ems-core/backend/app/core/cache.py

"""Redis caching layer with graceful fallback when Redis is unavailable."""
import json
import logging
from functools import wraps
from typing import Any, Optional

import redis.asyncio as aioredis

from app.core.config import get_settings

logger = logging.getLogger("cache")

_redis_pool: Optional[aioredis.Redis] = None


async def get_redis() -> Optional[aioredis.Redis]:
    """Get or create a global Redis connection pool.

    Returns None if Redis is disabled or connection fails.
    """
    global _redis_pool
    settings = get_settings()
    if not settings.REDIS_ENABLED:
        return None
    if _redis_pool is not None:
        return _redis_pool
    try:
        _redis_pool = aioredis.from_url(
            settings.REDIS_URL,
            decode_responses=True,
            max_connections=20,
        )
        # Verify connectivity
        await _redis_pool.ping()
        logger.info("Redis connection established: %s", settings.REDIS_URL)
        return _redis_pool
    except Exception as e:
        logger.warning("Redis unavailable, caching disabled: %s", e)
        _redis_pool = None
        return None


async def close_redis():
    """Close the global Redis connection pool."""
    global _redis_pool
    if _redis_pool:
        await _redis_pool.close()
        _redis_pool = None
        logger.info("Redis connection closed.")


class RedisCache:
    """Async Redis cache with JSON serialization and graceful fallback."""

    def __init__(self, redis_client: Optional[aioredis.Redis] = None):
        self._redis = redis_client

    async def _get_client(self) -> Optional[aioredis.Redis]:
        if self._redis is not None:
            return self._redis
        return await get_redis()

    async def get(self, key: str) -> Optional[Any]:
        """Get a value from cache. Returns None on miss or error."""
        client = await self._get_client()
        if not client:
            return None
        try:
            raw = await client.get(key)
            if raw is None:
                return None
            return json.loads(raw)
        except (json.JSONDecodeError, TypeError):
            return raw
        except Exception as e:
            logger.warning("Cache get error for key=%s: %s", key, e)
            return None

    async def set(self, key: str, value: Any, ttl: int = 300) -> bool:
        """Set a value in cache with TTL in seconds."""
        client = await self._get_client()
        if not client:
            return False
        try:
            serialized = json.dumps(value, ensure_ascii=False, default=str)
            await client.set(key, serialized, ex=ttl)
            return True
        except Exception as e:
            logger.warning("Cache set error for key=%s: %s", key, e)
            return False

    async def delete(self, key: str) -> bool:
        """Delete a key from cache."""
        client = await self._get_client()
        if not client:
            return False
        try:
            await client.delete(key)
            return True
        except Exception as e:
            logger.warning("Cache delete error for key=%s: %s", key, e)
            return False

    async def exists(self, key: str) -> bool:
        """Check if a key exists in cache."""
        client = await self._get_client()
        if not client:
            return False
        try:
            return bool(await client.exists(key))
        except Exception as e:
            logger.warning("Cache exists error for key=%s: %s", key, e)
            return False


def cache_response(prefix: str, ttl_seconds: int = 300):
    """Decorator to cache FastAPI endpoint responses in Redis.

    Builds cache key from prefix + sorted query params.
    Falls through to the endpoint when Redis is unavailable.
    """

    def decorator(func):
        @wraps(func)
        async def wrapper(*args, **kwargs):
            # Build cache key from all keyword arguments
            sorted_params = "&".join(
                f"{k}={v}" for k, v in sorted(kwargs.items())
                if v is not None and k != "db" and k != "user"
            )
            cache_key = f"{prefix}:{sorted_params}" if sorted_params else prefix

            cache = RedisCache()
            # Try cache hit
            cached = await cache.get(cache_key)
            if cached is not None:
                return cached

            # Call the actual endpoint
            result = await func(*args, **kwargs)

            # Store result in cache
            await cache.set(cache_key, result, ttl=ttl_seconds)
            return result

        return wrapper

    return decorator