from collections.abc import AsyncGenerator

from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine

from app.config import settings

engine = create_async_engine(
    settings.DATABASE_URL,
    echo=settings.DEBUG_SQL,
    pool_pre_ping=True,
)

AsyncSessionLocal = async_sessionmaker(engine, expire_on_commit=False)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency: yields a session, committing on success.

    Services that need multi-statement atomicity use ``async with db.begin()``
    blocks (those commit/rollback explicitly); a plain commit here persists
    the single-statement writes of the CRUD routers.
    """
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise