[GitHub] [airflow] ashb commented on a change in pull request #13930: WIP: POC of Timetable feature. Includes AbstractTimetable and CronTimetable classes.

[GitBox <gi...@apache.org>]

ashb commented on a change in pull request #13930:
URL: https://github.com/apache/airflow/pull/13930#discussion_r567834660



##########
File path: airflow/models/dag.py
##########
@@ -109,6 +110,312 @@ def get_last_dagrun(dag_id, session, include_externally_triggered=False):
     return query.first()
 
 
+class AbstractTimetable(LoggingMixin):
+    """Abstract class for Timetable."""
+
+    @abstractmethod
+    def normalized_schedule_interval(self) -> Optional[ScheduleInterval]:
+        raise NotImplementedError()
+
+    @abstractmethod
+    def is_fixed_time_schedule(self):
+        raise NotImplementedError()
+
+    @abstractmethod
+    def date_range(
+        self,
+        start_date: datetime,
+        num: Optional[int] = None,
+        end_date: Optional[datetime] = timezone.utcnow(),
+    ) -> List[datetime]:
+        raise NotImplementedError()
+
+    @abstractmethod
+    def following_schedule(self, dttm):
+        raise NotImplementedError()
+
+    @abstractmethod
+    def previous_schedule(self, dttm):
+        raise NotImplementedError()
+
+    @abstractmethod
+    def next_dagrun_info(
+        self,
+        date_last_automated_dagrun: Optional[pendulum.DateTime],
+        tasks,
+    ) -> Tuple[Optional[pendulum.DateTime], Optional[pendulum.DateTime]]:
+        raise NotImplementedError()
+
+    @abstractmethod
+    def get_run_dates(self, start_date, end_date=None):
+        raise NotImplementedError()
+
+
+class CronTimetable(AbstractTimetable):
+    """Timetable implementation for Cron."""
+
+    def __init__(
+        self,
+        schedule_interval=None,
+        timezone=None,
+        catchup=None,
+        start_date=None,
+        end_date=None,
+    ):
+        self.schedule_interval = schedule_interval
+        self.timezone = timezone
+        self.catchup = catchup
+        self.start_date = start_date
+        self.end_date = end_date
+
+    def normalized_schedule_interval(self) -> Optional[ScheduleInterval]:
+        """
+        Returns Normalized Schedule Interval. This is used internally by the Scheduler to
+        schedule DAGs.
+
+        1. Converts Cron Preset to a Cron Expression (e.g ``@monthly`` to ``0 0 1 * *``)
+        2. If Schedule Interval is "@once" return "None"
+        3. If not (1) or (2) returns schedule_interval
+        """
+        if isinstance(self.schedule_interval, str) and self.schedule_interval in cron_presets:

Review comment:
       Backport what?




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