from sqlmodel import Session, select

from app.models.models import (
    Account,
    AccountType,
    Bank,
    SavingsAccrual,
    Transaction,
)

MEMP_MONTHLY = 200000.0
MPAT_MONTHLY = 200000.0


def _get_savings_account(session: Session, bank: Bank) -> Account | None:
    return session.exec(
        select(Account).where(
            Account.account_type == AccountType.SAVINGS,
            Account.bank == bank,
        )
    ).first()


def maybe_apply_monthly_savings(session: Session, tx: Transaction) -> SavingsAccrual | None:
    """Apply monthly savings contribution if this is the first salary of the month.

    Idempotent: if a SavingsAccrual row already exists for (year, month), do nothing.
    Bumps MEMP and MPAT savings account balances and records the accrual.
    """
    year = tx.date.year
    month = tx.date.month

    existing = session.exec(
        select(SavingsAccrual).where(
            SavingsAccrual.year == year,
            SavingsAccrual.month == month,
        )
    ).first()
    if existing:
        return None

    memp = _get_savings_account(session, Bank.MEMP)
    mpat = _get_savings_account(session, Bank.MPAT)
    if memp is None or mpat is None:
        return None

    memp.balance += MEMP_MONTHLY
    mpat.balance += MPAT_MONTHLY
    session.add(memp)
    session.add(mpat)

    accrual = SavingsAccrual(
        year=year,
        month=month,
        memp_amount=MEMP_MONTHLY,
        mpat_amount=MPAT_MONTHLY,
        trigger_transaction_id=tx.id,
    )
    session.add(accrual)
    session.commit()
    session.refresh(accrual)
    return accrual