from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic
from django.contrib.auth.models import User, Group
from django.utils.translation import ugettext_lazy as _

class AlreadyHasPermission(Exception):
    """Defining exception for an already existing permission"""

    def __init__(self, user_or_group, name, obj=None):
        self.user_or_group = user_or_group
        self.perm_name = name
        self.obj = obj

    def __str__(self):
        if self.obj:
            return "%s has already permission:\"%s\" on %s" % (self.user_or_group,
                                                               self.perm_name,
                                                               self.obj)
        return "%s has already permission:\"%s\"" % (self.user_or_group,
                                                     self.perm_name)

class DoesNotHavePermission(Exception):
    """Defining exception for an already existing permission"""

    def __init__(self, user_or_group, name, obj=None):
        self.user_or_group = user_or_group
        self.perm_name = name
        self.obj = obj

    def __str__(self):
        if self.obj:
            return "%s has not permission:\"%s\" on %s" % (self.user_or_group,
                                                           self.perm_name,
                                                           self.obj)
        return "%s has not permission:\"%s\" " % (self.user_or_group,
                                                  self.perm_name)

class PermissionManager(models.Manager):

    def permissions_for_object(self, obj):
        object_type = ContentType.objects.get_for_model(obj)
        return self.filter(content_type__pk=object_type.id,
                           object_id=obj.id)


class Permission(models.Model):
    """
    A granular permission model, per-object permission in other words.
    This kind of permission is associated with a user/group and an object
    of any content type.
    """
    codename = models.CharField(_('codename'), max_length=100)
    content_type = models.ForeignKey(ContentType, related_name="row_permissions")
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')

    user = models.ForeignKey(User, null=True, blank=True, related_name='granted_permissions')
    group = models.ForeignKey(Group, null=True, blank=True)
    creator = models.ForeignKey(User, null=True, blank=True, related_name='created_permissions')

    objects = PermissionManager()

    def __unicode__(self):
        return "%s.%s" % (self.content_type.app_label, self.codename)

    class Meta:
        verbose_name = _('permission')
        verbose_name_plural = _('permissions')
        permissions = (
            ('change_foreign_permissions', 'Can change foreign permissions'),
            ('delete_foreign_permissions', 'Can delete foreign permissions'),
        )

from authority import autodiscover
autodiscover()