import datetime

from unittest import mock

from django.db import connections

from django.db.models.sql.compiler import cursor_iter

from django.test import TestCase

from .models import Article

class QuerySetIteratorTests(TestCase):

    itersize_index_in_mock_args = 3

    @classmethod

    def setUpTestData(cls):

        Article.objects.create(name="Article 1", created=datetime.datetime.now())

        Article.objects.create(name="Article 2", created=datetime.datetime.now())

    def test_iterator_invalid_chunk_size(self):

        for size in (0, -1):

            with self.subTest(size=size):

                with self.assertRaisesMessage(

                    ValueError, "Chunk size must be strictly positive."

                ):

                    Article.objects.iterator(chunk_size=size)

    def test_default_iterator_chunk_size(self):

        qs = Article.objects.iterator()

        with mock.patch(

            "django.db.models.sql.compiler.cursor_iter", side_effect=cursor_iter

        ) as cursor_iter_mock:

            next(qs)

        self.assertEqual(cursor_iter_mock.call_count, 1)

        mock_args, _mock_kwargs = cursor_iter_mock.call_args

        self.assertEqual(mock_args[self.itersize_index_in_mock_args], 2000)

    def test_iterator_chunk_size(self):

        batch_size = 3

        qs = Article.objects.iterator(chunk_size=batch_size)

        with mock.patch(

            "django.db.models.sql.compiler.cursor_iter", side_effect=cursor_iter

        ) as cursor_iter_mock:

            next(qs)

        self.assertEqual(cursor_iter_mock.call_count, 1)

        mock_args, _mock_kwargs = cursor_iter_mock.call_args

        self.assertEqual(mock_args[self.itersize_index_in_mock_args], batch_size)

    def test_no_chunked_reads(self):

        """

        If the database backend doesn't support chunked reads, then the

        result of SQLCompiler.execute_sql() is a list.

        """

        qs = Article.objects.all()

        compiler = qs.query.get_compiler(using=qs.db)

        features = connections[qs.db].features

        with mock.patch.object(features, "can_use_chunked_reads", False):

            result = compiler.execute_sql(chunked_fetch=True)

        self.assertIsInstance(result, list)