from __future__ import absolute_import
from typing import Any, Optional

import logging
import re

from email.header import decode_header
import email.message as message

from django.conf import settings

from zerver.lib.actions import decode_email_address, get_email_gateway_message_string_from_address, \
    internal_send_message
from zerver.lib.notifications import convert_html_to_markdown
from zerver.lib.redis_utils import get_redis_client
from zerver.lib.upload import upload_message_image
from zerver.lib.utils import generate_random_token
from zerver.lib.str_utils import force_text
from zerver.models import Stream, Recipient, get_user_profile_by_email, \
    get_user_profile_by_id, get_display_recipient, get_recipient, \
    Message, Realm, UserProfile
from six import text_type, binary_type
import six
import talon
from talon import quotations

talon.init()

logger = logging.getLogger(__name__)

def redact_stream(error_message):
    # type: (text_type) -> text_type
    domain = settings.EMAIL_GATEWAY_PATTERN.rsplit('@')[-1]
    stream_match = re.search(u'\\b(.*?)@' + domain, error_message)
    if stream_match:
        stream_name = stream_match.groups()[0]
        return error_message.replace(stream_name, "X" * len(stream_name))
    return error_message

def report_to_zulip(error_message):
    # type: (text_type) -> None
    if settings.ERROR_BOT is None:
        return
    error_bot = get_user_profile_by_email(settings.ERROR_BOT)
    error_stream = Stream.objects.get(name="errors", realm=error_bot.realm)
    send_zulip(settings.ERROR_BOT, error_stream, u"email mirror error",
               u"""~~~\n%s\n~~~""" % (error_message,))

def log_and_report(email_message, error_message, debug_info):
    # type: (message.Message, text_type, Dict[str, Any]) -> None
    scrubbed_error = u"Sender: %s\n%s" % (email_message.get("From"),
                                          redact_stream(error_message))

    if "to" in debug_info:
        scrubbed_error = u"Stream: %s\n%s" % (redact_stream(debug_info["to"]),
                                              scrubbed_error)

    if "stream" in debug_info:
        scrubbed_error = u"Realm: %s\n%s" % (debug_info["stream"].realm.domain,
                                             scrubbed_error)

    logger.error(scrubbed_error)
    report_to_zulip(scrubbed_error)


# Temporary missed message addresses

redis_client = get_redis_client()


def missed_message_redis_key(token):
    # type: (text_type) -> text_type
    return 'missed_message:' + token


def is_missed_message_address(address):
    # type: (text_type) -> bool
    msg_string = get_email_gateway_message_string_from_address(address)
    return is_mm_32_format(msg_string)

def is_mm_32_format(msg_string):
    # type: (text_type) -> bool
    '''
    Missed message strings are formatted with a little "mm" prefix
    followed by a randomly generated 32-character string.
    '''
    return msg_string.startswith('mm') and len(msg_string) == 34

def get_missed_message_token_from_address(address):
    # type: (text_type) -> text_type
    msg_string = get_email_gateway_message_string_from_address(address)

    if msg_string is None:
        raise ZulipEmailForwardError('Address not recognized by gateway.')

    if not is_mm_32_format(msg_string):
        raise ZulipEmailForwardError('Could not parse missed message address')

    # strip off the 'mm' before returning the redis key
    return msg_string[2:]

def create_missed_message_address(user_profile, message):
    # type: (UserProfile, Message) -> text_type
    if settings.EMAIL_GATEWAY_PATTERN == '':
        logging.warning("EMAIL_GATEWAY_PATTERN is an empty string, using "
                        "NOREPLY_EMAIL_ADDRESS in the 'from' field.")
        return settings.NOREPLY_EMAIL_ADDRESS

    if message.recipient.type == Recipient.PERSONAL:
        # We need to reply to the sender so look up their personal recipient_id
        recipient_id = get_recipient(Recipient.PERSONAL, message.sender_id).id
    else:
        recipient_id = message.recipient_id

    data = {
        'user_profile_id': user_profile.id,
        'recipient_id': recipient_id,
        'subject': message.subject,
    }

    while True:
        token = generate_random_token(32)
        key = missed_message_redis_key(token)
        if redis_client.hsetnx(key, 'uses_left', 1):
            break

    with redis_client.pipeline() as pipeline:
        pipeline.hmset(key, data)
        pipeline.expire(key, 60 * 60 * 24 * 5)
        pipeline.execute()

    address = u'mm' + token
    return settings.EMAIL_GATEWAY_PATTERN % (address,)


def mark_missed_message_address_as_used(address):
    # type: (text_type) -> None
    token = get_missed_message_token_from_address(address)
    key = missed_message_redis_key(token)
    with redis_client.pipeline() as pipeline:
        pipeline.hincrby(key, 'uses_left', -1)
        pipeline.expire(key, 60 * 60 * 24 * 5)
        new_value = pipeline.execute()[0]
    if new_value < 0:
        redis_client.delete(key)
        raise ZulipEmailForwardError('Missed message address has already been used')


def send_to_missed_message_address(address, message):
    # type: (text_type, message.Message) -> None
    token = get_missed_message_token_from_address(address)
    key = missed_message_redis_key(token)
    result = redis_client.hmget(key, 'user_profile_id', 'recipient_id', 'subject')
    if not all(val is not None for val in result):
        raise ZulipEmailForwardError('Missing missed message address data')
    user_profile_id, recipient_id, subject = result

    user_profile = get_user_profile_by_id(user_profile_id)
    recipient = Recipient.objects.get(id=recipient_id)
    display_recipient = get_display_recipient(recipient)

    # Testing with basestring so we don't depend on the list return type from
    # get_display_recipient
    if not isinstance(display_recipient, six.string_types):
        recipient_str = ','.join([user['email'] for user in display_recipient])
    else:
        recipient_str = display_recipient

    body = filter_footer(extract_body(message))
    body += extract_and_upload_attachments(message, user_profile.realm)
    if not body:
        body = '(No email body)'

    if recipient.type == Recipient.STREAM:
        recipient_type_name = 'stream'
    else:
        recipient_type_name = 'private'

    internal_send_message(user_profile.email, recipient_type_name,
                          recipient_str, subject, body)
    logging.info("Successfully processed email from %s to %s" % (
        user_profile.email, recipient_str))

## Sending the Zulip ##

class ZulipEmailForwardError(Exception):
    pass

def send_zulip(sender, stream, topic, content):
    # type: (text_type, Stream, text_type, text_type) -> None
    internal_send_message(
            sender,
            "stream",
            stream.name,
            topic[:60],
            content[:2000],
            stream.realm)

def valid_stream(stream_name, token):
    # type: (text_type, text_type) -> bool
    try:
        stream = Stream.objects.get(email_token=token)
        return stream.name.lower() == stream_name.lower()
    except Stream.DoesNotExist:
        return False

def get_message_part_by_type(message, content_type):
    # type: (message.Message, text_type) -> text_type
    charsets = message.get_charsets()

    for idx, part in enumerate(message.walk()):
        if part.get_content_type() == content_type:
            content = part.get_payload(decode=True)
            assert isinstance(content, binary_type)
            if charsets[idx]:
                text = content.decode(charsets[idx], errors="ignore")
            return text

def extract_body(message):
    # type: (message.Message) -> text_type
    # If the message contains a plaintext version of the body, use
    # that.
    plaintext_content = get_message_part_by_type(message, "text/plain")
    if plaintext_content:
        return quotations.extract_from_plain(plaintext_content)

    # If we only have an HTML version, try to make that look nice.
    html_content = get_message_part_by_type(message, "text/html")
    if html_content:
        html_content = quotations.extract_from_html(html_content)
        return convert_html_to_markdown(html_content)

    raise ZulipEmailForwardError("Unable to find plaintext or HTML message body")

def filter_footer(text):
    # type: (text_type) -> text_type
    # Try to filter out obvious footers.
    possible_footers = [line for line in text.split("\n") if line.strip().startswith("--")]
    if len(possible_footers) != 1:
        # Be conservative and don't try to scrub content if there
        # isn't a trivial footer structure.
        return text

    return text.partition("--")[0].strip()

def extract_and_upload_attachments(message, realm):
    # type: (message.Message, Realm) -> text_type
    user_profile = get_user_profile_by_email(settings.EMAIL_GATEWAY_BOT)
    attachment_links = []

    payload = message.get_payload()
    if not isinstance(payload, list):
        # This is not a multipart message, so it can't contain attachments.
        return ""

    for part in payload:
        content_type = part.get_content_type()
        filename = part.get_filename()
        if filename:
            attachment = part.get_payload(decode=True)
            if isinstance(attachment, binary_type):
                s3_url = upload_message_image(filename, content_type,
                                              attachment,
                                              user_profile,
                                              target_realm=realm)
                formatted_link = u"[%s](%s)" % (filename, s3_url)
                attachment_links.append(formatted_link)
            else:
                logger.warning("Payload is not bytes (invalid attachment %s in message from %s)." %
                               (filename, message.get("From")))

    return u"\n".join(attachment_links)

def extract_and_validate(email):
    # type: (text_type) -> Stream
    try:
        stream_name, token = decode_email_address(email)
    except (TypeError, ValueError):
        raise ZulipEmailForwardError("Malformed email recipient " + email)

    if not valid_stream(stream_name, token):
        raise ZulipEmailForwardError("Bad stream token from email recipient " + email)

    return Stream.objects.get(email_token=token)

def find_emailgateway_recipient(message):
    # type: (message.Message) -> text_type
    # We can't use Delivered-To; if there is a X-Gm-Original-To
    # it is more accurate, so try to find the most-accurate
    # recipient list in descending priority order
    recipient_headers = ["X-Gm-Original-To", "Delivered-To", "To"]
    recipients = [] # type: List[text_type]
    for recipient_header in recipient_headers:
        r = message.get_all(recipient_header, None)
        if r:
            recipients = r
            break

    pattern_parts = [re.escape(part) for part in settings.EMAIL_GATEWAY_PATTERN.split('%s')]
    match_email_re = re.compile(".*?".join(pattern_parts))
    for recipient_email in recipients:
        if match_email_re.match(recipient_email):
            return recipient_email

    raise ZulipEmailForwardError("Missing recipient in mirror email")

def process_stream_message(to, subject, message, debug_info):
    # type: (text_type, text_type, message.Message, Dict[str, Any]) -> None
    stream = extract_and_validate(to)
    body = filter_footer(extract_body(message))
    body += extract_and_upload_attachments(message, stream.realm)
    debug_info["stream"] = stream
    send_zulip(settings.EMAIL_GATEWAY_BOT, stream, subject, body)
    logging.info("Successfully processed email to %s (%s)" % (
        stream.name, stream.realm.domain))

def process_missed_message(to, message, pre_checked):
    # type: (text_type, message.Message, bool) -> None
    if not pre_checked:
        mark_missed_message_address_as_used(to)
    send_to_missed_message_address(to, message)

def process_message(message, rcpt_to=None, pre_checked=False):
    # type: (message.Message, Optional[text_type], bool) -> None
    subject_header = message.get("Subject", "(no subject)")
    encoded_subject, encoding = decode_header(subject_header)[0]
    if encoding is None:
        subject = force_text(encoded_subject) # encoded_subject has type str when encoding is None
    else:
        try:
            subject = encoded_subject.decode(encoding)
        except (UnicodeDecodeError, LookupError):
            subject = u"(unreadable subject)"

    debug_info = {}

    try:
        if rcpt_to is not None:
            to = rcpt_to
        else:
            to = find_emailgateway_recipient(message)
        debug_info["to"] = to

        if is_missed_message_address(to):
            process_missed_message(to, message, pre_checked)
        else:
            process_stream_message(to, subject, message, debug_info)
    except ZulipEmailForwardError as e:
        # TODO: notify sender of error, retry if appropriate.
        log_and_report(message, str(e), debug_info)
