"""Async database engine and session helpers."""

from collections.abc import AsyncGenerator

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

from app.config.settings import get_settings
from app.infra.db.base import Base

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


def get_async_engine() -> AsyncEngine:
    """Return the lazily created async SQLAlchemy engine."""

    global _engine
    if _engine is None:
        _engine = create_async_engine(
            get_settings().database_url,
            future=True,
            echo=False,
        )
    return _engine


def get_session_factory() -> async_sessionmaker[AsyncSession]:
    """Return the lazily created async session factory."""

    global _session_factory
    if _session_factory is None:
        _session_factory = async_sessionmaker(get_async_engine(), expire_on_commit=False)
    return _session_factory


async def get_db_session() -> AsyncGenerator[AsyncSession, None]:
    """Yield a database session for FastAPI dependencies."""

    async with get_session_factory()() as session:
        yield session


async def init_database() -> None:
    """Create database tables when running the MVP without migrations."""

    from app.infra.db.models.asset import AssetORM
    from app.infra.db.models.order import OrderORM
    from app.infra.db.models.review_task import ReviewTaskORM
    from app.infra.db.models.workflow_run import WorkflowRunORM
    from app.infra.db.models.workflow_step import WorkflowStepORM

    del AssetORM, OrderORM, ReviewTaskORM, WorkflowRunORM, WorkflowStepORM

    async with get_async_engine().begin() as connection:
        await connection.run_sync(Base.metadata.create_all)


async def dispose_database() -> None:
    """Dispose the active engine and clear cached session objects."""

    global _engine, _session_factory
    if _engine is not None:
        await _engine.dispose()
    _engine = None
    _session_factory = None