import copy

import unittest

from functools import wraps

from unittest import mock

from django.conf import settings

from django.db import DEFAULT_DB_ALIAS, connection

from django.db.models import Func

def skipUnlessGISLookup(*gis_lookups):

    """

    Skip a test unless a database supports all of gis_lookups.

    """

    def decorator(test_func):

        @wraps(test_func)

        def skip_wrapper(*args, **kwargs):

            if any(key not in connection.ops.gis_operators for key in gis_lookups):

                raise unittest.SkipTest(

                    "Database doesn't support all the lookups: %s"

                    % ", ".join(gis_lookups)

                )

            return test_func(*args, **kwargs)

        return skip_wrapper

    return decorator

_default_db = settings.DATABASES[DEFAULT_DB_ALIAS]["ENGINE"].rsplit(".")[-1]

# MySQL spatial indices can't handle NULL geometries.

gisfield_may_be_null = _default_db != "mysql"

class FuncTestMixin:

    """Assert that Func expressions aren't mutated during their as_sql()."""

    def setUp(self):

        def as_sql_wrapper(original_as_sql):

            def inner(*args, **kwargs):

                func = original_as_sql.__self__

                # Resolve output_field before as_sql() so touching it in

                # as_sql() won't change __dict__.

                func.output_field

                __dict__original = copy.deepcopy(func.__dict__)

                result = original_as_sql(*args, **kwargs)

                msg = (

                    "%s Func was mutated during compilation." % func.__class__.__name__

                )

                self.assertEqual(func.__dict__, __dict__original, msg)

                return result

            return inner

        def __getattribute__(self, name):

            if name != vendor_impl:

                return __getattribute__original(self, name)

            try:

                as_sql = __getattribute__original(self, vendor_impl)

            except AttributeError:

                as_sql = __getattribute__original(self, "as_sql")

            return as_sql_wrapper(as_sql)

        vendor_impl = "as_" + connection.vendor

        __getattribute__original = Func.__getattribute__

        self.func_patcher = mock.patch.object(

            Func, "__getattribute__", __getattribute__

        )

        self.func_patcher.start()

        super().setUp()

    def tearDown(self):

        super().tearDown()

        self.func_patcher.stop()