"""
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