add script to make datamatrix key backup

bin/gpg-key-to-datamatrix

@@ -0,0 +1,63 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -p typst dmtx-utils -i python
+
+import subprocess
+import argparse
+import shlex
+import tempfile
+from pathlib import Path
+from math import ceil
+
+
+def sub(cmd: str, *args, **kwargs):
+    return subprocess.check_output(shlex.split(cmd), *args, **kwargs)
+
+
+def typst_file_tmpl(files):
+    local_paths = [f.relative_to(Path.cwd()) for f in files]
+    return "\n".join(f'#image("{f}")' for f in local_paths)
+
+
+def chunk_key(key):
+    """
+    split byte string into even chunks
+    chunks will be <= 1555 bytes in length since
+    1555 is the maxiumum byte size for datamatrix
+    """
+    n = ceil(len(key) / ceil(len(key) / 1555))
+    return [key[i : i + n] for i in range(0, len(key), n)]
+
+
+def generate_pdf(byte_chunks, svgpath, outpath):
+    for f, data in zip(
+        files := [svgpath / f"dmtx-{i}.svg" for i, _ in enumerate(byte_chunks)],
+        byte_chunks,
+    ):
+        sub(f"dmtxwrite -e 8 -o {f}", input=data)
+    sub(f"typst compile - {outpath}", input=typst_file_tmpl(files), text=True)
+
+
+def get_key_data(key):
+    suffix = key if key else ""
+    return chunk_key(
+        sub(f"gpg --export-secret-key --export-options export-minimal {suffix}")
+    )
+
+
+def main():
+    p = argparse.ArgumentParser()
+    p.add_argument("--key", help="key id")
+    p.add_argument(
+        "--output", help="pdf to write matrices to", default=Path.cwd() / "key.pdf"
+    )
+
+    args = p.parse_args()
+    byte_chunks = get_key_data(args.key)
+
+    with tempfile.TemporaryDirectory(dir=Path.cwd()) as tmpdirname:
+        tmpdir = Path(tmpdirname)
+        generate_pdf(byte_chunks, tmpdir, args.output)
+
+
+if __name__ == "__main__":
+    main()