from unittest import mock

from django.contrib.postgres.indexes import (
    BloomIndex, BrinIndex, BTreeIndex, GinIndex, GistIndex, HashIndex, OpClass,
    SpGistIndex,
)
from django.db import NotSupportedError, connection
from django.db.models import CharField, F, Index, Q
from django.db.models.functions import Cast, Collate, Length, Lower
from django.test import skipUnlessDBFeature
from django.test.utils import modify_settings, register_lookup

from . import PostgreSQLSimpleTestCase, PostgreSQLTestCase
from .fields import SearchVector, SearchVectorField
from .models import CharFieldModel, IntegerArrayModel, Scene, TextFieldModel


class IndexTestMixin:

    def test_name_auto_generation(self):
        index = self.index_class(fields=['field'])
        index.set_name_with_model(CharFieldModel)
        self.assertRegex(index.name, r'postgres_te_field_[0-9a-f]{6}_%s' % self.index_class.suffix)

    def test_deconstruction_no_customization(self):
        index = self.index_class(fields=['title'], name='test_title_%s' % self.index_class.suffix)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.%s' % self.index_class.__name__)
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {'fields': ['title'], 'name': 'test_title_%s' % self.index_class.suffix})

    def test_deconstruction_with_expressions_no_customization(self):
        name = f'test_title_{self.index_class.suffix}'
        index = self.index_class(Lower('title'), name=name)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(
            path,
            f'django.contrib.postgres.indexes.{self.index_class.__name__}',
        )
        self.assertEqual(args, (Lower('title'),))
        self.assertEqual(kwargs, {'name': name})


class BloomIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = BloomIndex

    def test_suffix(self):
        self.assertEqual(BloomIndex.suffix, 'bloom')

    def test_deconstruction(self):
        index = BloomIndex(fields=['title'], name='test_bloom', length=80, columns=[4])
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.BloomIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {
            'fields': ['title'],
            'name': 'test_bloom',
            'length': 80,
            'columns': [4],
        })

    def test_invalid_fields(self):
        msg = 'Bloom indexes support a maximum of 32 fields.'
        with self.assertRaisesMessage(ValueError, msg):
            BloomIndex(fields=['title'] * 33, name='test_bloom')

    def test_invalid_columns(self):
        msg = 'BloomIndex.columns must be a list or tuple.'
        with self.assertRaisesMessage(ValueError, msg):
            BloomIndex(fields=['title'], name='test_bloom', columns='x')
        msg = 'BloomIndex.columns cannot have more values than fields.'
        with self.assertRaisesMessage(ValueError, msg):
            BloomIndex(fields=['title'], name='test_bloom', columns=[4, 3])

    def test_invalid_columns_value(self):
        msg = 'BloomIndex.columns must contain integers from 1 to 4095.'
        for length in (0, 4096):
            with self.subTest(length), self.assertRaisesMessage(ValueError, msg):
                BloomIndex(fields=['title'], name='test_bloom', columns=[length])

    def test_invalid_length(self):
        msg = 'BloomIndex.length must be None or an integer from 1 to 4096.'
        for length in (0, 4097):
            with self.subTest(length), self.assertRaisesMessage(ValueError, msg):
                BloomIndex(fields=['title'], name='test_bloom', length=length)


class BrinIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = BrinIndex

    def test_suffix(self):
        self.assertEqual(BrinIndex.suffix, 'brin')

    def test_deconstruction(self):
        index = BrinIndex(fields=['title'], name='test_title_brin', autosummarize=True, pages_per_range=16)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.BrinIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {
            'fields': ['title'],
            'name': 'test_title_brin',
            'autosummarize': True,
            'pages_per_range': 16,
        })

    def test_invalid_pages_per_range(self):
        with self.assertRaisesMessage(ValueError, 'pages_per_range must be None or a positive integer'):
            BrinIndex(fields=['title'], name='test_title_brin', pages_per_range=0)


class BTreeIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = BTreeIndex

    def test_suffix(self):
        self.assertEqual(BTreeIndex.suffix, 'btree')

    def test_deconstruction(self):
        index = BTreeIndex(fields=['title'], name='test_title_btree', fillfactor=80)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.BTreeIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {'fields': ['title'], 'name': 'test_title_btree', 'fillfactor': 80})


class GinIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = GinIndex

    def test_suffix(self):
        self.assertEqual(GinIndex.suffix, 'gin')

    def test_deconstruction(self):
        index = GinIndex(
            fields=['title'],
            name='test_title_gin',
            fastupdate=True,
            gin_pending_list_limit=128,
        )
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.GinIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {
            'fields': ['title'],
            'name': 'test_title_gin',
            'fastupdate': True,
            'gin_pending_list_limit': 128,
        })


class GistIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = GistIndex

    def test_suffix(self):
        self.assertEqual(GistIndex.suffix, 'gist')

    def test_deconstruction(self):
        index = GistIndex(fields=['title'], name='test_title_gist', buffering=False, fillfactor=80)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.GistIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {
            'fields': ['title'],
            'name': 'test_title_gist',
            'buffering': False,
            'fillfactor': 80,
        })


class HashIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = HashIndex

    def test_suffix(self):
        self.assertEqual(HashIndex.suffix, 'hash')

    def test_deconstruction(self):
        index = HashIndex(fields=['title'], name='test_title_hash', fillfactor=80)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.HashIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {'fields': ['title'], 'name': 'test_title_hash', 'fillfactor': 80})


class SpGistIndexTests(IndexTestMixin, PostgreSQLSimpleTestCase):
    index_class = SpGistIndex

    def test_suffix(self):
        self.assertEqual(SpGistIndex.suffix, 'spgist')

    def test_deconstruction(self):
        index = SpGistIndex(fields=['title'], name='test_title_spgist', fillfactor=80)
        path, args, kwargs = index.deconstruct()
        self.assertEqual(path, 'django.contrib.postgres.indexes.SpGistIndex')
        self.assertEqual(args, ())
        self.assertEqual(kwargs, {'fields': ['title'], 'name': 'test_title_spgist', 'fillfactor': 80})


@modify_settings(INSTALLED_APPS={'append': 'django.contrib.postgres'})
class SchemaTests(PostgreSQLTestCase):
    get_opclass_query = '''
        SELECT opcname, c.relname FROM pg_opclass AS oc
        JOIN pg_index as i on oc.oid = ANY(i.indclass)
        JOIN pg_class as c on c.oid = i.indexrelid
        WHERE c.relname = %s
    '''

    def get_constraints(self, table):
        """
        Get the indexes on the table using a new cursor.
        """
        with connection.cursor() as cursor:
            return connection.introspection.get_constraints(cursor, table)

    def test_gin_index(self):
        # Ensure the table is there and doesn't have an index.
        self.assertNotIn('field', self.get_constraints(IntegerArrayModel._meta.db_table))
        # Add the index
        index_name = 'integer_array_model_field_gin'
        index = GinIndex(fields=['field'], name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(IntegerArrayModel, index)
        constraints = self.get_constraints(IntegerArrayModel._meta.db_table)
        # Check gin index was added
        self.assertEqual(constraints[index_name]['type'], GinIndex.suffix)
        # Drop the index
        with connection.schema_editor() as editor:
            editor.remove_index(IntegerArrayModel, index)
        self.assertNotIn(index_name, self.get_constraints(IntegerArrayModel._meta.db_table))

    def test_gin_fastupdate(self):
        index_name = 'integer_array_gin_fastupdate'
        index = GinIndex(fields=['field'], name=index_name, fastupdate=False)
        with connection.schema_editor() as editor:
            editor.add_index(IntegerArrayModel, index)
        constraints = self.get_constraints(IntegerArrayModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], 'gin')
        self.assertEqual(constraints[index_name]['options'], ['fastupdate=off'])
        with connection.schema_editor() as editor:
            editor.remove_index(IntegerArrayModel, index)
        self.assertNotIn(index_name, self.get_constraints(IntegerArrayModel._meta.db_table))

    def test_partial_gin_index(self):
        with register_lookup(CharField, Length):
            index_name = 'char_field_gin_partial_idx'
            index = GinIndex(fields=['field'], name=index_name, condition=Q(field__length=40))
            with connection.schema_editor() as editor:
                editor.add_index(CharFieldModel, index)
            constraints = self.get_constraints(CharFieldModel._meta.db_table)
            self.assertEqual(constraints[index_name]['type'], 'gin')
            with connection.schema_editor() as editor:
                editor.remove_index(CharFieldModel, index)
            self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_partial_gin_index_with_tablespace(self):
        with register_lookup(CharField, Length):
            index_name = 'char_field_gin_partial_idx'
            index = GinIndex(
                fields=['field'],
                name=index_name,
                condition=Q(field__length=40),
                db_tablespace='pg_default',
            )
            with connection.schema_editor() as editor:
                editor.add_index(CharFieldModel, index)
                self.assertIn('TABLESPACE "pg_default" ', str(index.create_sql(CharFieldModel, editor)))
            constraints = self.get_constraints(CharFieldModel._meta.db_table)
            self.assertEqual(constraints[index_name]['type'], 'gin')
            with connection.schema_editor() as editor:
                editor.remove_index(CharFieldModel, index)
            self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_gin_parameters(self):
        index_name = 'integer_array_gin_params'
        index = GinIndex(fields=['field'], name=index_name, fastupdate=True, gin_pending_list_limit=64)
        with connection.schema_editor() as editor:
            editor.add_index(IntegerArrayModel, index)
        constraints = self.get_constraints(IntegerArrayModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], 'gin')
        self.assertEqual(constraints[index_name]['options'], ['gin_pending_list_limit=64', 'fastupdate=on'])
        with connection.schema_editor() as editor:
            editor.remove_index(IntegerArrayModel, index)
        self.assertNotIn(index_name, self.get_constraints(IntegerArrayModel._meta.db_table))

    def test_trigram_op_class_gin_index(self):
        index_name = 'trigram_op_class_gin'
        index = GinIndex(OpClass(F('scene'), name='gin_trgm_ops'), name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(Scene, index)
        with editor.connection.cursor() as cursor:
            cursor.execute(self.get_opclass_query, [index_name])
            self.assertCountEqual(cursor.fetchall(), [('gin_trgm_ops', index_name)])
        constraints = self.get_constraints(Scene._meta.db_table)
        self.assertIn(index_name, constraints)
        self.assertIn(constraints[index_name]['type'], GinIndex.suffix)
        with connection.schema_editor() as editor:
            editor.remove_index(Scene, index)
        self.assertNotIn(index_name, self.get_constraints(Scene._meta.db_table))

    def test_cast_search_vector_gin_index(self):
        index_name = 'cast_search_vector_gin'
        index = GinIndex(Cast('field', SearchVectorField()), name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(TextFieldModel, index)
            sql = index.create_sql(TextFieldModel, editor)
        table = TextFieldModel._meta.db_table
        constraints = self.get_constraints(table)
        self.assertIn(index_name, constraints)
        self.assertIn(constraints[index_name]['type'], GinIndex.suffix)
        self.assertIs(sql.references_column(table, 'field'), True)
        self.assertIn(' AS tsvector', str(sql))
        with connection.schema_editor() as editor:
            editor.remove_index(TextFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(table))

    def test_bloom_index(self):
        index_name = 'char_field_model_field_bloom'
        index = BloomIndex(fields=['field'], name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], BloomIndex.suffix)
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_bloom_parameters(self):
        index_name = 'char_field_model_field_bloom_params'
        index = BloomIndex(fields=['field'], name=index_name, length=512, columns=[3])
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], BloomIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['length=512', 'col1=3'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_brin_index(self):
        index_name = 'char_field_model_field_brin'
        index = BrinIndex(fields=['field'], name=index_name, pages_per_range=4)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], BrinIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['pages_per_range=4'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    @skipUnlessDBFeature('has_brin_autosummarize')
    def test_brin_parameters(self):
        index_name = 'char_field_brin_params'
        index = BrinIndex(fields=['field'], name=index_name, autosummarize=True)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], BrinIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['autosummarize=on'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_brin_autosummarize_not_supported(self):
        index_name = 'brin_options_exception'
        index = BrinIndex(fields=['field'], name=index_name, autosummarize=True)
        with self.assertRaisesMessage(NotSupportedError, 'BRIN option autosummarize requires PostgreSQL 10+.'):
            with mock.patch('django.db.backends.postgresql.features.DatabaseFeatures.has_brin_autosummarize', False):
                with connection.schema_editor() as editor:
                    editor.add_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_btree_index(self):
        # Ensure the table is there and doesn't have an index.
        self.assertNotIn('field', self.get_constraints(CharFieldModel._meta.db_table))
        # Add the index.
        index_name = 'char_field_model_field_btree'
        index = BTreeIndex(fields=['field'], name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        # The index was added.
        self.assertEqual(constraints[index_name]['type'], BTreeIndex.suffix)
        # Drop the index.
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_btree_parameters(self):
        index_name = 'integer_array_btree_fillfactor'
        index = BTreeIndex(fields=['field'], name=index_name, fillfactor=80)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], BTreeIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['fillfactor=80'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_gist_index(self):
        # Ensure the table is there and doesn't have an index.
        self.assertNotIn('field', self.get_constraints(CharFieldModel._meta.db_table))
        # Add the index.
        index_name = 'char_field_model_field_gist'
        index = GistIndex(fields=['field'], name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        # The index was added.
        self.assertEqual(constraints[index_name]['type'], GistIndex.suffix)
        # Drop the index.
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_gist_parameters(self):
        index_name = 'integer_array_gist_buffering'
        index = GistIndex(fields=['field'], name=index_name, buffering=True, fillfactor=80)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], GistIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['buffering=on', 'fillfactor=80'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    @skipUnlessDBFeature('supports_covering_gist_indexes')
    def test_gist_include(self):
        index_name = 'scene_gist_include_setting'
        index = GistIndex(name=index_name, fields=['scene'], include=['setting'])
        with connection.schema_editor() as editor:
            editor.add_index(Scene, index)
        constraints = self.get_constraints(Scene._meta.db_table)
        self.assertIn(index_name, constraints)
        self.assertEqual(constraints[index_name]['type'], GistIndex.suffix)
        self.assertEqual(constraints[index_name]['columns'], ['scene', 'setting'])
        with connection.schema_editor() as editor:
            editor.remove_index(Scene, index)
        self.assertNotIn(index_name, self.get_constraints(Scene._meta.db_table))

    def test_gist_include_not_supported(self):
        index_name = 'gist_include_exception'
        index = GistIndex(fields=['scene'], name=index_name, include=['setting'])
        msg = 'Covering GiST indexes requires PostgreSQL 12+.'
        with self.assertRaisesMessage(NotSupportedError, msg):
            with mock.patch(
                'django.db.backends.postgresql.features.DatabaseFeatures.supports_covering_gist_indexes',
                False,
            ):
                with connection.schema_editor() as editor:
                    editor.add_index(Scene, index)
        self.assertNotIn(index_name, self.get_constraints(Scene._meta.db_table))

    def test_tsvector_op_class_gist_index(self):
        index_name = 'tsvector_op_class_gist'
        index = GistIndex(
            OpClass(
                SearchVector('scene', 'setting', config='english'),
                name='tsvector_ops',
            ),
            name=index_name,
        )
        with connection.schema_editor() as editor:
            editor.add_index(Scene, index)
            sql = index.create_sql(Scene, editor)
        table = Scene._meta.db_table
        constraints = self.get_constraints(table)
        self.assertIn(index_name, constraints)
        self.assertIn(constraints[index_name]['type'], GistIndex.suffix)
        self.assertIs(sql.references_column(table, 'scene'), True)
        self.assertIs(sql.references_column(table, 'setting'), True)
        with connection.schema_editor() as editor:
            editor.remove_index(Scene, index)
        self.assertNotIn(index_name, self.get_constraints(table))

    def test_hash_index(self):
        # Ensure the table is there and doesn't have an index.
        self.assertNotIn('field', self.get_constraints(CharFieldModel._meta.db_table))
        # Add the index.
        index_name = 'char_field_model_field_hash'
        index = HashIndex(fields=['field'], name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        # The index was added.
        self.assertEqual(constraints[index_name]['type'], HashIndex.suffix)
        # Drop the index.
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_hash_parameters(self):
        index_name = 'integer_array_hash_fillfactor'
        index = HashIndex(fields=['field'], name=index_name, fillfactor=80)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], HashIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['fillfactor=80'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_spgist_index(self):
        # Ensure the table is there and doesn't have an index.
        self.assertNotIn('field', self.get_constraints(CharFieldModel._meta.db_table))
        # Add the index.
        index_name = 'char_field_model_field_spgist'
        index = SpGistIndex(fields=['field'], name=index_name)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        # The index was added.
        self.assertEqual(constraints[index_name]['type'], SpGistIndex.suffix)
        # Drop the index.
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_spgist_parameters(self):
        index_name = 'integer_array_spgist_fillfactor'
        index = SpGistIndex(fields=['field'], name=index_name, fillfactor=80)
        with connection.schema_editor() as editor:
            editor.add_index(CharFieldModel, index)
        constraints = self.get_constraints(CharFieldModel._meta.db_table)
        self.assertEqual(constraints[index_name]['type'], SpGistIndex.suffix)
        self.assertEqual(constraints[index_name]['options'], ['fillfactor=80'])
        with connection.schema_editor() as editor:
            editor.remove_index(CharFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(CharFieldModel._meta.db_table))

    def test_op_class(self):
        index_name = 'test_op_class'
        index = Index(
            OpClass(Lower('field'), name='text_pattern_ops'),
            name=index_name,
        )
        with connection.schema_editor() as editor:
            editor.add_index(TextFieldModel, index)
        with editor.connection.cursor() as cursor:
            cursor.execute(self.get_opclass_query, [index_name])
            self.assertCountEqual(cursor.fetchall(), [('text_pattern_ops', index_name)])

    def test_op_class_descending_collation(self):
        collation = connection.features.test_collations.get('non_default')
        if not collation:
            self.skipTest(
                'This backend does not support case-insensitive collations.'
            )
        index_name = 'test_op_class_descending_collation'
        index = Index(
            Collate(
                OpClass(Lower('field'), name='text_pattern_ops').desc(nulls_last=True),
                collation=collation,
            ),
            name=index_name,
        )
        with connection.schema_editor() as editor:
            editor.add_index(TextFieldModel, index)
            self.assertIn(
                'COLLATE %s' % editor.quote_name(collation),
                str(index.create_sql(TextFieldModel, editor)),
            )
        with editor.connection.cursor() as cursor:
            cursor.execute(self.get_opclass_query, [index_name])
            self.assertCountEqual(cursor.fetchall(), [('text_pattern_ops', index_name)])
        table = TextFieldModel._meta.db_table
        constraints = self.get_constraints(table)
        self.assertIn(index_name, constraints)
        self.assertEqual(constraints[index_name]['orders'], ['DESC'])
        with connection.schema_editor() as editor:
            editor.remove_index(TextFieldModel, index)
        self.assertNotIn(index_name, self.get_constraints(table))

    def test_op_class_descending_partial(self):
        index_name = 'test_op_class_descending_partial'
        index = Index(
            OpClass(Lower('field'), name='text_pattern_ops').desc(),
            name=index_name,
            condition=Q(field__contains='China'),
        )
        with connection.schema_editor() as editor:
            editor.add_index(TextFieldModel, index)
        with editor.connection.cursor() as cursor:
            cursor.execute(self.get_opclass_query, [index_name])
            self.assertCountEqual(cursor.fetchall(), [('text_pattern_ops', index_name)])
        constraints = self.get_constraints(TextFieldModel._meta.db_table)
        self.assertIn(index_name, constraints)
        self.assertEqual(constraints[index_name]['orders'], ['DESC'])

    def test_op_class_descending_partial_tablespace(self):
        index_name = 'test_op_class_descending_partial_tablespace'
        index = Index(
            OpClass(Lower('field').desc(), name='text_pattern_ops'),
            name=index_name,
            condition=Q(field__contains='China'),
            db_tablespace='pg_default',
        )
        with connection.schema_editor() as editor:
            editor.add_index(TextFieldModel, index)
            self.assertIn(
                'TABLESPACE "pg_default" ',
                str(index.create_sql(TextFieldModel, editor))
            )
        with editor.connection.cursor() as cursor:
            cursor.execute(self.get_opclass_query, [index_name])
            self.assertCountEqual(cursor.fetchall(), [('text_pattern_ops', index_name)])
        constraints = self.get_constraints(TextFieldModel._meta.db_table)
        self.assertIn(index_name, constraints)
        self.assertEqual(constraints[index_name]['orders'], ['DESC'])
