"""
cache_manager.py — Cache Layer Distribuito su Supabase A

Architettura:
  - Supabase A funge da archivio cache distribuito (read-only, non-critical)
  - TTL configurabile per invalidazione automatica
  - Fallback a B se A non disponibile
  - Supporta cache per query, memoria, embeddings, conversazioni

Strategie di Caching:
  1. Query Cache: Risultati query SELECT memorizzati con TTL
  2. Memory Cache: Memoria agente memorizzata per accesso veloce
  3. Embedding Cache: Embeddings pre-calcolati per RAG
  4. Conversation Cache: Conversazioni recenti per accesso veloce

Invalidazione:
  - TTL-based: Scadenza automatica dopo TTL
  - Event-based: Invalidazione su INSERT/UPDATE/DELETE su B
  - Manual: Invalidazione esplicita via API

Statistiche:
  - Hit rate: % di richieste servite da cache
  - Miss rate: % di richieste non in cache
  - Eviction rate: % di entry rimosse per TTL
"""

import os
import asyncio
import logging
import hashlib
import json
from typing import Optional, Dict, List, Any, Callable
from datetime import datetime, timedelta
from enum import Enum
import time

_logger = logging.getLogger("cache_manager")

# ── Configurazione Cache ───────────────────────────────────────────────────
CACHE_ENABLED = os.getenv("SUPABASE_CACHE_ENABLED", "true").lower() == "true"
CACHE_TTL_DEFAULT = int(os.getenv("SUPABASE_CACHE_TTL", "3600"))  # 1 ora
CACHE_MAX_SIZE = int(os.getenv("SUPABASE_CACHE_MAX_SIZE", "10000"))  # max entries
CACHE_STATS_ENABLED = os.getenv("SUPABASE_CACHE_STATS_ENABLED", "true").lower() == "true"

# ── Enumerazione Strategie Cache ───────────────────────────────────────────
class CacheStrategy(str, Enum):
    QUERY = "query"  # Cache risultati query
    MEMORY = "memory"  # Cache memoria agente
    EMBEDDING = "embedding"  # Cache embeddings
    CONVERSATION = "conversation"  # Cache conversazioni
    ANALYTICS = "analytics"  # Cache analytics/reporting


# ── TTL per Strategia ─────────────────────────────────────────────────────
CACHE_TTL_BY_STRATEGY = {
    CacheStrategy.QUERY: int(os.getenv("CACHE_TTL_QUERY", "600")),  # 10 min
    CacheStrategy.MEMORY: int(os.getenv("CACHE_TTL_MEMORY", "1800")),  # 30 min
    CacheStrategy.EMBEDDING: int(os.getenv("CACHE_TTL_EMBEDDING", "7200")),  # 2 ore
    CacheStrategy.CONVERSATION: int(os.getenv("CACHE_TTL_CONVERSATION", "3600")),  # 1 ora
    CacheStrategy.ANALYTICS: int(os.getenv("CACHE_TTL_ANALYTICS", "300")),  # 5 min
}

# ── Configurazione Supabase A ──────────────────────────────────────────────
SUPABASE_A_URL = os.getenv("SUPABASE_URL_A", "")
SUPABASE_A_KEY = os.getenv("SUPABASE_KEY_A", "")
SUPABASE_B_URL = os.getenv("SUPABASE_URL", "")
SUPABASE_B_KEY = os.getenv("SUPABASE_KEY", "")


# ── Client Cache ───────────────────────────────────────────────────────────
class CacheClient:
    """Client per gestire cache su Supabase A."""
    
    def __init__(self, url: str, key: str):
        self.url = url
        self.key = key
        self.base_url = f"{url}/rest/v1" if url else None
        self._stats = {
            "hits": 0,
            "misses": 0,
            "sets": 0,
            "deletes": 0,
            "evictions": 0,
        }
    
    def _generate_cache_key(self, strategy: str, identifier: str) -> str:
        """Genera una chiave cache univoca."""
        combined = f"{strategy}:{identifier}"
        return hashlib.sha256(combined.encode()).hexdigest()[:32]
    
    async def get(self, strategy: CacheStrategy, identifier: str) -> Optional[Dict]:
        """Recupera un valore dalla cache."""
        if not CACHE_ENABLED or not self.base_url:
            return None
        
        cache_key = self._generate_cache_key(strategy.value, identifier)
        
        try:
            import httpx
            
            url = f"{self.base_url}/cache_entries?cache_key=eq.{cache_key}"
            headers = {
                "apikey": self.key,
                "Authorization": f"Bearer {self.key}",
                "Content-Type": "application/json",
            }
            
            async with httpx.AsyncClient() as client:
                response = await client.get(url, headers=headers, timeout=5.0)
                
                if response.status_code == 200:
                    rows = response.json()
                    if rows:
                        entry = rows[0]
                        
                        # Verifica TTL
                        if self._is_expired(entry):
                            # Elimina entry scaduta
                            await self._delete_entry(cache_key)
                            if CACHE_STATS_ENABLED:
                                self._stats["evictions"] += 1
                            return None
                        
                        # Hit
                        if CACHE_STATS_ENABLED:
                            self._stats["hits"] += 1
                        
                        return {
                            "value": entry.get("value"),
                            "cached_at": entry.get("created_at"),
                            "ttl_remaining": self._get_ttl_remaining(entry),
                        }
                
                # Miss
                if CACHE_STATS_ENABLED:
                    self._stats["misses"] += 1
                return None
        
        except Exception as exc:
            _logger.error(f"Cache get error: {exc}")
            return None
    
    async def set(
        self,
        strategy: CacheStrategy,
        identifier: str,
        value: Any,
        ttl: Optional[int] = None,
    ) -> bool:
        """Memorizza un valore nella cache."""
        if not CACHE_ENABLED or not self.base_url:
            return False
        
        cache_key = self._generate_cache_key(strategy.value, identifier)
        ttl = ttl or CACHE_TTL_BY_STRATEGY.get(strategy, CACHE_TTL_DEFAULT)
        
        try:
            import httpx
            
            url = f"{self.base_url}/cache_entries"
            headers = {
                "apikey": self.key,
                "Authorization": f"Bearer {self.key}",
                "Content-Type": "application/json",
            }
            
            data = {
                "cache_key": cache_key,
                "strategy": strategy.value,
                "identifier": identifier,
                "value": json.dumps(value) if not isinstance(value, str) else value,
                "ttl_seconds": ttl,
                "created_at": datetime.now().isoformat(),
                "expires_at": (datetime.now() + timedelta(seconds=ttl)).isoformat(),
            }
            
            async with httpx.AsyncClient() as client:
                response = await client.post(url, json=data, headers=headers, timeout=5.0)
                
                if response.status_code in (200, 201):
                    if CACHE_STATS_ENABLED:
                        self._stats["sets"] += 1
                    return True
                else:
                    _logger.warning(f"Cache set failed: {response.status_code}")
                    return False
        
        except Exception as exc:
            _logger.error(f"Cache set error: {exc}")
            return False
    
    async def delete(self, strategy: CacheStrategy, identifier: str) -> bool:
        """Elimina un valore dalla cache."""
        if not CACHE_ENABLED or not self.base_url:
            return False
        
        cache_key = self._generate_cache_key(strategy.value, identifier)
        return await self._delete_entry(cache_key)
    
    async def _delete_entry(self, cache_key: str) -> bool:
        """Elimina un entry dalla cache per chiave."""
        try:
            import httpx
            
            url = f"{self.base_url}/cache_entries?cache_key=eq.{cache_key}"
            headers = {
                "apikey": self.key,
                "Authorization": f"Bearer {self.key}",
            }
            
            async with httpx.AsyncClient() as client:
                response = await client.delete(url, headers=headers, timeout=5.0)
                
                if response.status_code in (200, 204):
                    if CACHE_STATS_ENABLED:
                        self._stats["deletes"] += 1
                    return True
                return False
        
        except Exception as exc:
            _logger.error(f"Cache delete error: {exc}")
            return False
    
    def _is_expired(self, entry: Dict) -> bool:
        """Verifica se un entry è scaduto."""
        expires_at = entry.get("expires_at")
        if not expires_at:
            return False
        
        try:
            expires_dt = datetime.fromisoformat(expires_at)
            return datetime.now() > expires_dt
        except:
            return False
    
    def _get_ttl_remaining(self, entry: Dict) -> int:
        """Calcola il TTL rimanente in secondi."""
        expires_at = entry.get("expires_at")
        if not expires_at:
            return 0
        
        try:
            expires_dt = datetime.fromisoformat(expires_at)
            remaining = (expires_dt - datetime.now()).total_seconds()
            return max(0, int(remaining))
        except:
            return 0
    
    def get_stats(self) -> Dict[str, Any]:
        """Ritorna statistiche cache."""
        total = self._stats["hits"] + self._stats["misses"]
        hit_rate = (self._stats["hits"] / total * 100) if total > 0 else 0
        
        return {
            "enabled": CACHE_ENABLED,
            "hits": self._stats["hits"],
            "misses": self._stats["misses"],
            "sets": self._stats["sets"],
            "deletes": self._stats["deletes"],
            "evictions": self._stats["evictions"],
            "hit_rate_percent": round(hit_rate, 2),
            "total_requests": total,
        }
    
    def reset_stats(self):
        """Resetta le statistiche."""
        self._stats = {
            "hits": 0,
            "misses": 0,
            "sets": 0,
            "deletes": 0,
            "evictions": 0,
        }


# ── Cache Wrapper con Fallback ─────────────────────────────────────────────
class CacheManager:
    """Gestore cache con fallback intelligente."""
    
    def __init__(self):
        self.cache_client = CacheClient(SUPABASE_A_URL, SUPABASE_A_KEY) if SUPABASE_A_URL else None
        self.fallback_client = CacheClient(SUPABASE_B_URL, SUPABASE_B_KEY) if SUPABASE_B_URL else None
    
    async def get_or_fetch(
        self,
        strategy: CacheStrategy,
        identifier: str,
        fetch_fn: Callable,
        ttl: Optional[int] = None,
    ) -> Any:
        """
        Recupera valore da cache o lo genera con fetch_fn.
        
        Logica:
        1. Prova a leggere da cache A
        2. Se miss, chiama fetch_fn
        3. Memorizza risultato in cache A
        4. Ritorna valore
        """
        # Prova cache A
        if self.cache_client:
            cached = await self.cache_client.get(strategy, identifier)
            if cached:
                _logger.debug(f"Cache hit: {strategy.value}:{identifier}")
                return json.loads(cached["value"]) if isinstance(cached["value"], str) else cached["value"]
        
        # Cache miss → fetch
        _logger.debug(f"Cache miss: {strategy.value}:{identifier}, fetching...")
        try:
            value = await fetch_fn() if asyncio.iscoroutinefunction(fetch_fn) else fetch_fn()
        except Exception as exc:
            _logger.error(f"Fetch error: {exc}")
            return None
        
        # Memorizza in cache A
        if self.cache_client and value is not None:
            ttl = ttl or CACHE_TTL_BY_STRATEGY.get(strategy, CACHE_TTL_DEFAULT)
            await self.cache_client.set(strategy, identifier, value, ttl)
        
        return value
    
    async def invalidate(self, strategy: CacheStrategy, identifier: str) -> bool:
        """Invalida un entry cache."""
        if self.cache_client:
            return await self.cache_client.delete(strategy, identifier)
        return False
    
    async def invalidate_pattern(self, strategy: CacheStrategy, pattern: str) -> int:
        """Invalida tutti gli entry che corrispondono a un pattern."""
        # TODO: Implementare pattern matching
        return 0
    
    def get_stats(self) -> Dict[str, Any]:
        """Ritorna statistiche cache."""
        if self.cache_client:
            return self.cache_client.get_stats()
        return {"enabled": False}
    
    def reset_stats(self):
        """Resetta statistiche."""
        if self.cache_client:
            self.cache_client.reset_stats()


# ── Istanza Globale ───────────────────────────────────────────────────────
_cache_manager = CacheManager()


# ── Funzioni Pubbliche ────────────────────────────────────────────────────
async def get_cached(
    strategy: CacheStrategy,
    identifier: str,
    fetch_fn: Callable,
    ttl: Optional[int] = None,
) -> Any:
    """Recupera valore da cache o lo genera."""
    return await _cache_manager.get_or_fetch(strategy, identifier, fetch_fn, ttl)


async def invalidate_cache(strategy: CacheStrategy, identifier: str) -> bool:
    """Invalida un entry cache."""
    return await _cache_manager.invalidate(strategy, identifier)


def get_cache_stats() -> Dict[str, Any]:
    """Ritorna statistiche cache."""
    return _cache_manager.get_stats()


def reset_cache_stats():
    """Resetta statistiche cache."""
    _cache_manager.reset_stats()


# ── Decorator per Caching Automatico ───────────────────────────────────────
def cached(strategy: CacheStrategy, ttl: Optional[int] = None):
    """
    Decorator per caching automatico di funzioni.
    
    Uso:
        @cached(CacheStrategy.QUERY, ttl=600)
        async def get_user_data(user_id: str):
            return await fetch_user_from_db(user_id)
    """
    def decorator(func: Callable):
        async def wrapper(*args, **kwargs):
            # Genera identifier da args/kwargs
            identifier = f"{func.__name__}:{str(args)}:{str(kwargs)}"
            
            # Usa cache manager
            return await _cache_manager.get_or_fetch(
                strategy,
                identifier,
                lambda: func(*args, **kwargs),
                ttl,
            )
        
        return wrapper
    
    return decorator