policies: rewrite cache_key to prevent wrong cache

# Conflicts:
#	passbook/core/signals.py
#	passbook/policies/engine.py
#	passbook/policies/process.py

passbook/policies/signals.py

@@ -0,0 +1,25 @@
+"""passbook policy signals"""
+from django.core.cache import cache
+from django.db.models.signals import post_save
+from django.dispatch import receiver
+from structlog import get_logger
+
+LOGGER = get_logger()
+
+
+@receiver(post_save)
+# pylint: disable=unused-argument
+def invalidate_policy_cache(sender, instance, **_):
+    """Invalidate Policy cache when policy is updated"""
+    from passbook.policies.models import Policy, PolicyBinding
+    from passbook.policies.process import cache_key
+
+    if isinstance(instance, Policy):
+        LOGGER.debug("Invalidating policy cache", policy=instance)
+        total = 0
+        for binding in PolicyBinding.objects.filter(policy=instance):
+            prefix = f"policy_{binding.policy_binding_uuid.hex}_{binding.policy.pk.hex}" + "*"
+            keys = cache.keys(prefix)
+            total += len(keys)
+            cache.delete_many(keys)
+        LOGGER.debug("Deleted keys", len=total)