chat_agent/services/session_manager.py

"""Session management service for chat agent."""

import json
import logging
from datetime import datetime, timedelta
from typing import Optional, List, Dict, Any
from uuid import uuid4

import redis
from sqlalchemy.exc import SQLAlchemyError

from ..models.chat_session import ChatSession
from ..models.base import db


logger = logging.getLogger(__name__)


class SessionManagerError(Exception):
    """Base exception for session manager errors."""
    pass


class SessionNotFoundError(SessionManagerError):
    """Raised when a session is not found."""
    pass


class SessionExpiredError(SessionManagerError):
    """Raised when a session has expired."""
    pass


class SessionManager:
    """Manages user chat sessions with Redis caching and PostgreSQL persistence."""
    
    def __init__(self, redis_client: redis.Redis, session_timeout: int = 3600):
        """
        Initialize the session manager.
        
        Args:
            redis_client: Redis client instance for caching
            session_timeout: Session timeout in seconds (default: 1 hour)
        """
        self.redis_client = redis_client
        self.session_timeout = session_timeout
        self.cache_prefix = "session:"
        self.user_sessions_prefix = "user_sessions:"
        
    def create_session(self, user_id: str, language: str = 'python', 
                      session_metadata: Optional[Dict[str, Any]] = None) -> ChatSession:
        """
        Create a new chat session.
        
        Args:
            user_id: User identifier
            language: Programming language for the session (default: python)
            session_metadata: Additional session metadata
            
        Returns:
            ChatSession: The created session
            
        Raises:
            SessionManagerError: If session creation fails
        """
        try:
            # Create session in database
            session = ChatSession.create_session(
                user_id=user_id,
                language=language,
                session_metadata=session_metadata or {}
            )
            
            # Cache session in Redis
            self._cache_session(session)
            
            # Add session to user's session list
            self._add_to_user_sessions(user_id, session.id)
            
            logger.info(f"Created new session {session.id} for user {user_id}")
            return session
            
        except SQLAlchemyError as e:
            logger.error(f"Database error creating session: {e}")
            raise SessionManagerError(f"Failed to create session: {e}")
        except redis.RedisError as e:
            logger.error(f"Redis error caching session: {e}")
            # Session was created in DB, continue without cache
            return session
    
    def get_session(self, session_id: str) -> ChatSession:
        """
        Get a session by ID, checking cache first then database.
        
        Args:
            session_id: Session identifier
            
        Returns:
            ChatSession: The session object
            
        Raises:
            SessionNotFoundError: If session doesn't exist
            SessionExpiredError: If session has expired
        """
        # Try to get from cache first
        cached_session = self._get_cached_session(session_id)
        if cached_session:
            # Check if session is expired
            if self._is_session_expired(cached_session):
                self._expire_session(session_id)
                raise SessionExpiredError(f"Session {session_id} has expired")
            return cached_session
        
        # Get from database
        try:
            session = db.session.query(ChatSession).filter(
                ChatSession.id == session_id,
                ChatSession.is_active == True
            ).first()
            
            if not session:
                raise SessionNotFoundError(f"Session {session_id} not found")
            
            # Check if session is expired
            if session.is_expired(self.session_timeout):
                session.deactivate()
                raise SessionExpiredError(f"Session {session_id} has expired")
            
            # Cache the session
            self._cache_session(session)
            
            return session
            
        except SQLAlchemyError as e:
            logger.error(f"Database error getting session {session_id}: {e}")
            raise SessionManagerError(f"Failed to get session: {e}")
    
    def update_session_activity(self, session_id: str) -> None:
        """
        Update session activity timestamp.
        
        Args:
            session_id: Session identifier
            
        Raises:
            SessionNotFoundError: If session doesn't exist
        """
        try:
            session = self.get_session(session_id)
            session.update_activity()
            
            # Update cache
            self._cache_session(session)
            
            logger.debug(f"Updated activity for session {session_id}")
            
        except (SessionNotFoundError, SessionExpiredError):
            raise
        except Exception as e:
            logger.error(f"Error updating session activity: {e}")
            raise SessionManagerError(f"Failed to update session activity: {e}")
    
    def get_user_sessions(self, user_id: str, active_only: bool = True) -> List[ChatSession]:
        """
        Get all sessions for a user.
        
        Args:
            user_id: User identifier
            active_only: Whether to return only active sessions
            
        Returns:
            List[ChatSession]: List of user sessions
        """
        try:
            query = db.session.query(ChatSession).filter(ChatSession.user_id == user_id)
            
            if active_only:
                query = query.filter(ChatSession.is_active == True)
            
            sessions = query.order_by(ChatSession.last_active.desc()).all()
            
            # Filter out expired sessions
            if active_only:
                active_sessions = []
                for session in sessions:
                    if not session.is_expired(self.session_timeout):
                        active_sessions.append(session)
                    else:
                        # Mark as inactive
                        session.deactivate()
                        self._remove_from_cache(session.id)
                
                return active_sessions
            
            return sessions
            
        except SQLAlchemyError as e:
            logger.error(f"Database error getting user sessions: {e}")
            raise SessionManagerError(f"Failed to get user sessions: {e}")
    
    def cleanup_inactive_sessions(self) -> int:
        """
        Clean up inactive and expired sessions.
        
        Returns:
            int: Number of sessions cleaned up
        """
        try:
            # Clean up expired sessions in database
            cleaned_count = ChatSession.cleanup_expired_sessions(self.session_timeout)
            
            # Clean up expired sessions from cache
            self._cleanup_expired_cache_sessions()
            
            logger.info(f"Cleaned up {cleaned_count} expired sessions")
            return cleaned_count
            
        except SQLAlchemyError as e:
            logger.error(f"Database error during cleanup: {e}")
            raise SessionManagerError(f"Failed to cleanup sessions: {e}")
    
    def delete_session(self, session_id: str) -> None:
        """
        Delete a session completely.
        
        Args:
            session_id: Session identifier
            
        Raises:
            SessionNotFoundError: If session doesn't exist
        """
        try:
            session = db.session.query(ChatSession).filter(
                ChatSession.id == session_id
            ).first()
            
            if not session:
                raise SessionNotFoundError(f"Session {session_id} not found")
            
            user_id = session.user_id
            
            # Delete from database (cascade will handle related records)
            db.session.delete(session)
            db.session.commit()
            
            # Remove from cache
            self._remove_from_cache(session_id)
            
            # Remove from user sessions list
            self._remove_from_user_sessions(user_id, session_id)
            
            logger.info(f"Deleted session {session_id}")
            
        except SQLAlchemyError as e:
            logger.error(f"Database error deleting session: {e}")
            raise SessionManagerError(f"Failed to delete session: {e}")
    
    def set_session_language(self, session_id: str, language: str) -> None:
        """
        Set the programming language for a session.
        
        Args:
            session_id: Session identifier
            language: Programming language
            
        Raises:
            SessionNotFoundError: If session doesn't exist
        """
        try:
            session = self.get_session(session_id)
            session.set_language(language)
            
            # Update cache
            self._cache_session(session)
            
            logger.info(f"Set language to {language} for session {session_id}")
            
        except (SessionNotFoundError, SessionExpiredError):
            raise
        except Exception as e:
            logger.error(f"Error setting session language: {e}")
            raise SessionManagerError(f"Failed to set session language: {e}")
    
    def increment_message_count(self, session_id: str) -> None:
        """
        Increment the message count for a session.
        
        Args:
            session_id: Session identifier
        """
        try:
            session = self.get_session(session_id)
            session.increment_message_count()
            
            # Update cache
            self._cache_session(session)
            
        except (SessionNotFoundError, SessionExpiredError):
            raise
        except Exception as e:
            logger.error(f"Error incrementing message count: {e}")
            raise SessionManagerError(f"Failed to increment message count: {e}")
    
    def _cache_session(self, session: ChatSession) -> None:
        """Cache a session in Redis."""
        if not self.redis_client:
            return  # Skip caching if Redis is not available
            
        try:
            cache_key = f"{self.cache_prefix}{session.id}"
            session_data = {
                'id': session.id,
                'user_id': session.user_id,
                'language': session.language,
                'created_at': session.created_at.isoformat(),
                'last_active': session.last_active.isoformat(),
                'message_count': session.message_count,
                'is_active': session.is_active,
                'session_metadata': session.session_metadata
            }
            
            # Set with expiration
            self.redis_client.setex(
                cache_key,
                self.session_timeout + 300,  # Add 5 minutes buffer
                json.dumps(session_data)
            )
            
        except redis.RedisError as e:
            logger.warning(f"Failed to cache session {session.id}: {e}")
    
    def _get_cached_session(self, session_id: str) -> Optional[ChatSession]:
        """Get a session from Redis cache."""
        if not self.redis_client:
            return None  # Skip cache lookup if Redis is not available
            
        try:
            cache_key = f"{self.cache_prefix}{session_id}"
            cached_data = self.redis_client.get(cache_key)
            
            if not cached_data:
                return None
            
            session_data = json.loads(cached_data)
            
            # Create a ChatSession object from cached data
            session = ChatSession(
                user_id=session_data['user_id'],
                language=session_data['language'],
                session_metadata=session_data['session_metadata']
            )
            session.id = session_data['id']
            session.created_at = datetime.fromisoformat(session_data['created_at'])
            session.last_active = datetime.fromisoformat(session_data['last_active'])
            session.message_count = session_data['message_count']
            session.is_active = session_data['is_active']
            
            return session
            
        except (redis.RedisError, json.JSONDecodeError, KeyError) as e:
            logger.warning(f"Failed to get cached session {session_id}: {e}")
            return None
    
    def _remove_from_cache(self, session_id: str) -> None:
        """Remove a session from Redis cache."""
        if not self.redis_client:
            return  # Skip cache removal if Redis is not available
            
        try:
            cache_key = f"{self.cache_prefix}{session_id}"
            self.redis_client.delete(cache_key)
        except redis.RedisError as e:
            logger.warning(f"Failed to remove session {session_id} from cache: {e}")
    
    def _add_to_user_sessions(self, user_id: str, session_id: str) -> None:
        """Add session to user's session list in Redis."""
        if not self.redis_client:
            return  # Skip user session tracking if Redis is not available
            
        try:
            user_sessions_key = f"{self.user_sessions_prefix}{user_id}"
            self.redis_client.sadd(user_sessions_key, session_id)
            # Set expiration for user sessions list
            self.redis_client.expire(user_sessions_key, self.session_timeout * 2)
        except redis.RedisError as e:
            logger.warning(f"Failed to add session to user sessions list: {e}")
    
    def _remove_from_user_sessions(self, user_id: str, session_id: str) -> None:
        """Remove session from user's session list in Redis."""
        if not self.redis_client:
            return  # Skip user session tracking if Redis is not available
            
        try:
            user_sessions_key = f"{self.user_sessions_prefix}{user_id}"
            self.redis_client.srem(user_sessions_key, session_id)
        except redis.RedisError as e:
            logger.warning(f"Failed to remove session from user sessions list: {e}")
    
    def _is_session_expired(self, session: ChatSession) -> bool:
        """Check if a session is expired."""
        return session.is_expired(self.session_timeout)
    
    def _expire_session(self, session_id: str) -> None:
        """Mark a session as expired and clean up."""
        try:
            # Mark as inactive in database
            session = db.session.query(ChatSession).filter(
                ChatSession.id == session_id
            ).first()
            
            if session:
                session.deactivate()
                self._remove_from_user_sessions(session.user_id, session_id)
            
            # Remove from cache
            self._remove_from_cache(session_id)
            
        except SQLAlchemyError as e:
            logger.error(f"Error expiring session {session_id}: {e}")
    
    def _cleanup_expired_cache_sessions(self) -> None:
        """Clean up expired sessions from Redis cache."""
        try:
            # Get all session keys
            pattern = f"{self.cache_prefix}*"
            session_keys = self.redis_client.keys(pattern)
            
            expired_keys = []
            for key in session_keys:
                try:
                    cached_data = self.redis_client.get(key)
                    if cached_data:
                        session_data = json.loads(cached_data)
                        last_active = datetime.fromisoformat(session_data['last_active'])
                        
                        if datetime.utcnow() - last_active > timedelta(seconds=self.session_timeout):
                            expired_keys.append(key)
                except (json.JSONDecodeError, KeyError, ValueError):
                    # Invalid data, mark for deletion
                    expired_keys.append(key)
            
            # Delete expired keys
            if expired_keys:
                self.redis_client.delete(*expired_keys)
                logger.info(f"Cleaned up {len(expired_keys)} expired cache entries")
                
        except redis.RedisError as e:
            logger.warning(f"Failed to cleanup expired cache sessions: {e}")


def create_session_manager(redis_client: redis.Redis, session_timeout: int = 3600) -> SessionManager:
    """
    Factory function to create a SessionManager instance.
    
    Args:
        redis_client: Redis client instance
        session_timeout: Session timeout in seconds
        
    Returns:
        SessionManager: Configured session manager instance
    """
    return SessionManager(redis_client, session_timeout)