from django.db import connection, models

from django.test import SimpleTestCase

from .utils import FuncTestMixin

def test_mutation(raises=True):

    def wrapper(mutation_func):

        def test(test_case_instance, *args, **kwargs):

            class TestFunc(models.Func):

                output_field = models.IntegerField()

                def __init__(self):

                    self.attribute = "initial"

                    super().__init__("initial", ["initial"])

                def as_sql(self, *args, **kwargs):

                    mutation_func(self)

                    return "", ()

            if raises:

                msg = "TestFunc Func was mutated during compilation."

                with test_case_instance.assertRaisesMessage(AssertionError, msg):

                    getattr(TestFunc(), "as_" + connection.vendor)(None, None)

            else:

                getattr(TestFunc(), "as_" + connection.vendor)(None, None)

        return test

    return wrapper

class FuncTestMixinTests(FuncTestMixin, SimpleTestCase):

    @test_mutation()

    def test_mutated_attribute(func):

        func.attribute = "mutated"

    @test_mutation()

    def test_mutated_expressions(func):

        func.source_expressions.clear()

    @test_mutation()

    def test_mutated_expression(func):

        func.source_expressions[0].name = "mutated"

    @test_mutation()

    def test_mutated_expression_deep(func):

        func.source_expressions[1].value[0] = "mutated"

    @test_mutation(raises=False)

    def test_not_mutated(func):

        pass