from collections.abc import AsyncGenerator

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

from app.core.config import settings

_engine = None
_session_factory: async_sessionmaker[AsyncSession] | None = None


def get_engine():
    global _engine
    if _engine is None:
        _engine = create_async_engine(
            settings.database_url,
            echo=False,
            pool_pre_ping=True,
            pool_recycle=3600,
        )
    return _engine


def get_session_factory() -> async_sessionmaker[AsyncSession]:
    global _session_factory
    if _session_factory is None:
        _session_factory = async_sessionmaker(
            get_engine(),
            class_=AsyncSession,
            expire_on_commit=False,
        )
    return _session_factory


async def connect_to_database() -> None:
    engine = get_engine()
    async with engine.begin() as conn:
        await conn.run_sync(lambda _: None)


async def close_database_connection() -> None:
    global _engine, _session_factory
    if _engine is not None:
        await _engine.dispose()
    _engine = None
    _session_factory = None


async def get_session() -> AsyncGenerator[AsyncSession, None]:
    factory = get_session_factory()
    async with factory() as session:
        yield session


# Backwards-compatible aliases used during migration
connect_to_mongodb = connect_to_database
close_mongodb_connection = close_database_connection
ensure_mongodb = connect_to_database