from collections.abc import AsyncGenerator

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

from app.core.config import settings

_engine_kwargs: dict[str, object] = {
    "echo": settings.debug,
    "pool_pre_ping": True,
}

if not settings.database_url.startswith("sqlite"):
    _engine_kwargs.update(
        pool_size=10,
        max_overflow=20,
    )

engine = create_async_engine(settings.database_url, **_engine_kwargs)

AsyncSessionLocal = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency — yields a database session."""
    async with AsyncSessionLocal() as session:
        yield session


async def create_tables() -> None:
    """
    Create all tables from SQLAlchemy metadata.
    For development only — use SQL migrations in production.
    """
    # Import models so SQLAlchemy registers their metadata
    import app.models  # noqa: F401

    from app.models.base import Base

    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)