"""SQLAlchemy engine/session plumbing and ORM base class."""

from __future__ import annotations

from collections.abc import Generator

from sqlalchemy import create_engine
from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker

from app.config import get_settings

_engine = None
_SessionFactory: sessionmaker[Session] | None = None


class Base(DeclarativeBase):
    pass


def _url_with_driver() -> str:
    url = get_settings().database_url
    # Accept plain postgresql:// URLs by normalising to the psycopg driver.
    if url.startswith("postgresql://"):
        url = url.replace("postgresql://", "postgresql+psycopg://", 1)
    return url


def get_engine():
    global _engine
    if _engine is None:
        _engine = create_engine(_url_with_driver(), pool_pre_ping=True, future=True)
    return _engine


def get_session_factory() -> sessionmaker[Session]:
    global _SessionFactory
    if _SessionFactory is None:
        _SessionFactory = sessionmaker(bind=get_engine(), future=True)
    return _SessionFactory


def get_db() -> Generator[Session, None, None]:
    """FastAPI dependency yielding a database session per request."""
    factory = get_session_factory()
    session = factory()
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise
    finally:
        session.close()