from __future__ import annotations

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

from .config import Config

_engine: AsyncEngine | None = None
_sessionmaker: async_sessionmaker[AsyncSession] | None = None


def get_engine() -> AsyncEngine:
    """Lazily create the process-wide async engine.

    Lazy so the app (and unit tests) can import/boot without a live database —
    only routes that actually touch data open a connection.
    """
    global _engine, _sessionmaker
    if _engine is None:
        _engine = create_async_engine(Config.DATABASE_URL, pool_pre_ping=True)
        _sessionmaker = async_sessionmaker(_engine, expire_on_commit=False)
    return _engine


def get_sessionmaker() -> async_sessionmaker[AsyncSession]:
    if _sessionmaker is None:
        get_engine()
    assert _sessionmaker is not None
    return _sessionmaker


def session_scope() -> AsyncSession:
    """Open a new AsyncSession. Use as `async with session_scope() as db: ...`."""
    return get_sessionmaker()()


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