from decimal import Decimal

from django.db.models import DecimalField, Sum, Value
from django.db.models.functions import Coalesce

from finance.models import Account, ReconciliationCheckpoint, Transaction

from .base import lock, money, save, write


_MONEY_FIELD = DecimalField(max_digits=24, decimal_places=2)
_ZERO = Decimal("0.00")


def _ledger_balance_through(account_id, as_of_date):
    total = Transaction.objects.filter(
        account_id=account_id,
        posting_date__lte=as_of_date,
    ).aggregate(
        total=Coalesce(
            Sum("amount"),
            Value(_ZERO),
            output_field=_MONEY_FIELD,
        )
    )["total"]
    return money(total, allow_zero=True)


@write("reconciliation_checkpoint.created")
def create_reconciliation_checkpoint(*, account_id, as_of_date, institution_balance):
    account = lock(Account, account_id, active=True)
    institution_balance = money(institution_balance, allow_zero=True)
    ledger_balance = _ledger_balance_through(account.pk, as_of_date)
    checkpoint = save(ReconciliationCheckpoint(
        account=account,
        as_of_date=as_of_date,
        institution_balance=institution_balance,
        ledger_balance_at_creation=ledger_balance,
        difference_at_creation=money(institution_balance - ledger_balance, allow_zero=True),
    ))
    return checkpoint, [
        "account",
        "as_of_date",
        "institution_balance",
        "ledger_balance_at_creation",
        "difference_at_creation",
    ]