from django import http

from django.contrib.contenttypes.models import ContentType

from django.contrib.sites.models import Site

from django.core.exceptions import ObjectDoesNotExist

def shortcut(request, content_type_id, object_id):

    "Redirect to an object's page based on a content-type ID and an object ID."

    # Look up the object, making sure it's got a get_absolute_url() function.

    try:

        content_type = ContentType.objects.get(pk=content_type_id)

        obj = content_type.get_object_for_this_type(pk=object_id)

    except ObjectDoesNotExist:

        raise http.Http404("Content type %s object %s doesn't exist" % (content_type_id, object_id))

    try:

        absurl = obj.get_absolute_url()

    except AttributeError:

        raise http.Http404("%s objects don't have get_absolute_url() methods" % content_type.name)

    # Try to figure out the object's domain, so we can do a cross-site redirect

    # if necessary.

    # If the object actually defines a domain, we're done.

    if absurl.startswith('http://') or absurl.startswith('https://'):

        return http.HttpResponseRedirect(absurl)

    # Otherwise, we need to introspect the object's relationships for a

    # relation to the Site object

    object_domain = None

    opts = obj._meta

    # First, look for an many-to-many relationship to Site.

    for field in opts.many_to_many:

        if field.rel.to is Site:

            try:

                # Caveat: In the case of multiple related Sites, this just

                # selects the *first* one, which is arbitrary.

                object_domain = getattr(obj, field.name).all()[0].domain

            except IndexError:

                pass

            if object_domain is not None:

                break

    # Next, look for a many-to-one relationship to Site.

    if object_domain is None:

        for field in obj._meta.fields:

            if field.rel and field.rel.to is Site:

                try:

                    object_domain = getattr(obj, field.name).domain

                except Site.DoesNotExist:

                    pass

                if object_domain is not None:

                    break

    # Fall back to the current site (if possible).

    if object_domain is None:

        try:

            object_domain = Site.objects.get_current().domain

        except Site.DoesNotExist:

            pass

    # If all that malarkey found an object domain, use it. Otherwise, fall back

    # to whatever get_absolute_url() returned.

    if object_domain is not None:

        protocol = request.is_secure() and 'https' or 'http'

        return http.HttpResponseRedirect('%s://%s%s' % (protocol, object_domain, absurl))

    else:

        return http.HttpResponseRedirect(absurl)