#!/usr/bin/env python3
# Copyright (c) 2018-2019 Achim D. Brucker.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in
#    the documentation and/or other materials provided with the
#    distribution.
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#
# SPDX-License-Identifier: BSD-2-Clause

import sys
import os.path as path
import os
import stat
import argparse
import re
from bs4 import BeautifulSoup
from urllib.parse import urlparse, parse_qs, urlunparse
import cchardet as chardet


def sanitize_safelink(url):
    if "safelinks.protection.outlook.com" in url:
        try:
            target = urlparse(parse_qs(urlparse(url).query)['url'][0])
            return target.geturl()
        except:
            return " Warning: Removed corrupted safelink. "
    else:
        return url


def remove_external_sender_warning_txt(content):
    warning_re = re.compile(
        r'\nCAUTION: This email originated from outside of the organi[zs]ation. '
        +
        r'Do not click links or open attachments unless you recogni[zs]e the sender '
        + r'and know the content is safe.\n', re.MULTILINE)
    return re.sub(warning_re, lambda x: "", content).rstrip()


def unsanitize_txt(content):
    url_re = re.compile(
        r'(http[s]?://' +
        '(?:[a-zA-Z]|[0-9]|[$-\'\/\+-;=\?-@.&+_]|[!*,]|(?:%[0-9a-fA-F][0-9a-fA-F]))+)',
        re.MULTILINE)
    return re.sub(url_re, lambda x: (sanitize_safelink(x.group(1))),
                  content).rstrip()


def unsanitize_html(content):
    soup = BeautifulSoup(content, "html.parser")
    for a in soup.findAll('a'):
        if a.has_attr('originalsrc'):
            a['safelink'] = a['href']
            a['href'] = a['originalsrc']
            del a['originalsrc']
    return str(soup)

def remove_external_sender_warning_html(content):
    warning_re = re.compile(
        r'CAUTION: This email originated from outside of the organi[zs]ation. '
        +
        r'Do not click links or open attachments unless you recogni[zs]e the sender '
        + r'and know the content is safe.', re.MULTILINE)
    soup = BeautifulSoup(content, "html.parser")
    for d in soup.findAll('div'):
        if re.search(warning_re,str(d.text)):
            d.decompose()
    return str(soup)

def main():
    """Main function of the safelink tool."""
    parser = argparse.ArgumentParser()
    parser.add_argument("--html",
                        help="HTML",
                        action="store_true",
                        default=False)
    parser.add_argument("-i",
                        "--in-situ",
                        help="modify file",
                        action="store_true",
                        default=False)
    parser.add_argument("-v",
                        "--verbose",
                        help="increase verbosity",
                        action="store_true")
    parser.add_argument('file', nargs='?', default=None)
    args = parser.parse_args()

    # parse command line
    if args.file:
        fhandle = open(args.file, mode="rb")
    else:
        fhandle = sys.stdin.buffer

    data = fhandle.read()

    if fhandle is not sys.stdin.buffer:
        fhandle.close()

    encoding = chardet.detect(data)['encoding']
    if encoding:
        content = data.decode(encoding=encoding, errors="replace")
    else:
        content = data.decode(encoding='utf8', errors="replace")

    if args.html:
        content = unsanitize_html(content)
        content = remove_external_sender_warning_html(content)
    else:
        content = unsanitize_txt(content)
        content = remove_external_sender_warning_txt(content)

    if args.file and args.in_situ:
        st = os.stat(args.file)
        os.chmod(args.file, st.st_mode | stat.S_IWRITE)
        with open(args.file, "w+") as fhandle:
            fhandle.write(content)
            fhandle.truncate()
            fhandle.close
    else:
        print(content)


if __name__ == "__main__":
    main()