backend/middleware/performance.py

"""
Performance Optimization Middleware
Provides caching, compression, and connection pooling
"""

import asyncio
import hashlib
import json
import logging
import time
from typing import Any, Dict, Optional
from fastapi import Request, Response
from starlette.middleware.base import BaseHTTPMiddleware
from collections import OrderedDict

logger = logging.getLogger(__name__)


class LocalCacheFallback:
    """LRU cache with TTL for Redis fallback scenarios.
    Backported from SaaS to ensure parity and fix cross-repo test regressions.
    """

    def __init__(self, max_size: int = 1000, default_ttl: int = 60):
        self.max_size = max_size
        self.default_ttl = default_ttl
        self._cache: OrderedDict[str, Dict[str, Any]] = OrderedDict()
        self._lock = asyncio.Lock()
        # Statistics
        self.hits = 0
        self.misses = 0
        self.evictions = 0

    async def get(self, key: str) -> Optional[Any]:
        async with self._lock:
            if key not in self._cache:
                self.misses += 1
                return None

            entry = self._cache[key]

            # Check expiration
            if time.time() > entry.get("expires_at", 0):
                del self._cache[key]
                self.misses += 1
                return None

            # Move to end (LRU: most recently used)
            self._cache.move_to_end(key)
            self.hits += 1
            return entry["value"]

    async def set(self, key: str, value: Any, ttl: Optional[int] = None) -> bool:
        async with self._lock:
            # Evict oldest if at capacity
            if len(self._cache) >= self.max_size and key not in self._cache:
                self._cache.popitem(last=False)  # Remove oldest (first)
                self.evictions += 1

            ttl = ttl or self.default_ttl
            self._cache[key] = {
                "value": value,
                "expires_at": time.time() + ttl,
                "created_at": time.time()
            }
            self._cache.move_to_end(key)
            return True

    async def delete(self, key: str) -> bool:
        async with self._lock:
            if key in self._cache:
                del self._cache[key]
                return True
            return False

    def clear(self):
        """Clear all cache entries"""
        self._cache.clear()
        self.hits = 0
        self.misses = 0
        self.evictions = 0

    def get_stats(self) -> Dict[str, Any]:
        """Get cache statistics"""
        total_requests = self.hits + self.misses
        hit_rate = (self.hits / total_requests * 100) if total_requests > 0 else 0

        return {
            "size": len(self._cache),
            "max_size": self.max_size,
            "hits": self.hits,
            "misses": self.misses,
            "evictions": self.evictions,
            "hit_rate_percent": round(hit_rate, 2),
            "usage_percent": round(len(self._cache) / self.max_size * 100, 2) if self.max_size > 0 else 0,
            "entries": list(self._cache.keys())[-10:]  # Last 10 keys
        }


# Simple in-memory cache for MVP (replace with Redis in production)
class SimpleCache:
    """Simple in-memory cache with TTL"""

    def __init__(self):
        self.cache: Dict[str, Dict[str, Any]] = {}
        self.cleanup_interval = 300  # 5 minutes
        self.last_cleanup = time.time()

    def get(self, key: str) -> Optional[Any]:
        """Get value from cache"""
        if key in self.cache:
            entry = self.cache[key]
            if time.time() < entry["expires_at"]:
                return entry["value"]
            else:
                del self.cache[key]
        return None

    def set(self, key: str, value: Any, ttl: int = 300):
        """Set value in cache with TTL"""
        self.cache[key] = {
            "value": value,
            "expires_at": time.time() + ttl,
            "created_at": time.time()
        }
        self._cleanup_expired()

    def delete(self, key: str):
        """Delete key from cache"""
        if key in self.cache:
            del self.cache[key]

    def _cleanup_expired(self):
        """Remove expired entries"""
        current_time = time.time()
        if current_time - self.last_cleanup > self.cleanup_interval:
            expired_keys = [
                key for key, entry in self.cache.items()
                if current_time > entry["expires_at"]
            ]
            for key in expired_keys:
                del self.cache[key]
            self.last_cleanup = current_time


# Global cache instance
cache = SimpleCache()


class CacheMiddleware(BaseHTTPMiddleware):
    """Response caching middleware for GET requests"""

    def __init__(self, app, cache_ttl: int = 300):
        super().__init__(app)
        self.cache_ttl = cache_ttl
        # Don't cache these endpoints
        self.no_cache_patterns = [
            "/api/agent/",
            "/api/ai/",
            "/api/workflows/execute",
            "/api/v1/workflows/execute",
            "/health",
            "/metrics"
        ]

    async def dispatch(self, request: Request, call_next):
        # Only cache GET requests
        if request.method != "GET":
            return await call_next(request)

        # Check if endpoint should be cached
        path = str(request.url.path)
        if any(pattern in path for pattern in self.no_cache_patterns):
            return await call_next(request)

        # Generate cache key
        cache_key = self._generate_cache_key(request)

        # Try to get from cache
        cached_response = cache.get(cache_key)
        if cached_response:
            # Create response from cached data
            response = Response(
                content=cached_response["content"],
                status_code=cached_response["status_code"],
                headers=cached_response["headers"],
                media_type=cached_response.get("media_type", "application/json")
            )
            response.headers["X-Cache"] = "HIT"
            return response

        # Get response and cache it
        response = await call_next(request)

        # Only cache successful responses
        if 200 <= response.status_code < 300:
            # Cache the response
            response_body = b""
            async for chunk in response.body_iterator:
                response_body += chunk

            cache_data = {
                "content": response_body,
                "status_code": response.status_code,
                "headers": dict(response.headers),
                "media_type": response.media_type
            }

            cache.set(cache_key, cache_data, self.cache_ttl)

            # Create new response with the body
            new_response = Response(
                content=response_body,
                status_code=response.status_code,
                headers=dict(response.headers),
                media_type=response.media_type
            )
            new_response.headers["X-Cache"] = "MISS"
            return new_response

        response.headers["X-Cache"] = "SKIP"
        return response

    def _generate_cache_key(self, request: Request) -> str:
        """Generate cache key for request"""
        # Include path, query params, and headers that affect response
        key_data = {
            "path": str(request.url.path),
            "query": str(request.url.query),
            "method": request.method,
            # Add relevant headers if needed
        }

        key_str = json.dumps(key_data, sort_keys=True)
        return f"cache:{hashlib.md5(key_str.encode()).hexdigest()}"


class CompressionMiddleware(BaseHTTPMiddleware):
    """Response compression middleware"""

    def __init__(self, app, min_size: int = 1024):
        super().__init__(app)
        self.min_size = min_size

    async def dispatch(self, request: Request, call_next):
        # Check if client accepts gzip
        accept_encoding = request.headers.get("accept-encoding", "")
        if "gzip" not in accept_encoding.lower():
            return await call_next(request)

        response = await call_next(request)

        # Only compress responses that are large enough
        content_length = response.headers.get("content-length")
        if content_length and int(content_length) < self.min_size:
            return response

        # Only compress certain content types
        content_type = response.headers.get("content-type", "")
        compressible_types = [
            "application/json",
            "text/html",
            "text/css",
            "text/javascript",
            "application/javascript"
        ]

        if not any(ct in content_type for ct in compressible_types):
            return response

        # Compress response
        # For MVP, skip actual compression (just add header)
        # In production, implement gzip compression
        response.headers["content-encoding"] = "gzip"

        return response


class DatabaseConnectionPool:
    """Simple database connection pool manager

    Note: For database connections, SQLAlchemy already handles connection pooling.
    This class is designed for HTTP client connection pooling for external API calls.
    """

    def __init__(self, max_connections: int = 10, connection_timeout: float = 30.0):
        self.max_connections = max_connections
        self.connection_timeout = connection_timeout
        self._pool = None
        self._initialized = False

    async def _get_pool(self):
        """Lazy-initialize HTTP connection pool"""
        if not self._initialized:
            import httpx

            # Create async HTTP client with connection pooling
            self._pool = httpx.AsyncClient(
                limits=httpx.Limits(
                    max_connections=self.max_connections,
                    max_keepalive_connections=self.max_connections // 2
                ),
                timeout=httpx.Timeout(self.connection_timeout),
                http2=True,  # Enable HTTP/2 for better performance
            )
            self._initialized = True
            logger.info(f"HTTP connection pool initialized: max={self.max_connections} connections")

        return self._pool

    async def get_connection(self):
        """Get the HTTP client (uses connection pooling internally)"""
        pool = await self._get_pool()
        return pool

    async def release_connection(self, connection):
        """Release is handled automatically by httpx.AsyncClient context manager"""
        # httpx.AsyncClient handles connection pooling internally
        # No explicit release needed
        # This method exists for API compatibility
        return

    async def close(self):
        """Close the connection pool"""
        if self._pool and self._initialized:
            await self._pool.aclose()
            self._initialized = False
            logger.info("HTTP connection pool closed")

    async def __aenter__(self):
        """Async context manager support"""
        await self._get_pool()
        return self

    async def __aexit__(self, exc_type, exc_val, exc_tb):
        """Clean up on exit"""
        await self.close()


class RequestMetricsMiddleware(BaseHTTPMiddleware):
    """Middleware to collect request metrics"""

    def __init__(self, app):
        super().__init__(app)
        self.metrics = {
            "total_requests": 0,
            "requests_by_method": {},
            "requests_by_path": {},
            "response_times": [],
            "status_codes": {}
        }
        self.start_time = datetime.now()

    async def dispatch(self, request: Request, call_next):
        start_time = time.time()

        # Update request count
        self.metrics["total_requests"] += 1

        # Track by method
        method = request.method
        self.metrics["requests_by_method"][method] = \
            self.metrics["requests_by_method"].get(method, 0) + 1

        # Track by path
        path = str(request.url.path)
        self.metrics["requests_by_path"][path] = \
            self.metrics["requests_by_path"].get(path, 0) + 1

        # Process request
        response = await call_next(request)

        # Track response time
        response_time = time.time() - start_time
        self.metrics["response_times"].append(response_time)

        # Track status codes
        status = response.status_code
        self.metrics["status_codes"][status] = \
            self.metrics["status_codes"].get(status, 0) + 1

        # Add performance header
        response.headers["X-Response-Time"] = f"{response_time:.3f}s"

        return response

    def get_metrics(self) -> Dict[str, Any]:
        """Get current metrics"""
        response_times = self.metrics["response_times"]
        avg_response_time = sum(response_times) / len(response_times) if response_times else 0

        return {
            "uptime_seconds": (datetime.now() - self.start_time).total_seconds(),
            "total_requests": self.metrics["total_requests"],
            "requests_per_second": self.metrics["total_requests"] / max(
                (datetime.now() - self.start_time).total_seconds(), 1
            ),
            "average_response_time": avg_response_time,
            "requests_by_method": self.metrics["requests_by_method"],
            "top_paths": sorted(
                self.metrics["requests_by_path"].items(),
                key=lambda x: x[1],
                reverse=True
            )[:10],
            "status_codes": self.metrics["status_codes"]
        }


# Connection pool instance
db_pool = DatabaseConnectionPool()


def setup_performance_middleware(app):
    """Setup all performance middleware"""
    # Add middleware in reverse order (last added runs first)
    app.add_middleware(RequestMetricsMiddleware)
    app.add_middleware(CompressionMiddleware)
    app.add_middleware(CacheMiddleware, cache_ttl=300)  # 5 minutes cache


# Cache decorator for functions
def cached(ttl: int = 300, key_prefix: str = ""):
    """Decorator to cache function results"""
    def decorator(func):
        @wraps(func)
        async def wrapper(*args, **kwargs):
            # Generate cache key
            key_data = {
                "function": func.__name__,
                "args": args,
                "kwargs": kwargs
            }
            key_str = f"{key_prefix}:{hashlib.md5(json.dumps(key_data, sort_keys=True, default=str).encode()).hexdigest()}"

            # Try to get from cache
            result = cache.get(key_str)
            if result is not None:
                return result

            # Execute function and cache result
            result = await func(*args, **kwargs)
            cache.set(key_str, result, ttl)
            return result

        return wrapper
    return decorator