Source code for kotti.views.slots

"""This module allows add-ons to assign views to slots defined in
the overall page.  In other systems, these are called portlets or
viewlets.

A simple example that'll include the output of the 'hello_world' view
in in the left column of every page::

  from kotti.views.slots import assign_slot
  assign_slot('hello_world', 'left')

It is also possible to pass parameters to the view::

  assign_slot('last_tweets', 'right', params=dict(user='foo'))

In the view you can get the slot in that the view is rendered from
the request::

    @view_config(name='last_tweets')
    def view(request, context):
        slot = request.kotti_slot
        # ...

If no view can be found for the given request and slot, the slot
remains empty.  If you want to force your slot not to be rendered,
raise :class:`pyramid.exceptions.PredicateMismatch` inside your view::

    from pyramid.exceptions import PredicateMismatch

    @view_config(name='last_tweets')
    def view(request, context):
        if some_condition:
            raise PredicateMismatch()
        return {...}

Usually you'll want to call :func:`kotti.views.slots.assign_slot`
inside an ``includeme`` function and not on a module level, to allow
users of your package to include your slot assignments through the
``pyramid.includes`` configuration setting.
"""

import urllib

from pyramid.exceptions import PredicateMismatch
from pyramid.httpexceptions import HTTPException
from pyramid.httpexceptions import HTTPForbidden
from pyramid.request import Request
from pyramid.view import render_view

from kotti.events import ObjectEvent
from kotti.events import objectevent_listeners

REQUEST_ATTRS_TO_COPY = ('context', 'registry', 'user', 'cookies', 'session')


def _encode(params):
    if not params:
        return u''
    return urllib.urlencode(
        dict((k, v.encode('utf-8')) for k, v in params.items()))


def _render_view_on_slot_event(view_name, event, params):
    context = event.object
    request = event.request

    view_request = Request.blank(
        "{0}/{1}".format(request.path.rstrip('/'), view_name),
        base_url=request.application_url,
        POST=_encode(params))

    post_items = request.POST.items()
    if post_items:
        view_request.POST.extend(post_items)

    # This is quite brittle:
    for name in REQUEST_ATTRS_TO_COPY:
        setattr(view_request, name, getattr(request, name))
    setattr(view_request, 'kotti_slot', event.name)

    try:
        result = render_view(context, view_request, view_name)
    except (PredicateMismatch, HTTPForbidden):
        return None
    if isinstance(context, HTTPException):
        return None
    return result.decode('utf-8')


def assign_slot(view_name, slot, params=None):
    """Assign view to slot.

    :param view_name: Name of the view to assign.
    :type view_name: str

    :param slot: Name of the slot to assign to.  Possible values are: left,
                 right, abovecontent, belowcontent, inhead, beforebodyend,
                 edit_inhead
    :type slot: str

    :param params: Optionally allows to pass POST parameters to the view.
    :type params: dict
    """

    event = [e for e in slot_events if e.name == slot]
    if not event:
        raise KeyError("Unknown slot '{0}'".format(slot))
    objectevent_listeners[(event[0], None)].append(
        lambda ev: _render_view_on_slot_event(view_name, ev, params))


class RenderLeftSlot(ObjectEvent):
    name = u'left'


class RenderRightSlot(ObjectEvent):
    name = u'right'


class RenderAboveContent(ObjectEvent):
    name = u'abovecontent'


class RenderBelowContent(ObjectEvent):
    name = u'belowcontent'


class RenderInHead(ObjectEvent):
    name = u'inhead'


class RenderBeforeBodyEnd(ObjectEvent):
    name = u'beforebodyend'


class RenderEditInHead(ObjectEvent):
    name = u'edit_inhead'

slot_events = [
    RenderLeftSlot, RenderRightSlot, RenderAboveContent, RenderBelowContent,
    RenderInHead, RenderBeforeBodyEnd, RenderEditInHead, ]