from datetime import timedelta
from decimal import Decimal

from sqlalchemy import select

from factories import make_account, make_txn, month_back, refresh
from fintracker.db import get_sessionmaker
from fintracker.models import AccountRole, MetricRunway


async def row() -> MetricRunway | None:
    async with get_sessionmaker()() as session:
        return (await session.execute(select(MetricRunway))).scalars().one_or_none()


async def test_reserve_and_three_month_average(app):
    card = await make_account(name="Карта", balance="200000")
    await make_account(name="Вклад", balance="100000", role=AccountRole.savings)
    await make_account(name="Брокер", balance="900000", role=AccountRole.investment)
    for months_ago, amount in ((1, "10000"), (2, "20000"), (3, "30000"), (4, "999999")):
        await make_txn(
            month_back(months_ago) + timedelta(days=2), outcome=amount, outcome_account_id=card
        )
    await refresh()

    r = await row()
    assert r is not None
    # reserve = liquid + savings only; investments are not runway
    assert r.liquid_reserve_rub == Decimal("300000")
    # last three COMPLETE months: 10000, 20000, 30000 -> 20000 (the 4th is out of window)
    assert r.avg_baseline_3m_rub == Decimal("20000")
    assert r.runway_months == Decimal("15")


async def test_one_off_is_out_of_the_divisor(app):
    from factories import make_rule
    from fintracker.models import RuleKind, RuleMatchType

    card = await make_account(name="Карта", balance="100000")
    m = month_back(1)
    await make_txn(m + timedelta(days=1), outcome="10000", outcome_account_id=card, payee="Лента")
    await make_txn(m + timedelta(days=2), outcome="90000", outcome_account_id=card, payee="Отпуск")
    await make_rule(kind=RuleKind.one_off, match_type=RuleMatchType.payee, pattern="Отпуск")
    await refresh()

    r = await row()
    assert r is not None
    # 10000 baseline in the previous month, 0 in the two before it: (10000 + 0 + 0) / 3
    assert r.avg_baseline_3m_rub == Decimal("3333.3333333333")
    assert r.runway_months == Decimal("30")


async def test_a_month_without_spending_counts_as_zero(app):
    """The divisor is the three named complete months, not the last three rows that exist:
    a gap month spent nothing and must dilute the average."""
    card = await make_account(name="Карта", balance="90000")
    for months_ago, amount in ((1, "30000"), (3, "30000")):  # month -2 has no transactions
        await make_txn(
            month_back(months_ago) + timedelta(days=3), outcome=amount, outcome_account_id=card
        )
    await refresh()

    r = await row()
    assert r is not None
    # (30000 + 0 + 30000) / 3 = 20000, not the 30000 an average over existing rows would give
    assert r.avg_baseline_3m_rub == Decimal("20000")
    assert r.runway_months == Decimal("4.5")


async def test_months_older_than_the_window_are_ignored(app):
    card = await make_account(name="Карта", balance="60000")
    await make_txn(month_back(4) + timedelta(days=3), outcome="90000", outcome_account_id=card)
    await refresh()

    r = await row()
    assert r is not None
    assert r.avg_baseline_3m_rub == Decimal("0")
    assert r.runway_months is None


async def test_no_history_gives_null_runway(app):
    await make_account(name="Карта", balance="50000")
    await refresh()

    r = await row()
    assert r is not None
    assert r.avg_baseline_3m_rub == Decimal("0")
    assert r.runway_months is None