'''
Created on Apr 10, 2012

@author: leifj
'''

from django.db import models
from django.db.models.fields import DateTimeField
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic
from django_extensions.db.fields import UUIDField
from django.dispatch.dispatcher import receiver
from django.db.models.signals import post_save, pre_delete
from django.core.exceptions import ObjectDoesNotExist
from django.db.models.base import ModelBase

class NotAModel(Exception):
    pass

class RecursiveRegistration(Exception):
    pass

class UninitializedObject(Exception):
    pass

class Resource(models.Model):
    uuid = UUIDField(unique=True)
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    lastupdated = DateTimeField(auto_now=True)
    timecreated = DateTimeField(auto_now_add=True)
    
    def __unicode__(self):
        return self.uuid
        
def object_for_uuid(uuid):
    try:
        r = Resource.objects.get(uuid=uuid)
        return r.content_object
    except ObjectDoesNotExist:
        return None

def uuid_for_object(o):
    if not o.id:
        raise UninitializedObject("Can't obtain uuid for non-persisted objects")
    
    typ = ContentType.objects.get_for_model(o)
    r,cr = Resource.objects.get_or_create(object_id=o.id,content_type=typ)
    return r.uuid

def add_resource(o):
    typ = ContentType.objects.get_for_model(o)
    r,cr = Resource.objects.get_or_create(object_id=o.id,content_type=typ)
    return r.uuid

def delete_resource(o):
    typ = ContentType.objects.get_for_model(o)
    try:
        r = Resource.objects.get(object_id=o.id,content_type=typ)
        r.delete()
    except ObjectDoesNotExist:
        pass

class ResourceClassRegistry():
    def __init__(self):
        self._registry = []

    def register(self,model,addField=True):
        if not isinstance(model,ModelBase):
            raise NotAModel('%s does not appear to be a model!' % model)
        if not model in self._registry:
            if addField:
                setattr(model,'uuid',property(lambda x: uuid_for_object(x)))
            self._registry.append(model)
            
resources = ResourceClassRegistry()

def register(model):
    resources.register(model)

@receiver(post_save)
def auto_create_resource(sender,**kwargs):
    if sender in resources._registry and kwargs['created']:
        add_resource(kwargs['instance'])

@receiver(pre_delete)
def auto_delete_resource(sender,**kwargs):
    if sender in resources._registry:
        delete_resource(kwargs['instance'])