"""Parsing of the `bbox` input: an Arrow struct carrying boxes and labels."""

import numpy as np

from dora_image_view.view import Bboxes


def parse(value, bbox_format: str) -> Bboxes:
    """Read a `bbox` payload. `bbox_format` is the `format` metadata parameter."""
    fields = value[0]
    corners = _flat(fields, "bbox").reshape(-1, 4)

    if bbox_format == "xyxy":
        pass
    elif bbox_format == "xywh":
        # xywh is centre-based: x and y are the box centre, not a corner.
        x, y, w, h = corners.T
        corners = np.stack([x - w / 2, y - h / 2, x + w / 2, y + h / 2], axis=1)
    else:
        raise RuntimeError(f"unsupported bbox format: {bbox_format}")

    return Bboxes(
        corners=corners,
        conf=_flat(fields, "conf"),
        labels=_flat(fields, "labels", numeric=False),
    )


def _flat(fields, name: str, numeric: bool = True) -> np.ndarray:
    """Read a struct field as a flat numpy array.

    Senders wrap each field in a single-element list -- that is what
    `pa.array([{...}])` produces from numpy arrays -- so unwrap it when present.
    """
    column = fields[name]
    column = getattr(column, "values", column)
    return column.to_numpy(zero_copy_only=False) if not numeric else column.to_numpy()