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#
#   http://www.apache.org/licenses/LICENSE-2.0
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import logging
from datetime import datetime, timedelta, timezone as dt_timezone
from typing import Iterator

from croniter import croniter
from pytz import timezone as pytz_timezone, UnknownTimeZoneError

from superset import app

logger = logging.getLogger(__name__)


def cron_schedule_window(cron: str, timezone: str) -> Iterator[datetime]:
    window_size = app.config["ALERT_REPORTS_CRON_WINDOW_SIZE"]
    # create a time-aware datetime in utc
    time_now = datetime.now(tz=dt_timezone.utc)
    try:
        tz = pytz_timezone(timezone)
    except UnknownTimeZoneError:
        # fallback to default timezone
        tz = pytz_timezone("UTC")
        logger.warning("Timezone %s was invalid. Falling back to 'UTC'", timezone)
    utc = pytz_timezone("UTC")
    # convert the current time to the user's local time for comparison
    time_now = time_now.astimezone(tz)
    start_at = time_now - timedelta(seconds=1)
    stop_at = time_now + timedelta(seconds=window_size)
    crons = croniter(cron, start_at)
    for schedule in crons.all_next(datetime):
        if schedule >= stop_at:
            break
        # convert schedule back to utc
        yield schedule.astimezone(utc).replace(tzinfo=None)