"""命台租约（authoritative_runtime_seat）：同一人物唯一权威运行位置。

- 活跃租约（未过期、非本人）存在时，其他持有者获取被拒（SeatConflict）；
- 租约过期可接管，epoch 递增（旧持有者写入按 epoch 失效——M2 运行时接入）；
- 事件（seat.acquired / released / contested）由 API 层在事务提交后发射，
  避免事务内跨连接写冲突；M1 为 API 级租约，Kernel 前台串行仍为进程内锁，多进程一致在 M2 收口。
"""

from __future__ import annotations

from datetime import timedelta

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.time import as_utc, utc_now
from app.models.jingsheng import RuntimeSeat


class SeatConflict(Exception):
    """命台被其他持有者占用（HJ-1101 语义）；调用方须留痕 seat.contested。"""

    def __init__(self, seat: RuntimeSeat) -> None:
        super().__init__(f"命台被 {seat.holder} 占用至 {seat.lease_expires_at}")
        self.seat = seat


async def acquire_lease(
    session: AsyncSession, character_id: str, holder: str, ttl_seconds: int = 60
) -> RuntimeSeat:
    """获取或续期命台租约；冲突抛 SeatConflict（不在此发事件，避免事务内跨连接写）。"""
    seat = await session.scalar(select(RuntimeSeat).where(RuntimeSeat.character_id == character_id))
    if seat is None:
        seat = RuntimeSeat(character_id=character_id, epoch=0)
        session.add(seat)
    now = utc_now()
    if (
        seat.holder is not None
        and seat.holder != holder
        and seat.lease_expires_at is not None
        and as_utc(seat.lease_expires_at) > now
    ):
        raise SeatConflict(seat)
    # 仅"从其他持有者手中接管"递增 epoch；无人持有时首次获取沿用当前纪元
    takeover = seat.holder is not None and seat.holder != holder
    seat.holder = holder
    seat.lease_expires_at = now + timedelta(seconds=ttl_seconds)
    if takeover:
        seat.epoch += 1
    await session.flush()
    return seat


async def release_lease(session: AsyncSession, character_id: str, holder: str) -> bool:
    """释放租约；返回是否实际释放（holder 不匹配时无操作）。"""
    seat = await session.scalar(select(RuntimeSeat).where(RuntimeSeat.character_id == character_id))
    if seat is None or seat.holder != holder:
        return False
    seat.holder = None
    seat.lease_expires_at = None
    await session.flush()
    return True


async def emit_seat_event(
    event_type: str,
    character_id: str,
    holder: str | None,
    epoch: int | None,
    *,
    requester: str | None = None,
) -> None:
    """事务外发射命台事件（一炁，visibility=internal）。"""
    from app.domains import one_qi

    payload: dict = {"holder": holder, "epoch": epoch}
    if requester is not None:
        payload["requester"] = requester
    await one_qi.emit(
        event_type,
        character_id=character_id,
        payload=payload,
        visibility="internal",
        source="jingsheng",
    )