Convert directories full of LDraw .dat files to a single .mpd file

manydat2mpd.py

from pathlib import Path
from queue import Queue
import sys

def stream_files(q, basedir, mpd):
    first = True
    seen = set()
    while q:
        datpath = basedir / q.pop()
        if not datpath.exists():
            print(f'warning: {datpath.name} not found', file=sys.stderr)
            continue
        with open(datpath, 'r') as dat:
            if not first:
                mpd.write('\n')
            mpd.write(f'0 FILE {datpath.name}\n')
            for line in dat:
                match line.split():
                    case '1', *rest:
                        refdat = rest[-1]
                        if refdat not in seen:
                            q.append(Path(refdat))
                            seen.add(refdat)
                    case _:
                        pass
                mpd.write(line)
            first = False


def main(argv):
    if len(argv) != 2:
        print(f'Usage: {argv[0]} main-dat-file', file=sys.stderr)
        return 2

    datpath = Path(argv[1])
    mpdpath = datpath.with_suffix('.mpd')
    basedir = datpath.parent

    with open(mpdpath, 'w') as mpd:
        stream_files([datpath.relative_to(basedir)], basedir, mpd)


if __name__ == '__main__':
    sys.exit(main(sys.argv))