"""cv2.FaceDetectorYN caches its input size and is not thread-safe, so camera
workers must not share one. Skipped when the model is absent, matching the
faiss-optional pattern in test_index.py — the suite stays runnable with no
models installed."""
import threading
from pathlib import Path

import numpy as np
import pytest

from behavision.config import Config
from behavision.detection import YUNET_FILENAME, FaceDetector

MODELS = Path(__file__).resolve().parent.parent / "models"
pytestmark = pytest.mark.skipif(not (MODELS / YUNET_FILENAME).exists(),
                                reason="YuNet model not installed")


def _detector():
    d = Config().detection
    return FaceDetector(MODELS, d.score_threshold, d.nms_threshold,
                        d.max_faces, d.min_face_px)


def _hammer(det, size, errors, n=40):
    w, h = size
    frame = np.zeros((h, w, 3), dtype=np.uint8)
    for _ in range(n):
        try:
            det.detect(frame)
        except Exception as exc:  # noqa: BLE001 - cv2 raises on size mismatch
            errors.append(exc)
            return


def _race(det_a, det_b):
    errors = []
    threads = [threading.Thread(target=_hammer, args=(det_a, (1280, 720), errors)),
               threading.Thread(target=_hammer, args=(det_b, (640, 480), errors))]
    for t in threads:
        t.start()
    for t in threads:
        t.join()
    return errors


def test_a_shared_detector_really_does_race():
    """Guards the premise: if this ever stops failing, the test below is
    proving nothing and the per-camera split can be revisited."""
    shared = _detector()
    assert _race(shared, shared), "expected a shared detector to race"


def test_per_camera_detectors_do_not_race():
    assert _race(_detector(), _detector()) == []