from django.db import connection

from django.contrib.auth.models import User

try: 

    set 

except NameError: 

    from sets import Set as set # Python 2.3 fallback

class ModelBackend(object):

    """

    Authenticate against django.contrib.auth.models.User

    """

    # TODO: Model, login attribute name and password attribute name should be

    # configurable.

    def authenticate(self, username=None, password=None):

        try:

            user = User.objects.get(username=username)

            if user.check_password(password):

                return user

        except User.DoesNotExist:

            return None

    def get_group_permissions(self, user_obj):

        "Returns a list of permission strings that this user has through his/her groups."

        if not hasattr(user_obj, '_group_perm_cache'):

            cursor = connection.cursor()

            # The SQL below works out to the following, after DB quoting:

            # cursor.execute("""

            #     SELECT ct."app_label", p."codename"

            #     FROM "auth_permission" p, "auth_group_permissions" gp, "auth_user_groups" ug, "django_content_type" ct

            #     WHERE p."id" = gp."permission_id"

            #         AND gp."group_id" = ug."group_id"

            #         AND ct."id" = p."content_type_id"

            #         AND ug."user_id" = %s, [self.id])

            qn = connection.ops.quote_name

            sql = """

                SELECT ct.%s, p.%s

                FROM %s p, %s gp, %s ug, %s ct

                WHERE p.%s = gp.%s

                    AND gp.%s = ug.%s

                    AND ct.%s = p.%s

                    AND ug.%s = %%s""" % (

                qn('app_label'), qn('codename'),

                qn('auth_permission'), qn('auth_group_permissions'),

                qn('auth_user_groups'), qn('django_content_type'),

                qn('id'), qn('permission_id'),

                qn('group_id'), qn('group_id'),

                qn('id'), qn('content_type_id'),

                qn('user_id'),)

            cursor.execute(sql, [user_obj.id])

            user_obj._group_perm_cache = set(["%s.%s" % (row[0], row[1]) for row in cursor.fetchall()])

        return user_obj._group_perm_cache

    def get_all_permissions(self, user_obj):

        if not hasattr(user_obj, '_perm_cache'):

            user_obj._perm_cache = set([u"%s.%s" % (p.content_type.app_label, p.codename) for p in user_obj.user_permissions.select_related()])

            user_obj._perm_cache.update(self.get_group_permissions(user_obj))

        return user_obj._perm_cache

    def has_perm(self, user_obj, perm):

        return perm in self.get_all_permissions(user_obj)

    def has_module_perms(self, user_obj, app_label):

        return bool(len([p for p in self.get_all_permissions(user_obj) if p[:p.index('.')] == app_label]))

    def get_user(self, user_id):

        try:

            return User.objects.get(pk=user_id)

        except User.DoesNotExist:

            return None