# Copyright (C) 2007-2017 by the Free Software Foundation, Inc.
#
# This file is part of GNU Mailman.
#
# GNU Mailman 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 3 of the License, or (at your option)
# any later version.
#
# GNU Mailman 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
# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.

"""Application level bounce handling."""

import re
import uuid
import logging

from email.mime.message import MIMEMessage
from email.mime.text import MIMEText
from email.utils import parseaddr
from mailman.config import config
from mailman.core.i18n import _
from mailman.email.message import OwnerNotification, UserNotification
from mailman.interfaces.bounce import UnrecognizedBounceDisposition
from mailman.interfaces.listmanager import IListManager
from mailman.interfaces.pending import IPendable, IPendings
from mailman.interfaces.subscriptions import ISubscriptionService
from mailman.interfaces.template import ITemplateLoader
from mailman.utilities.email import split_email
from mailman.utilities.string import expand, oneline, wrap
from public import public
from string import Template
from zope.component import getUtility
from zope.interface import implementer


log = logging.getLogger('mailman.config')
elog = logging.getLogger('mailman.error')
blog = logging.getLogger('mailman.bounce')

DOT = '.'
NL = '\n'


@public
def bounce_message(mlist, msg, error=None):
    """Bounce the message back to the original author.

    :param mlist: The mailing list that the message was posted to.
    :type mlist: `IMailingList`
    :param msg: The original message.
    :type msg: `email.message.Message`
    :param error: Optional exception causing the bounce.  The exception
        instance must have a `.message` attribute.  The exception *may* have a
        non-None `.reasons` attribute which would be a list of reasons for the
        rejection, and it may have a non-None `.substitutions` attribute.  The
        latter, along with the formatted reasons will be interpolated into the
        message (`.reasons` gets put into the `$reasons` placeholder).
    :type error: RejectMessage
    """
    # Bounce a message back to the sender, with an error message if provided
    # in the exception argument.  .sender might be None or the empty string.
    if not msg.sender:
        # We can't bounce the message if we don't know who it's supposed to go
        # to.
        return
    subject = msg.get('subject', _('(no subject)'))
    subject = oneline(subject, mlist.preferred_language.charset)
    notice = (_('[No bounce details are available]')
              if error is None
              else str(error))
    # Currently we always craft bounces as MIME messages.
    bmsg = UserNotification(msg.sender, mlist.owner_address, subject,
                            lang=mlist.preferred_language)
    # BAW: Be sure you set the type before trying to attach, or you'll get
    # a MultipartConversionError.
    bmsg.set_type('multipart/mixed')
    txt = MIMEText(notice, _charset=mlist.preferred_language.charset)
    bmsg.attach(txt)
    bmsg.attach(MIMEMessage(msg))
    bmsg.send(mlist)


class _BaseVERPParser:
    """Base class for parsing VERP messages.

    Sadly not every MTA bounces VERP messages correctly, or consistently.
    First, the To: header is checked, then Delivered-To: (Postfix),
    Envelope-To: (Exim) and Apparently-To:.  Note that there can be multiple
    headers so we need to search them all
    """

    def __init__(self, pattern):
        self._pattern = pattern
        self._cre = re.compile(pattern, re.IGNORECASE)

    def get_verp(self, mlist, msg):
        """Extract a set of VERP bounce addresses.

        :param mlist: The mailing list being checked.
        :type mlist: `IMailingList`
        :param msg: The message being parsed.
        :type msg: `email.message.Message`
        :return: The set of addresses extracted from the VERP headers.
        :rtype: set of strings
        """
        blocal, bdomain = split_email(mlist.bounces_address)
        values = set()
        verp_matches = set()
        for header in ('to', 'delivered-to', 'envelope-to', 'apparently-to'):
            values.update(msg.get_all(header, []))
        for field in values:
            address = parseaddr(field)[1]
            if not address:
                # This header was empty.
                continue
            mo = self._cre.search(address)
            if not mo:
                # This did not match the VERP regexp.
                continue
            try:
                if blocal != mo.group('bounces'):
                    # This was not a bounce to our mailing list.
                    continue
                original_address = self._get_address(mo)
            except IndexError:
                elog.error('Bad VERP pattern: {0}'.format(self._pattern))
                return set()
            else:
                if original_address is not None:
                    verp_matches.add(original_address)
        return verp_matches


@public
class StandardVERP(_BaseVERPParser):
    def __init__(self):
        super().__init__(config.mta.verp_regexp)

    def _get_address(self, match_object):
        return '{0}@{1}'.format(*match_object.group('local', 'domain'))


@public
class ProbeVERP(_BaseVERPParser):
    def __init__(self):
        super().__init__(config.mta.verp_probe_regexp)

    def _get_address(self, match_object):
        # Extract the token and get the matching address.
        token = match_object.group('token')
        pendable = getUtility(IPendings).confirm(token)
        if pendable is None:
            # The token must have already been confirmed, or it may have been
            # evicted from the database already.
            return None
        # We had to pend the uuid as a unicode.
        member_id = uuid.UUID(hex=pendable['member_id'])
        member = getUtility(ISubscriptionService).get_member(member_id)
        if member is None:
            return None
        return member.address.email


@implementer(IPendable)
class _ProbePendable(dict):
    """The pendable dictionary for probe messages."""
    PEND_TYPE = 'probe'


@public
def send_probe(member, msg):
    """Send a VERP probe to the member.

    :param member: The member to send the probe to.  From this object, both
        the user and the mailing list can be determined.
    :type member: IMember
    :param msg: The bouncing message that caused the probe to be sent.
    :type msg:
    :return: The token representing this probe in the pendings database.
    :rtype: string
    """
    mlist = getUtility(IListManager).get_by_list_id(
        member.mailing_list.list_id)
    template = getUtility(ITemplateLoader).get(
        'list:user:notice:probe', mlist,
        language=member.preferred_language.code,
        # For backward compatibility.
        code=member.preferred_language.code,
        )
    text = wrap(expand(template, mlist, dict(
        sender_email=member.subscriber.email,
        # For backward compatibility.
        address=member.address.email,
        email=member.address.email,
        owneraddr=mlist.owner_address,
        )))
    message_id = msg['message-id']
    if isinstance(message_id, bytes):
        message_id = message_id.decode('ascii')
    pendable = _ProbePendable(
        # We can only pend unicodes.
        member_id=member.member_id.hex,
        message_id=message_id,
        )
    token = getUtility(IPendings).add(pendable)
    mailbox, domain_parts = split_email(mlist.bounces_address)
    probe_sender = Template(config.mta.verp_probe_format).safe_substitute(
        bounces=mailbox,
        token=token,
        domain=DOT.join(domain_parts),
        )
    # Calculate the Subject header, in the member's preferred language.
    with _.using(member.preferred_language.code):
        subject = _('$mlist.display_name mailing list probe message')
    # Craft the probe message.  This will be a multipart where the first part
    # is the probe text and the second part is the message that caused this
    # probe to be sent.
    probe = UserNotification(member.address.email, probe_sender,
                             subject, lang=member.preferred_language)
    probe.set_type('multipart/mixed')
    notice = MIMEText(text, _charset=mlist.preferred_language.charset)
    probe.attach(notice)
    probe.attach(MIMEMessage(msg))
    # Probes should not have the Precedence: bulk header.
    probe.send(mlist, envsender=probe_sender, verp=False, probe_token=token,
               add_precedence=False)
    return token


@public
def maybe_forward(mlist, msg):
    """Possibly forward bounce messages with no recognizable addresses.

    :param mlist: The mailing list.
    :type mlist: `IMailingList`
    :param msg: The bounce message to scan.
    :type msg: `Message`
    """
    message_id = msg['message-id']
    if (mlist.forward_unrecognized_bounces_to
            is UnrecognizedBounceDisposition.discard):
        blog.error('Discarding unrecognized bounce: {0}'.format(message_id))
        return
    # The notification is either going to go to the list's administrators
    # (owners and moderators), or to the site administrators.  Most of the
    # notification is exactly the same in either case.
    subject = _('Uncaught bounce notification')
    template = getUtility(ITemplateLoader).get(
        'list:admin:notice:unrecognized', mlist)
    text = expand(template, mlist)
    text_part = MIMEText(text, _charset=mlist.preferred_language.charset)
    attachment = MIMEMessage(msg)
    if (mlist.forward_unrecognized_bounces_to
            is UnrecognizedBounceDisposition.administrators):
        keywords = dict(roster=mlist.administrators)
    elif (mlist.forward_unrecognized_bounces_to
          is UnrecognizedBounceDisposition.site_owner):
        keywords = {}
    else:
        raise AssertionError('Invalid forwarding disposition: {0}'.format(
                             mlist.forward_unrecognized_bounces_to))
    # Create the notification and send it.
    notice = OwnerNotification(mlist, subject, **keywords)
    notice.set_type('multipart/mixed')
    notice.attach(text_part)
    notice.attach(attachment)
    notice.send(mlist)