from django.conf import settings
from django.core.exceptions import ValidationError
from django.core.urlresolvers import reverse
from django.db import models

from .validators import less_than_one


class AbstractItem(models.Model):
    name = models.CharField(max_length=130)
    description = models.TextField(blank=True)

    def __str__(self):
        return self.name

    def get_use_class(self):
        raise NotImplemented

    def used(self, except_by=None):
        """ Return the used fraction of an item

        :type: Service
        :param except_by: exclude this service from the math
        :rtype: float
        """
        sharing_costs = self.get_use_class().objects.filter(resource=self)
        if except_by:
            sharing_costs = sharing_costs.exclude(service=except_by)

        existing_uses_sum = sum(
            sharing_costs.values_list('share', flat=True))

        return existing_uses_sum

    class Meta:
        abstract = True


class Cost(AbstractItem):
    """ A monthtly cost we have to pay
    """
    price = models.FloatField(help_text="Coût mensuel")

    def get_use_class(self):
        return CostUse

    class Meta:
        verbose_name = 'Coût'


class Good(AbstractItem):
    """ A good, which replacement is provisioned
    """
    price = models.FloatField()
    provisioning_duration = models.DurationField(
        choices=settings.PROVISIONING_DURATIONS)

    def get_use_class(self):
        return GoodUse

    def monthly_provision(self):
        return self.price/self.provisioning_duration.days*(365.25/12)

    class Meta:
        verbose_name = 'Bien'


class AbstractUse(models.Model):
    share = models.FloatField(validators=[less_than_one])
    service = models.ForeignKey('Service')

    class Meta:
        abstract = True

    def clean(self):
        if hasattr(self, 'resource'):
            if (self.resource.used(except_by=self.service) + self.share) > 1:
                raise ValidationError(
                    "Cannot use more than 100% of {})".format(self.resource))


class CostUse(AbstractUse):
    resource = models.ForeignKey(Cost)

    def cost_share(self):
        return self.share*self.resource.price

    def unit_cost_share(self):
        subscriptions_count = self.service.subscriptions_count
        if subscriptions_count == 0:
            return 0
        else:
            return self.cost_share()/self.service.subscriptions_count


class GoodUse(AbstractUse):
    resource = models.ForeignKey(Good)

    def monthly_provision_share(self):
        return self.real_share()*self.resource.monthly_provision()

    def unit_monthly_provision_share(self):
        subscriptions_count = self.service.subscriptions_count
        monthly_share = self.monthly_provision_share()
        if subscriptions_count == 0:
            return 0
        else:
            return monthly_share/subscriptions_count


class Service(AbstractItem):
    """ A service we sell

    (considered monthly)
    """
    costs = models.ManyToManyField(
        Cost,
        through=CostUse,
        related_name='using_services')
    goods = models.ManyToManyField(
        Good,
        through=GoodUse,
        related_name='using_services')
    # services = models.ManyToMany('Service') #TODO

    subscriptions_count = models.PositiveIntegerField(default=0)

    def get_absolute_url(self):
        return reverse('detail-service', kwargs={'pk': self.pk})