from django.conf import settings
from django.core.exceptions import ValidationError
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)

    class Meta:
        abstract = True


class Cost(AbstractItem):
    """ A monthtly cost we have to pay
    """
    price = models.PositiveIntegerField()

    def used(self):
        sharing_costs = CostUse.objects.filter(resource=self)
        existing_uses_sum = sum(
            sharing_costs.values_list('share', flat=True))

        return existing_uses_sum


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


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

    class Meta:
        abstract = True

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


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


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


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