#!/usr/bin/env python3
"""Assemble an Alpine-derived, shell-free runtime from an explicit ELF allowlist."""
import os
from pathlib import Path
import shutil
import subprocess
import sys

root = Path(sys.argv[1])
root.mkdir(parents=True, exist_ok=True)

copied = set()

def copy(source):
    source = Path(os.path.normpath(source))
    if source in copied:
        return
    copied.add(source)
    target = root / str(source).lstrip('/')
    target.parent.mkdir(parents=True, exist_ok=True)
    if source.is_symlink():
        link = os.readlink(source)
        if not target.is_symlink():
            target.symlink_to(link)
        # Preserve every hop, not just the final file in a multi-link chain.
        copy(link if os.path.isabs(link) else source.parent / link)
    elif source.is_dir():
        target.mkdir(exist_ok=True)
        for child in source.iterdir():
            copy(child)
    else:
        shutil.copy2(source, target)

for executable in sys.argv[2:]:
    result = subprocess.run(['lddtreepax', '-l', executable], check=True, text=True, capture_output=True)
    paths = result.stdout.splitlines()
    if not paths or any(not p.startswith('/') or not Path(p).exists() for p in paths):
        raise SystemExit(f'Unresolved runtime dependency for {executable}: {result.stdout}')
    copy(executable)
    for path in paths:
        copy(path)

# musl uses this file for nonstandard library directories (for example Lua).
for search_path in Path('/etc').glob('ld-musl-*.path'):
    copy(search_path)

# Postfix loads database maps and SASL mechanisms dynamically.
for folder in ['/usr/lib/postfix', '/usr/lib/sasl2']:
    for plugin in Path(folder).glob('*.so*'):
        result = subprocess.run(['lddtreepax', '-l', str(plugin)], check=True,
                                text=True, capture_output=True,
                                env={**os.environ, 'LD_LIBRARY_PATH': '/lib:/usr/lib:/usr/lib/postfix'})
        for dependency in result.stdout.splitlines():
            if not dependency.startswith('/') or not Path(dependency).exists():
                raise SystemExit(f'Unresolved plugin dependency: {dependency}')
            copy(dependency)
        copy(plugin)
for data in ['/etc/postfix', '/etc/passwd', '/etc/group', '/etc/aliases',
             '/etc/aliases.lmdb', '/etc/ssl/certs/ca-certificates.crt', '/etc/ssl/cert.pem',
             '/etc/ssl/openssl.cnf', '/usr/lib/ossl-modules', '/usr/share/zoneinfo',
             '/usr/share/icu', '/usr/lib/icu', '/etc/services', '/etc/protocols', '/etc/alpine-release', '/etc/os-release']:
    if Path(data).exists():
        copy(data)
for directory in ['tmp', 'root', 'dev', 'var/mail', 'var/lib/postfix', 'var/spool/postfix']:
    (root / directory).mkdir(parents=True, exist_ok=True)
os.chmod(root / 'tmp', 0o1777)
# Preserve the Postfix command group and setgid bits for queue submission.
for command in ['postdrop', 'postqueue', 'postlog']:
    source = Path('/usr/sbin') / command
    target = root / str(source).lstrip('/')
    stat = source.stat()
    os.chown(target, stat.st_uid, stat.st_gid)
    os.chmod(target, stat.st_mode & 0o7777)
for forbidden in ['bin/sh', 'bin/bash', 'bin/busybox', 'sbin/apk', 'usr/bin/apk',
                  'usr/bin/python3', 'usr/bin/go', 'usr/sbin/postfix']:
    assert not (root / forbidden).exists(), f'Unexpected runtime tool: {forbidden}'