#!/usr/bin/env python

# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Example of an interface to Courier's mail filter.
"""

LOGFILE = "/tmp/filter.log"

# Setup log file
from twisted.python import log

log.startLogging(open(LOGFILE, "a"))
import sys

sys.stderr = log.logfile

# Twisted imports
from twisted.internet import reactor, stdio
from twisted.internet.protocol import Factory, Protocol
from twisted.protocols import basic

FILTERS = "/var/lib/courier/filters"
ALLFILTERS = "/var/lib/courier/allfilters"
FILTERNAME = "twistedfilter"

import email.message
import email.parser
import os
import os.path
from syslog import LOG_MAIL, openlog, syslog


def trace_dump():
    t, v, tb = sys.exc_info()
    openlog(FILTERNAME, 0, LOG_MAIL)
    syslog(f"Unhandled exception: {v} - {t}")
    while tb:
        syslog(
            "Trace: {}:{} {}".format(
                tb.tb_frame.f_code.co_filename, tb.tb_frame.f_code.co_name, tb.tb_lineno
            )
        )
        tb = tb.tb_next
    # just to be safe
    del tb


def safe_del(file):
    try:
        if os.path.isdir(file):
            os.removedirs(file)
        else:
            os.remove(file)
    except OSError:
        pass


class DieWhenLost(Protocol):
    def connectionLost(self, reason=None):
        reactor.stop()


class MailProcessor(basic.LineReceiver):
    """
    I process a mail message.

    Override filterMessage to do any filtering you want.
    """

    messageFilename = None
    delimiter = "\n"

    def connectionMade(self):
        log.msg(f"Connection from {self.transport}")
        self.state = "connected"
        self.metaInfo = []

    def lineReceived(self, line):
        if self.state == "connected":
            self.messageFilename = line
            self.state = "gotMessageFilename"
        if self.state == "gotMessageFilename":
            if line:
                self.metaInfo.append(line)
            else:
                if not self.metaInfo:
                    self.transport.loseConnection()
                    return
                self.filterMessage()

    def filterMessage(self):
        """Override this.

        A trivial example is included.
        """
        try:
            emailParser = email.parser.Parser()
            with open(self.messageFilename) as f:
                emailParser.parse(f)
            self.sendLine(b"200 Ok")
        except BaseException:
            trace_dump()
            self.sendLine(b"435 " + FILTERNAME.encode("ascii") + b" processing error")


def main():
    # Listen on the UNIX socket
    f = Factory()
    f.protocol = MailProcessor
    safe_del(f"{ALLFILTERS}/{FILTERNAME}")
    reactor.listenUNIX(f"{ALLFILTERS}/{FILTERNAME}", f, 10)

    # Once started, close fd 3 to let Courier know we're ready
    reactor.callLater(0, os.close, 3)

    # When stdin is closed, it's time to exit.
    stdio.StandardIO(DieWhenLost())

    # Go!
    reactor.run()


if __name__ == "__main__":
    main()