from functools import lru_cache
import logging
import os
from typing import Optional, TYPE_CHECKING
import redis

logger = logging.getLogger(__name__)


REDIS_URL = os.getenv("REDIS_URL", "").strip()
REDIS_CONNECT_TIMEOUT_SECONDS = float(os.getenv("REDIS_CONNECT_TIMEOUT_SECONDS", "2"))
REDIS_SOCKET_TIMEOUT_SECONDS = float(os.getenv("REDIS_SOCKET_TIMEOUT_SECONDS", "2"))

_redis_client: Optional["redis.Redis"] = None
_initialized = False

@lru_cache
def get_redis_client() -> Optional["redis.Redis"]:
    """Return a singleton Redis client, or None when Redis is unavailable."""
    global _redis_client, _initialized

    if _initialized:
        return _redis_client

    _initialized = True

    if not REDIS_URL:
        logger.info("REDIS_URL 未配置，验证码将回退到内存存储")
        _redis_client = None
        return _redis_client

    try:
        _redis_client = redis.Redis.from_url(
            REDIS_URL,
            decode_responses=True,
            socket_connect_timeout=REDIS_CONNECT_TIMEOUT_SECONDS,
            socket_timeout=REDIS_SOCKET_TIMEOUT_SECONDS,
            health_check_interval=30,
        )
        _redis_client.ping()
        logger.info("Redis 连接成功，验证码将优先使用 Redis")
    except Exception as exc:  # pragma: no cover
        logger.warning("Redis 连接失败，将回退到数据库存储。error=%s", exc)
        _redis_client = None

    return _redis_client