from decimal import Decimal
from django.contrib.auth.models import Group
from django.db import models
from django.utils.translation import ugettext_lazy as _
from product import signals
from product.models import Product
from product.prices import PriceAdjustment, PriceAdjustmentCalc
from satchmo_utils.fields import CurrencyField
from threaded_multihost import threadlocals
import datetime
import logging

log = logging.getLogger('tieredpricing.models')

class PricingTierManager(models.Manager):

    def by_user(self, user):
        """Get the pricing tiers for a user"""
        key = 'TIER_%i' % user.id
        current = threadlocals.get_thread_variable(key)

        if current is None:
            groups = user.groups.all()
            if groups:
                q = self.all()
                for group in groups:
                    q = q.filter(group=group)
                if q.count() > 0:
                    current = list(q)

            if current is None:
                current = "no"

            threadlocals.set_thread_variable(key, current)

        if current == "no":
            raise PricingTier.DoesNotExist

        return current

class PricingTier(models.Model):
    """A specific pricing tier, such as "trade customers"
    """
    group = models.OneToOneField(Group, help_text=_('The user group that will receive the discount'))
    title = models.CharField(_('Title'), max_length=50)
    discount_percent = models.DecimalField(_("Discount Percent"), null=True, blank=True,
        max_digits=5, decimal_places=2,
        help_text=_("This is the discount that will be applied to every product if no explicit Tiered Price exists for that product.  Leave as 0 if you don't want any automatic discount in that case."))

    objects = PricingTierManager()

    def __unicode__(self):
        return self.title

class TieredPriceManager(models.Manager):

    def by_product_qty(self, tier, product, qty=Decimal('1')):
        """Get the tiered price for the specified product and quantity."""

        qty_discounts = product.tieredprices.exclude(expires__isnull=False, expires__lt=datetime.date.today()).filter(quantity__lte=qty, pricingtier=tier)

        if qty_discounts.count() > 0:
            # Get the price with the quantity closest to the one specified without going over
            return qty_discounts.order_by('-quantity')[0]
        raise TieredPrice.DoesNotExist

class TieredPrice(models.Model):
    """
    A Price which applies only to special tiers.
    """
    pricingtier = models.ForeignKey(PricingTier, related_name="tieredprices")
    product = models.ForeignKey(Product, related_name="tieredprices")
    price = CurrencyField(_("Price"), max_digits=14, decimal_places=6, )
    quantity = models.DecimalField(_("Discount Quantity"), max_digits=18, decimal_places=6,  default='1', help_text=_("Use this price only for this quantity or higher"))
    expires = models.DateField(_("Expires"), null=True, blank=True)

    objects = TieredPriceManager()

    def _dynamic_price(self):
        """Get the current price as modified by all listeners."""
        adjust = PriceAdjustmentCalc(self)
        signals.satchmo_price_query.send(self, adjustment=adjust,
            slug=self.product.slug, discountable=self.product.is_discountable)
        return adjust.final_price()

    dynamic_price = property(fget=_dynamic_price)

    def save(self, **kwargs):
        prices = TieredPrice.objects.filter(product=self.product, quantity=self.quantity, pricingtier=self.pricingtier)
        if self.expires:
            prices = prices.filter(expires=self.expires)
        else:
            prices = prices.filter(expires__isnull=True)
        if self.id:
            prices = prices.exclude(id=self.id)
        if prices.count():
            return #Duplicate Price

        super(TieredPrice, self).save(**kwargs)

    class Meta:
        ordering = ['pricingtier', 'expires', '-quantity']
        verbose_name = _("Tiered Price")
        verbose_name_plural = _("Tiered Prices")
        unique_together = (("pricingtier", "product", "quantity", "expires"),)

def tiered_price_listener(signal, adjustment=None, **kwargs):
    """Listens for satchmo_price_query signals, and returns a tiered price instead of the
    default price.

    Requires threaded_multihost.ThreadLocalMiddleware to be installed so
    that it can determine the current user."""

    if kwargs.has_key('discountable'):
        discountable = kwargs['discountable']
    else:
        discountable = adjustment.product.is_discountable

    if discountable:
        product = adjustment.product
        user = threadlocals.get_current_user()
        if user and not user.is_anonymous():
            try:
                tiers = PricingTier.objects.by_user(user)
                log.debug('got tiers: %s', tiers)
                best = None
                besttier = None
                currentprice = adjustment.final_price()
                qty = adjustment.price.quantity
                for tier in tiers:
                    candidate = None
                    try:
                        tp = TieredPrice.objects.by_product_qty(tier, product, qty)
                        log.debug("Found a Tiered Price for %s qty %d = %s", product.slug, qty, tp.price)
                        candidate = tp.price
                    except TieredPrice.DoesNotExist:
                        pcnt = tier.discount_percent
                        if pcnt is not None and pcnt != 0:
                            candidate = currentprice * (100-pcnt)/100

                    if best is None or (candidate and candidate < best):
                        best = candidate
                        besttier = tier

                        log.debug('best = %s', best)

                if best is not None:
                    delta = currentprice - best
                    adjustment += PriceAdjustment(
                        'tieredpricing',
                        _('Tiered Pricing for %(tier)s' % { 'tier': besttier.group.name}),
                        delta)

            except PricingTier.DoesNotExist:
                pass

signals.satchmo_price_query.connect(tiered_price_listener)
