"""命台席位控制：同一人物同一时刻只有一条前台意识流。

M0 为进程内实现（单人物粒度 asyncio 锁 + 等待计数）；多副本部署在标准档
切换 Redis 租约（lingtai-runtime.md §8），接口保持不变。
"""

from __future__ import annotations

from collections import defaultdict
from contextlib import asynccontextmanager
from collections.abc import AsyncIterator
import asyncio


class SeatManager:
    """人物粒度的前台席位。后台受托 Run（kind=background_task）不占席位。"""

    def __init__(self) -> None:
        self._locks: dict[str, asyncio.Lock] = {}
        self._waiting: dict[str, int] = defaultdict(int)

    def _lock(self, character_id: str) -> asyncio.Lock:
        if character_id not in self._locks:
            self._locks[character_id] = asyncio.Lock()
        return self._locks[character_id]

    @asynccontextmanager
    async def foreground(self, character_id: str) -> AsyncIterator[None]:
        """占用前台席位；同人物并发请求在此排队（Kernel 不变量 2）。"""
        lock = self._lock(character_id)
        if lock.locked():
            self._waiting[character_id] += 1
            try:
                async with lock:
                    yield
            finally:
                self._waiting[character_id] -= 1
        else:
            async with lock:
                yield

    def queue_depth(self, character_id: str) -> int:
        """该人物当前排队等待前台席位的请求数（HJ-1101 附带信息）。"""
        return self._waiting.get(character_id, 0)