from __future__ import annotations

import io

import numpy as np
from PIL import Image


def depth_to_png16_bytes(depth: np.ndarray, target_hw: tuple[int, int] | None = None) -> bytes:
    depth = np.asarray(depth, dtype=np.float32).squeeze()
    if depth.ndim != 2:
        raise ValueError(f"depth 应为二维数组，实际 shape={depth.shape}")
    if target_hw is not None:
        th, tw = int(target_hw[0]), int(target_hw[1])
        if th > 0 and tw > 0 and (depth.shape[0] != th or depth.shape[1] != tw):
            im = Image.fromarray(depth, mode="F")
            im = im.resize((tw, th), Image.Resampling.BILINEAR)
            depth = np.asarray(im, 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()