From 3c68ba2526a43a8f4eb447238399178fcec94ec6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Germ=C3=A1n=20Larra=C3=ADn?=
 <glarrain@users.noreply.github.com>
Date: Fri, 3 May 2019 22:38:31 -0400
Subject: [PATCH] libs.mm_utils: add `validate_no_unexpected_input_fields`

---
 cl_sii/libs/mm_utils.py     | 42 +++++++++++++++++++++++++++++++++++++
 tests/test_libs_mm_utils.py | 13 ++++++++++--
 2 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/cl_sii/libs/mm_utils.py b/cl_sii/libs/mm_utils.py
index 52d33411..8f319bea 100644
--- a/cl_sii/libs/mm_utils.py
+++ b/cl_sii/libs/mm_utils.py
@@ -6,6 +6,48 @@
 import marshmallow.utils
 
 
+###############################################################################
+# validators
+###############################################################################
+
+def validate_no_unexpected_input_fields(
+    schema: marshmallow.Schema,
+    data: dict,
+    original_data: dict,
+) -> None:
+    """
+    Fail validation if there was an unexpected input field.
+
+    Usage::
+
+        class MySchema(marshmallow.Schema):
+
+            class Meta:
+                strict = True
+
+            folio = marshmallow.fields.Integer()
+
+            @marshmallow.validates_schema(pass_original=True)
+            def validate_schema(self, data: dict, original_data: dict) -> None:
+                validate_no_unexpected_input_fields(self, data, original_data)
+
+    """
+    # Original inspiration from
+    #   https://marshmallow.readthedocs.io/en/2.x-line/extending.html#validating-original-input-data
+    fields_name_or_load_from = {
+        field.name if field.load_from is None else field.load_from
+        for field_key, field in schema.fields.items()
+    }
+    unexpected_input_fields = set(original_data) - fields_name_or_load_from
+    if unexpected_input_fields:
+        raise marshmallow.ValidationError(
+            "Unexpected input field.", field_names=list(unexpected_input_fields))
+
+
+###############################################################################
+# fields
+###############################################################################
+
 class CustomMarshmallowDateField(marshmallow.fields.Field):
     """
     A formatted date string.
diff --git a/tests/test_libs_mm_utils.py b/tests/test_libs_mm_utils.py
index d1a0c8b3..6957a42c 100644
--- a/tests/test_libs_mm_utils.py
+++ b/tests/test_libs_mm_utils.py
@@ -1,10 +1,19 @@
 import unittest
 
-from cl_sii.libs.mm_utils import CustomMarshmallowDateField  # noqa: F401
+from cl_sii.libs.mm_utils import (  # noqa: F401
+    CustomMarshmallowDateField, validate_no_unexpected_input_fields,
+)
 
 
 class CustomMarshmallowDateFieldTest(unittest.TestCase):
 
     def test_x(self) -> None:
-        # TODO: implement!
+        # TODO: implement for 'CustomMarshmallowDateField'.
+        pass
+
+
+class FunctionsTest(unittest.TestCase):
+
+    def test_validate_no_unexpected_input_fields(self):
+        # TODO: implement for 'validate_no_unexpected_input_fields'.
         pass