"""Small Redis lock helpers for background tasks."""

from dataclasses import dataclass
import uuid

import redis

from app.core.config import settings


@dataclass(frozen=True)
class RedisLockHandle:
    client: redis.Redis
    key: str
    token: bytes


def acquire_redis_lock(key: str, *, ttl_seconds: int) -> RedisLockHandle | None:
    """Acquire a single-owner Redis lock or return None when unavailable."""
    client = redis.from_url(settings.redis_url, decode_responses=False)
    token = uuid.uuid4().hex.encode("utf-8")
    if not client.set(key, token, nx=True, ex=ttl_seconds):
        return None
    return RedisLockHandle(client=client, key=key, token=token)


def release_redis_lock(handle: RedisLockHandle | None) -> None:
    """Release the lock only if we still own it."""
    if handle is None:
        return
    handle.client.eval(
        """
        if redis.call("GET", KEYS[1]) == ARGV[1] then
            return redis.call("DEL", KEYS[1])
        end
        return 0
        """,
        1,
        handle.key,
        handle.token,
    )