Docserver: Consolidate features caching and access.

chrome/common/extensions/docs/server2/features.py

+# Copyright 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+from copy import deepcopy
+
+import features_utility
+from third_party.json_schema_compiler.json_parse import Parse
+
+class Features(object):
+  '''Provides cached access to data for a specific features set. This can be
+  subclassed to provide special transformation or handling during the feature
+  parsing process by overriding Parse, FilterByPlatform, and/or
+  CreateCache.
+  '''
+  def __init__(self, compiled_fs_factory, features_path):
+    self._features_path = features_path
+    self._cache = compiled_fs_factory.Create(self._CreateFeatures, type(self))
+
+  def _CreateFeatures(self, _, content):
+    features = self.Parse(Parse(content))
+    cache = self.CreateCache(features)
+    cache['all'] = features
+    return cache
+
+  def Parse(self, features_json):

[not at google - send to devlin, 2013/09/23 18:31:30]

I don't quite understand the inheritance structure here. why can't Feature
basically implement everything and each of the *Feature classes provide
functionality on top of that? The overriding behaviour of
Parse/FilterByPLatform/CreateCache is confusing. Particularly since you've
implemented it here and then reimplemented it in the other places.

and rather than the magical get('all'), get('apps'), get('extensions'), have
real methods.

+    return features_utility.Parse(features_json)
+
+  def FilterByPlatform(self, features, platform):
+    filtered_features = {}
+    for name, feature in features.iteritems():
+      platforms = features_utility.GetPlatformSetForExtensionTypes(
+          feature.get('extension_types', ()))
+      if not platform or platform in platforms:
+        filtered_features[name] = deepcopy(feature)
+    return filtered_features
+
+  def CreateCache(self, features):
+    return {
+      'apps': self.FilterByPlatform(features, 'apps'),
+      'extensions': self.FilterByPlatform(features, 'extensions'),
+    }
+
+  def get(self, key):
+    return self._cache.GetFromFile(self._features_path)[key]
+