"""Tests fuer src/audit.py - diff() + _to_json() Helpers."""
import json
from audit import diff, _to_json


def test_diff_returns_only_changed_fields():
    before = {"name": "Alt", "status": "active", "max_users": 5}
    after  = {"name": "Neu", "status": "active", "max_users": 5}
    result = diff(before, after)
    assert result == {"name": {"old": "Alt", "new": "Neu"}}


def test_diff_no_changes_returns_none():
    same = {"a": 1, "b": "x"}
    assert diff(same, dict(same)) is None


def test_diff_with_none_returns_none():
    assert diff(None, {"a": 1}) is None
    assert diff({"a": 1}, None) is None


def test_diff_added_or_removed_fields():
    before = {"a": 1}
    after = {"a": 1, "b": 2}
    result = diff(before, after)
    assert result == {"b": {"old": None, "new": 2}}


def test_to_json_handles_none():
    assert _to_json(None) is None


def test_to_json_handles_dict():
    out = _to_json({"x": 1, "y": "hallo"})
    assert json.loads(out) == {"x": 1, "y": "hallo"}


def test_to_json_handles_non_serializable_via_str_default():
    """Custom Objekte werden via default=str zu Strings."""
    class Foo:
        def __str__(self):
            return "FooObj"
    out = _to_json({"obj": Foo()})
    assert "FooObj" in out


def test_to_json_preserves_umlauts():
    """ensure_ascii=False soll deutsche Umlaute durchlassen."""
    out = _to_json({"name": "Müller"})
    assert "Müller" in out