Add serializer to response wrapper

It can be useful, when the response fully or partially need to be stored
in a database in a JSON serialized form.

From python 3.8, the `_unwrap` method could be replaced with
using singledispatchmethod.

checkout_sdk/checkout_response.py

@@ -1,3 +1,7 @@
+from collections.abc import Iterable, Mapping
+from inspect import isfunction, ismethod
+
+
 class ResponseWrapper:
 
     def __init__(self, http_metadata=None, data=None):
@@ -21,3 +25,77 @@ def _wrap(self, value):
     @staticmethod
     def _is_collection(value):
         return isinstance(value, (tuple, list, set, frozenset))
+
+    def dict(self):
+        """
+        Serializes the instance to a dictionary recursively.
+
+        The result shall only contain JSON compatible data structures.
+
+        Circular references shall be replaced with representations of appropriate
+        JSON references (https://json-spec.readthedocs.io/reference.html).
+        """
+        return self._unwrap_object(self, cache={}, path=['#'])
+
+    @staticmethod
+    def _cache(method):
+        def decorated_method(cls, data, cache, path):
+            if id(data) in cache:
+                for ref_path in cache[id(data)]:
+                    if path[:len(ref_path)] == ref_path:
+                        return {'$ref': '/'.join(ref_path)}
+
+                cache[id(data)].append(path)
+
+            else:
+                cache[id(data)] = [path]
+
+            return method(cls, data, cache, path)
+
+        return decorated_method
+
+    @classmethod
+    @_cache
+    def _unwrap_object(cls, data, cache, path):
+        return {
+            key: cls._unwrap(attr, cache, path + [key])
+            for key in dir(data)
+            if not key.startswith('__')
+            and not cls._is_function(attr := getattr(data, key))
+        }
+
+    @classmethod
+    def _unwrap(cls, data, cache, path):
+        if isinstance(data, (str, int, float, bool, type(None))):
+            return data
+
+        elif isinstance(data, Mapping):
+            return cls._unwrap_mapping(data, cache, path)
+
+        elif isinstance(data, Iterable):
+            return cls._unwrap_iterable(data, cache, path)
+
+        else:
+            return cls._unwrap_object(data, cache, path)
+
+    @classmethod
+    @_cache
+    def _unwrap_mapping(cls, data: Mapping, cache, path):
+        return {
+            key: cls._unwrap(value, cache, path + [key])
+            for key, value in data.items()
+            if not cls._is_function(value)
+        }
+
+    @classmethod
+    @_cache
+    def _unwrap_iterable(cls, data: Iterable, cache, path):
+        return [
+            cls._unwrap(value, cache, path + [str(idx)])
+            for idx, value in enumerate(data)
+            if not cls._is_function(value)
+        ]
+
+    @staticmethod
+    def _is_function(data):
+        return isfunction(data) or ismethod(data)

tests/checkout_response_test.py

@@ -0,0 +1,214 @@
+from checkout_sdk.checkout_response import ResponseWrapper
+
+
+def test_serialize_atomic_types():
+    unwrapped_data = {
+        'str_attr': 'attr-value',
+        'int_attr': 1234,
+        'float_attr': 56.78,
+        'bool_attr': True,
+        'none_attr': None,
+    }
+
+    wrapped_data = ResponseWrapper(data=unwrapped_data)
+
+    assert wrapped_data.dict() == unwrapped_data
+
+
+def test_serialize_object():
+    class ObjAttr:
+        str_attr_2 = 'attr-value-2'
+        int_attr = 1234
+        float_attr = 56.78
+        bool_attr = True
+        none_attr = None
+
+        def callable_attr(self):
+            pass
+
+    wrapped_data = ResponseWrapper(
+        data={
+            'str_attr_1': 'attr-value-1',
+            'obj_attr': ObjAttr(),
+        }
+    )
+
+    assert isinstance(wrapped_data.obj_attr, ObjAttr)
+
+    assert wrapped_data.dict() == {
+        'str_attr_1': 'attr-value-1',
+        'obj_attr': {
+            'str_attr_2': 'attr-value-2',
+            'int_attr': 1234,
+            'float_attr': 56.78,
+            'bool_attr': True,
+            'none_attr': None,
+        },
+    }
+
+
+def test_serialize_nested_objects():
+    unwrapped_data = {
+        'str_attr_1': 'attr-value-1',
+        'int_attr_1': 123,
+        'float_attr_1': 89.1,
+
+        'obj_attr_1': {
+            'str_attr_2': 'attr-value-2',
+            'int_attr_2': 456,
+            'float_attr_2': 91.2,
+
+            'obj_attr_2': {
+                'str_attr_3': 'attr-value-3',
+                'int_attr_3': 789,
+                'float_attr_3': 12.3,
+            }
+        }
+    }
+
+    wrapped_data = ResponseWrapper(data=unwrapped_data)
+
+    assert isinstance(wrapped_data.obj_attr_1, ResponseWrapper)
+    assert isinstance(wrapped_data.obj_attr_1.obj_attr_2, ResponseWrapper)
+
+    assert wrapped_data.dict() == unwrapped_data
+
+
+def test_serialize_mapping():
+    unwrapped_data = {
+        'str_attr_1': 'attr-value-1',
+        'int_attr_1': 123,
+        'float_attr_1': 45.6,
+
+        'mapping_attr': {
+            'str_attr_2': 'attr-value-2',
+            'obj_attr': {
+                'str_attr_3': 'attr-value-3'
+            },
+        },
+    }
+
+    wrapped_data = ResponseWrapper(data=unwrapped_data)
+
+    isinstance(wrapped_data.mapping_attr.obj_attr, ResponseWrapper)
+
+    mapping = unwrapped_data['mapping_attr'].copy()
+    mapping['obj_attr'] = wrapped_data.mapping_attr.obj_attr
+    mapping['callable_attr'] = lambda: None
+    wrapped_data.mapping_attr = mapping
+
+    assert wrapped_data.dict() == unwrapped_data
+
+
+def test_serialize_iterable():
+    unwrapped_data = {
+        'str_attr_1': 'attr-value-1',
+        'int_attr_1': 123,
+        'float_attr_1': 45.6,
+
+        'iterable_attr': [
+            'list-item-1',
+            {
+                'str_attr_2': 'attr-value-2'
+            },
+        ],
+    }
+
+    wrapped_data = ResponseWrapper(data=unwrapped_data)
+
+    assert isinstance(wrapped_data.iterable_attr, list)
+    assert isinstance(wrapped_data.iterable_attr[1], ResponseWrapper)
+
+    wrapped_data.iterable_attr.append(lambda: None)
+
+    assert wrapped_data.dict() == unwrapped_data
+
+
+def test_serialize_list_from_any_iterables():
+    unwrapped_data = {
+        'tuple_attr': (
+            'tuple-item-1',
+            'tuple-item-2',
+            12.34,
+        ),
+        'set_attr': {
+            'set-item-1',
+            'set-item-2',
+            56.78,
+        },
+    }
+
+    wrapped_data = ResponseWrapper(data=unwrapped_data)
+
+    assert isinstance(wrapped_data.tuple_attr, tuple)
+    assert isinstance(wrapped_data.set_attr, set)
+
+    serialized_data = wrapped_data.dict()
+
+    assert isinstance(serialized_data['tuple_attr'], list)
+    assert isinstance(serialized_data['set_attr'], list)
+
+    assert tuple(serialized_data['tuple_attr']) == unwrapped_data['tuple_attr']
+    assert set(serialized_data['set_attr']) == unwrapped_data['set_attr']
+
+
+def test_serialize_circular_references():
+    unwrapped_data = {
+        'str_attr': 'attr-value',
+        'iterable_attr_1': [
+            0,
+            1,
+            2,
+            {
+                'obj_attr': {
+                    'iterable_attr_2': [3, 4],
+                },
+            },
+        ],
+        'iterable_attr_3': [5, 6],
+        'iterable_attr_4': [7, 8],
+        'iterable_attr_5': [9, 0],
+    }
+    unwrapped_data['iterable_attr_1'][3]['obj_attr']['circular_ref'] = \
+        unwrapped_data['iterable_attr_1']
+
+    unwrapped_data['iterable_attr_1'][3]['obj_attr']['forward_ref'] = \
+        unwrapped_data['iterable_attr_3']
+
+    unwrapped_data['iterable_attr_1'][3]['obj_attr']['iterable_attr_2'][1] = \
+        unwrapped_data['iterable_attr_1'][3]
+
+    unwrapped_data['iterable_attr_4'][0] = unwrapped_data['iterable_attr_5']
+    unwrapped_data['iterable_attr_5'][1] = unwrapped_data['iterable_attr_4']
+
+    wrapped_data = ResponseWrapper(http_metadata=unwrapped_data)
+
+    assert wrapped_data.dict() == {
+        'http_metadata': {
+            'str_attr': 'attr-value',
+            'iterable_attr_1': [
+                0,
+                1,
+                2,
+                {
+                    'obj_attr': {
+                        'iterable_attr_2': [
+                            3,
+                            {'$ref': '#/http_metadata/iterable_attr_1/3'}
+                        ],
+                        'circular_ref': {'$ref': '#/http_metadata/iterable_attr_1'},
+                        'forward_ref': [5, 6],
+                    },
+                },
+            ],
+            'iterable_attr_3': [5, 6],
+            'iterable_attr_4': [
+                [9, {'$ref': '#/http_metadata/iterable_attr_4'}],
+                8,
+            ],
+            'iterable_attr_5': [
+                9,
+                [{'$ref': '#/http_metadata/iterable_attr_5'}, 8],
+            ],
+        },
+    }