"""Redis 会话归档分布式锁。"""

from __future__ import annotations

import uuid


class SessionArchiveLock:
    """保证同一会话同一时刻只被一个归档任务处理。"""

    KEY = "session:archive:lock:{session_id}"
    DEFAULT_TTL = 120
    RELEASE_SCRIPT = """
    if redis.call('get', KEYS[1]) == ARGV[1] then
        return redis.call('del', KEYS[1])
    end
    return 0
    """

    def __init__(self, redis, *, default_ttl: int = DEFAULT_TTL):
        self.redis = redis
        self.default_ttl = default_ttl

    @classmethod
    def key(cls, session_id: str) -> str:
        """生成会话级锁 Key。"""
        return cls.KEY.format(session_id=session_id)

    async def acquire(self, session_id: str, *, ttl: int | None = None) -> str | None:
        """尝试获取锁，成功返回随机 token，失败返回 None。"""
        lock_ttl = self.default_ttl if ttl is None else ttl
        if lock_ttl <= 0:
            raise ValueError("锁 TTL 必须为正整数")
        token = uuid.uuid4().hex
        acquired = await self.redis.set(
            self.key(session_id), token, nx=True, ex=lock_ttl
        )
        return token if acquired else None

    async def release(self, session_id: str, token: str) -> bool:
        """仅当 token 属于当前持有者时释放锁。"""
        if not token:
            return False
        result = await self.redis.eval(
            self.RELEASE_SCRIPT,
            1,
            self.key(session_id),
            token,
        )
        return bool(result)


__all__ = ["SessionArchiveLock"]