from django.db.models.functions import Lag, Lead, NthValue, Ntile

from django.test import SimpleTestCase

class ValidationTests(SimpleTestCase):

    def test_nth_negative_nth_value(self):

        msg = "NthValue requires a positive integer as for nth"

        with self.assertRaisesMessage(ValueError, msg):

            NthValue(expression="salary", nth=-1)

    def test_nth_null_expression(self):

        msg = "NthValue requires a non-null source expression"

        with self.assertRaisesMessage(ValueError, msg):

            NthValue(expression=None)

    def test_lag_negative_offset(self):

        msg = "Lag requires a positive integer for the offset"

        with self.assertRaisesMessage(ValueError, msg):

            Lag(expression="salary", offset=-1)

    def test_lead_negative_offset(self):

        msg = "Lead requires a positive integer for the offset"

        with self.assertRaisesMessage(ValueError, msg):

            Lead(expression="salary", offset=-1)

    def test_null_source_lead(self):

        msg = "Lead requires a non-null source expression"

        with self.assertRaisesMessage(ValueError, msg):

            Lead(expression=None)

    def test_null_source_lag(self):

        msg = "Lag requires a non-null source expression"

        with self.assertRaisesMessage(ValueError, msg):

            Lag(expression=None)

    def test_negative_num_buckets_ntile(self):

        msg = "num_buckets must be greater than 0"

        with self.assertRaisesMessage(ValueError, msg):

            Ntile(num_buckets=-1)