Improve User Experience by adding an info REST entrypoint

This patch allow the user to query the API in order to:

* Get current collector configuration (period, services, etc)
* Get collected metadata list for a given service (using currently
  configured collector)

For this, the following work have been made:

* Each transformer can now export available metadata for a given
  resource (using a FakeData object and the strip_resource_data method)
* Each collector can now export information for a given resource
  about metadata (using associated transformer) and unit
* A new REST controller 'info' provides API entrypoints to those
  information:
  * configuration with GET /v1/info/config
  * all active services information with GET /v1/info/services
  * given active service information with GET /v1/info/services/SERVICE

Change-Id: I02b1bc5709371785748661b63c5e6f0705ce891b
Implements: blueprint user-experience-improvement (PARTIAL)

cloudkitty/api/v1/controllers/info.py

@@ -0,0 +1,83 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 Objectif Libre
+#
+#    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.
+#
+# @author: Maxime Cottret
+#
+from oslo_config import cfg
+import pecan
+from pecan import rest
+import six
+from wsme import types as wtypes
+import wsmeext.pecan as wsme_pecan
+
+from cloudkitty.api.v1.datamodels import info as info_models
+from cloudkitty.api.v1 import types as ck_types
+from cloudkitty import collector
+from cloudkitty.common import policy
+
+CONF = cfg.CONF
+METADATA = collector.get_collector_metadata()
+
+
+class ServiceInfoController(rest.RestController):
+    """REST Controller mananging collected services information."""
+
+    @wsme_pecan.wsexpose(info_models.CloudkittyServiceInfoCollection)
+    def get_all(self):
+        """Get the service list.
+
+        :return: List of every services.
+        """
+        policy.enforce(pecan.request.context, 'info:list_services_info', {})
+        services_info_list = []
+        for service, metadata in METADATA.items():
+            info = metadata.copy()
+            info['service_id'] = service
+            services_info_list.append(
+                info_models.CloudkittyServiceInfo(**info))
+        return info_models.CloudkittyServiceInfoCollection(
+            services=services_info_list)
+
+    @wsme_pecan.wsexpose(info_models.CloudkittyServiceInfo, wtypes.text)
+    def get_one(self, service_name):
+        """Return a service.
+
+        :param service_name: name of the service.
+        """
+        policy.enforce(pecan.request.context, 'info:get_service_info', {})
+        try:
+            info = METADATA[service_name].copy()
+            info['service_id'] = service_name
+            return info_models.CloudkittyServiceInfo(**info)
+        except KeyError:
+            pecan.abort(404, six.text_type(service_name))
+
+
+class InfoController(rest.RestController):
+    """REST Controller managing Cloudkitty general information."""
+
+    services = ServiceInfoController()
+
+    _custom_actions = {'config': ['GET']}
+
+    @wsme_pecan.wsexpose({
+        str: ck_types.MultiType(wtypes.text, int, float, dict, list)
+    })
+    def config(self):
+        """Return current configuration."""
+        policy.enforce(pecan.request.context, 'info:get_config', {})
+        info = {}
+        info["collect"] = {key: value for key, value in CONF.collect.items()}
+        return info