from django.core.cache import cache

from django.conf import settings

from guardian.core import ObjectPermissionChecker

from django.contrib.auth.models import User

from django.db.models import Q

from guardian.shortcuts import assign

from django.utils.encoding import smart_str

import re

import hashlib

def get_cached_checker(user):

    key_name = get_key(user.username)

    checker = cache.get(key_name)

    if checker:

        return checker

    checker = ObjectPermissionChecker(user)

    cache.set(key_name, checker)

    return checker

def cached_assign(perm, user_or_group, object_inst):

    assign(perm, user_or_group, object_inst)

    if hasattr(user_or_group, 'username'):

        key = get_key(user_or_group.username)

    else:

        key = get_key(user_or_group.name)

    cache.delete(key)

def get_cached_userlist():

    userlist = cache.get('userlist')

    if userlist:

        return userlist

    query = Q(id=settings.ANONYMOUS_USER_ID) | Q(is_superuser=True)

    userlist = User.objects.exclude(query)

    cache.set('userlist', userlist)

    return userlist

def get_key(name):

    name = smart_str(name, encoding="ascii", errors="replace") 

    name = re.sub(r"[^\w\s_\-]", '', name)

    name = re.sub(r"\s+", '_', name)

    key = "checker_%s" % name

    if len(key) > 250:

        key = hashlib.sha512(key).hexdigest()

    return key