#!/usr/bin/env python3

"""
Forward messages sent to the configured email gateway to Zulip.

For zulip.com, messages to that address go to the Inbox of emailgateway@zulip.com.
Zulip voyager configurations will differ.

Messages meant for Zulip have a special recipient form of

    <stream name>+<regenerable stream token>@streams.zulip.com

This pattern is configurable via the EMAIL_GATEWAY_PATTERN settings.py
variable.

Run this in a cronjob every N minutes if you have configured Zulip to poll
an external IMAP mailbox for messages. The script will then connect to
your IMAP server and batch-process all messages.

We extract and validate the target stream from information in the
recipient address and retrieve, forward, and archive the message.

"""


from __future__ import absolute_import
from __future__ import print_function

import six
from typing import Any, List, Generator

import logging

from django.conf import settings
from django.core.management.base import BaseCommand

from zerver.lib.queue import queue_json_publish
from zerver.lib.email_mirror import logger, process_message, \
    extract_and_validate, ZulipEmailForwardError, \
    mark_missed_message_address_as_used, is_missed_message_address

import email
from email.message import Message
from imaplib import IMAP4_SSL

## Setup ##

log_format = "%(asctime)s: %(message)s"
logging.basicConfig(format=log_format)

formatter = logging.Formatter(log_format)
file_handler = logging.FileHandler(settings.EMAIL_MIRROR_LOG_PATH)
file_handler.setFormatter(formatter)
logger.setLevel(logging.DEBUG)
logger.addHandler(file_handler)


def get_imap_messages():
    # type: () -> Generator[Message, None, None]
    mbox = IMAP4_SSL(settings.EMAIL_GATEWAY_IMAP_SERVER, settings.EMAIL_GATEWAY_IMAP_PORT)
    mbox.login(settings.EMAIL_GATEWAY_LOGIN, settings.EMAIL_GATEWAY_PASSWORD)
    try:
        mbox.select(settings.EMAIL_GATEWAY_IMAP_FOLDER)
        try:
            status, num_ids_data = mbox.search(None, 'ALL')  # type: bytes, List[bytes]
            for msgid in num_ids_data[0].split():
                status, msg_data = mbox.fetch(msgid, '(RFC822)')
                msg_as_bytes = msg_data[0][1]
                if six.PY2:
                    message = email.message_from_string(msg_as_bytes)
                else:
                    message = email.message_from_bytes(msg_as_bytes)
                yield message
                mbox.store(msgid, '+FLAGS', '\\Deleted')
            mbox.expunge()
        finally:
            mbox.close()
    finally:
        mbox.logout()


class Command(BaseCommand):
    help = __doc__

    def handle(self, *args, **options):
        # type: (*Any, **str) -> None
        # We're probably running from cron, try to batch-process mail
        if (not settings.EMAIL_GATEWAY_BOT or not settings.EMAIL_GATEWAY_LOGIN or
            not settings.EMAIL_GATEWAY_PASSWORD or not settings.EMAIL_GATEWAY_IMAP_SERVER or
                not settings.EMAIL_GATEWAY_IMAP_PORT or not settings.EMAIL_GATEWAY_IMAP_FOLDER):
            print("Please configure the Email Mirror Gateway in /etc/zulip/, "
                  "or specify $ORIGINAL_RECIPIENT if piping a single mail.")
            exit(1)
        for message in get_imap_messages():
            process_message(message)