1 files changed, 128 insertions, 0 deletions
diff --git a/pendulum/tz/zoneinfo/timezone.py b/pendulum/tz/zoneinfo/timezone.py
new file mode 100644
index 0000000..2147774
--- /dev/null
+++ b/pendulum/tz/zoneinfo/timezone.py
@@ -0,0 +1,128 @@
+from datetime import datetime
+from typing import List
+from typing import Optional
+
+from pendulum.constants import DAYS_PER_YEAR
+from pendulum.constants import SECS_PER_YEAR
+from pendulum.helpers import is_leap
+from pendulum.helpers import local_time
+from pendulum.helpers import timestamp
+from pendulum.helpers import week_day
+
+from .posix_timezone import PosixTimezone
+from .transition import Transition
+from .transition_type import TransitionType
+
+
+class Timezone:
+    def __init__(
+        self,
+        transitions,  # type: List[Transition]
+        posix_rule=None,  # type: Optional[PosixTimezone]
+        extended=True,  # type: bool
+    ):
+        self._posix_rule = posix_rule
+        self._transitions = transitions
+
+        if extended:
+            self._extends()
+
+    @property
+    def transitions(self):  # type: () -> List[Transition]
+        return self._transitions
+
+    @property
+    def posix_rule(self):
+        return self._posix_rule
+
+    def _extends(self):
+        if not self._posix_rule:
+            return
+
+        posix = self._posix_rule
+
+        if not posix.dst_abbr:
+            # std only
+            # The future specification should match the last/default transition
+            ttype = self._transitions[-1].ttype
+            if not self._check_ttype(ttype, posix.std_offset, False, posix.std_abbr):
+                raise ValueError("Posix spec does not match last transition")
+
+            return
+
+        if len(self._transitions) < 2:
+            raise ValueError("Too few transitions for POSIX spec")
+
+        # Extend the transitions for an additional 400 years
+        # using the future specification
+
+        # The future specification should match the last two transitions,
+        # and those transitions should have different is_dst flags.
+        tr0 = self._transitions[-1]
+        tr1 = self._transitions[-2]
+        tt0 = tr0.ttype
+        tt1 = tr1.ttype
+        if tt0.is_dst():
+            dst = tt0
+            std = tt1
+        else:
+            dst = tt1
+            std = tt0
+
+        self._check_ttype(dst, posix.dst_offset, True, posix.dst_abbr)
+        self._check_ttype(std, posix.std_offset, False, posix.std_abbr)
+
+        # Add the transitions to tr1 and back to tr0 for each extra year.
+        last_year = local_time(tr0.local, 0, 0)[0]
+        leap_year = is_leap(last_year)
+        jan1 = datetime(last_year, 1, 1)
+        jan1_time = timestamp(jan1)
+        jan1_weekday = week_day(jan1.year, jan1.month, jan1.day) % 7
+
+        if local_time(tr1.local, 0, 0)[0] != last_year:
+            # Add a single extra transition to align to a calendar year.
+            if tt0.is_dst():
+                pt1 = posix.dst_end
+            else:
+                pt1 = posix.dst_start
+
+            tr1_offset = pt1.trans_offset(leap_year, jan1_weekday)
+            tr = Transition(jan1_time + tr1_offset - tt0.offset, tr1.ttype, tr0)
+            tr0 = tr
+            tr1 = tr0
+            tt0 = tr0.ttype
+            tt1 = tr1.ttype
+
+        if tt0.is_dst():
+            pt1 = posix.dst_end
+            pt0 = posix.dst_start
+        else:
+            pt1 = posix.dst_start
+            pt0 = posix.dst_end
+
+        tr = tr0
+        for year in range(last_year + 1, last_year + 401):
+            jan1_time += SECS_PER_YEAR[leap_year]
+            jan1_weekday = (jan1_weekday + DAYS_PER_YEAR[leap_year]) % 7
+            leap_year = not leap_year and is_leap(year)
+
+            tr1_offset = pt1.trans_offset(leap_year, jan1_weekday)
+            tr = Transition(jan1_time + tr1_offset - tt0.offset, tt1, tr)
+            self._transitions.append(tr)
+
+            tr0_offset = pt0.trans_offset(leap_year, jan1_weekday)
+            tr = Transition(jan1_time + tr0_offset - tt1.offset, tt0, tr)
+            self._transitions.append(tr)
+
+    def _check_ttype(
+        self,
+        ttype,  # type: TransitionType
+        offset,  # type: int
+        is_dst,  # type: bool
+        abbr,  # type: str
+    ):  # type: (...) -> bool
+        return (
+            ttype.offset == offset
+            and ttype.is_dst() == is_dst
+            and ttype.abbreviation == abbr
+        )