"""Database engine/session setup.

Each `Database` instance owns its own engine and session factory, so a
production run and a test can each get a fully isolated database instead of
sharing process-global state (see `main.create_app`).
"""
from __future__ import annotations

import os
from typing import Iterator, Optional

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

from .models import Base

DEFAULT_DATABASE_URL = "sqlite:///./labeling.db"


class Database:
    def __init__(self, database_url: Optional[str] = None):
        self.url = database_url or os.environ.get("DATABASE_URL", DEFAULT_DATABASE_URL)
        connect_args = {"check_same_thread": False} if self.url.startswith("sqlite") else {}
        self.engine = create_engine(self.url, connect_args=connect_args)
        self.session_factory = sessionmaker(autocommit=False, autoflush=False, bind=self.engine)

    def init_models(self) -> None:
        Base.metadata.create_all(bind=self.engine)

    def get_session(self) -> Iterator[Session]:
        session = self.session_factory()
        try:
            yield session
        finally:
            session.close()


def get_db() -> Iterator[Session]:
    """Marker dependency; `create_app` overrides this with a real `Database.get_session`."""
    raise NotImplementedError("get_db must be overridden via app.dependency_overrides")