"""预约留资服务（T-P3-22）。

topic 预留通用性，首期只有 full_report（全面报告上线提醒）。
幂等口径：UniqueConstraint(user_id, topic)——重复预约返回已有记录
（created=false，HTTP 仍 200），绝不堆行。

指标口径：预约率 = rp_reservation(topic='full_report') 行数 ÷ 埋点
full_report.card_view 去重曝光数；决策门槛 ≥8%（产品方案 §2.2.3）。
"""

from __future__ import annotations

from dataclasses import dataclass

from sqlalchemy.ext.asyncio import AsyncSession

from packages.domain.ids import next_id
from packages.report import repo
from packages.shared.models import RpReservation


@dataclass(frozen=True, slots=True)
class ReservationResult:
    reservation: RpReservation
    created: bool  # false=幂等命中已有记录


class ReservationService:
    def __init__(self, session: AsyncSession) -> None:
        self._session = session

    async def reserve(self, *, user_id: int, topic: str) -> ReservationResult:
        """幂等预约：同 user+topic 已存在即返回原记录。"""
        existing = await repo.get_reservation(self._session, user_id=user_id, topic=topic)
        if existing is not None:
            return ReservationResult(reservation=existing, created=False)
        row = RpReservation(reservation_id=next_id(), user_id=user_id, topic=topic)
        self._session.add(row)
        await self._session.flush()
        return ReservationResult(reservation=row, created=True)

    async def list_topics(self, *, user_id: int, topic: str | None = None) -> list[str]:
        return await repo.list_reservation_topics(self._session, user_id=user_id, topic=topic)