"""core.config: round-trip, tolerance, and the helios_port regression.

The old dict-based writer rebuilt the JSON from only the main window's
fields, silently discarding helios_port every time a port was edited.
ScanDefaults.save() always writes every field.
"""
import json

from core.config import ScanDefaults


def test_roundtrip(tmp_path):
    p = tmp_path / "defaults.json"
    d = ScanDefaults(t3r_port="/dev/ttyACM3", helios_port="/dev/ttyUSB9")
    d.save(p)
    loaded = ScanDefaults.load(p)
    assert loaded == d


def test_missing_file_creates_defaults(tmp_path):
    p = tmp_path / "defaults.json"
    d = ScanDefaults.load(p)
    assert d == ScanDefaults()
    assert p.exists()


def test_corrupt_file_falls_back(tmp_path):
    p = tmp_path / "defaults.json"
    p.write_text("{not json")
    assert ScanDefaults.load(p) == ScanDefaults()


def test_unknown_keys_ignored(tmp_path):
    p = tmp_path / "defaults.json"
    p.write_text(json.dumps({"t3r_port": "/dev/ttyACM7", "laser_freq_hz": 20000.0}))
    d = ScanDefaults.load(p)
    assert d.t3r_port == "/dev/ttyACM7"
    assert d.helios_port == ScanDefaults().helios_port


def test_helios_port_survives_partial_update(tmp_path):
    """Regression: editing main-window ports must not clobber helios_port."""
    p = tmp_path / "defaults.json"
    ScanDefaults(helios_port="/dev/ttyUSB7").save(p)

    d = ScanDefaults.load(p)
    d.t3r_port = "/dev/ttyACM1"     # what _persist_defaults does
    d.save(p)

    assert ScanDefaults.load(p).helios_port == "/dev/ttyUSB7"