Fixed delay returned when a task has a start_time in the future. (#208)

When a task has a start_time in the future, the scheduler now returns
a delay that corresponds to the number of seconds from the current date
to the start_time.

This should fix issue #195, at least partially.

Author: izimobil

django_celery_beat/schedulers.py

@@ -3,6 +3,7 @@
 
 import datetime
 import logging
+import math
 
 from multiprocessing.util import Finalize
 
@@ -111,10 +112,13 @@ def is_due(self):
 
         # START DATE: only run after the `start_time`, if one exists.
         if self.model.start_time is not None:
-            if maybe_make_aware(self._default_now()) < self.model.start_time:
+            now = maybe_make_aware(self._default_now())
+            if now < self.model.start_time:
                 # The datetime is before the start date - don't run.
-                _, delay = self.schedule.is_due(self.last_run_at)
-                # use original delay for re-check
+                # send a delay to retry on start_time
+                delay = math.ceil(
+                    (self.model.start_time - now).total_seconds()
+                )
                 return schedules.schedstate(False, delay)
 
         # ONE OFF TASK: Disable one off tasks after they've ran once

t/unit/test_schedulers.py

@@ -1,5 +1,6 @@
 from __future__ import absolute_import, unicode_literals
 
+import math
 import time
 import pytest
 
@@ -151,7 +152,7 @@ def test_task_with_start_time(self):
         e2 = self.Entry(m2, app=self.app)
         isdue, delay = e2.is_due()
         assert not isdue
-        assert delay == interval
+        assert delay == math.ceil((tomorrow - right_now).total_seconds())
 
     def test_one_off_task(self):
         interval = 10