import logging
from typing import Any, Dict, List, Union

import bleach
import cssutils
import markdown
from django.conf import settings
from django.core.mail import EmailMultiAlternatives, get_connection
from django.template.loader import get_template
from django.utils.translation import ugettext as _
from i18nfield.strings import LazyI18nString
from inlinestyler.utils import inline_css

from pretix.base.i18n import language
from pretix.base.models import Event, InvoiceAddress, Order
from pretix.celery_app import app
from pretix.multidomain.urlreverse import build_absolute_uri

logger = logging.getLogger('pretix.base.mail')
INVALID_ADDRESS = 'invalid-pretix-mail-address'
cssutils.log.setLevel(logging.CRITICAL)


class TolerantDict(dict):

    def __missing__(self, key):
        return key


class SendMailException(Exception):
    pass


def mail(email: str, subject: str, template: Union[str, LazyI18nString],
         context: Dict[str, Any]=None, event: Event=None, locale: str=None,
         order: Order=None, headers: dict=None, sender: str=None):
    """
    Sends out an email to a user. The mail will be sent synchronously or asynchronously depending on the installation.

    :param email: The email address of the recipient

    :param subject: The email subject. Should be localized to the recipients's locale or a lazy object that will be
        localized by being casted to a string.

    :param template: The filename of a template to be used. It will be rendered with the locale given in the locale
        argument and the context given in the next argument. Alternatively, you can pass a LazyI18nString and
        ``context`` will be used as the argument to a  Python ``.format_map()`` call on the template.

    :param context: The context for rendering the template (see ``template`` parameter)

    :param event: The event this email is related to (optional). If set, this will be used to determine the sender,
        a possible prefix for the subject and the SMTP server that should be used to send this email.

    :param order: The order this email is related to (optional). If set, this will be used to include a link to the
        order below the email.

    :param headers: A dict of custom mail headers to add to the mail

    :param locale: The locale to be used while evaluating the subject and the template

    :param sender: Set the sender email address. If not set and ``event`` is set, the event's default will be used,
        otherwise the system default.

    :raises MailOrderException: on obvious, immediate failures. Not raising an exception does not necessarily mean
        that the email has been sent, just that it has been queued by the email backend.
    """
    if email == INVALID_ADDRESS:
        return

    headers = headers or {}

    with language(locale):
        if isinstance(context, dict) and order:
            try:
                context.update({
                    'invoice_name': order.invoice_address.name,
                    'invoice_company': order.invoice_address.company
                })
            except InvoiceAddress.DoesNotExist:
                context.update({
                    'invoice_name': '',
                    'invoice_company': ''
                })
        body, body_md = render_mail(template, context)
        subject = str(subject).format_map(context)
        sender = sender or (event.settings.get('mail_from') if event else settings.MAIL_FROM)

        subject = str(subject)
        body_plain = body

        htmlctx = {
            'site': settings.PRETIX_INSTANCE_NAME,
            'site_url': settings.SITE_URL,
            'body': body_md,
            'color': '#8E44B3'
        }

        if event:
            htmlctx['event'] = event
            htmlctx['color'] = event.settings.primary_color

            if event.settings.mail_from == settings.DEFAULT_FROM_EMAIL and event.settings.contact_mail and not headers.get('Reply-To'):
                headers['Reply-To'] = event.settings.contact_mail

            prefix = event.settings.get('mail_prefix')
            if prefix:
                subject = "[%s] %s" % (prefix, subject)

            body_plain += "\r\n\r\n-- \r\n"

            signature = str(event.settings.get('mail_text_signature'))
            if signature:
                signature = signature.format(event=event.name)
                signature_md = signature.replace('\n', '<br>\n')
                signature_md = bleach.linkify(bleach.clean(markdown.markdown(signature_md), tags=bleach.ALLOWED_TAGS + ['p', 'br']))
                htmlctx['signature'] = signature_md
                body_plain += signature
                body_plain += "\r\n\r\n-- \r\n"

            if order:
                body_plain += _(
                    "You are receiving this email because you placed an order for {event}."
                ).format(event=event.name)
                htmlctx['order'] = order
                body_plain += "\r\n"
                body_plain += _(
                    "You can view your order details at the following URL:\n{orderurl}."
                ).replace("\n", "\r\n").format(
                    event=event.name, orderurl=build_absolute_uri(
                        order.event, 'presale:event.order', kwargs={
                            'order': order.code,
                            'secret': order.secret
                        }
                    )
                )
            body_plain += "\r\n"

        tpl = get_template('pretixbase/email/plainwrapper.html')
        body_html = tpl.render(htmlctx)
        return mail_send([email], subject, body_plain, body_html, sender, event.id if event else None, headers)


@app.task
def mail_send_task(to: List[str], subject: str, body: str, html: str, sender: str,
                   event: int=None, headers: dict=None, bcc: List[str]=None) -> bool:
    email = EmailMultiAlternatives(subject, body, sender, to=to, bcc=bcc, headers=headers)
    if html is not None:
        email.attach_alternative(inline_css(html), "text/html")
    if event:
        event = Event.objects.get(id=event)
        backend = event.get_mail_backend()
    else:
        backend = get_connection(fail_silently=False)

    try:
        backend.send_messages([email])
    except Exception:
        logger.exception('Error sending email')
        raise SendMailException('Failed to send an email to {}.'.format(to))


def mail_send(*args, **kwargs):
    mail_send_task.apply_async(args=args, kwargs=kwargs)


def render_mail(template, context):
    if isinstance(template, LazyI18nString):
        body = str(template)
        if context:
            body = body.format_map(TolerantDict(context))
        body_md = bleach.linkify(bleach.clean(markdown.markdown(body), tags=bleach.ALLOWED_TAGS + [
            'p', 'pre'
        ]))
    else:
        tpl = get_template(template)
        body = tpl.render(context)
        body_md = bleach.linkify(markdown.markdown(body))
    return body, body_md