#!/usr/bin/env python3
"""Minimal zipalign: uncompressed entries start on 4-byte boundaries (like the SDK's
`zipalign 4`). Safe after v1 (JAR) signing, which covers entry contents, not zip layout.
usage: zipalign.py in.apk out.apk"""
import struct
import sys
import zipfile

src, dst = sys.argv[1], sys.argv[2]
with zipfile.ZipFile(src) as zin, open(dst, "wb") as f:
    with zipfile.ZipFile(f, "w") as zout:
        for info in zin.infolist():
            data = zin.read(info.filename)
            out = zipfile.ZipInfo(info.filename, info.date_time)
            out.compress_type = info.compress_type
            out.external_attr = info.external_attr
            if info.compress_type == zipfile.ZIP_STORED:
                header_end = f.tell() + 30 + len(info.filename.encode("utf-8"))
                out.extra = b"\0" * ((4 - header_end % 4) % 4)
            zout.writestr(out, data)

with open(dst, "rb") as raw, zipfile.ZipFile(dst) as z:
    for info in z.infolist():
        if info.compress_type == zipfile.ZIP_STORED:
            raw.seek(info.header_offset + 26)
            n, m = struct.unpack("<HH", raw.read(4))
            assert (info.header_offset + 30 + n + m) % 4 == 0, info.filename
print("aligned", dst)