"""月份行锁同时保护工资生成与分配事实修改。"""

from datetime import datetime, timedelta, timezone

from sqlalchemy import select
from sqlalchemy.dialects.mysql import insert

from app.core.exceptions import BadRequestError, ForbiddenError
from app.core.month import validate_month
from app.models import MonthlySettlement, PayrollMonth
from app.services.payroll_access import ensure_payroll_writer


def current_month() -> str:
    return datetime.now(timezone(timedelta(hours=8))).strftime("%Y-%m")


def month_state(session, month):
    """查询生成锁及制作人，兼容升级前已存在的月结记录。"""
    validate_month(month)
    control = session.scalar(select(PayrollMonth).where(PayrollMonth.month == month))
    existing = session.scalar(
        select(MonthlySettlement.id).where(MonthlySettlement.settlement_month == month)
    )
    return {
        "month": month,
        "allocation_locked": bool(existing or (control and control.generated_at)),
        "maker_name": control.maker_name if control else None,
    }


def lock_month(session, month, operator, *, require_maker=True):
    """INSERT 的唯一键串行化首次建行，避免两个请求同时认为月份不存在。"""
    if require_maker:
        ensure_payroll_writer(operator)
    validate_month(month)
    values = {"month": month, "maker_id": operator.id, "maker_name": operator.username}
    if session.bind.dialect.name == "mysql":
        stmt = insert(PayrollMonth).values(**values)
        session.execute(stmt.on_duplicate_key_update(month=stmt.inserted.month))
    elif session.scalar(select(PayrollMonth.id).where(PayrollMonth.month == month)) is None:
        session.add(PayrollMonth(**values))
        session.flush()
    control = session.scalar(
        select(PayrollMonth).where(PayrollMonth.month == month).with_for_update()
    )
    if control.generated_at is not None and control.maker_id != operator.id:
        raise ForbiddenError("该月工资由其他制作人生成，不可代为修改或重新生成")
    if control.generated_at is None:
        control.maker_id, control.maker_name = operator.id, operator.username
    return control


def ensure_allocation_editable(session, month, operator, *, require_maker=True):
    control = lock_month(session, month, operator, require_maker=require_maker)
    # 兼容升级前已有月结；没有控制行不代表历史工资可以修改。
    old = session.scalar(
        select(MonthlySettlement.id).where(MonthlySettlement.settlement_month == month)
    )
    if control.generated_at is not None or old is not None:
        raise BadRequestError("该月工资已生成，二次分配已锁定；差额请走当月调整单")
    return control