import itertools

from . import inventory

from django.core.exceptions import ValidationError

from django.db import models

from django.utils.encoding import python_2_unicode_compatible

from django.utils.translation import ugettext_lazy as _

from model_utils.managers import InheritanceManager

@python_2_unicode_compatible

class DiscountBase(models.Model):

    ''' Base class for discounts. This class is subclassed with special

    attributes which are used to determine whether or not the given discount

    is available to be added to the current cart.

    Attributes:

        description (str): Display text that appears on the attendee's Invoice

            when the discount is applied to a Product on that invoice.

    '''

        if len(cats) > 1:

            raise ValidationError(

                _("You may only have one discount line per category"))

    discount = models.ForeignKey(DiscountBase, on_delete=models.CASCADE)

    category = models.ForeignKey(inventory.Category, on_delete=models.CASCADE)

    percentage = models.DecimalField(

        max_digits=4,

        decimal_places=1)

    quantity = models.PositiveIntegerField()

    ''' Discounts that are generally available, but are limited by timespan or

    usage count. This is for e.g. Early Bird discounts.

    Attributes:

        start_time (Optional[datetime]): When the discount should start being

            offered.

        end_time (Optional[datetime]): When the discount should stop being

            offered.

        limit (Optional[int]): How many times the discount is allowed to be

            applied -- to all users.

    '''

    class Meta:

        app_label = "registrasion"

        verbose_name = _("discount (time/stock limit)")

        verbose_name_plural = _("discounts (time/stock limit)")

    ''' Discounts that are enabled when a voucher code is in the current

    cart. These are normally configured in the Admin page at the same time as

    creating a Voucher object.

    Attributes:

        voucher (inventory.Voucher): The voucher that enables this discount.

    '''

    class Meta:

        app_label = "registrasion"

        verbose_name = _("discount (enabled by voucher)")

        verbose_name_plural = _("discounts (enabled by voucher)")

    ''' Discounts that are enabled because another product has been purchased.

    e.g. A conference ticket includes a free t-shirt.

    Attributes:

        enabling_products ([inventory.Product, ...]): The products that enable

            the discount.

    '''

    class Meta:

        app_label = "registrasion"

        verbose_name = _("discount (product inclusions)")

        verbose_name_plural = _("discounts (product inclusions)")

class RoleDiscount(object):

    ''' Discounts that are enabled because the active user has a specific

    role. This is for e.g. volunteers who can get a discount ticket. '''

    # TODO: implement RoleDiscount

    pass

@python_2_unicode_compatible

class FlagBase(models.Model):

    ''' This defines a condition which allows products or categories to

    be made visible, or be prevented from being visible.

        related_name="flagbase_set",

    )

    categories = models.ManyToManyField(

        inventory.Category,

        blank=True,

        help_text=_("Categories whose products are affected by this flag's "

                    "condition."

                    ),

        related_name="flagbase_set",

    )

    ''' Product groupings that can be used to enable a product during a

    specific date range, or when fewer than a limit of products have been

    sold.

    Attributes:

        start_time (Optional[datetime]): This condition is only met after this

            time.

        end_time (Optional[datetime]): This condition is only met before this

            time.

        limit (Optional[int]): The number of products that *all users* can

            purchase under this limit, regardless of their per-user limits.

    '''

    class Meta:

        app_label = "registrasion"

        verbose_name = _("flag (time/stock limit)")

        verbose_name_plural = _("flags (time/stock limit)")

@python_2_unicode_compatible

    ''' The condition is met because a specific product is purchased.

    Attributes:

        enabling_products ([inventory.Product, ...]): The products that cause

            this condition to be met.

    '''

    class Meta:

        app_label = "registrasion"

        verbose_name = _("flag (dependency on product)")

        verbose_name_plural = _("flags (dependency on product)")

    def __str__(self):

        return "Enabled by products: " + str(self.enabling_products.all())

@python_2_unicode_compatible

class CategoryFlag(FlagBase):

    ''' The condition is met because a product in a particular product is

    purchased.

    Attributes:

        enabling_category (inventory.Category): The category that causes this

            condition to be met.

     '''

    class Meta:

    def __str__(self):

        return "Enabled by product in category: " + str(self.enabling_category)

    enabling_category = models.ForeignKey(

        inventory.Category,

        help_text=_("If a product from this category is purchased, this "

                    "condition is met."),

    )

@python_2_unicode_compatible

    ''' The condition is met because a Voucher is present. This is for e.g.

    enabling sponsor tickets. '''

    class Meta:

        app_label = "registrasion"

        verbose_name = _("flag (dependency on voucher)")

        verbose_name_plural = _("flags (dependency on voucher)")

    def __str__(self):

        return "Enabled by voucher: %s" % self.voucher

# @python_2_unicode_compatible

class RoleFlag(object):

    ''' The condition is met because the active user has a particular Role.

    This is for e.g. enabling Team tickets. '''

    # TODO: implement RoleFlag

    pass