"""Package an existing macOS app with Unix symlinks intact (stdlib only)."""
import argparse
import os
from pathlib import Path
import stat
import time
import zipfile


def package(app, output):
    app = Path(app).resolve()
    output = Path(output).resolve()
    assert app.is_dir() and app.suffix == '.app'
    with zipfile.ZipFile(output, 'w', compression=zipfile.ZIP_DEFLATED, compresslevel=6) as archive:
        def add(path):
            st = path.lstat()
            name = path.relative_to(app.parent).as_posix()
            is_dir = stat.S_ISDIR(st.st_mode)
            info = zipfile.ZipInfo(name + ('/' if is_dir else ''), time.localtime(st.st_mtime)[:6])
            info.create_system = 3
            info.external_attr = st.st_mode << 16
            if is_dir:
                info.external_attr |= 0x10
            info.compress_type = zipfile.ZIP_STORED if is_dir else zipfile.ZIP_DEFLATED
            if stat.S_ISLNK(st.st_mode):
                archive.writestr(info, os.readlink(path).encode('utf-8'))
            elif is_dir:
                archive.writestr(info, b'')
                for child in sorted(path.iterdir()):
                    add(child)
            elif stat.S_ISREG(st.st_mode):
                with path.open('rb') as src, archive.open(info, 'w') as dst:
                    while chunk := src.read(1024 * 1024):
                        dst.write(chunk)
            else:
                raise ValueError(f'Unsupported file type: {path}')
        add(app)
    with zipfile.ZipFile(output) as archive:
        assert archive.testzip() is None
        for item in archive.infolist():
            source = app.parent / item.filename.rstrip('/')
            assert (item.external_attr >> 16) == source.lstat().st_mode
            if source.is_symlink():
                assert archive.read(item).decode('utf-8') == os.readlink(source)
    print(output)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('app')
    parser.add_argument('output')
    args = parser.parse_args()
    package(args.app, args.output)