from __future__ import annotations

import io

import numpy as np
from PIL import Image


def depth_to_png16_bytes(depth: np.ndarray) -> bytes:
    depth = np.asarray(depth, dtype=np.float32)
    dmin = float(depth.min())
    dmax = float(depth.max())
    if dmax > dmin:
        norm = (depth - dmin) / (dmax - dmin)
    else:
        norm = np.zeros_like(depth, dtype=np.float32)
    # 前后端约定：最远=255，最近=0（8-bit）
    u8 = ((1.0 - norm) * 255.0).clip(0, 255).astype(np.uint8)
    img = Image.fromarray(u8, mode="L")
    buf = io.BytesIO()
    img.save(buf, format="PNG")
    return buf.getvalue()