"""引擎工厂（utils/db.py）单测（B7 评审 P1-1）：单例复用 + dispose 真实释放。

create_engine 与缓存字典均 monkeypatch 替换，不触网；验证 dispose_engines
对每个缓存 Engine 显式调用 dispose() 并清空缓存（不再是仅 cache_clear）。
"""

from app.utils import db


class SpyEngine:
    def __init__(self):
        self.dispose_calls = 0

    def dispose(self, close: bool = True) -> None:
        self.dispose_calls += 1


def _patch(monkeypatch):
    created_urls = []

    def fake_create_engine(url, **kwargs):
        created_urls.append(url)
        return SpyEngine()

    monkeypatch.setattr(db, "create_engine", fake_create_engine)
    monkeypatch.setattr(db, "_engines", {})
    return created_urls


def test_get_engine_caches_one_engine_per_database(monkeypatch):
    created = _patch(monkeypatch)
    e1 = db.get_engine("db_a")
    e2 = db.get_engine("db_a")
    e3 = db.get_engine("db_b")
    assert e1 is e2
    assert e1 is not e3
    assert len(created) == 2


def test_dispose_engines_calls_dispose_and_clears_cache(monkeypatch):
    _patch(monkeypatch)
    e = db.get_engine("db_a")
    db.dispose_engines()
    assert e.dispose_calls == 1
    assert db._engines == {}
    # 缓存已清：重建新实例而非复用已 dispose 的旧实例
    fresh = db.get_engine("db_a")
    assert fresh is not e
    assert fresh.dispose_calls == 0


def test_dispose_engines_on_empty_cache_is_noop(monkeypatch):
    _patch(monkeypatch)
    db.dispose_engines()  # 不抛异常即可