"""
Async SQLAlchemy engine + session factory.
All application code uses `get_db()` as a FastAPI dependency.
"""
from collections.abc import AsyncGenerator

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

from app.config import get_settings


class Base(DeclarativeBase):
    pass


def _make_engine():
    settings = get_settings()
    return create_async_engine(
        settings.database_url,
        echo=False,
        connect_args={"check_same_thread": False},
    )


# Module-level engine and session factory (created once at import time)
engine = _make_engine()
AsyncSessionLocal = async_sessionmaker(engine, expire_on_commit=False)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency that yields a database session."""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise