# Copyright (C) 2009-2016 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/>.

"""Fake MTA for testing purposes."""

import logging

from lazr.smtptest.controller import QueueController
from lazr.smtptest.server import Channel, QueueServer
from mailman import public
from mailman.interfaces.mta import IMailTransportAgentLifecycle
from queue import Empty, Queue
from zope.interface import implementer


log = logging.getLogger('lazr.smtptest')


@public
@implementer(IMailTransportAgentLifecycle)
class FakeMTA:
    """Fake MTA for testing purposes."""

    def create(self, mlist):
        pass

    def delete(self, mlist):
        pass

    def regenerate(self, output=None):
        pass


class StatisticsChannel(Channel):
    """A channel that can answers to the fake STAT command."""

    def __init__(self, server, connection, address):
        super().__init__(server, connection, address)
        self._auth_response = None
        self._waiting_for_auth_response = False

    def smtp_EHLO(self, arg):
        if not arg:
            self.push('501 Syntax: HELO hostname')
            return
        if self._SMTPChannel__greeting:
            self.push('503 Duplicate HELO/EHLO')
        else:
            self._SMTPChannel__greeting = arg
            self.push('250-%s' % self._SMTPChannel__fqdn)
            self.push('250 AUTH PLAIN')

    def smtp_STAT(self, arg):
        """Cause the server to send statistics to its controller."""
        self._server.send_statistics()
        self.push('250 Ok')

    def _check_auth(self, response):
        # Base 64 for "testuser:testpass"
        if response == 'AHRlc3R1c2VyAHRlc3RwYXNz':
            self.push('235 Ok')
            self._server.send_auth(response)
        else:
            self.push('571 Bad authentication')

    def smtp_AUTH(self, arg):
        """Record that the AUTH occurred."""
        args = arg.split()
        if args[0].lower() == 'plain':
            if len(args) == 2:
                # The second argument is the AUTH PLAIN <initial-response>
                # which must be equal to the base 64 equivalent of the
                # expected login string "testuser:testpass".
                self._check_auth(args[1])
            else:
                assert len(args) == 1, args
                # Send a challenge and set us up to wait for the response.
                self.push('334 ')
                self._waiting_for_auth_response = True
        else:
            self.push('571 Bad authentication')

    def smtp_RCPT(self, arg):
        """For testing, sometimes cause a non-25x response."""
        code = self._server.next_error('rcpt')
        if code is None:
            # Everything's cool.
            Channel.smtp_RCPT(self, arg)
        else:
            # The test suite wants this to fail.  The message corresponds to
            # the exception we expect smtplib.SMTP to raise.
            self.push('%d Error: SMTPRecipientsRefused' % code)

    def smtp_MAIL(self, arg):
        """For testing, sometimes cause a non-25x response."""
        code = self._server.next_error('mail')
        if code is None:
            # Everything's cool.
            Channel.smtp_MAIL(self, arg)
        else:
            # The test suite wants this to fail.  The message corresponds to
            # the exception we expect smtplib.SMTP to raise.
            self.push('%d Error: SMTPResponseException' % code)

    def found_terminator(self):
        # Are we're waiting for the AUTH challenge response?
        if self._waiting_for_auth_response:
            line = self._emptystring.join(self.received_lines)
            self._auth_response = line
            self._waiting_for_auth_response = False
            self.received_lines = []
            # Now check to see if they authenticated correctly.
            self._check_auth(line)
        else:
            super().found_terminator()


class ConnectionCountingServer(QueueServer):
    """Count the number of SMTP connections opened."""

    def __init__(self, host, port, queue, oob_queue, err_queue):
        """See `lazr.smtptest.server.QueueServer`.

        :param oob_queue: A queue for communicating information back to the
            controller, e.g. statistics.
        :type oob_queue: `Queue.Queue`
        :param err_queue: A queue for allowing the controller to request SMTP
            errors from the server.
        :type err_queue: `Queue.Queue`
        """
        QueueServer.__init__(self, host, port, queue)
        self._connection_count = 0
        self.last_auth = None
        # The out-of-band queue is where the server sends statistics to the
        # controller upon request.
        self._oob_queue = oob_queue
        self._err_queue = err_queue
        self._last_error = None

    def next_error(self, command):
        """Return the next error for the SMTP command, if there is one.

        :param command: The SMTP command for which an error might be
            expected.  If the next error matches the given command, the
            expected error code is returned.
        :type command: string, lower-cased
        :return: An SMTP error code
        :rtype: integer
        """
        # If the last error we pulled from the queue didn't match, then we're
        # caching it, and it might match this expected error.  If there is no
        # last error in the cache, get one from the queue now.
        if self._last_error is None:
            try:
                self._last_error = self._err_queue.get_nowait()
            except Empty:
                # No error is expected
                return None
        if self._last_error[0] == command:
            code = self._last_error[1]
            self._last_error = None
            return code
        return None

    def handle_accept(self):
        """See `lazr.smtp.server.Server`."""
        connection, address = self.accept()
        self._connection_count += 1
        log.info('[ConnectionCountingServer] accepted: %s', address)
        StatisticsChannel(self, connection, address)

    def process_message(self, peer, mailfrom, rcpttos, data):
        # Provide a guaranteed order to recpttos.
        QueueServer.process_message(
            self, peer, mailfrom, sorted(rcpttos), data)

    def reset(self):
        """See `lazr.smtp.server.Server`."""
        QueueServer.reset(self)
        self._connection_count = 0

    def send_statistics(self):
        """Send the current connection statistics to the controller."""
        # Do not count the connection caused by the STAT connect.
        self._connection_count -= 1
        self._oob_queue.put(self._connection_count)

    def send_auth(self, arg):
        """Echo back the authentication data."""
        self._oob_queue.put(arg)


class ConnectionCountingController(QueueController):
    """Count the number of SMTP connections opened."""

    def __init__(self, host, port):
        """See `lazr.smtptest.controller.QueueController`."""
        self.oob_queue = Queue()
        self.err_queue = Queue()
        QueueController.__init__(self, host, port)

    def _make_server(self, host, port):
        """See `lazr.smtptest.controller.QueueController`."""
        self.server = ConnectionCountingServer(
            host, port, self.queue, self.oob_queue, self.err_queue)

    def start(self):
        """See `lazr.smtptest.controller.QueueController`."""
        QueueController.start(self)
        # Reset the connection statistics, since the base class's start()
        # method causes a connection to occur.
        self.reset()

    def get_connection_count(self):
        """Retrieve the number of connections.

        :return: The number of connections to the server that have been made.
        :rtype: integer
        """
        smtpd = self._connect()
        smtpd.docmd('STAT')
        # An Empty exception will occur if the data isn't available in 10
        # seconds.  Let that propagate.
        return self.oob_queue.get(block=True, timeout=10)

    def get_authentication_credentials(self):
        """Retrieve the last authentication credentials."""
        return self.oob_queue.get(block=True, timeout=10)

    @property
    def messages(self):
        """Return all the messages received by the SMTP server."""
        yield from self

    def clear(self):
        """Clear all the messages from the queue."""
        list(self)

    def reset(self):
        smtpd = self._connect()
        smtpd.docmd('RSET')