# Copyright (C) 1998-2007 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.

"""Do more detailed spam detection.

This module hard codes site wide spam detection.  By hacking the
KNOWN_SPAMMERS variable, you can set up more regular expression matches
against message headers.  If spam is detected the message is discarded
immediately.

TBD: This needs to be made more configurable and robust.
"""

import re

from cStringIO import StringIO
from email.Generator import Generator

from Mailman import Errors
from Mailman import i18n
from Mailman.Handlers.Hold import hold_for_approval
from Mailman.configuration import config

# First, play footsie with _ so that the following are marked as translated,
# but aren't actually translated until we need the text later on.
def _(s):
    return s



class SpamDetected(Errors.DiscardMessage):
    """The message contains known spam"""

class HeaderMatchHold(Errors.HoldMessage):
    reason = _('The message headers matched a filter rule')


# And reset the translator
_ = i18n._



class Tee:
    def __init__(self, outfp_a, outfp_b):
        self._outfp_a = outfp_a
        self._outfp_b = outfp_b

    def write(self, s):
        self._outfp_a.write(s)
        self._outfp_b.write(s)


# Class to capture the headers separate from the message body
class HeaderGenerator(Generator):
    def __init__(self, outfp, mangle_from_=True, maxheaderlen=78):
        Generator.__init__(self, outfp, mangle_from_, maxheaderlen)
        self._headertxt = ''

    def _write_headers(self, msg):
        sfp = StringIO()
        oldfp = self._fp
        self._fp = Tee(oldfp, sfp)
        try:
            Generator._write_headers(self, msg)
        finally:
            self._fp = oldfp
        self._headertxt = sfp.getvalue()

    def header_text(self):
        return self._headertxt



def process(mlist, msg, msgdata):
    if msgdata.get('approved'):
        return
    # First do site hard coded header spam checks
    for header, regex in config.KNOWN_SPAMMERS:
        cre = re.compile(regex, re.IGNORECASE)
        for value in msg.get_all(header, []):
            mo = cre.search(value)
            if mo:
                # we've detected spam, so throw the message away
                raise SpamDetected
    # Now do header_filter_rules
    # TK: Collect headers in sub-parts because attachment filename
    # extension may be a clue to possible virus/spam.
    headers = ''
    for p in msg.walk():
        g = HeaderGenerator(StringIO())
        g.flatten(p)
        headers += g.header_text()
    # Now reshape headers (remove extra CR and connect multiline).
    headers = re.sub('\n+', '\n', headers)
    headers = re.sub('\n\s', ' ', headers)
    for patterns, action, empty in mlist.header_filter_rules:
        if action == config.DEFER:
            continue
        for pattern in patterns.splitlines():
            if pattern.startswith('#'):
                continue
            if re.search(pattern, headers, re.IGNORECASE|re.MULTILINE):
                if action == config.DISCARD:
                    raise Errors.DiscardMessage
                if action == config.REJECT:
                    if msgdata.get('toowner'):
                        # Don't send rejection notice if addressed to '-owner'
                        # because it may trigger a loop of notices if the
                        # sender address is forged.  We just discard it here.
                        raise Errors.DiscardMessage
                    raise Errors.RejectMessage(
                        _('Message rejected by filter rule match'))
                if action == config.HOLD:
                    if msgdata.get('toowner'):
                        # Don't hold '-owner' addressed message.  We just
                        # pass it here but list-owner can set this to be
                        # discarded on the GUI if he wants.
                        return
                    hold_for_approval(mlist, msg, msgdata, HeaderMatchHold)
                if action == config.ACCEPT:
                    return