"""SQLAlchemy async engine and session management."""
from collections.abc import AsyncGenerator

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

from src.config import get_settings

settings = get_settings()


class Base(DeclarativeBase):
    """Base class for all SQLAlchemy models."""

    pass


engine = create_async_engine(
    settings.database_url,
    pool_size=settings.database_pool_size,
    max_overflow=settings.database_max_overflow,
    pool_timeout=settings.database_pool_timeout_seconds,
    pool_pre_ping=True,
    echo=settings.debug,
    connect_args={
        # asyncpg: fail fast when DATABASE_URL host is unroutable (drops packets / wrong network).
        "timeout": settings.database_connect_timeout_seconds,
    },
)

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


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency: one async session per request.

    Plain async generator keeps FastAPI dependency handling straightforward.
    """
    async with async_session_factory() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise