimeDelta
+from .constants import _DAYS_BEFORE_MONTH, _DAYS_IN_MONTH
+
+
+alias _DI400Y = 146097  # number of days in 400 years
+alias _DI100Y = 36524  #    "    "   "   " 100   "
+alias _DI4Y = 1461  #    "    "   "   "   4   "
 
 
 @value
@@ -38,17 +44,17 @@ struct Morrow:
         self.TimeZone = TimeZone
 
     @staticmethod
-    fn now() raises -> Morrow:
+    fn now() raises -> Self:
         let t = c_gettimeofday()
-        return Morrow._fromtimestamp(t, False)
+        return Self._fromtimestamp(t, False)
 
     @staticmethod
-    fn utcnow() raises -> Morrow:
+    fn utcnow() raises -> Self:
         let t = c_gettimeofday()
-        return Morrow._fromtimestamp(t, True)
+        return Self._fromtimestamp(t, True)
 
     @staticmethod
-    fn _fromtimestamp(t: CTimeval, utc: Bool) raises -> Morrow:
+    fn _fromtimestamp(t: CTimeval, utc: Bool) raises -> Self:
         let tm: CTm
         let tz: TimeZone
         if utc:
@@ -58,7 +64,7 @@ struct Morrow:
             tm = c_localtime(t.tv_sec)
             tz = TimeZone(tm.tm_gmtoff.to_int(), "local")
 
-        let result = Morrow(
+        let result = Self(
             tm.tm_year.to_int() + 1900,
             tm.tm_mon.to_int() + 1,
             tm.tm_mday.to_int(),
@@ -71,21 +77,21 @@ struct Morrow:
         return result
 
     @staticmethod
-    fn fromtimestamp(timestamp: Float64) raises -> Morrow:
+    fn fromtimestamp(timestamp: Float64) raises -> Self:
         let timestamp_ = normalize_timestamp(timestamp)
         let t = CTimeval(timestamp_.to_int())
-        return Morrow._fromtimestamp(t, False)
+        return Self._fromtimestamp(t, False)
 
     @staticmethod
-    fn utcfromtimestamp(timestamp: Float64) raises -> Morrow:
+    fn utcfromtimestamp(timestamp: Float64) raises -> Self:
         let timestamp_ = normalize_timestamp(timestamp)
         let t = CTimeval(timestamp_.to_int())
-        return Morrow._fromtimestamp(t, True)
+        return Self._fromtimestamp(t, True)
 
     @staticmethod
     fn strptime(
         date_str: String, fmt: String, tzinfo: TimeZone = TimeZone.none()
-    ) raises -> Morrow:
+    ) raises -> Self:
         """
         Create a Morrow instance from a date string and format,
         in the style of ``datetime.strptime``.  Optionally replaces the parsed TimeZone.
@@ -97,7 +103,7 @@ struct Morrow:
         """
         let tm = c_strptime(date_str, fmt)
         let tz = TimeZone(tm.tm_gmtoff.to_int()) if tzinfo.is_none() else tzinfo
-        return Morrow(
+        return Self(
             tm.tm_year.to_int() + 1900,
             tm.tm_mon.to_int() + 1,
             tm.tm_mday.to_int(),
@@ -109,7 +115,7 @@ struct Morrow:
         )
 
     @staticmethod
-    fn strptime(date_str: String, fmt: String, tz_str: String) raises -> Morrow:
+    fn strptime(date_str: String, fmt: String, tz_str: String) raises -> Self:
         """
         Create a Morrow instance by time_zone_string with utc format
 
@@ -119,7 +125,7 @@ struct Morrow:
             <Morrow [2019-01-20T15:49:10+08:00]>
         """
         let tzinfo = TimeZone.from_utc(tz_str)
-        return Morrow.strptime(date_str, fmt, tzinfo)
+        return Self.strptime(date_str, fmt, tzinfo)
 
     fn isoformat(
         self, sep: String = "T", timespec: StringLiteral = "auto"
@@ -193,10 +199,85 @@ struct Morrow:
         """
         return _ymd2ord(self.year, self.month, self.day)
 
+    @staticmethod
+    fn fromordinal(ordinal: Int) raises -> Self:
+        """Construct a Morrow from a proleptic Gregorian ordinal.
+
+        January 1 of year 1 is day 1.  Only the year, month and day are
+        non-zero in the result.
+        """
+        # n is a 1-based index, starting at 1-Jan-1.  The pattern of leap years
+        # repeats exactly every 400 years.  The basic strategy is to find the
+        # closest 400-year boundary at or before n, then work with the offset
+        # from that boundary to n.  Life is much clearer if we subtract 1 from
+        # n first -- then the values of n at 400-year boundaries are exactly
+        # those divisible by _DI400Y:
+        #
+        #     D  M   Y            n              n-1
+        #     -- --- ----        ----------     ----------------
+        #     31 Dec -400        -_DI400Y       -_DI400Y -1
+        #      1 Jan -399         -_DI400Y +1   -_DI400Y      400-year boundary
+        #     ...
+        #     30 Dec  000        -1             -2
+        #     31 Dec  000         0             -1
+        #      1 Jan  001         1              0            400-year boundary
+        #      2 Jan  001         2              1
+        #      3 Jan  001         3              2
+        #     ...
+        #     31 Dec  400         _DI400Y        _DI400Y -1
+        #      1 Jan  401         _DI400Y +1     _DI400Y      400-year boundary
+        var n = ordinal
+        n -= 1
+        let n400 = n // _DI400Y
+        n = n % _DI400Y
+        var year = n400 * 400 + 1  # ..., -399, 1, 401, ...
+
+        # Now n is the (non-negative) offset, in days, from January 1 of year, to
+        # the desired date.  Now compute how many 100-year cycles precede n.
+        # Note that it's possible for n100 to equal 4!  In that case 4 full
+        # 100-year cycles precede the desired day, which implies the desired
+        # day is December 31 at the end of a 400-year cycle.
+        let n100 = n // _DI100Y
+        n = n % _DI100Y
+
+        # Now compute how many 4-year cycles precede it.
+        let n4 = n // _DI4Y
+        n = n % _DI4Y
+
+        # And now how many single years.  Again n1 can be 4, and again meaning
+        # that the desired day is December 31 at the end of the 4-year cycle.
+        let n1 = n // 365
+        n = n % 365
+
+        year += n100 * 100 + n4 * 4 + n1
+        if n1 == 4 or n100 == 4:
+            return Self(year - 1, 12, 31)
+
+        # Now the year is correct, and n is the offset from January 1.  We find
+        # the month via an estimate that's either exact or one too large.
+        let leapyear = n1 == 3 and (n4 != 24 or n100 == 3)
+        var month = (n + 50) >> 5
+        var preceding: Int
+        if month > 2 and leapyear:
+            preceding = _DAYS_BEFORE_MONTH[month] + 1
+        else:
+            preceding = _DAYS_BEFORE_MONTH[month]
+        if preceding > n:  # estimate is too large
+            month -= 1
+            if month == 2 and leapyear:
+                preceding -= (_DAYS_BEFORE_MONTH[month] + 1)
+            else:
+                preceding -= _DAYS_BEFORE_MONTH[month]
+        n -= preceding
+
+        # Now the year and month are correct, and n is the offset from the
+        # start of that month:  we're done!
+        return Self(year, month, n+1)
+
     fn __str__(self) raises -> String:
         return self.isoformat()
 
-    fn __sub__(self, other: Morrow) raises -> TimeDelta:
+    fn __sub__(self, other: Self) raises -> TimeDelta:
         let days1 = self.toordinal()
         let days2 = other.toordinal()
         let secs1 = self.second + self.minute * 60 + self.hour * 3600

morrow/util.mojo

@@ -1,12 +1,5 @@
 from .constants import MAX_TIMESTAMP, MAX_TIMESTAMP_MS, MAX_TIMESTAMP_US
-
-
-alias _DAYS_IN_MONTH = VariadicList[Int](
-    -1, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
-)
-alias _DAYS_BEFORE_MONTH = VariadicList[Int](
-    -1, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
-)  # -1 is a placeholder for indexing purposes.
+from .constants import _DAYS_IN_MONTH, _DAYS_BEFORE_MONTH
 
 
 fn _is_leap(year: Int) -> Bool:

test.mojo

@@ -78,6 +78,17 @@ def test_strptime():
     m = Morrow.strptime("2023-10-18 15:49:10", "%Y-%m-%d %H:%M:%S", "+09:00")
     assert_equal(m.__str__(), "2023-10-18T15:49:10.000000+09:00")
 
+def test_ordinal():
+    print("Running test_ordinal()")
+    m = Morrow(2023, 10, 1)
+    o = m.toordinal()
+    assert_equal(o, 738794)
+
+    m2 = Morrow.fromordinal(o)
+    assert_equal(m2.year, 2023)
+    assert_equal(m.month, 10)
+    assert_equal(m.day, 1)
+
 
 def test_sub():
     print("Running test_sub()")