"""Async SQLAlchemy engine and session factory."""
from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
from sqlalchemy.orm import DeclarativeBase

from app.core.config import settings

engine_kwargs = {"echo": settings.APP_ENV == "development"}
if "postgresql" in settings.DATABASE_URL:
    engine_kwargs.update({"pool_size": 10, "max_overflow": 20})

engine = create_async_engine(
    settings.DATABASE_URL,
    **engine_kwargs,
)

SessionLocal = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autoflush=False,
)


class Base(DeclarativeBase):
    pass


async def get_db() -> AsyncSession:
    """FastAPI dependency that yields a DB session."""
    async with SessionLocal() as session:
        try:
            yield session
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()