policies/expression: move evaluation code into separate class

passbook/policies/expression/models.py

@@ -1,17 +1,11 @@
 """passbook expression Policy Models"""
-from django.core.exceptions import ValidationError
 from django.db import models
 from django.utils.translation import gettext as _
-from jinja2.exceptions import TemplateSyntaxError, UndefinedError
-from jinja2.nativetypes import NativeEnvironment
-from structlog import get_logger
 
 from passbook.core.models import Policy
+from passbook.policies.expression.evaluator import Evaluator
 from passbook.policies.struct import PolicyRequest, PolicyResult
 
-LOGGER = get_logger()
-NATIVE_ENVIRONMENT = NativeEnvironment()
-
 
 class ExpressionPolicy(Policy):
     """Jinja2-based Expression policy that allows Admins to write their own logic"""
@@ -22,25 +16,10 @@ class ExpressionPolicy(Policy):
 
     def passes(self, request: PolicyRequest) -> PolicyResult:
         """Evaluate and render expression. Returns PolicyResult(false) on error."""
-        try:
-            expression = NATIVE_ENVIRONMENT.from_string(self.expression)
-        except TemplateSyntaxError as exc:
-            return PolicyResult(False, str(exc))
-        try:
-            result = expression.render(request=request)
-            if isinstance(result, list) and len(result) == 2:
-                return PolicyResult(*result)
-            if result:
-                return PolicyResult(result)
-            return PolicyResult(False)
-        except UndefinedError as exc:
-            return PolicyResult(False, str(exc))
+        return Evaluator().evaluate(self.expression, request)
 
     def save(self, *args, **kwargs):
-        try:
-            NATIVE_ENVIRONMENT.from_string(self.expression)
-        except TemplateSyntaxError as exc:
-            raise ValidationError("Expression Syntax Error") from exc
+        Evaluator().validate(self.expression)
         return super().save(*args, **kwargs)
 
     class Meta: