import re

from django.db import models
from django.utils.translation import gettext_lazy as _
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic
from django.db.models.signals import post_save
from django.core.exceptions import ObjectDoesNotExist
from django.core.cache import cache
from django.core.urlresolvers import reverse
from django.db.models.query import QuerySet

import mptt
from mptt.utils import previous_current_next


class Item(object):
    def __init__(self, node):
        self.parent = None
        self.node = node
        self.children = []
        self.active = False
    
    def __repr__(self):
        return str(self.node)
    
    def add_child(self, item):
        if hasattr(self, '_enabled_children'):
            del self._enabled_children
        item.parent = self
        self.children.append(item)
    
    @property
    def enabled_children(self):
        children = getattr(self, '_enabled_children', None)
        if children is None:
            children = [c for c in self.children if c.node.is_enabled]
            self._enabled_children = children
        return children
    
    def set_active(self, href):
        active_node = None
        if (self.node.href.startswith('^') and
            re.match(self.node.href, href)) or self.node.href == href:
            self.active = True
            parent = self.parent
            while parent:
                parent.active = True
                parent = parent.parent
            active_node = self
        for child in self.children:
            child = child.set_active(href)
            if child:
                active_node = child
        return active_node
    
    def get_active_items(self):
        if not self.parent:
            return [self]
        else:
            return self.parent.get_active_items() + [self]
    
    def to_dict(self):
        return {
            'node': self.node,
            'active': self.active,
            'children': [c.to_dict() for c in self.children],
        }


def delete_cache():
    cache.delete('menus')
    for menu in MenuItem.objects.all():
        cache.delete('menu-%s' % menu.slug)
        cache.delete('menu-tree-%s' % menu.slug)


class MenuUnCacheQuerySet(QuerySet):
    def delete(self, *args, **kwargs):
        delete_cache()
        super(MenuUnCacheQuerySet, self).delete(*args, **kwargs)
        
    def update(self, *args, **kwargs):
        delete_cache()
        super(MenuUnCacheQuerySet, self).update(*args, **kwargs)

    
class MenuItemManager(models.Manager):
    def get_query_set(self):    
        return MenuUnCacheQuerySet(self.model)

    
class MenuItem(models.Model):

    parent = models.ForeignKey(
        'MenuItem',
        related_name='children',
        null=True,
        blank=True,
    )
    label = models.CharField(
        _('label'),
        max_length=255,
        help_text="The display name on the web site.",
    )
    slug = models.SlugField(
        _('slug'),
        unique=True,
        max_length=255,
        help_text="Unique identifier for this menu item (also CSS ID)"
    )
    order = models.IntegerField(
        _('order'),
        choices=[(x, x) for x in xrange(0, 51)],
    )
    is_enabled = models.BooleanField(default=True)
    link = models.CharField(
        _('link'),
        max_length=255,
        help_text="The view of the page you want to link to, as a python path or the shortened URL name.",
        blank=True,
    )
    content_type = models.ForeignKey(
        ContentType,
        null=True,
        blank=True,
    )
    object_id = models.PositiveIntegerField(
        null=True,
        blank=True,
    )
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    href = models.CharField(_('href'), editable=False, max_length=255)
    objects = MenuItemManager()
    
    class Meta:
        ordering = ('lft', 'tree_id')
    
    def to_tree(self):
        cache_key = 'menu-tree-%s' % self.slug
        root = cache.get(cache_key)
        if not root:
            item = root = Item(self)
            descendents = self.get_descendants()
            for prev, curr, next in previous_current_next(descendents):
                previous_item = item
                item = Item(curr)
                if not prev or prev.level < curr.level:
                    previous_item.add_child(item)
                elif prev and prev.level > curr.level:
                    parent = previous_item
                    while parent.node.level >= curr.level:
                        parent = parent.parent
                    parent.add_child(item)
                else:
                    previous_item.parent.add_child(item)
            cache.set(cache_key, root)
        return root
    
    def save(self, *args, **kwargs):
        literal_url_prefixes = ('/', 'http://', 'https://')
        regex_url_prefixes = ('^',)
        if self.link:
            if any([self.link.startswith(s) for s in literal_url_prefixes]):
                self.href = self.link
            elif any([self.link.startswith(s) for s in regex_url_prefixes]):
                self.href = '' # regex should not be used as an actual URL
            else:
                self.href = reverse(self.link)
        elif self.content_object:
            self.href = self.content_object.get_absolute_url()
        else:
            self.href = ''
        delete_cache()
        super(MenuItem, self).save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        delete_cache()
        super(MenuItem, self).delete(*args, **kwargs)
    
    def __unicode__(self):
        return self.slug

mptt.register(MenuItem, order_insertion_by=['order'])


def treenav_save_other_object_handler(sender, instance, created, **kwargs):
    """
    This signal attempts to update the HREF of any menu items that point to
    another model object, when that objects is saved.
    """
    cache_key = 'django-treenav-menumodels'
    if sender == MenuItem:
        cache.delete(cache_key)
    menu_models = cache.get(cache_key)
    if not menu_models:
        menu_models = []
        for menu_item in MenuItem.objects.exclude(content_type__isnull=True):
            menu_models.append(menu_item.content_type.model_class())
        cache.set(cache_key, menu_models)
    # only attempt to update MenuItem if sender is known to be referenced
    if sender in menu_models:
        ct = ContentType.objects.get_for_model(sender)
        items = MenuItem.objects.filter(content_type=ct, object_id=instance.pk)
        for item in items:
            if item.href != instance.get_absolute_url():
                item.href = instance.get_absolute_url()
                item.save()
post_save.connect(treenav_save_other_object_handler)

@@ -70,16 +70,17 @@
  import 
+u
 gettext_

Change translation to ugettext_lazy.