"""Redis 缓存工具模块。

提供 Redis 连接管理和缓存读写操作，所有操作在 Redis 不可用时静默降级。
被 OrderService、CustomerService、pricing 路由等调用。
"""

import hashlib
import json
import logging

import redis

from backend.app.core.config import get_settings

logger = logging.getLogger(__name__)

_redis_client: redis.Redis | None = None


def get_redis() -> redis.Redis | None:
    """获取 Redis 连接单例，连接失败时返回 None。"""
    global _redis_client
    if _redis_client is not None:
        return _redis_client
    try:
        settings = get_settings()
        _redis_client = redis.Redis(
            host=settings.redis_host,
            port=settings.redis_port,
            db=settings.redis_db,
            password=settings.redis_password or None,
            decode_responses=True,
            socket_connect_timeout=2,
            socket_timeout=2,
        )
        _redis_client.ping()
        logger.info("Redis 连接成功: %s:%s/%s", settings.redis_host, settings.redis_port, settings.redis_db)
        return _redis_client
    except Exception as exc:
        logger.warning("Redis 连接失败，降级为无缓存模式: %s", exc)
        _redis_client = None
        return None


def cache_get(key: str):
    """读取缓存，返回反序列化后的 dict/list，未命中或异常返回 None。"""
    try:
        r = get_redis()
        if r is None:
            return None
        raw = r.get(key)
        if raw is None:
            return None
        return json.loads(raw)
    except Exception:
        return None


def cache_set(key: str, data, ttl: int = 60) -> None:
    """写入缓存，JSON 序列化后存储并设置 TTL（秒）。异常时静默跳过。"""
    try:
        r = get_redis()
        if r is None:
            return
        r.set(key, json.dumps(data, ensure_ascii=False, default=str), ex=ttl)
    except Exception:
        pass


def cache_delete(key: str) -> None:
    """精确删除单个缓存 key。"""
    try:
        r = get_redis()
        if r is not None:
            r.delete(key)
    except Exception:
        pass


def cache_delete_pattern(pattern: str) -> None:
    """按模式批量删除缓存（SCAN + DELETE），如 "order:list:*"。"""
    try:
        r = get_redis()
        if r is None:
            return
        cursor = 0
        while True:
            cursor, keys = r.scan(cursor=cursor, match=pattern, count=100)
            if keys:
                r.delete(*keys)
            if cursor == 0:
                break
    except Exception:
        pass


def make_cache_key(prefix: str, **params) -> str:
    """生成带参数哈希的缓存 key。

    例: make_cache_key("order:list", user_id=1, status="draft")
    → "order:list:a1b2c3d4"
    """
    raw = json.dumps(params, sort_keys=True, ensure_ascii=False, default=str)
    suffix = hashlib.md5(raw.encode()).hexdigest()[:8]
    return f"{prefix}:{suffix}"