"""Periodic Finance tasks."""

from __future__ import annotations

import logging
from calendar import monthrange
from datetime import date

from celery import shared_task
from django.core.exceptions import ValidationError
from django.db import IntegrityError, transaction
from django.utils import timezone

from .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_monthly_payroll_period(reference_date: date | None = None):
    """Create the open payroll period for a month unless it already exists."""

    reference_date = reference_date or timezone.localdate()
    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,
    ).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="RUB",
        created_by=None,
    )

    try:
        with transaction.atomic():
            period.full_clean()
            period.save(force_insert=True)
            PayrollAuditEvent.objects.create(
                actor=None,
                action="payroll.period_created",
                object_type=period._meta.label_lower,
                object_id=str(period.pk),
                period=period,
                metadata={"channel": "automation", "schedule": "monthly"},
            )
    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,
        ).first()
        if existing is not None:
            return existing, False
        raise
    except ValidationError as error:
        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


@shared_task
def open_monthly_payroll_period():
    """Open the current calendar month's payroll period."""

    period, created = ensure_monthly_payroll_period()
    return {"period_id": period.pk, "code": period.code, "created": created}