from django.db import models

from django.utils.translation import ugettext_lazy as _

from django.utils.encoding import smart_unicode

class ContentTypeManager(models.Manager):

    # Cache to avoid re-looking up ContentType objects all over the place.

    # This cache is shared by all the get_for_* methods.

    _cache = {}

    def get_for_model(self, model):

        """

        Returns the ContentType object for a given model, creating the

        ContentType if necessary. Lookups are cached so that subsequent lookups

        for the same model don't hit the database.

        """

        opts = model._meta

        key = (opts.app_label, opts.object_name.lower())

        try:

            ct = self.__class__._cache[key]

        except KeyError:

            # Load or create the ContentType entry. The smart_unicode() is 

            # needed around opts.verbose_name_raw because name_raw might be a

            # django.utils.functional.__proxy__ object.

            ct, created = self.get_or_create(

                app_label = opts.app_label,

                model = opts.object_name.lower(), 

                defaults = {'name': smart_unicode(opts.verbose_name_raw)},

            )

            self._add_to_cache(ct)

        return ct

    def get_for_id(self, id):

        """

        Lookup a ContentType by ID. Uses the same shared cache as get_for_model

        (though ContentTypes are obviously not created on-the-fly by get_by_id).

        """

        try:

            ct = self.__class__._cache[id]

        except KeyError:

            # This could raise a DoesNotExist; that's correct behavior and will

            # make sure that only correct ctypes get stored in the cache dict.

            ct = self.get(pk=id)

            self._add_to_cache(ct)

        return ct

    def clear_cache(self):

        """

        Clear out the content-type cache. This needs to happen during database

        flushes to prevent caching of "stale" content type IDs (see

        django.contrib.contenttypes.management.update_contenttypes for where

        this gets called).

        """

        self.__class__._cache.clear()

    def _add_to_cache(self, ct):

        """Insert a ContentType into the cache."""

        model = ct.model_class()

        key = (model._meta.app_label, model._meta.object_name.lower())

        self.__class__._cache[key] = ct

        self.__class__._cache[ct.id] = ct

class ContentType(models.Model):

    name = models.CharField(max_length=100)

    app_label = models.CharField(max_length=100)

    model = models.CharField(_('python model class name'), max_length=100)

    objects = ContentTypeManager()

    class Meta:

        verbose_name = _('content type')

        verbose_name_plural = _('content types')

        db_table = 'django_content_type'

        ordering = ('name',)

        unique_together = (('app_label', 'model'),)

    def __unicode__(self):

        return self.name

    def model_class(self):

        "Returns the Python model class for this type of content."

        from django.db import models

        return models.get_model(self.app_label, self.model)

    def get_object_for_this_type(self, **kwargs):

        """

        Returns an object of this type for the keyword arguments given.

        Basically, this is a proxy around this object_type's get_object() model

        method. The ObjectNotExist exception, if thrown, will not be caught,

        so code that calls this method should catch it.

        """

        return self.model_class()._default_manager.get(**kwargs)