"""Calendar payroll period factory shared by scheduling and period closure."""

import logging
from calendar import monthrange
from datetime import date

from django.core.exceptions import ValidationError
from django.db import IntegrityError, transaction

from finance.models import PayrollAuditEvent, PayrollPeriod

logger = logging.getLogger(__name__)

MONTH_NAMES_RU = (
    "",
    "Январь",
    "Февраль",
    "Март",
    "Апрель",
    "Май",
    "Июнь",
    "Июль",
    "Август",
    "Сентябрь",
    "Октябрь",
    "Ноябрь",
    "Декабрь",
)


def ensure_calendar_payroll_period(
    reference_date: date,
    *,
    currency="RUB",
    actor=None,
    channel="automation",
    metadata=None,
):
    """Create the open payroll period for a month unless it already exists."""

    date_from = reference_date.replace(day=1)
    date_to = reference_date.replace(
        day=monthrange(reference_date.year, reference_date.month)[1]
    )

    existing = PayrollPeriod.objects.filter(
        date_from=date_from,
        date_to=date_to,
        currency=currency,
    ).first()
    if existing is not None:
        return existing, False

    period = PayrollPeriod(
        code=date_from.strftime("%Y-%m"),
        name=f"{MONTH_NAMES_RU[date_from.month]} {date_from.year}",
        date_from=date_from,
        date_to=date_to,
        currency=currency,
        created_by=actor,
    )

    try:
        with transaction.atomic():
            period.full_clean()
            period.save(force_insert=True)
            PayrollAuditEvent.objects.create(
                actor=actor,
                action="payroll.period_created",
                object_type=period._meta.label_lower,
                object_id=str(period.pk),
                period=period,
                metadata={"channel": channel, **(metadata or {})},
            )
    except IntegrityError:
        # Celery retries or two workers can race. The database constraint makes
        # creation safe; return the winner when it covers the same month.
        existing = PayrollPeriod.objects.filter(
            date_from=date_from,
            date_to=date_to,
            currency=currency,
        ).first()
        if existing is not None:
            return existing, False
        raise
    except ValidationError as error:
        # A concurrent opening can win between the first lookup and full_clean.
        existing = PayrollPeriod.objects.filter(
            date_from=date_from, date_to=date_to, currency=currency
        ).first()
        if existing is not None:
            return existing, False
        logger.exception(
            "Payroll period opening failed",
            extra={
                "event": "finance.payroll_period.open_failed",
                "payroll_period_id": period.pk,
                "period_code": period.code,
                "error_type": type(error).__name__,
            },
        )
        raise

    logger.info(
        "Payroll period opened",
        extra={
            "event": "finance.payroll_period.opened",
            "payroll_period_id": period.pk,
            "period_code": period.code,
        },
    )
    return period, True