from datetime import datetime, timedelta
from decimal import Decimal
from unittest import skipIf, skipUnless

from django.db import connection
from django.db.models.expressions import RawSQL
from django.db.models.functions import Coalesce, Greatest
from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
from django.utils import timezone

from ..models import Article, Author, DecimalModel, Fan


class GreatestTests(TestCase):

    def test_basic(self):
        now = timezone.now()
        before = now - timedelta(hours=1)
        Article.objects.create(title='Testing with Django', written=before, published=now)
        articles = Article.objects.annotate(last_updated=Greatest('written', 'published'))
        self.assertEqual(articles.first().last_updated, now)

    @skipUnlessDBFeature('greatest_least_ignores_nulls')
    def test_ignores_null(self):
        now = timezone.now()
        Article.objects.create(title='Testing with Django', written=now)
        articles = Article.objects.annotate(last_updated=Greatest('written', 'published'))
        self.assertEqual(articles.first().last_updated, now)

    @skipIfDBFeature('greatest_least_ignores_nulls')
    def test_propagates_null(self):
        Article.objects.create(title='Testing with Django', written=timezone.now())
        articles = Article.objects.annotate(last_updated=Greatest('written', 'published'))
        self.assertIsNone(articles.first().last_updated)

    @skipIf(connection.vendor == 'mysql', "This doesn't work on MySQL")
    def test_coalesce_workaround(self):
        past = datetime(1900, 1, 1)
        now = timezone.now()
        Article.objects.create(title='Testing with Django', written=now)
        articles = Article.objects.annotate(
            last_updated=Greatest(
                Coalesce('written', past),
                Coalesce('published', past),
            ),
        )
        self.assertEqual(articles.first().last_updated, now)

    @skipUnless(connection.vendor == 'mysql', "MySQL-specific workaround")
    def test_coalesce_workaround_mysql(self):
        past = datetime(1900, 1, 1)
        now = timezone.now()
        Article.objects.create(title='Testing with Django', written=now)
        past_sql = RawSQL("cast(%s as datetime)", (past,))
        articles = Article.objects.annotate(
            last_updated=Greatest(
                Coalesce('written', past_sql),
                Coalesce('published', past_sql),
            ),
        )
        self.assertEqual(articles.first().last_updated, now)

    def test_all_null(self):
        Article.objects.create(title='Testing with Django', written=timezone.now())
        articles = Article.objects.annotate(last_updated=Greatest('published', 'updated'))
        self.assertIsNone(articles.first().last_updated)

    def test_one_expressions(self):
        with self.assertRaisesMessage(ValueError, 'Greatest must take at least two expressions'):
            Greatest('written')

    def test_related_field(self):
        author = Author.objects.create(name='John Smith', age=45)
        Fan.objects.create(name='Margaret', age=50, author=author)
        authors = Author.objects.annotate(highest_age=Greatest('age', 'fans__age'))
        self.assertEqual(authors.first().highest_age, 50)

    def test_update(self):
        author = Author.objects.create(name='James Smith', goes_by='Jim')
        Author.objects.update(alias=Greatest('name', 'goes_by'))
        author.refresh_from_db()
        self.assertEqual(author.alias, 'Jim')

    def test_decimal_filter(self):
        obj = DecimalModel.objects.create(n1=Decimal('1.1'), n2=Decimal('1.2'))
        self.assertCountEqual(
            DecimalModel.objects.annotate(
                greatest=Greatest('n1', 'n2'),
            ).filter(greatest=Decimal('1.2')),
            [obj],
        )