#!/usr/bin/env python3
"""Repair a GLB whose material references a texture with no image source.

Blender's WebP glTF export occasionally emits a texture slot whose image failed to encode
(no `source`, no `EXT_texture_webp.source`) — e.g. a packed metallic-roughness/AO map. three.js
GLTFLoader then throws `Cannot read properties of undefined (reading 'uri')` when a material points
at it. This strips every material texture-slot that points at a sourceless texture (base-colour /
normal are kept; the orphaned texture is never loaded because GLTFLoader loads textures lazily),
then repacks the GLB (BIN chunk untouched).

    python3 fix_glb_textures.py in.glb out.glb
"""
import json, struct, sys

SLOTS = ("baseColorTexture", "metallicRoughnessTexture", "normalTexture",
         "occlusionTexture", "emissiveTexture")


def read_glb(path):
    d = open(path, "rb").read()
    off, gltf, chunks = 12, None, []
    while off < len(d):
        clen, ctype = struct.unpack("<II", d[off:off + 8])
        body = d[off + 8: off + 8 + clen]
        if ctype == 0x4E4F534A:
            gltf = json.loads(body.decode("utf-8"))
        chunks.append((ctype, body))
        off += 8 + clen
    return gltf, chunks


def has_source(tex):
    if "source" in tex:
        return True
    ext = tex.get("extensions", {})
    return any("source" in v for v in ext.values() if isinstance(v, dict))


def repair(gltf):
    textures = gltf.get("textures", [])
    bad = {i for i, t in enumerate(textures) if not has_source(t)}
    if not bad:
        return 0
    stripped = 0
    for m in gltf.get("materials", []):
        pbr = m.get("pbrMetallicRoughness", {})
        for container in (m, pbr):
            for slot in list(container.keys()):
                if slot in SLOTS and isinstance(container[slot], dict) \
                        and container[slot].get("index") in bad:
                    del container[slot]
                    stripped += 1
    return stripped


def write_glb(gltf, chunks, out):
    new_json = json.dumps(gltf, separators=(",", ":")).encode("utf-8")
    new_json += b" " * ((4 - len(new_json) % 4) % 4)          # pad to 4 bytes
    body = struct.pack("<II", len(new_json), 0x4E4F534A) + new_json
    for ctype, data in chunks:
        if ctype == 0x4E4F534A:
            continue
        pad = b"\x00" * ((4 - len(data) % 4) % 4)
        body += struct.pack("<II", len(data) + len(pad), ctype) + data + pad
    header = struct.pack("<III", 0x46546C67, 2, 12 + len(body))
    open(out, "wb").write(header + body)


def main():
    inp, out = sys.argv[1], sys.argv[2]
    gltf, chunks = read_glb(inp)
    n = repair(gltf)
    write_glb(gltf, chunks, out)
    print(f"stripped {n} material slot(s) pointing at sourceless textures → {out}")


if __name__ == "__main__":
    main()