"""

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.http import HttpResponseRedirect, HttpResponsePermanentRedirect

from django.db.models.manager import Manager

from django.db.models.query import QuerySet

from django.core import urlresolvers

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 redirect(to, *args, **kwargs):

    """

    Returns an HttpResponseRedirect to the apropriate URL for the arguments

    passed.

    The arguments could be:

        * A model: the model's `get_absolute_url()` function will be called.

        * A view name, possibly with arguments: `urlresolvers.reverse()` will

          be used to reverse-resolve the name.

        * A URL, which will be used as-is for the redirect location.

    By default issues a temporary redirect; pass permanent=True to issue a

    permanent redirect

    """

    if kwargs.pop('permanent', False):

        redirect_class = HttpResponsePermanentRedirect

    else:

        redirect_class = HttpResponseRedirect

    # If it's a model, use get_absolute_url()

    if hasattr(to, 'get_absolute_url'):

        return redirect_class(to.get_absolute_url())

    # Next try a reverse URL resolution.

    try:

        return redirect_class(urlresolvers.reverse(to, args=args, kwargs=kwargs))

    except urlresolvers.NoReverseMatch:

        # If this is a callable, re-raise.

        if callable(to):

            raise

        # If this doesn't "feel" like a URL, re-raise.

        if '/' not in to and '.' not in to:

            raise

    # Finally, fall back and assume it's a URL

    return redirect_class(to)

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