"""

This module collects helper functions and classes that "span" multiple levels

of MVC. In other words, these functions/classes introduce controlled coupling

for convenience's sake.

"""

from django.template import loader

from django.http import HttpResponse, Http404

from django.db.models.manager import Manager

from django.db.models.query import QuerySet

def render_to_response(*args, **kwargs):

    """

    Returns a HttpResponse whose content is filled with the result of calling

    django.template.loader.render_to_string() with the passed arguments.

    """

    httpresponse_kwargs = {'mimetype': kwargs.pop('mimetype', None)}

    return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs)

def _get_queryset(klass):

    """

    Returns a QuerySet from a Model, Manager, or QuerySet. Created to make

    get_object_or_404 and get_list_or_404 more DRY.

    """

    if isinstance(klass, QuerySet):

        return klass

    elif isinstance(klass, Manager):

        manager = klass

    else:

        manager = klass._default_manager

    return manager.all()

def get_object_or_404(klass, *args, **kwargs):

    """

    Uses get() to return an object, or raises a Http404 exception if the object

    does not exist.

    klass may be a Model, Manager, or QuerySet object. All other passed

    arguments and keyword arguments are used in the get() query.

    Note: Like with get(), an MultipleObjectsReturned will be raised if more than one

    object is found.

    """

    queryset = _get_queryset(klass)

    try:

        return queryset.get(*args, **kwargs)

    except queryset.model.DoesNotExist:

        raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)

def get_list_or_404(klass, *args, **kwargs):

    """

    Uses filter() to return a list of objects, or raise a Http404 exception if

    the list is empty.

    klass may be a Model, Manager, or QuerySet object. All other passed

    arguments and keyword arguments are used in the filter() query.

    """

    queryset = _get_queryset(klass)

    obj_list = list(queryset.filter(*args, **kwargs))

    if not obj_list:

        raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)

    return obj_list