Unifies Horizon conf.

Centralizes all of Horizon's configuration options so that
they're all uniformly accesible from a single place and always
guaranteed to exist.

Implements blueprint unify-config.

Change-Id: I3279b7ccd58302fcff4f0d273f89f282a285c442

horizon/base.py

@@ -39,26 +39,13 @@ from django.utils.module_loading import module_has_submodule
 from django.utils.translation import ugettext as _
 
 from horizon import loaders
+from horizon import conf
 from horizon.decorators import require_auth, require_perms, _current_component
 
 
 LOG = logging.getLogger(__name__)
 
 
-# Default configuration dictionary. Do not mutate directly. Use copy.copy().
-HORIZON_CONFIG = {
-    # Allow for ordering dashboards; list or tuple if provided.
-    'dashboards': None,
-    # Name of a default dashboard; defaults to first alphabetically if None
-    'default_dashboard': None,
-    # Default redirect url for users' home
-    'user_home': settings.LOGIN_REDIRECT_URL,
-    'exceptions': {'unauthorized': [],
-                   'not_found': [],
-                   'recoverable': []}
-}
-
-
 def _decorate_urlconf(urlpatterns, decorator, *args, **kwargs):
     for pattern in urlpatterns:
         if getattr(pattern, 'callback', None):
@@ -591,9 +578,7 @@ class Site(Registry, HorizonComponent):
 
     @property
     def _conf(self):
-        conf = copy.copy(HORIZON_CONFIG)
-        conf.update(getattr(settings, 'HORIZON_CONFIG', {}))
-        return conf
+        return conf.HORIZON_CONFIG
 
     @property
     def dashboards(self):
@@ -633,11 +618,11 @@ class Site(Registry, HorizonComponent):
         """ Returns an ordered tuple of :class:`~horizon.Dashboard` modules.
 
         Orders dashboards according to the ``"dashboards"`` key in
-        ``settings.HORIZON_CONFIG`` or else returns all registered dashboards
+        ``HORIZON_CONFIG`` or else returns all registered dashboards
         in alphabetical order.
 
         Any remaining :class:`~horizon.Dashboard` classes registered with
-        Horizon but not listed in ``settings.HORIZON_CONFIG['dashboards']``
+        Horizon but not listed in ``HORIZON_CONFIG['dashboards']``
         will be appended to the end of the list alphabetically.
         """
         if self.dashboards:
@@ -660,7 +645,7 @@ class Site(Registry, HorizonComponent):
     def get_default_dashboard(self):
         """ Returns the default :class:`~horizon.Dashboard` instance.
 
-        If ``"default_dashboard"`` is specified in ``settings.HORIZON_CONFIG``
+        If ``"default_dashboard"`` is specified in ``HORIZON_CONFIG``
         then that dashboard will be returned. If not, the first dashboard
         returned by :func:`~horizon.get_dashboards` will be returned.
         """
@@ -680,7 +665,7 @@ class Site(Registry, HorizonComponent):
 
         An alternative function can be supplied to customize this behavior
         by specifying a either a URL or a function which returns a URL via
-        the ``"user_home"`` key in ``settings.HORIZON_CONFIG``. Each of these
+        the ``"user_home"`` key in ``HORIZON_CONFIG``. Each of these
         would be valid::
 
             {"user_home": "/home",}  # A URL
@@ -741,9 +726,8 @@ class Site(Registry, HorizonComponent):
             dash._autodiscover()
 
         # Allow for override modules
-        config = getattr(settings, "HORIZON_CONFIG", {})
-        if config.get("customization_module", None):
-            customization_module = config["customization_module"]
+        if self._conf.get("customization_module", None):
+            customization_module = self._conf["customization_module"]
             bits = customization_module.split('.')
             mod_name = bits.pop()
             package = '.'.join(bits)