[COST-5793] remove croniter dependency (#5435)

Pipfile

@@ -4,7 +4,6 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-# Direct dependencies
 adal = "*"
 app-common-python = ">=0.2.3"
 azure-identity = "*"
@@ -19,7 +18,6 @@ cachetools = ">=4.1.0"
 celery = ">=5.2.2"
 ciso8601 = ">=2.1"
 confluent-kafka = ">=2.1.0"
-croniter = "*"
 Django = "~=4.2.0"
 django-cors-headers = ">=3.1"
 django-environ = ">=0.4"

koku/koku/celery.py

@@ -9,10 +9,10 @@
 from celery import Celery
 from celery import Task
 from celery.schedules import crontab
+from celery.schedules import ParseException
 from celery.signals import celeryd_after_setup
 from celery.signals import worker_process_init
 from celery.signals import worker_process_shutdown
-from croniter import croniter
 from django.conf import settings
 from kombu.exceptions import OperationalError
 
@@ -23,7 +23,6 @@
 from koku.probe_server import ProbeServer
 from koku.probe_server import start_probe_server
 
-
 LOG = logging.getLogger(__name__)
 
 
@@ -85,11 +84,16 @@ def readiness_check(self):
         self._write_response(ProbeResponse(status, msg))
 
 
-def validate_cron_expression(expresssion, default="0 * * * *"):
-    if not croniter.is_valid(expresssion):
-        print(f"Invalid report-download-schedule {expresssion}. Falling back to default {default}")
-        expresssion = default
-    return expresssion
+def validate_cron_expression(expression, default="0 * * * *"):
+    if len(expression.split(" ", 5)) != 5:
+        print(f"Invalid cron expression: {expression}. Falling back to default {default}")
+        expression = default
+    try:
+        crontab(*expression.split(" ", 5))
+    except (ValueError, ParseException) as e:
+        print(f"Invalid cron expression: {expression}. Falling back to default {default}, Error: {e}")
+        expression = default
+    return expression
 
 
 os.environ.setdefault("DJANGO_SETTINGS_MODULE", "koku.settings")
@@ -235,9 +239,10 @@ def validate_cron_expression(expresssion, default="0 * * * *"):
 @celeryd_after_setup.connect
 def wait_for_migrations(sender, instance, **kwargs):  # pragma: no cover
     """Wait for migrations to complete before completing worker startup."""
-    from .database import check_migrations
     from masu.celery.tasks import collect_queue_metrics
 
+    from .database import check_migrations
+
     httpd = start_probe_server(WorkerProbeServer)
 
     # This is a special case because check_migrations() returns three values