"""Detector factory: build a Detector from AppConfig.

Kept separate from ``app.py`` so both the app bootstrap and the UI can build
detectors without an import cycle. Raises ``ValueError`` (not ``SystemExit``) on
bad config so the GUI can show the message instead of exiting.

YOLO-only, but multi-model: every path in ``config.detector_models`` (ticked under
models/yolo/<category>/) becomes a YoloDetector tagged with its category, and they
run together via :class:`~.multi.MultiYoloDetector`. The classic-CV detector and the
``combined`` composite were removed (noisy/approximate on real footage).
"""

from __future__ import annotations

from pathlib import Path

from ...config import AppConfig
from .base import Detector
from .registry import category_of


def build_detector(config: AppConfig) -> Detector:
    models = [m for m in config.detector_models if Path(m).is_file()]
    if not models:
        raise ValueError(
            "Не выбрана ни одна модель детекции.\n"
            "Положите веса YOLO в models/yolo/<категория>/ (например models/yolo/mosaic/) "
            "и отметьте их галочкой в меню «Модели». См. README."
        )
    # lazy imports: YoloDetector pulls in torch/ultralytics only when a detect runs
    from .multi import MultiYoloDetector
    from .yolo import YoloDetector

    nms_iou = config.nms_iou if config.cross_model_nms else None
    return MultiYoloDetector(
        [YoloDetector(m, config.detection, label=category_of(m)) for m in models],
        nms_iou=nms_iou,
    )