from django.forms.models import ModelFormMetaclass, ModelForm

from django.template import RequestContext, loader

from django.http import Http404, HttpResponse, HttpResponseRedirect

from django.core.xheaders import populate_xheaders

from django.core.exceptions import ObjectDoesNotExist, ImproperlyConfigured

from django.utils.translation import ugettext

from django.contrib.auth.views import redirect_to_login

from django.views.generic import GenericViewError

from django.contrib import messages

def apply_extra_context(extra_context, context):

    """

    Adds items from extra_context dict to context.  If a value in extra_context

    is callable, then it is called and the result is added to context.

    """

    for key, value in extra_context.iteritems():

        if callable(value):

            context[key] = value()

        else:

            context[key] = value

def get_model_and_form_class(model, form_class):

    """

    Returns a model and form class based on the model and form_class

    parameters that were passed to the generic view.

    If ``form_class`` is given then its associated model will be returned along

    with ``form_class`` itself.  Otherwise, if ``model`` is given, ``model``

    itself will be returned along with a ``ModelForm`` class created from

    ``model``.

    """

    if form_class:

        return form_class._meta.model, form_class

    if model:

        # The inner Meta class fails if model = model is used for some reason.

        tmp_model = model

        # TODO: we should be able to construct a ModelForm without creating

        # and passing in a temporary inner class.

        class Meta:

            model = tmp_model

        class_name = model.__name__ + 'Form'

        form_class = ModelFormMetaclass(class_name, (ModelForm,), {'Meta': Meta})

        return model, form_class

    raise GenericViewError("Generic view must be called with either a model or"

                           " form_class argument.")

def redirect(post_save_redirect, obj):

    """

    Returns a HttpResponseRedirect to ``post_save_redirect``.

    ``post_save_redirect`` should be a string, and can contain named string-

    substitution place holders of ``obj`` field names.

    If ``post_save_redirect`` is None, then redirect to ``obj``'s URL returned

    by ``get_absolute_url()``.  If ``obj`` has no ``get_absolute_url`` method,

    then raise ImproperlyConfigured.

    This function is meant to handle the post_save_redirect parameter to the

    ``create_object`` and ``update_object`` views.

    """

    if post_save_redirect:

        return HttpResponseRedirect(post_save_redirect % obj.__dict__)

    elif hasattr(obj, 'get_absolute_url'):

        return HttpResponseRedirect(obj.get_absolute_url())

    else:

        raise ImproperlyConfigured(

            "No URL to redirect to.  Either pass a post_save_redirect"

            " parameter to the generic view or define a get_absolute_url"

            " method on the Model.")

def lookup_object(model, object_id, slug, slug_field):

    """

    Return the ``model`` object with the passed ``object_id``.  If

    ``object_id`` is None, then return the object whose ``slug_field``

    equals the passed ``slug``.  If ``slug`` and ``slug_field`` are not passed,

    then raise Http404 exception.

    """

    lookup_kwargs = {}

    if object_id:

        lookup_kwargs['%s__exact' % model._meta.pk.name] = object_id

    elif slug and slug_field:

        lookup_kwargs['%s__exact' % slug_field] = slug

    else:

        raise GenericViewError(

            "Generic view must be called with either an object_id or a"

            " slug/slug_field.")

    try:

        return model.objects.get(**lookup_kwargs)

    except ObjectDoesNotExist:

        raise Http404("No %s found for %s"

                      % (model._meta.verbose_name, lookup_kwargs))

def create_object(request, model=None, template_name=None,

        template_loader=loader, extra_context=None, post_save_redirect=None,

        login_required=False, context_processors=None, form_class=None):

    """

    Generic object-creation function.

    Templates: ``<app_label>/<model_name>_form.html``

    Context:

        form

            the form for the object

    """

    if extra_context is None: extra_context = {}

    if login_required and not request.user.is_authenticated():

        return redirect_to_login(request.path)

    model, form_class = get_model_and_form_class(model, form_class)

    if request.method == 'POST':

        form = form_class(request.POST, request.FILES)

        if form.is_valid():

            new_object = form.save()

            msg = ugettext("The %(verbose_name)s was created successfully.") %\

                                    {"verbose_name": model._meta.verbose_name}

            messages.success(request, msg, fail_silently=True)

            return redirect(post_save_redirect, new_object)

    else:

        form = form_class()

    # Create the template, context, response

    if not template_name:

        template_name = "%s/%s_form.html" % (model._meta.app_label, model._meta.object_name.lower())

    t = template_loader.get_template(template_name)

    c = RequestContext(request, {

        'form': form,

    }, context_processors)

    apply_extra_context(extra_context, c)

    return HttpResponse(t.render(c))

def update_object(request, model=None, object_id=None, slug=None,

        slug_field='slug', template_name=None, template_loader=loader,

        extra_context=None, post_save_redirect=None, login_required=False,

        context_processors=None, template_object_name='object',

        form_class=None):

    """

    Generic object-update function.

    Templates: ``<app_label>/<model_name>_form.html``

    Context:

        form

            the form for the object

        object

            the original object being edited

    """

    if extra_context is None: extra_context = {}

    if login_required and not request.user.is_authenticated():

        return redirect_to_login(request.path)

    model, form_class = get_model_and_form_class(model, form_class)

    obj = lookup_object(model, object_id, slug, slug_field)

    if request.method == 'POST':

        form = form_class(request.POST, request.FILES, instance=obj)

        if form.is_valid():

            obj = form.save()

            msg = ugettext("The %(verbose_name)s was updated successfully.") %\

                                    {"verbose_name": model._meta.verbose_name}

            messages.success(request, msg, fail_silently=True)

            return redirect(post_save_redirect, obj)

    else:

        form = form_class(instance=obj)

    if not template_name:

        template_name = "%s/%s_form.html" % (model._meta.app_label, model._meta.object_name.lower())

    t = template_loader.get_template(template_name)

    c = RequestContext(request, {

        'form': form,

        template_object_name: obj,

    }, context_processors)

    apply_extra_context(extra_context, c)

    response = HttpResponse(t.render(c))

    populate_xheaders(request, response, model, getattr(obj, obj._meta.pk.attname))

    return response

def delete_object(request, model, post_delete_redirect, object_id=None,

        slug=None, slug_field='slug', template_name=None,

        template_loader=loader, extra_context=None, login_required=False,

        context_processors=None, template_object_name='object'):

    """

    Generic object-delete function.

    The given template will be used to confirm deletetion if this view is

    fetched using GET; for safty, deletion will only be performed if this

    view is POSTed.

    Templates: ``<app_label>/<model_name>_confirm_delete.html``

    Context:

        object

            the original object being deleted

    """

    if extra_context is None: extra_context = {}

    if login_required and not request.user.is_authenticated():

        return redirect_to_login(request.path)

    obj = lookup_object(model, object_id, slug, slug_field)

    if request.method == 'POST':

        obj.delete()

        msg = ugettext("The %(verbose_name)s was deleted.") %\

                                    {"verbose_name": model._meta.verbose_name}

        messages.success(request, msg, fail_silently=True)

        return HttpResponseRedirect(post_delete_redirect)

    else:

        if not template_name:

            template_name = "%s/%s_confirm_delete.html" % (model._meta.app_label, model._meta.object_name.lower())

        t = template_loader.get_template(template_name)

        c = RequestContext(request, {

            template_object_name: obj,

        }, context_processors)

        apply_extra_context(extra_context, c)

        response = HttpResponse(t.render(c))

        populate_xheaders(request, response, model, getattr(obj, obj._meta.pk.attname))

        return response