"""Application context singleton."""

from sqlalchemy.ext.asyncio import AsyncEngine, async_sessionmaker, create_async_engine
from hubgw.core.config import AppSettings


class AppContext:
    """Application context singleton."""
    
    _instance = None
    
    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance
    
    def __init__(self):
        if not hasattr(self, 'initialized'):
            self.settings = AppSettings()
            self.engine: AsyncEngine = None
            self.session_factory: async_sessionmaker = None
            self.initialized = True
    
    async def startup(self):
        """Initialize database engine and session factory."""
        self.engine = create_async_engine(
            self.settings.DB_DSN,
            pool_size=self.settings.DB_POOL_SIZE,
            max_overflow=self.settings.DB_MAX_OVERFLOW
        )
        self.session_factory = async_sessionmaker(
            self.engine,
            expire_on_commit=False
        )
    
    async def shutdown(self):
        """Close database engine."""
        if self.engine:
            await self.engine.dispose()