Use an enum for DST status

Author: jepler

src/wwvb/__init__.py

@@ -323,6 +323,16 @@ def _hamming_parity(value: int) -> int:
 ]
 
 
+@enum.unique
+class DstStatus(enum.IntEnum):
+    """Constants that describe the DST status of a minute"""
+
+    DST_NOT_IN_EFFECT = 0b00
+    DST_STARTS_TODAY = 0b01
+    DST_ENDS_TODAY = 0b10
+    DST_IN_EFFECT = 0b11
+
+
 class _WWVBMinute(NamedTuple):
     """Uniquely identifies a minute of time in the WWVB system.
 
@@ -341,7 +351,7 @@ class _WWVBMinute(NamedTuple):
     min: int
     """Minute of hour"""
 
-    dst: int
+    dst: DstStatus
     """2-bit DST code """
 
     ut1: int
@@ -368,16 +378,13 @@ def __new__(  # noqa: PYI034
         days: int,
         hour: int,
         minute: int,
-        dst: int | None = None,
+        dst: DstStatus | int | None = None,
         ut1: int | None = None,
         ls: bool | None = None,
         ly: bool | None = None,
     ) -> WWVBMinute:
         """Construct a WWVBMinute"""
-        if dst is None:
-            dst = cls.get_dst(year, days)
-        if dst not in (0, 1, 2, 3):
-            raise ValueError("dst value should be 0..3")
+        dst = cls.get_dst(year, days) if dst is None else DstStatus(dst)
         if ut1 is None and ls is None:
             ut1, ls = cls._get_dut1_info(year, days)
         elif ut1 is None or ls is None:
@@ -407,13 +414,13 @@ def full_year(cls, year: int) -> int:
         return year
 
     @staticmethod
-    def get_dst(year: int, days: int) -> int:
+    def get_dst(year: int, days: int) -> DstStatus:
         """Get the 2-bit WWVB DST value for the given day"""
         d0 = datetime.datetime(year, 1, 1, tzinfo=datetime.timezone.utc) + datetime.timedelta(days - 1)
         d1 = d0 + datetime.timedelta(1)
         dst0 = isdst(d0)
         dst1 = isdst(d1)
-        return dst1 * 2 + dst0
+        return DstStatus(dst1 * 2 + dst0)
 
     def __str__(self) -> str:
         """Implement str()"""