from unittest import mock

from django.contrib.auth import get_user_model
from django.utils import timezone
from django.urls import reverse

from rest_framework import status

User = get_user_model()


class GenericAPITestCaseMixin:
    """
    Base mixin for testing one or more operations on a model.

    The specifics of each operation is not implemented here.
    Each operation has its own TestCase, which relies on methods/attributes
    defined here (some or all).

    The "real" mixins for each operation are:
    [List,Create,Retrieve,Update,Destroy]APITestCaseMixin.

    Example:

        E.g. for a creation test, your testcase should be something like:

        class MyModelCreateAPITestCase(
                CreateAPITestCaseMixin,
                GenericAPITestCaseMixin,
                APITestCase,
                ):
            ...

    Attributes:
        # General
        model (models.Model): The model class under test.
        url_label (str): Use to get the API urls of the model under test:
            - The model url is:`reverse('{url_label}-list).
                This is used by `[List,Create]APITestCaseMixin`.
                The url can also be customized by defining `get_url_model`
                method.
            - The url of a model object is: `reverse('{label}-detail')`.
                This is used by `[Retrieve,Update,Destroy]APITestCaseMixin`.
                The url can also be customized by defining `get_url_object`
                method.

        # Authentication
        user_auth (User instance): If given, this user is authenticated for
            each request sent to the API. Default to `None`.
            See section 'Authenticate requests'.
        user_auth_mapping (dict of str: User instance): Associates a user to
            authenticate for each type of API request.
            See section 'Authenticate requests'.

    Authenticate requests:
        Each real testcase call `get_user` method with a label for the
        operation under test (e.g. UpdateAPITestCaseMixin will call
        `get_user('update')`. If it returns a user, this latter is
        authenticated with `force_authenticate` method of the test client.

        The default behavior, which can be customized by replacing `get_user`
        method, is to return `user_auth` attribute/property if not None. Else,
        `user_auth_mapping[operation_type_label]` or None if key is missing.

        A basic user is created during setUp. It can be found as `user`
        attribute.

    """
    model = None
    url_label = ''

    user_auth = None
    user_auth_mapping = {}

    def setUp(self):
        """
        Prepare a test execution.

        Don't forget to call super().setUp() if you define this in subclass.
        """
        # Dict comparison can be large.
        self.maxDiff = 2000

        # This will be returned by django.utils.timezone.now thanks to the mock
        # in test methods.
        # This can be useful to check auto_now and auto_now_add fields.
        self.now = timezone.now()

        # A very basic user.
        self.user = User.objects.create_user(
            username='user', password='user',
            first_name='first', last_name='last',
        )

    def get_user(self, action):
        """
        Returns a user to authenticate for requests of type 'action'.

        Property `user_auth` has precedence over the property
        `user_auth_mapping`.

        Args:
            action (str): Operation label. See LCRUD TestCases for reserved
                labels, before setting your own if you create a new common
                operation TestCase.

        Returns:
            User instance | None:
                If None, no user should be authenticated for this request.
                Else, the returned user should be authenticated.
        """
        if self.user_auth is not None:
            return self.user_auth
        return self.user_auth_mapping.get(action)

    def get_url_model(self, *args, **kwargs):
        """
        Returns the API url for the model.

        Default to a reverse on `{url_label}-list`.

        Used by `[List,Create]APITestCaseMixin`.

        """
        return reverse(
            '{label}-list'.format(label=self.url_label),
            args=args, kwargs=kwargs,
        )

    def get_url_object(self, *args, **kwargs):
        """
        Returns the API url for a particular object of model.

        Default to a reverse on `{url_label}-detail`.

        Used by `[Retrieve,Update,Destroy]APITestCaseMixin`.

        """
        return reverse(
            '{label}-detail'.format(label=self.url_label),
            args=args, kwargs=kwargs,
        )

    def db_create(self, data):
        """
        Create a model instance in DB from data given as argument.

        `data` can define M2M fields.

        Operations:
            - Create object from non-M2M fields.
            - Link the M2M fields with `set` on the created object.

        Returns:
            The created object.
        """
        fields, m2m_fields = {}, {}
        for name, value in data.items():
            if self.model._meta.get_field(name).many_to_many:
                m2m_fields[name] = value
            else:
                fields[name] = value

        instance = self.model.objects.create(**fields)
        for name, value in m2m_fields.items():
            getattr(instance, name).set(value)

        return instance

    def get_expected_data(self, instance):
        """
        Returns the data the API should reply for the object `instance`.

        This should be the same result of the serializer used for the sent
        request.

        Must be defined by subclasses, except for DestroyAPITestCaseMixin.

        Args:
            instance (a `model` object)

        Returns:
            JSON-decoded data of this instance.

        """
        raise NotImplementedError(
            "Subclass must implement 'get_expected_data(instance)' method."
        )

    def assertInstanceEqual(self, instance, expected):
        """
        Checks if instance verifies expected.

        For each key/value pair of expected, it verifies that instance.key is
        equal to value. `assertEqual` is used, except for M2M fields where
        `assertQuerysetEqual(ordered=True, ...)` is used.

        Args:
            instance (`model` object): E.g. obtained from DB after a create
                operation.
            expected (dict): Expected data of instance.

        """
        for key, exp_value in expected.items():
            field = self.model._meta.get_field(key)
            value = getattr(instance, key)
            if field.many_to_many:
                self.assertQuerysetEqual(
                    value.all(), map(repr, exp_value),
                    ordered=False,
                )
            else:
                self.assertEqual(value, exp_value)

    @property
    def instances_data(self):
        """
        Instances data of the model which will be created if necessary.

        For example, ListAPITestCaseMixin uses these before sending the list
        request.

        The first is also used, if `instance_data` is not re-defined, for RUD
        operations.

        """
        raise NotImplementedError(
            "Property or attribute 'instances_data' must be declared by "
            "subclass."
        )

    @property
    def instance_data(self):
        """
        Data of a single instance of model.

        For example, this data is used to create the instance of model to apply
        RUD operations.

        Default to the first item of the `instances_data` property.

        """
        return self.instances_data[0]


class ListAPITestCaseMixin:
    """
    Mixin to test the "List" API request of a model.

    Has hooks to check the returned objects and their ordering.

    Authentication:
        This operation use the label 'list'.
        See `GenericAPITestCaseMixin`#`Authenticate requests` for further
        informations.

    Attributes:
        list_ordering (list of str | str): The ordering of objects that should
            be respected by the API response.
            Same format as the ordering Meta attribute of models, e.g.
            '-created_at' or ['-event', 'created_at'].
            Ordering on '__' fields are currently not supported.

    Todo:
        * Allow '__' in ordering.
        * Support pages. Currently we expect returned objects are on a single
            page.

    """
    list_ordering = []

    @property
    def list_expected(self):
        """
        Model instances the API should returned.

        Default to all objects of models.
        Eventually sorted according to `list_ordering` attribute.

        """
        qs = self.model.objects.all()
        if self.list_ordering:
            qs = qs.order_by(self.list_ordering)
        return qs

    @property
    def list_expected_count(self):
        """
        Number of objects the API should returned.

        Default to the length of expected returned objects.
        """
        return len(self.list_expected)

    @property
    def list_expected_ordering(self):
        """
        Use this to get expected ordering, instead of relying directly on the
        `list_ordering`, if you write subclasses.
        """
        if isinstance(self.list_ordering, (tuple, list)):
            return self.list_ordering
        return [self.list_ordering]

    def assertOrdered(self, results, ordering):
        """
        Check `results` are sorted according to `ordering`.

        Attributes:
            results (list of model instances)
            ordering (list of fields as str)

        """
        _ordering = [
            (f[1:], True) if f.startswith('-') else (f, False)
            for f in ordering
        ]

        it = iter(results)

        previous = next(it)

        for current in it:
            self._assertOrdered(previous, current, _ordering)
            previous = current

    def _assertOrdered(self, d1, d2, ordering):
        if not ordering:
            return True

        field, desc = ordering[0]

        v1, v2 = d1[field], d2[field]

        if v1 == v2:
            self._assertOrdered(v1, v2, ordering[1:])
        elif desc:
            self.assertGreater(v1, v2, msg=(
                "Ordering on '%s' (DESC) is not respected for the following "
                "objects.\n- First: %r.\n- Second: %r."
                % (field, d1, d2)
            ))
        else:
            self.assertLess(v1, v2, msg=(
                "Ordering on '%s' (ASC) is not respected for the following "
                "objects:\n- First: %r.\n- Second: %r."
                % (field, d1, d2)
            ))

    @mock.patch('django.utils.timezone.now')
    def test_list(self, mock_now):
        """
        The test.

        Preparation:
            - Create instances from `instances_data` property.
            - Optionally, authenticate client.

        Execution:
            - HTTP GET request on model url.

        Check:
            - Response status code: 200.
            - The base response: count (pages not supported).
            - Results (serialized instances) are formatted as expected and
                their ordering.

        """
        mock_now.return_value = self.now

        # Setup database.

        for data in self.instances_data:
            self.db_create(data)

        # Call API to get instances list.
        user = self.get_user('list')
        if user:
            self.client.force_authenticate(user)

        r = self.client.get(self.get_url_model())

        # Check API response.
        self.assertEqual(r.status_code, status.HTTP_200_OK)

        base_response = {
            'count': self.list_expected_count,
            'previous': None,
            'next': None,
        }
        self.assertDictContainsSubset(base_response, r.data)

        results = r.data['results']

        # Check API response ordering.
        self.assertOrdered(results, self.list_expected_ordering)

        # Check API response data.
        for result, instance in zip(results, self.list_expected):
            self.assertDictEqual(result, self.get_expected_data(instance))


class CreateAPITestCaseMixin:
    """
    Mixin to test the "Create" API request of a model.

    Authentication:
        This operation use the label 'create'.
        See `GenericAPITestCaseMixin`#`Authenticate requests` for further
        informations.

    Note:
        The request is sent assuming the payload is JSON.

    """

    @property
    def create_data(self):
        """
        Payload of the create request sent to the API.
        """
        raise NotImplementedError(
            "Subclass must define a 'create_data' attribute/property. This is "
            "the payload of the POST request to the model url."
        )

    @property
    def create_expected(self):
        """
        Data of model instance which should be created.
        """
        raise NotImplementedError(
            "Subclass must define a create_expected attribute/property. It is "
            "a dict-like object whose value should be equal to the key "
            "attribute of the created instance."
        )

    @mock.patch('django.utils.timezone.now')
    def test_create(self, mock_now):
        """
        The test.

        Preparation:
            - Optionally, authenticate client.

        Execution:
            - HTTP POST request on model url. Payload from `create_data`.

        Check:
            - Response status code: 201.
            - Instance has been created in DB.
            - Instance created is as expected (check with `create_expected`).
            - Instance is correctly serialized (in response' data).

        """
        mock_now.return_value = self.now

        # Call API to create an instance of model.
        user = self.get_user('create')
        if user:
            self.client.force_authenticate(user)

        r = self.client.post(self.get_url_model(), self.create_data)

        # Check database.
        instances = self.model.objects.all()
        self.assertEqual(len(instances), 1)

        instance = instances[0]
        self.assertInstanceEqual(instance, self.create_expected)

        # Check API response.
        self.assertEqual(r.status_code, status.HTTP_201_CREATED)
        self.assertDictEqual(r.data, self.get_expected_data(instance))


class RetrieveAPITestCaseMixin:
    """
    Mixin to test the "Retrieve" API request of a model object.

    Authentication:
        This operation use the label 'retrieve'.
        See `GenericAPITestCaseMixin`#`Authenticate requests` for further
        informations.

    """

    @mock.patch('django.utils.timezone.now')
    def test_retrieve(self, mock_now):
        """
        The test.

        Preparation:
            - Create a model instance from `instance_data` property.
            - Optionally, authenticate client.

        Execution:
            - Get url of the object with its pk.
            - HTTP GET request on this url.

        Check:
            - Response status code: 200.
            - Instance is correctly serialized (in response' data).

        """
        mock_now.return_value = self.now

        # Setup database.
        data = self.instance_data
        instance = self.db_create(data)

        # Call API to retrieve the event data.
        user = self.get_user('retrieve')
        if user:
            self.client.force_authenticate(user)

        r = self.client.get(self.get_url_object(pk=1))

        # Check API response.
        self.assertEqual(r.status_code, status.HTTP_200_OK)
        self.assertDictEqual(r.data, self.get_expected_data(instance))


class UpdateAPITestCaseMixin:
    """
    Mixin to test the "Update" API request of a model.

    Authentication:
        This operation use the label 'update'.
        See `GenericAPITestCaseMixin`#`Authenticate requests` for further
        informations.

    Notes:
        * A single test using partial update / PATCH HTTP method is written.
        * The request is sent assuming the payload is JSON.

    Todo:
        * Add test for update / PUT HTTP method.

    """

    @property
    def update_data(self):
        """
        Payload of the update request sent to the API.
        """
        raise NotImplementedError(
            "Subclass must define a update_data attribute/property. This is "
            "the payload of the PUT request to the instance url."
        )

    @property
    def update_expected(self):
        """
        Data of model instance which should be updated.
        """
        raise NotImplementedError(
            "Subclass must define a update_expected attribute/property. It is "
            "a dict-like object whose value should be equal to the key "
            "attribute of the updated instance."
        )

    @mock.patch('django.utils.timezone.now')
    def test_update(self, mock_now):
        """
        The test.

        Preparation:
            - Create a model instance from `instance_data` property.
            - Optionally, authenticate client.

        Execution:
            - Get url of the object with its pk.
            - HTTP PATCH request on this url. Payload from `update_data`.

        Check:
            - Response status code: 200.
            - No instance has been created or deleted in DB.
            - Updated instance is as expected (check with `update_expected`).
            - Instance is correctly serialized (in response' data).

        """
        mock_now.return_value = self.now

        # Setup database.
        data = self.instance_data
        instance = self.db_create(data)

        # Call API to update the event.
        user = self.get_user('update')
        if user:
            self.client.force_authenticate(user)

        r = self.client.patch(self.get_url_object(pk=1), self.update_data)

        # Check database.
        instances = self.model.objects.all()
        self.assertEqual(len(instances), 1)

        instance.refresh_from_db()
        self.assertInstanceEqual(instance, self.update_expected)

        # Check API response.
        self.assertEqual(r.status_code, status.HTTP_200_OK)
        self.assertDictEqual(r.data, self.get_expected_data(instance))


class DestroyAPITestCaseMixin:
    """
    Mixin to test the "Destroy" API request of a model.

    Authentication:
        This operation use the label 'destroy'.
        See `GenericAPITestCaseMixin`#`Authenticate requests` for further
        informations.

    """

    @mock.patch('django.utils.timezone.now')
    def test_destroy(self, mock_now):
        """
        The test.

        Preparation:
            - Create a model instance from `instance_data` property.
            - Optionally, authenticate client.

        Execution:
            - Get url of the object with its pk.
            - HTTP DELETE request on this url.

        Check:
            - Response status code: 204.
            - Instance is no longer present in DB.

        """
        mock_now.return_value = self.now

        # Setup database.
        data = self.instance_data
        instance = self.db_create(data)

        # Call API to update the event.
        user = self.get_user('destroy')
        if user:
            self.client.force_authenticate(user)

        r = self.client.delete(self.get_url_object(pk=1))

        # Check database.
        instances = self.model.objects.all()
        self.assertEqual(len(instances), 0)

        with self.assertRaises(self.model.DoesNotExist):
            instance.refresh_from_db()

        # Check API response.
        self.assertEqual(r.status_code, status.HTTP_204_NO_CONTENT)
        self.assertIsNone(r.data)


class ModelAPITestCaseMixin(
        ListAPITestCaseMixin, CreateAPITestCaseMixin, RetrieveAPITestCaseMixin,
        UpdateAPITestCaseMixin, DestroyAPITestCaseMixin,
        GenericAPITestCaseMixin,
        ):
    """
    Tests all LCRUD operations on a model.

    See general docs in GenericAPITestCaseMixin.
    See docs for a specific operation in [Operation]APITestCaseMixin.

    Example:

        class EventAPITestCase(ModelAPITestCaseMixin, APITestCase):
            model = Event
            ...

            @property
            def create_data(self):
                ...

            @property
            def create_expected(self):
                ...

            ...

        If you want to run only a few operations, consider using
        specific-mixins individually. You can still have something as
        `EventAPITestCaseMixin` to provide common atributes/properties/methods.

    """
    pass