#!/usr/bin/env python3

"""Unpack a MIME message into a directory of files."""

import os
import email
import mimetypes

from email.policy import default

from argparse import ArgumentParser


def main():
 parser = ArgumentParser(description="""\
Unpack a MIME message into a directory of files.
""")
 parser.add_argument('-d', '--directory', required=True,
 help="""Unpack the MIME message into the named
 directory, which will be created if it doesn't already
 exist.""")
 parser.add_argument('msgfile')
 args = parser.parse_args()

 with open(args.msgfile, 'rb') as fp:
 msg = email.message_from_binary_file(fp, policy=default)

 try:
 os.mkdir(args.directory)
 except FileExistsError:
 pass

 counter = 1
 for part in msg.walk():
 # multipart/* are just containers
 if part.get_content_maintype() == 'multipart':
 continue
 # Applications should really sanitize the given filename so that an
 # email message can't be used to overwrite important files
 filename = part.get_filename()
 if not filename:
 ext = mimetypes.guess_extension(part.get_content_type())
 if not ext:
 # Use a generic bag-of-bits extension
 ext = '.bin'
 filename = 'part-%03d%s' % (counter, ext)
 counter += 1
 with open(os.path.join(args.directory, filename), 'wb') as fp:
 fp.write(part.get_payload(decode=True))


if __name__ == '__main__':
 main()