# Copyright (C) 2002-2018 by the Free Software Foundation, Inc.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
# USA.

"""MIME-stripping filter for Mailman.

This module scans a message for MIME content, removing those sections whose
MIME types match one of a list of matches.  multipart/alternative sections are
replaced by the first non-empty component, and multipart/mixed sections
wrapping only single sections after other processing are replaced by their
contents.
"""

import os
import errno
import tempfile
import html2text
from os.path import splitext

from email.iterators import typed_subpart_iterator

from Mailman import mm_cfg
from Mailman import Errors
from Mailman.Message import UserNotification
from Mailman.Queue.sbcache import get_switchboard
from Mailman.Version import VERSION
from Mailman.i18n import _
from Mailman.Utils import oneline



def process(mlist, msg, msgdata):
    # Short-circuits
    if not mlist.filter_content:
        return
    if msgdata.get('isdigest'):
        return
    # We also don't care about our own digests or plaintext
    ctype = msg.get_content_type()
    mtype = msg.get_content_maintype()
    # Check to see if the outer type matches one of the filter types
    filtertypes = mlist.filter_mime_types
    passtypes = mlist.pass_mime_types
    if ctype in filtertypes or mtype in filtertypes:
        dispose(mlist, msg, msgdata,
                _("The message's content type was explicitly disallowed"))
    # Check to see if there is a pass types and the outer type doesn't match
    # one of these types
    if passtypes and not (ctype in passtypes or mtype in passtypes):
        dispose(mlist, msg, msgdata,
                _("The message's content type was not explicitly allowed"))
    # Filter by file extensions
    filterexts = mlist.filter_filename_extensions
    passexts = mlist.pass_filename_extensions
    fext = get_file_ext(msg)
    if fext:
        if fext in filterexts:
            dispose(mlist, msg, msgdata,
                 _("The message's file extension was explicitly disallowed"))
        if passexts and not (fext in passexts):
            dispose(mlist, msg, msgdata,
                 _("The message's file extension was not explicitly allowed"))
    numparts = len([subpart for subpart in msg.walk()])
    # If the message is a multipart, filter out matching subparts
    if msg.is_multipart():
        # Recursively filter out any subparts that match the filter list
        prelen = len(msg.get_payload())
        filter_parts(msg, filtertypes, passtypes, filterexts, passexts)
        # If the outer message is now an empty multipart (and it wasn't
        # before!) then, again it gets discarded.
        postlen = len(msg.get_payload())
        if postlen == 0 and prelen > 0:
            dispose(mlist, msg, msgdata,
                    _("After content filtering, the message was empty"))
    # Now replace all multipart/alternatives with just the first non-empty
    # alternative.  BAW: We have to special case when the outer part is a
    # multipart/alternative because we need to retain most of the outer part's
    # headers.  For now we'll move the subpart's payload into the outer part,
    # and then copy over its Content-Type: and Content-Transfer-Encoding:
    # headers (any others?).
    if mlist.collapse_alternatives:
        collapse_multipart_alternatives(msg)
        if ctype == 'multipart/alternative':
            firstalt = msg.get_payload(0)
            reset_payload(msg, firstalt)
    # Now that we've collapsed the MPA parts, go through the message
    # and recast any multipart parts with only one sub-part as just
    # the sub-part.
    if msg.is_multipart():
        recast_multipart(msg)
    # If we removed some parts, make note of this
    changedp = 0
    if numparts != len([subpart for subpart in msg.walk()]):
        changedp = 1
    # Now perhaps convert all text/html to text/plain
    if mlist.convert_html_to_plaintext and mm_cfg.HTML_TO_PLAIN_TEXT_COMMAND:
        changedp += to_plaintext(msg)
    # If we're left with only two parts, an empty body and one attachment,
    # recast the message to one of just that part
    if msg.is_multipart() and len(msg.get_payload()) == 2:
        if msg.get_payload(0).get_payload() == '':
            useful = msg.get_payload(1)
            reset_payload(msg, useful)
            changedp = 1
    if changedp:
        msg['X-Content-Filtered-By'] = 'Mailman/MimeDel %s' % VERSION



def reset_payload(msg, subpart):
    # Reset payload of msg to contents of subpart, and fix up content headers
    payload = subpart.get_payload()
    msg.set_payload(payload)
    del msg['content-type']
    del msg['content-transfer-encoding']
    del msg['content-disposition']
    del msg['content-description']
    msg['Content-Type'] = subpart.get('content-type', 'text/plain')
    cte = subpart.get('content-transfer-encoding')
    if cte:
        msg['Content-Transfer-Encoding'] = cte
    cdisp = subpart.get('content-disposition')
    if cdisp:
        msg['Content-Disposition'] = cdisp
    cdesc = subpart.get('content-description')
    if cdesc:
        msg['Content-Description'] = cdesc



def filter_parts(msg, filtertypes, passtypes, filterexts, passexts):
    # Look at all the message's subparts, and recursively filter
    if not msg.is_multipart():
        return 1
    payload = msg.get_payload()
    prelen = len(payload)
    newpayload = []
    for subpart in payload:
        keep = filter_parts(subpart, filtertypes, passtypes,
                            filterexts, passexts)
        if not keep:
            continue
        ctype = subpart.get_content_type()
        mtype = subpart.get_content_maintype()
        if ctype in filtertypes or mtype in filtertypes:
            # Throw this subpart away
            continue
        if passtypes and not (ctype in passtypes or mtype in passtypes):
            # Throw this subpart away
            continue
        # check file extension
        fext = get_file_ext(subpart)
        if fext:
            if fext in filterexts:
                continue
            if passexts and not (fext in passexts):
                continue
        newpayload.append(subpart)
    # Check to see if we discarded all the subparts
    postlen = len(newpayload)
    msg.set_payload(newpayload)
    if postlen == 0 and prelen > 0:
        # We threw away everything
        return 0
    return 1



def collapse_multipart_alternatives(msg):
    if not msg.is_multipart():
        return
    newpayload = []
    for subpart in msg.get_payload():
        if subpart.get_content_type() == 'multipart/alternative':
            try:
                firstalt = subpart.get_payload(0)
                if msg.get_content_type() == 'message/rfc822':
                    # This is a multipart/alternative message in a
                    # message/rfc822 part. We treat it specially so as not to
                    # lose the headers.
                    reset_payload(subpart, firstalt)
                    newpayload.append(subpart)
                else:
                    newpayload.append(firstalt)
            except (IndexError, TypeError):
                pass
        elif subpart.is_multipart():
            collapse_multipart_alternatives(subpart)
            newpayload.append(subpart)
        else:
            newpayload.append(subpart)
    msg.set_payload(newpayload)



def recast_multipart(msg):
    # If we're left with a multipart message with only one sub-part, recast
    # the message to just the sub-part, but not if the part is message/rfc822
    # because we don't want to lose the headers.
    # Also, if this is a multipart/signed part, stop now as the original part
    # may have had a multipart sub-part with only one sub-sub-part, the sig
    # may still be valid and going further may break it.  (LP: #1551075)
    if msg.get_content_type() == 'multipart/signed':
        return
    if msg.is_multipart():
        if (len(msg.get_payload()) == 1 and
                msg.get_content_type() != 'message/rfc822'):
            reset_payload(msg, msg.get_payload(0))
            # now that we've recast this part, check the subordinate parts
            recast_multipart(msg)
        else:
            # This part's OK but check deeper.
            for part in msg.get_payload():
                recast_multipart(part)



def to_plaintext(msg):
    changedp = 0
    # Get the subparts (ensure you're iterating through them)
    subparts = list(typed_subpart_iterator(msg, 'text', 'html'))

    # Iterate through the subparts
    for subpart in subparts:

        # Get the HTML content (ensure it's decoded if it's in bytes)
        html_content = subpart.get_payload(decode=1)  # Get the payload as bytes

        if isinstance(html_content, bytes):
            html_content = html_content.decode('utf-8')  # Decode bytes to string

        # Now convert HTML to plain text
        plaintext = html2text.html2text(html_content)

        # Now replace the payload of the subpart and twiddle the Content-Type:
        del subpart['content-transfer-encoding']  # Remove encoding if necessary
        subpart.set_payload(plaintext)  # Set the new plaintext payload
        subpart.set_type('text/plain')  # Change the content type to 'text/plain'
        changedp = 1

    return changedp



def dispose(mlist, msg, msgdata, why):
    # filter_action == 0 just discards, see below
    if mlist.filter_action == 1:
        # Bounce the message to the original author
        raise Errors.RejectMessage(why)
    if mlist.filter_action == 2:
        # Forward it on to the list owner
        listname = mlist.internal_name()
        mlist.ForwardMessage(
            msg,
            text=_("""\
The attached message matched the %(listname)s mailing list's content filtering
rules and was prevented from being forwarded on to the list membership.  You
are receiving the only remaining copy of the discarded message.

"""),
            subject=_('Content filtered message notification'))
    if mlist.filter_action == 3 and \
           mm_cfg.OWNERS_CAN_PRESERVE_FILTERED_MESSAGES:
        badq = get_switchboard(mm_cfg.BADQUEUE_DIR)
        badq.enqueue(msg, msgdata)
    # Most cases also discard the message
    raise Errors.DiscardMessage

def get_file_ext(m):
    """
    Get filename extension. Caution: some virus don't put filename
    in 'Content-Disposition' header.
"""
    fext = ''
    filename = m.get_filename('') or m.get_param('name', '')
    if filename:
        fext = splitext(oneline(filename,'utf-8'))[1]
        if len(fext) > 1:
            fext = fext[1:]
        else:
            fext = ''
    return fext.lower()