"""
Rate Limiting System

Système de limitation de débit avec algorithme token bucket.
Fiche #23: API Security & Governance
"""

import os
import time
import threading
import logging
from typing import Dict, Optional, Tuple
from dataclasses import dataclass, field
from collections import defaultdict

from ..system.safety_switch import get_safety_switch

logger = logging.getLogger(__name__)


@dataclass
class TokenBucket:
    """
    Implémentation d'un token bucket pour rate limiting.
    
    Algorithme:
    - Capacité maximale de tokens
    - Refill rate (tokens par seconde)
    - Consommation de tokens par requête
    """
    capacity: int
    refill_rate: float  # tokens par seconde
    tokens: float = field(init=False)
    last_refill: float = field(init=False)
    lock: threading.Lock = field(default_factory=threading.Lock, init=False)
    
    def __post_init__(self):
        self.tokens = float(self.capacity)
        self.last_refill = time.time()
    
    def consume(self, tokens_needed: int = 1) -> bool:
        """
        Tente de consommer des tokens.
        
        Args:
            tokens_needed: Nombre de tokens nécessaires
            
        Returns:
            True si les tokens ont pu être consommés
        """
        with self.lock:
            now = time.time()
            
            # Refill des tokens basé sur le temps écoulé
            time_passed = now - self.last_refill
            tokens_to_add = time_passed * self.refill_rate
            
            self.tokens = min(self.capacity, self.tokens + tokens_to_add)
            self.last_refill = now
            
            # Vérifier si on a assez de tokens
            if self.tokens >= tokens_needed:
                self.tokens -= tokens_needed
                return True
            
            return False
    
    def get_status(self) -> Dict:
        """Retourne le statut actuel du bucket."""
        with self.lock:
            now = time.time()
            time_passed = now - self.last_refill
            current_tokens = min(self.capacity, self.tokens + (time_passed * self.refill_rate))
            
            return {
                "capacity": self.capacity,
                "current_tokens": current_tokens,
                "refill_rate": self.refill_rate,
                "time_to_refill": max(0, (self.capacity - current_tokens) / self.refill_rate) if self.refill_rate > 0 else 0
            }


@dataclass
class RateLimitConfig:
    """Configuration pour un endpoint ou utilisateur."""
    requests_per_minute: int = 60
    burst_capacity: int = 10
    tokens_per_request: int = 1


class RateLimitExceeded(Exception):
    """Exception levée quand la limite de débit est dépassée."""
    
    def __init__(self, message: str, retry_after: float = 0):
        super().__init__(message)
        self.retry_after = retry_after


class RateLimiter:
    """
    Gestionnaire de limitation de débit avec token buckets.
    
    Fonctionnalités:
    - Limitation par IP, utilisateur, endpoint
    - Configuration flexible par règle
    - Headers HTTP informatifs
    - Nettoyage automatique des buckets inactifs
    """
    
    def __init__(self):
        self._buckets: Dict[str, TokenBucket] = {}
        self._configs: Dict[str, RateLimitConfig] = {}
        self._lock = threading.Lock()
        self._safety = get_safety_switch()
        self._load_config()
        
        # Nettoyage périodique des buckets inactifs
        self._last_cleanup = time.time()
        self._cleanup_interval = 300  # 5 minutes
    
    @classmethod
    def from_env(cls):
        """Crée une instance depuis les variables d'environnement (compatibilité FastAPI)."""
        return cls()
    
    def _load_config(self):
        """Charge la configuration depuis les variables d'environnement."""
        # Configuration par défaut
        default_rpm = int(os.getenv("DEFAULT_RATE_LIMIT_RPM", "60"))
        default_burst = int(os.getenv("DEFAULT_RATE_LIMIT_BURST", "10"))
        
        self._default_config = RateLimitConfig(
            requests_per_minute=default_rpm,
            burst_capacity=default_burst
        )
        
        # Configurations spécifiques par endpoint
        # Format: RATE_LIMIT_<ENDPOINT>=rpm:burst
        for key, value in os.environ.items():
            if key.startswith("RATE_LIMIT_") and key != "RATE_LIMIT_RPM" and key != "RATE_LIMIT_BURST":
                endpoint = key[11:].lower()  # Enlever "RATE_LIMIT_"
                
                try:
                    if ":" in value:
                        rpm_str, burst_str = value.split(":", 1)
                        rpm = int(rpm_str)
                        burst = int(burst_str)
                    else:
                        rpm = int(value)
                        burst = default_burst
                    
                    self._configs[endpoint] = RateLimitConfig(
                        requests_per_minute=rpm,
                        burst_capacity=burst
                    )
                    logger.debug(f"Rate limit config for {endpoint}: {rpm} RPM, {burst} burst")
                    
                except ValueError as e:
                    logger.error(f"Invalid rate limit config for {key}: {value} - {e}")
        
        logger.info(f"RateLimiter initialized with default {default_rpm} RPM, {default_burst} burst")
    
    def _get_config(self, endpoint: Optional[str] = None) -> RateLimitConfig:
        """Retourne la configuration pour un endpoint."""
        if endpoint and endpoint.lower() in self._configs:
            return self._configs[endpoint.lower()]
        return self._default_config
    
    def _get_bucket_key(self, identifier: str, endpoint: Optional[str] = None) -> str:
        """Génère une clé unique pour le bucket."""
        if endpoint:
            return f"{identifier}:{endpoint}"
        return identifier
    
    def _get_or_create_bucket(self, key: str, config: RateLimitConfig) -> TokenBucket:
        """Récupère ou crée un token bucket."""
        with self._lock:
            if key not in self._buckets:
                # Convertir RPM en tokens par seconde
                refill_rate = config.requests_per_minute / 60.0
                
                self._buckets[key] = TokenBucket(
                    capacity=config.burst_capacity,
                    refill_rate=refill_rate
                )
                logger.debug(f"Created token bucket for {key}: {config.burst_capacity} capacity, {refill_rate:.2f} refill/s")
            
            return self._buckets[key]
    
    def check(self, identifier: str) -> Tuple[bool, float]:
        """
        Vérifie la limite de débit (compatibilité FastAPI).
        
        Args:
            identifier: Identifiant unique
            
        Returns:
            Tuple (allowed, retry_after_seconds)
        """
        allowed, headers = self.check_rate_limit(identifier)
        retry_after = float(headers.get("Retry-After", "0"))
        return allowed, retry_after
    
    def check_rate_limit(self, identifier: str, endpoint: Optional[str] = None, 
                        tokens_needed: int = 1) -> Tuple[bool, Dict[str, str]]:
        """
        Vérifie la limite de débit pour un identifiant.
        
        Args:
            identifier: Identifiant unique (IP, user_id, etc.)
            endpoint: Endpoint optionnel pour des limites spécifiques
            tokens_needed: Nombre de tokens nécessaires
            
        Returns:
            Tuple (allowed, headers) où headers contient les informations de rate limiting
        """
        if not self._safety.is_feature_enabled("rate_limiting"):
            return True, {}
        
        # Nettoyage périodique
        self._cleanup_inactive_buckets()
        
        config = self._get_config(endpoint)
        bucket_key = self._get_bucket_key(identifier, endpoint)
        bucket = self._get_or_create_bucket(bucket_key, config)
        
        # Tenter de consommer les tokens
        allowed = bucket.consume(tokens_needed)
        
        # Générer les headers informatifs
        status = bucket.get_status()
        headers = {
            "X-RateLimit-Limit": str(config.requests_per_minute),
            "X-RateLimit-Remaining": str(int(status["current_tokens"])),
            "X-RateLimit-Reset": str(int(time.time() + status["time_to_refill"]))
        }
        
        if not allowed:
            headers["Retry-After"] = str(int(status["time_to_refill"]) + 1)
            logger.warning(f"Rate limit exceeded for {identifier} on {endpoint or 'default'}")
        
        return allowed, headers
    
    def enforce_rate_limit(self, identifier: str, endpoint: Optional[str] = None, 
                          tokens_needed: int = 1) -> Dict[str, str]:
        """
        Applique la limitation de débit et lève une exception si dépassée.
        
        Args:
            identifier: Identifiant unique
            endpoint: Endpoint optionnel
            tokens_needed: Nombre de tokens nécessaires
            
        Returns:
            Headers de rate limiting
            
        Raises:
            RateLimitExceeded: Si la limite est dépassée
        """
        allowed, headers = self.check_rate_limit(identifier, endpoint, tokens_needed)
        
        if not allowed:
            retry_after = float(headers.get("Retry-After", "60"))
            raise RateLimitExceeded(
                f"Rate limit exceeded for {identifier}. Try again in {retry_after} seconds.",
                retry_after=retry_after
            )
        
        return headers
    
    def _cleanup_inactive_buckets(self):
        """Nettoie les buckets inactifs pour économiser la mémoire."""
        now = time.time()
        
        if now - self._last_cleanup < self._cleanup_interval:
            return
        
        with self._lock:
            inactive_keys = []
            cutoff_time = now - 3600  # 1 heure d'inactivité
            
            for key, bucket in self._buckets.items():
                if bucket.last_refill < cutoff_time:
                    inactive_keys.append(key)
            
            for key in inactive_keys:
                del self._buckets[key]
            
            if inactive_keys:
                logger.debug(f"Cleaned up {len(inactive_keys)} inactive rate limit buckets")
            
            self._last_cleanup = now
    
    def reset_rate_limit(self, identifier: str, endpoint: Optional[str] = None) -> bool:
        """
        Remet à zéro la limite de débit pour un identifiant.
        
        Args:
            identifier: Identifiant à remettre à zéro
            endpoint: Endpoint optionnel
            
        Returns:
            True si remis à zéro avec succès
        """
        bucket_key = self._get_bucket_key(identifier, endpoint)
        
        with self._lock:
            if bucket_key in self._buckets:
                del self._buckets[bucket_key]
                logger.info(f"Reset rate limit for {identifier} on {endpoint or 'default'}")
                return True
        
        return False
    
    def get_rate_limit_status(self, identifier: str, endpoint: Optional[str] = None) -> Dict:
        """
        Retourne le statut de rate limiting pour un identifiant.
        
        Args:
            identifier: Identifiant à vérifier
            endpoint: Endpoint optionnel
            
        Returns:
            Statut du rate limiting
        """
        bucket_key = self._get_bucket_key(identifier, endpoint)
        config = self._get_config(endpoint)
        
        with self._lock:
            if bucket_key in self._buckets:
                bucket_status = self._buckets[bucket_key].get_status()
                return {
                    "identifier": identifier,
                    "endpoint": endpoint,
                    "config": {
                        "requests_per_minute": config.requests_per_minute,
                        "burst_capacity": config.burst_capacity
                    },
                    "current_status": bucket_status
                }
            else:
                return {
                    "identifier": identifier,
                    "endpoint": endpoint,
                    "config": {
                        "requests_per_minute": config.requests_per_minute,
                        "burst_capacity": config.burst_capacity
                    },
                    "current_status": {
                        "capacity": config.burst_capacity,
                        "current_tokens": config.burst_capacity,
                        "refill_rate": config.requests_per_minute / 60.0,
                        "time_to_refill": 0
                    }
                }
    
    def get_global_status(self) -> Dict:
        """Retourne le statut global du rate limiter."""
        with self._lock:
            return {
                "enabled": self._safety.is_feature_enabled("rate_limiting"),
                "active_buckets": len(self._buckets),
                "default_config": {
                    "requests_per_minute": self._default_config.requests_per_minute,
                    "burst_capacity": self._default_config.burst_capacity
                },
                "endpoint_configs": {
                    endpoint: {
                        "requests_per_minute": config.requests_per_minute,
                        "burst_capacity": config.burst_capacity
                    }
                    for endpoint, config in self._configs.items()
                }
            }


# Instance globale
_rate_limiter = None


def get_rate_limiter() -> RateLimiter:
    """Retourne l'instance globale du rate limiter."""
    global _rate_limiter
    if _rate_limiter is None:
        _rate_limiter = RateLimiter()
    return _rate_limiter


def check_rate_limit(identifier: str, endpoint: Optional[str] = None) -> Tuple[bool, Dict[str, str]]:
    """
    Fonction utilitaire pour vérifier une limite de débit.
    
    Args:
        identifier: Identifiant unique
        endpoint: Endpoint optionnel
        
    Returns:
        Tuple (allowed, headers)
    """
    return get_rate_limiter().check_rate_limit(identifier, endpoint)