# Copyright 2012 Nebula, Inc.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

from django.conf import settings
from django import shortcuts
from django import template
from django.utils import encoding
from django.views import generic
from osprofiler import profiler

import horizon
from horizon import exceptions


class PageTitleMixin(object):
    """A mixin that renders out a page title into a view.

    Many views in horizon have a page title that would ordinarily be
    defined and passed through in get_context_data function, this often
    leads to a lot of duplicated work in each view.

    This mixin standardises the process of defining a page title, letting
    views simply define a variable that is rendered into the context for
    them.

    There are cases when page title in a view may also display some context
    data, for that purpose the page_title variable supports the django
    templating language and will be rendered using the context defined by the
    views get_context_data.
    """

    page_title = ""

    def render_context_with_title(self, context):
        """Render a page title and insert it into the context.

        This function takes in a context dict and uses it to render the
        page_title variable. It then appends this title to the context using
        the 'page_title' key. If there is already a page_title key defined in
        context received then this function will do nothing.
        """

        if "page_title" not in context:
            con = template.Context(context)
            # NOTE(sambetts): Use force_text to ensure lazy translations
            # are handled correctly.
            temp = template.Template(encoding.force_text(self.page_title))
            context["page_title"] = temp.render(con)
        return context

    def render_to_response(self, context):
        """render_to_response() with a page title.

        This is an override of the default render_to_response function that
        exists in the django generic views. This is here to inject the
        page title into the context before the main template is rendered.
        """

        context = self.render_context_with_title(context)
        return super(PageTitleMixin, self).render_to_response(context)


def trace(name):
    def decorator(func):
        if getattr(settings, 'OPENSTACK_PROFILER', {}).get('enabled', False):
            return profiler.trace(name, info=None, hide_args=False,
                                  allow_multiple_trace=True)(func)
        else:
            return func
    return decorator


class HorizonTemplateView(PageTitleMixin, generic.TemplateView):
    @trace('horizon.render_to_response')
    def render_to_response(self, context):
        return super(HorizonTemplateView, self).render_to_response(context)


class HorizonFormView(PageTitleMixin, generic.FormView):
    pass


def user_home(request):
    """Reversible named view to direct a user to the appropriate homepage."""
    return shortcuts.redirect(horizon.get_user_home(request.user))


class APIView(HorizonTemplateView):
    """A quick class-based view for putting API data into a template.

    Subclasses must define one method, ``get_data``, and a template name
    via the ``template_name`` attribute on the class.

    Errors within the ``get_data`` function are automatically caught by
    the :func:`horizon.exceptions.handle` error handler if not otherwise
    caught.
    """

    def get_data(self, request, context, *args, **kwargs):
        """Load necessary API data into the context.

        This method should handle any necessary API calls, update the
        context object, and return the context object at the end.
        """
        return context

    def get(self, request, *args, **kwargs):
        context = self.get_context_data(**kwargs)
        try:
            context = self.get_data(request, context, *args, **kwargs)
        except Exception:
            exceptions.handle(request)
        return self.render_to_response(context)
