# Packs a .gltf with external buffers and images into one self-contained .glb, which is the only
# model format Singe loads.  Usage:  python3 util/packGlb.py Model.gltf Model.glb
import json, os, struct, sys
src, out = sys.argv[1], sys.argv[2]
base = os.path.dirname(src)
g = json.load(open(src))
binary = bytearray()
views = g.setdefault('bufferViews', [])
def add(data):
    while len(binary) % 4: binary.append(0)
    off = len(binary); binary.extend(data)
    return off
# Buffers:  concatenate, remapping views.
offsets = []
for b in g.get('buffers', []):
    data = open(os.path.join(base, b['uri']), 'rb').read()
    offsets.append(add(data))
for v in views:
    v['byteOffset'] = v.get('byteOffset', 0) + offsets[v.get('buffer', 0)]
    v['buffer'] = 0
# Images:  each becomes a buffer view with a mime type.
for img in g.get('images', []):
    uri = img.pop('uri')
    data = open(os.path.join(base, uri), 'rb').read()
    ext = uri.lower().rsplit('.', 1)[-1]
    views.append({'buffer': 0, 'byteOffset': add(data), 'byteLength': len(data)})
    img['bufferView'] = len(views) - 1
    img['mimeType'] = 'image/png' if ext == 'png' else 'image/jpeg'
while len(binary) % 4: binary.append(0)
g['buffers'] = [{'byteLength': len(binary)}]
js = json.dumps(g, separators=(',', ':')).encode()
while len(js) % 4: js += b' '
with open(out, 'wb') as f:
    f.write(struct.pack('<4sII', b'glTF', 2, 12 + 8 + len(js) + 8 + len(binary)))
    f.write(struct.pack('<II', len(js), 0x4E4F534A)); f.write(js)
    f.write(struct.pack('<II', len(binary), 0x004E4942)); f.write(binary)
print(out, os.path.getsize(out), 'bytes')