Allowing logical expression on condition statements

requirements.txt

@@ -36,3 +36,4 @@ tqdm==4.32.1
 twine==1.13.0
 urllib3==1.25.3
 webencodings==0.5.1
+pyparsing==2.4.7

rest_access_policy/access_policy.py

@@ -3,9 +3,12 @@
 
 from django.conf import settings
 from django.db.models import prefetch_related_objects
-from rest_access_policy import AccessPolicyException
+from pyparsing import infixNotation, opAssoc
 from rest_framework import permissions
 
+from rest_access_policy import AccessPolicyException
+from .parsing import ConditionOperand, boolOperand, BoolNot, BoolAnd, BoolOr
+
 
 class AccessPolicy(permissions.BasePermission):
     statements = []
@@ -157,7 +160,17 @@ def _get_statements_matching_context_conditions(
             fails = 0
 
             for condition in statement["condition"]:
-                passed = self._check_condition(condition, request, view, action)
+
+                ConditionOperand.check_condition_fn = lambda _, cond: self._check_condition(cond, request, view, action)
+                boolOperand.setParseAction(ConditionOperand)
+
+                boolExpr = infixNotation(boolOperand, [
+                    ("not", 1, opAssoc.RIGHT, BoolNot),
+                    ("and", 2, opAssoc.LEFT, BoolAnd),
+                    ("or", 2, opAssoc.LEFT, BoolOr),
+                ])
+
+                passed = bool(boolExpr.parseString(condition)[0])
 
                 if not passed:
                     fails += 1

rest_access_policy/parsing.py

@@ -0,0 +1,67 @@
+from pyparsing import Keyword, Word, alphanums
+
+
+class ConditionOperand(object):
+    check_condition_fn = None
+
+    def __init__(self, t):
+        self.label = t[0]
+
+        assert self.check_condition_fn is not None, 'The check_condition_fn should should be set'
+        assert callable(self.check_condition_fn), 'The check_condition_fn should should be callable'
+
+        self.value = self.check_condition_fn(t[0])
+
+    def __bool__(self):
+        return self.value
+
+    def __str__(self):
+        return self.label
+
+    __repr__ = __str__
+    __nonzero__ = __bool__
+
+
+class BoolBinOp(object):
+    def __init__(self, t):
+        self.args = t[0][0::2]
+
+    def __str__(self):
+        sep = " %s " % self.reprsymbol
+        return "(" + sep.join(map(str, self.args)) + ")"
+
+    def __bool__(self):
+        return self.evalop(bool(a) for a in self.args)
+
+    __nonzero__ = __bool__
+    __repr__ = __str__
+
+
+class BoolAnd(BoolBinOp):
+    reprsymbol = '&'
+    evalop = all
+
+
+class BoolOr(BoolBinOp):
+    reprsymbol = '|'
+    evalop = any
+
+
+class BoolNot(object):
+    def __init__(self, t):
+        self.arg = t[0][1]
+
+    def __bool__(self):
+        v = bool(self.arg)
+        return not v
+
+    def __str__(self):
+        return "~" + str(self.arg)
+
+    __repr__ = __str__
+    __nonzero__ = __bool__
+
+
+TRUE = Keyword("True")
+FALSE = Keyword("False")
+boolOperand = TRUE | FALSE | Word(alphanums + '_:.', max=256)