#!/usr/bin/env python

# This software is provided 'as-is', without any express or implied
# warranty.  In no event will the author be held liable for any damages
# arising from the use of this software.
#
# Permission is granted to anyone to use this software for any purpose,
# including commercial applications, and to alter it and redistribute it
# freely, subject to the following restrictions:
#
# 1. The origin of this software must not be misrepresented; you must not
#    claim that you wrote the original software. If you use this software
#    in a product, an acknowledgment in the product documentation would be
#    appreciated but is not required.
# 2. Altered source versions must be plainly marked as such, and must not be
#    misrepresented as being the original software.
# 3. This notice may not be removed or altered from any source distribution.
#
# Copyright (c) 2008 Greg Hewgill http://hewgill.com
#
# This has been modified from the original software.
# Copyright (c) 2011 William Grant <me@williamgrant.id.au>
# Copyright (c) 2017 Scott Kitterman <scott@kitterman.com>

from __future__ import print_function

import sys
import argparse

import dkim

# Backward compatibility hack because argparse doesn't support optional
# positional arguments
arguments=['--'+arg if arg[:8] == 'identity' else arg for arg in sys.argv[1:]]
parser = argparse.ArgumentParser(
    description='Produce DKIM signature for email messages.',
    epilog="message to be signed follows commands on stdin")
parser.add_argument('selector', action="store")
parser.add_argument('domain', action="store")
parser.add_argument('privatekeyfile', action="store")
parser.add_argument('--hcanon', choices=['simple', 'relaxed'],
    default='relaxed',
    help='Header canonicalization algorithm: default=relaxed')
parser.add_argument('--bcanon', choices=['simple', 'relaxed'],
    default='simple',
    help='Body canonicalization algorithm: default=simple')
parser.add_argument('--signalg', choices=['rsa-sha256', 'ed25519-sha256', 'rsa-sha1'],
    default='rsa-sha256',
    help='Signature algorithm: default=rsa-sha256')
parser.add_argument('--identity', help='Optional value for i= tag.')
args=parser.parse_args(arguments)
include_headers = None
length = None
logger = None

if sys.version_info[0] >= 3:
    args.selector = bytes(args.selector, encoding='UTF-8')
    args.domain = bytes(args.domain, encoding='UTF-8')
    if args.identity is not None:
        args.identity = bytes(args.identity, encoding='UTF-8')
    args.hcanon = bytes(args.hcanon, encoding='UTF-8')
    args.bcanon = bytes(args.bcanon, encoding='UTF-8')
    args.signalg = bytes(args.signalg, encoding='UTF-8')
    # Make sys.stdin and stdout binary streams.
    sys.stdin = sys.stdin.detach()
    sys.stdout = sys.stdout.detach()
canonicalize = (args.hcanon, args.bcanon)

message = sys.stdin.read()
try:
    d = dkim.DKIM(message,logger=logger,
                  signature_algorithm=args.signalg)
    sig = d.sign(args.selector, args.domain, open(
                 args.privatekeyfile, "rb").read(), identity = args.identity,
                 canonicalize=canonicalize, include_headers=include_headers,
                 length=length)
    sys.stdout.write(sig)
    sys.stdout.write(message)
except Exception as e:
    print(e, file=sys.stderr)
    sys.stdout.write(message)
