from django.contrib.auth import get_user_model
from django.core.exceptions import FieldDoesNotExist, FieldError
from django.db import models
from django.utils.translation import ugettext_lazy as _

from communication.models import SubscriptionMixin

from .validators import ColorValidator

User = get_user_model()


class Event(SubscriptionMixin, models.Model):
    title = models.CharField(
        _("nom de l'évènement"),
        max_length=200,
    )
    slug = models.SlugField(
        _("identificateur"),
        unique=True,
        help_text=_(
            "Seulement des lettres, des chiffres ou les caractères '_' ou '-'."
        ),
    )
    created_by = models.ForeignKey(
        User,
        verbose_name=_("créé par"),
        on_delete=models.SET_NULL,
        related_name="created_events",
        editable=False, null=True,
    )
    created_at = models.DateTimeField(
                    _('date de création'),
                    auto_now_add=True,
                )
    description = models.TextField(_('description'))
    beginning_date = models.DateTimeField(
                    _('date de début'),
                    help_text=_("date publique de l'évènement"),
                )
    ending_date = models.DateTimeField(
                    _('date de fin'),
                    help_text=_("date publique de l'évènement"),
            )

    class Meta:
        verbose_name = _("évènement")
        verbose_name_plural = _("évènements")

    def __str__(self):
        return self.title


class EventSpecificMixin(models.Model):
    """Mixin allowing for event-specific models instances
    or not (depending on whether the event field is null)"""

    event = models.ForeignKey(
        Event,
        verbose_name=_("évènement"),
        help_text=_(
            "Si spécifié, l'instance du modèle est spécifique à l'évènement "
            "en question."
        ),
        on_delete=models.CASCADE,
        blank=True, null=True,
    )

    class Meta:
        abstract = True


class Place(EventSpecificMixin, models.Model):
    name = models.CharField(
        _("nom du lieu"),
        max_length=200,
    )
    description = models.TextField(blank=True)

    class Meta:
        verbose_name = _("lieu")
        verbose_name_plural = _("lieux")

    def __str__(self):
        return self.name


class ActivityTag(EventSpecificMixin, models.Model):
    name = models.CharField(
        _("nom du tag"),
        max_length=200,
    )
    is_public = models.BooleanField(
        _("est public"),
        help_text=_(
            "Sert à faire une distinction dans l'affichage selon que le tag "
            "soit destiné au public ou à l'organisation."
        ),
    )
    color = models.CharField(
        _('couleur'),
        max_length=7,
        validators=[ColorValidator],
        help_text=_("Rentrer une couleur en hexadécimal (#XXX ou #XXXXXX)."),
    )

    class Meta:
        verbose_name = _("tag")
        verbose_name_plural = _("tags")

    def __str__(self):
        return self.name


class AbstractActivityTemplate(SubscriptionMixin, models.Model):
    title = models.CharField(
        _("nom de l'activité"),
        max_length=200,
        blank=True, null=True,
    )
    # FIXME: voir comment on traite l'héritage de `event`
    event = models.ForeignKey(
        Event,
        verbose_name=_("évènement"),
        on_delete=models.CASCADE,
        editable=False,
    )
    is_public = models.NullBooleanField(
        _("est public"),
        blank=True,
    )
    has_perm = models.NullBooleanField(
        _("inscription de permanents"),
        blank=True,
    )
    min_perm = models.PositiveSmallIntegerField(
        _('nombre minimum de permanents'),
        blank=True, null=True,
    )
    max_perm = models.PositiveSmallIntegerField(
        _('nombre maximum de permanents'),
        blank=True, null=True,
    )
    description = models.TextField(
        _('description'),
        help_text=_("Visible par tout le monde si l'événément est public."),
        blank=True, null=True,
    )
    remarks = models.TextField(
        _('remarques'),
        help_text=_("Visible uniquement par les organisateurs."),
        blank=True, null=True,
    )
    tags = models.ManyToManyField(
        ActivityTag,
        verbose_name=_('tags'),
        blank=True,
    )
    places = models.ManyToManyField(
        Place,
        verbose_name=_('lieux'),
        blank=True,
    )

    class Meta:
        abstract = True


class ActivityTemplate(AbstractActivityTemplate):
    class Meta:
        verbose_name = _("template activité")
        verbose_name_plural = _("templates activité")

    def __str__(self):
        return self.title


class Activity(AbstractActivityTemplate):
    parent = models.ForeignKey(
        ActivityTemplate,
        verbose_name=_("template"),
        on_delete=models.PROTECT,
        related_name="children",
        blank=True, null=True,
    )
    staff = models.ManyToManyField(
        User,
        verbose_name=_("permanents"),
        related_name="in_perm_activities",
        blank=True,
    )

    beginning = models.DateTimeField(_("heure de début"))
    end = models.DateTimeField(_("heure de fin"))

    def get_herited(self, attrname):
        try:
            tpl_field = ActivityTemplate._meta.get_field(attrname)
        except FieldDoesNotExist:
            raise FieldError(
                "%(attrname)s field can't be herited.",
                params={'attrname': attrname},
            )

        value = getattr(self, attrname)

        if tpl_field.many_to_many:
            if value.exists():
                return value
            else:
                return getattr(self.parent, attrname)
        elif value is None:
            return getattr(self.parent, attrname)
        else:
            return value

    class Meta:
        verbose_name = _("activité")
        verbose_name_plural = _("activités")

    def __str__(self):
        return self.get_herited('title')