"""Async database engine and session factory."""

from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)
from sqlalchemy.orm import DeclarativeBase

from app.config import settings

engine = create_async_engine(
    settings.DATABASE_URL,
    echo=settings.DEBUG,
    pool_size=10,
    max_overflow=20,
)

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


class Base(DeclarativeBase):
    pass


async def get_db() -> AsyncSession:
    """Dependency that yields an async database session.

    Handlers are responsible for committing or rolling back their own
    transactions.  This avoids the double-commit problem where the
    session is committed both here and in the handler.
    """
    async with async_session_factory() as session:
        try:
            yield session
        except Exception:
            await session.rollback()
            raise