provide the timezone so that the UI doesn't have to

this will also ensure that UI doesn't use a different front end library
that will yield different results than the underlying Python code

awx/api/serializers.py

@@ -4511,9 +4511,14 @@ class SchedulePreviewSerializer(BaseSerializer):
 class ScheduleSerializer(LaunchConfigurationBaseSerializer, SchedulePreviewSerializer):
     show_capabilities = ['edit', 'delete']
 
+    timezone = serializers.SerializerMethodField()
+
     class Meta:
         model = Schedule
-        fields = ('*', 'unified_job_template', 'enabled', 'dtstart', 'dtend', 'rrule', 'next_run',)
+        fields = ('*', 'unified_job_template', 'enabled', 'dtstart', 'dtend', 'rrule', 'next_run', 'timezone',)
+
+    def get_timezone(self, obj):
+        return obj.timezone
 
     def get_related(self, obj):
         res = super(ScheduleSerializer, self).get_related(obj)

awx/api/views.py

@@ -745,11 +745,7 @@ class ScheduleZoneInfo(APIView):
     swagger_topic = 'System Configuration'
 
     def get(self, request):
-        from dateutil.zoneinfo import get_zonefile_instance
-        return Response([
-            {'name': zone}
-            for zone in sorted(get_zonefile_instance().zones)
-        ])
+        return Response(Schedule.get_zoneinfo())
 
 
 class LaunchConfigCredentialsBase(SubListAttachDetachAPIView):

awx/main/models/schedules.py

@@ -4,7 +4,9 @@
 import logging
 import datetime
 import dateutil.rrule
-from dateutil.tz import datetime_exists
+from operator import itemgetter
+import dateutil.parser
+from dateutil.tz import datetime_exists, tzutc
 
 # Django
 from django.db import models
@@ -94,6 +96,33 @@ class Schedule(CommonModel, LaunchTimeConfig):
         help_text=_("The next time that the scheduled action will run.")
     )
 
+    @classmethod
+    def get_zoneinfo(self):
+        from dateutil.zoneinfo import get_zonefile_instance
+        return [
+            {'name': zone}
+            for zone in sorted(get_zonefile_instance().zones)
+        ]
+
+    @property
+    def timezone(self):
+        utc = tzutc()
+        _rrule = dateutil.rrule.rrulestr(
+            self.rrule,
+            tzinfos={x: utc for x in dateutil.parser.parserinfo().UTCZONE}
+        )
+        tzinfo = _rrule._dtstart.tzinfo
+        if tzinfo == utc:
+            return 'UTC'
+        fname = tzinfo._filename
+        all_zones = map(itemgetter('name'), Schedule.get_zoneinfo())
+        all_zones.sort(key = lambda x: -len(x))
+        for zone in all_zones:
+            if fname.endswith(zone):
+                return zone
+        logger.warn('Could not detect valid zoneinfo for {}'.format(self.rrule))
+        return ''
+
     @classmethod
     def rrulestr(cls, rrule, **kwargs):
         """

awx/main/tests/functional/models/test_schedule.py

@@ -203,3 +203,18 @@ def test_beginning_of_time(job_template):
     )
     with pytest.raises(ValueError):
         s.save()
+
+
+@pytest.mark.django_db
+@pytest.mark.parametrize('rrule, tz', [
+    ['DTSTART:20300112T210000Z RRULE:FREQ=DAILY;INTERVAL=1', 'UTC'],
+    ['DTSTART;TZID=America/New_York:20300112T210000 RRULE:FREQ=DAILY;INTERVAL=1', 'America/New_York']
+])
+def test_timezone_property(job_template, rrule, tz):
+    # ensure that really large generators don't have performance issues
+    s = Schedule(
+        name='Some Schedule',
+        rrule=rrule,
+        unified_job_template=job_template
+    )
+    assert s.timezone == tz