"""Unit tests: engine/session helpers (no live database required).

Creating a SQLAlchemy engine/session is lazy — no connection opens until the
first query — so these run anywhere.
"""
from __future__ import annotations

from sqlalchemy import Engine
from sqlalchemy.orm import Session

from app import db as app_db


def test_engine_and_session_factory_are_lazy() -> None:
    assert isinstance(app_db.engine, Engine)
    session = app_db.SessionLocal()
    try:
        assert isinstance(session, Session)
    finally:
        session.close()


def test_get_db_yields_session_and_closes_generator() -> None:
    gen = app_db.get_db()
    session = next(gen)
    assert isinstance(session, Session)
    session.close()
    gen.close()  # exercises the finally: db.close()


def test_db_available_true_on_select_one(monkeypatch) -> None:
    class _FakeConn:
        def __enter__(self):
            return self

        def __exit__(self, *exc: object) -> None:
            return None

        def execute(self, _stmt: object) -> None:
            return None

    class _FakeEngine:
        def connect(self) -> _FakeConn:
            return _FakeConn()

    monkeypatch.setattr(app_db, "engine", _FakeEngine())
    assert app_db.db_available() is True


def test_db_available_false_on_error(monkeypatch) -> None:
    class _BrokenEngine:
        def connect(self) -> object:
            raise ConnectionError("db is down")

    monkeypatch.setattr(app_db, "engine", _BrokenEngine())
    assert app_db.db_available() is False