app/utils/cache.py

from typing import Optional, Any, Dict, Callable, TypeVar
import json
import inspect
import redis.asyncio as redis
from ..core.config import settings
from ..utils.logger import logger

T = TypeVar('T')

class RedisCache:
    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super(RedisCache, cls).__new__(cls)
            cls._instance.is_connected = False
            cls._instance.fallback_cache = {}
            cls._instance.redis = redis.Redis(
                host=settings.REDIS_HOST,
                port=settings.REDIS_PORT,
                password=settings.REDIS_PASSWORD,
                username=settings.REDIS_USERNAME,
                decode_responses=True
            )
        return cls._instance

    async def initialize(self):
        """Initialize Redis connection with fallback to dummy cache"""
        try:
            await self.redis.ping()
            self.is_connected = True
            logger.info("Redis cache initialized successfully")
        except Exception as e:
            self.is_connected = False
            self.fallback_cache = {}
            logger.warning(f"Redis connection failed, using in-memory fallback: {str(e)}")

    async def set_cache(self, key: str, value: Any, expire: int = 3600):
        """Set a cache entry with optional expiration time (default 1 hour)"""
        try:
            if not self.is_connected:
                self.fallback_cache[key] = value
                return
            
            await self.redis.set(key, json.dumps(value), ex=expire)
        except Exception as e:
            logger.error(f"Cache set error: {str(e)}")
            self.fallback_cache[key] = value

    async def get_cache(self, key: str) -> Optional[Any]:
        """Get a cached value by key"""
        try:
            if not self.is_connected:
                return self.fallback_cache.get(key)
            
            value = await self.redis.get(key)
            if value:
                return json.loads(value)
        except Exception as e:
            logger.error(f"Cache get error: {str(e)}")
            return self.fallback_cache.get(key)
        return None

    async def delete_cache(self, key: str) -> bool:
        """Delete a cache entry by key"""
        try:
            if not self.is_connected:
                return bool(self.fallback_cache.pop(key, None))
            
            return bool(await self.redis.delete(key))
        except Exception as e:
            logger.error(f"Cache delete error: {str(e)}")
            return False

    async def clear_cache_pattern(self, pattern: str) -> bool:
        """Clear all cache entries matching a pattern"""
        try:
            if not self.is_connected:
                # Basic pattern matching for fallback cache
                removed = 0
                for key in list(self.fallback_cache.keys()):
                    if pattern in key:
                        del self.fallback_cache[key]
                        removed += 1
                return removed > 0
            
            # Get all keys matching pattern
            keys = [key async for key in self.redis.scan_iter(pattern)]
            if keys:
                await self.redis.delete(*keys)
            return bool(keys)
        except Exception as e:
            logger.error(f"Cache pattern clear error: {str(e)}")
            return False

    async def check_connection(self) -> bool:
        """Check if Redis connection is alive"""
        try:
            await self.redis.ping()
            self.is_connected = True
            return True
        except Exception:
            self.is_connected = False
            return False

    async def cleanup_expired(self):
        """Clean up expired cache entries"""
        # Redis automatically handles expiration, only need to clean fallback
        if not self.is_connected:
            self.fallback_cache = {}

def cached(ttl_seconds: int):
    """Decorator to cache function results"""
    def decorator(func: Callable[..., T]) -> Callable[..., T]:
        async def async_wrapper(*args, **kwargs) -> T:
            # Create cache key from function name and arguments
            key = f"{func.__name__}:{str(args)}:{str(kwargs)}"
            
            # Try to get from cache first
            cached_value = await cache.get_cache(key)
            if cached_value is not None:
                return cached_value
            
            # If not in cache, execute function
            result = await func(*args, **kwargs)
            
            # Cache the result
            await cache.set_cache(key, result, expire=ttl_seconds)
            
            return result

        def sync_wrapper(*args, **kwargs) -> T:
            # Create cache key from function name and arguments
            key = f"{func.__name__}:{str(args)}:{str(kwargs)}"
            
            # For sync functions, we can't use async cache directly
            # So we use the fallback cache
            if key in cache.fallback_cache:
                return cache.fallback_cache[key]
            
            # If not in cache, execute function
            result = func(*args, **kwargs)
            
            # Cache the result in fallback
            cache.fallback_cache[key] = result
            
            return result

        return async_wrapper if inspect.iscoroutinefunction(func) else sync_wrapper
    return decorator

cache = RedisCache()