#!/usr/bin/env python3

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

import os
import sys
import email
import errno
import mimetypes

from optparse import OptionParser


def main():
    parser = OptionParser(usage="""\
Unpack a MIME message into a directory of files.

Usage: %prog [options] msgfile
""")
    parser.add_option('-d', '--directory',
                      type='string', action='store',
                      help="""Unpack the MIME message into the named
                      directory, which will be created if it doesn't already
                      exist.""")
    opts, args = parser.parse_args()
    if not opts.directory:
        parser.print_help()
        sys.exit(1)

    try:
        msgfile = args[0]
    except IndexError:
        parser.print_help()
        sys.exit(1)

    try:
        os.mkdir(opts.directory)
    except OSError as e:
        # Ignore directory exists error
        if e.errno != errno.EEXIST:
            raise

    fp = open(msgfile)
    msg = email.message_from_file(fp)
    fp.close()

    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
        fp = open(os.path.join(opts.directory, filename), 'wb')
        fp.write(part.get_payload(decode=True))
        fp.close()


if __name__ == '__main__':
    main()
