"""分期应缴日：小数月间隔（30 天/月）与提前天数规则"""

import unittest

from app.services.protocol_payment_installment import calc_fq_installment_due_date


class TestCalcFqInstallmentDueDate(unittest.TestCase):
    def test_first_period_equals_start_date(self):
        self.assertEqual(calc_fq_installment_due_date("20260604", 0, 0.5), "20260604")

    def test_fractional_interval_half_month_six_periods(self):
        start = "20260604"
        interval = 0.5
        expected = [
            "20260604",
            "20260520",
            "20260604",
            "20260619",
            "20260705",
            "20260720",
        ]
        for i, exp in enumerate(expected):
            self.assertEqual(
                calc_fq_installment_due_date(start, i, interval),
                exp,
                msg=f"period {i + 1}",
            )

    def test_fractional_interval_0_1_advance_30_days(self):
        # +3 天 = 20260607，再提前 30 天
        self.assertEqual(calc_fq_installment_due_date("20260604", 1, 0.1), "20260508")

    def test_integer_interval_six_months(self):
        # +6 日历月 = 20261204，再提前 30 天
        self.assertEqual(calc_fq_installment_due_date("20260604", 1, 6), "20261104")

    def test_fractional_interval_0_3(self):
        # index=2 → 0.6 月 → 18 天 → 20260622，再提前 30 天
        self.assertEqual(calc_fq_installment_due_date("20260604", 2, 0.3), "20260523")

    def test_custom_advance_days_15(self):
        self.assertEqual(
            calc_fq_installment_due_date("20260604", 1, 6, advance_days=15),
            "20261119",
        )


if __name__ == "__main__":
    unittest.main()