# -*- coding: utf-8 -*-

from __future__ import unicode_literals

import subprocess

from django.conf import settings
from django.db import models
from django.db.models.signals import pre_save, post_save, m2m_changed
from django.dispatch import receiver

from coin.members.models import Member


class MaillingList(models.Model):
    short_name = models.CharField(
        'identifiant technique', max_length=50,
        help_text=(
            "c'est l'identifiant qui servira à "
            "communiquer avec le système de mailling-list"
            "(typiquement, la partie avant le \"@\" dans l'adress )"
        )
    )
    email = models.EmailField("adresse mail d'envoi")
    verbose_name = models.CharField(
        'nom complet', max_length=130,
        help_text="Nom affiché dans l'interface membre"
    )
    description = models.TextField()
    subscribers = models.ManyToManyField(
        Member, related_name='subscribed_maillinglists',
        verbose_name='abonné·e·s')

    class Meta:
        verbose_name = 'liste mail'
        verbose_name_plural = 'listes mail'

    def __unicode__(self):
        return '{} ({})'.format(self.verbose_name, self.email)

    def as_text_listing(self):
        """ One subscriber email per line
        """
        return '\n'.join(
                self.subscribers.values_list('email', flat=True))

    def sync_to_list_server(self, force_clear=False):
        if not settings.MAILLIST_SYNC_COMMAND:
            raise ValueError('You should define MAILLIST_SYNC_COMMAND'
                             ' setting to use maillist module')
        else:
            cmd = settings.MAILLIST_SYNC_COMMAND.format(
                email=self.email,
                short_name=self.short_name,
            )
            p = subprocess.Popen(
                cmd, shell=True,
                stdin=subprocess.PIPE, stderr=subprocess.PIPE)
            if force_clear:
                text_listing = ''
            else:
                text_listing = self.as_text_listing()
            out_stdout, out_stderr = p.communicate(text_listing)
            if p.returncode != 0:
                raise SystemError(
                    "Erreur à l'appel de la commande : \"{}\"".format(
                        out_stderr.decode('utf-8')))


@receiver(m2m_changed, sender=MaillingList.subscribers.through)
def push_updated_list(sender, instance, action, reverse, model, pk_set, **kwargs):
    if action in ('post_add', 'post_remove'):
        if reverse:
            impacted_mls = MaillingList.objects.filter(pk__in=pk_set)
        else:
            impacted_mls = [instance]
    elif action == 'post_clear' and not reverse:
        impacted_mls = [instance]

    # cannot be handled at post_clear (we would have lost the information on
    # what has been removed)
    elif action == 'pre_clear' and reverse:
        impacted_mls = instance.subscribed_maillinglists.all()

    else:
        return

    for ml in impacted_mls:
        if action == 'pre_clear':
            # We have to force it because it has not yet been reflected in DB.
            ml.sync_to_list_server(force_clear=True)
        else:
            ml.sync_to_list_server()


@receiver(pre_save, sender=Member)
def store_previous_email(sender, instance, *args, **kwargs):
    """Record the email address for post_save handler

    update_an_email_address needs the old email address for comparison, but
    this information is not available at post_save stage.
    """
    member = instance

    # if not, this is a user creation, nothing to do
    if member.pk:
        old_member = Member.objects.get(pk=member.pk)
        member._previous_email = old_member.email


@receiver(post_save, sender=Member)
def update_an_email_address(sender, instance, *args, **kwargs):
    """Check if the member email has changed and sync mail lists if so.

    We do that at post_save stage because we need the new information to be
    recorded in database, otherwise, sync_list_to_server() would use the old
    email.
    """
    member = instance
    old_email = getattr(member, '_previous_email', None)

    if old_email and (old_email != member.email):
        for maillist in member.subscribed_maillinglists.all():
            maillist.sync_to_list_server()

            # Error handling