"""Checks the binary-frame sniff in _try_parse_json: JPEG frames (0xff lead
byte) must be rejected without attempting utf-8 decode (previously raised
UnicodeDecodeError on every frame)."""

from typing import cast

from aare.gui.threads.prediction_subscriber import PredictionSubscriber


def _parse(part: bytes):
    # Called unbound: _try_parse_json touches no instance state, so no
    # QThread/zmq construction is needed. cast keeps basedpyright happy
    # about the stand-in self.
    return PredictionSubscriber._try_parse_json(cast(PredictionSubscriber, object()), part)


def test_binary_jpeg_frame_is_not_json():
    assert _parse(b"\xff\xd8\xff\xe0somejpegbytes") is None


def test_json_dict_is_parsed():
    assert _parse(b'{"encoding": "jpeg"}') == {"encoding": "jpeg"}


def test_json_non_dict_is_rejected():
    assert _parse(b"[1, 2]") is None
    assert _parse(b"") is None