"""检查混元 GLB 内嵌贴图能否解码。损坏 PNG 在 Blender 里是品红，烘进 color 就会整灯发紫。"""
from __future__ import annotations

import json
import struct
from pathlib import Path
from typing import List, Tuple


def _glb_chunks(data: bytes) -> Tuple[dict, bytes]:
    if len(data) < 12 or data[:4] != b"glTF":
        raise ValueError("不是 glTF GLB")
    offset = 12
    gltf = None
    blob = b""
    while offset + 8 <= len(data):
        chunk_len, chunk_type = struct.unpack_from("<I4s", data, offset)
        offset += 8
        chunk = data[offset : offset + chunk_len]
        offset += chunk_len
        offset = (offset + 3) & ~3
        if chunk_type == b"JSON":
            gltf = json.loads(chunk.decode("utf-8"))
        elif chunk_type == b"BIN\x00":
            blob = chunk
    if gltf is None:
        raise ValueError("GLB 没有 JSON chunk")
    return gltf, blob


def _image_blobs(gltf: dict, blob: bytes) -> List[bytes]:
    views = gltf.get("bufferViews") or []
    out: List[bytes] = []
    for image in gltf.get("images") or []:
        uri = image.get("uri")
        if isinstance(uri, str) and uri.startswith("data:"):
            continue
        index = image.get("bufferView")
        if index is None:
            continue
        view = views[int(index)]
        start = int(view.get("byteOffset") or 0)
        length = int(view.get("byteLength") or 0)
        out.append(blob[start : start + length])
    return out


def glb_textures_ok(path: Path) -> Tuple[bool, str]:
    """内嵌贴图都能解码则 (True, '')。无贴图或损坏返回 False 与原因。"""
    path = Path(path)
    if not path.is_file() or path.stat().st_size < 12:
        return False, "文件不存在或过短"
    data = path.read_bytes()
    if data[:4] != b"glTF":
        return False, "文件头不是 glTF"
    try:
        gltf, blob = _glb_chunks(data)
        blobs = _image_blobs(gltf, blob)
    except Exception as exc:  # noqa: BLE001
        return False, str(exc)
    if not blobs:
        return False, "没有内嵌贴图"
    try:
        from PIL import Image
    except ImportError:
        for raw in blobs:
            if not (raw.startswith(b"\x89PNG") or raw[:2] == b"\xff\xd8"):
                return False, "内嵌贴图不是 PNG/JPEG"
        return True, ""
    import io

    for i, raw in enumerate(blobs):
        try:
            img = Image.open(io.BytesIO(raw))
            img.load()
            if img.size[0] < 8 or img.size[1] < 8:
                return False, f"贴图 {i} 尺寸无效 {img.size}"
        except Exception as exc:  # noqa: BLE001
            return False, f"贴图 {i} 无法解码: {exc}"
    return True, ""


def assert_glb_textures_ok(path: Path) -> None:
    ok, reason = glb_textures_ok(path)
    if not ok:
        raise RuntimeError(
            f"{path} 内嵌贴图不可用（{reason}）。Blender 会显示品红并烘进 color。"
        )