Docserver: Pull knowledge of host file systems into a single

chrome/common/extensions/docs/server2/app_yaml_helper.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.
 
 import logging
 
 _APP_YAML_CONTAINER = '''
 application: chrome-apps-doc
 version: %s
 runtime: python27
 api_version: 1
 threadsafe: false
 '''
 
 class AppYamlHelper(object):
   '''Parses the app.yaml file, and is able to step back in the host file
   system's revision history to find when it changed to some given version.
   '''
   def __init__(self,
                app_yaml_path,
-               file_system_at_head,
                object_store_creator,
-               host_file_system_creator):
+               host_file_system_provider):
     self._app_yaml_path = app_yaml_path
-    self._file_system_at_head = file_system_at_head
     self._store = object_store_creator.Create(
         AppYamlHelper,
-        category=file_system_at_head.GetIdentity(),
+        category=host_file_system_provider.GetTrunk().GetIdentity(),
         start_empty=False)
-    self._host_file_system_creator = host_file_system_creator
+    self._host_file_system_provider = host_file_system_provider
 
   @staticmethod
   def ExtractVersion(app_yaml, key='version'):
     '''Extracts the 'version' key from the contents of an app.yaml file.
     Allow overriding the key to parse e.g. the cron file ('target').
     '''
     # We could properly parse this using a yaml library but Python doesn't have
     # one built in so whatevs.
     key_colon = '%s:' % key
     versions = [line.strip()[len(key_colon):].strip()
@@ skipping 26 matching lines @@
   def GenerateAppYaml(version):
     '''Probably only useful for tests.
     '''
     return _APP_YAML_CONTAINER % version
 
   def IsUpToDate(self, app_version):
     '''Returns True if the |app_version| is up to date with respect to the one
     checked into the host file system.
     '''
     checked_in_app_version = AppYamlHelper.ExtractVersion(
-        self._file_system_at_head.ReadSingle(self._app_yaml_path))
+        self._host_file_system_provider.GetTrunk().ReadSingle(
+            self._app_yaml_path))
     if app_version == checked_in_app_version:
       return True
     if AppYamlHelper.IsGreater(app_version, checked_in_app_version):
       logging.warning(
           'Server is too new! Checked in %s < currently running %s' % (
               checked_in_app_version, app_version))
       return True
     return False
 
   def GetFirstRevisionGreaterThan(self, app_version):
@@ skipping 14 matching lines @@
   def _GetFirstRevisionGreaterThanImpl(self, app_version):
     def get_app_yaml_revision(file_system):
       return int(file_system.Stat(self._app_yaml_path).version)
 
     def has_greater_app_version(file_system):
       app_version_in_file_system = AppYamlHelper.ExtractVersion(
           file_system.ReadSingle(self._app_yaml_path))
       return AppYamlHelper.IsGreater(app_version_in_file_system, app_version)
 
     found = None
-    next_file_system = self._file_system_at_head
+    next_file_system = self._host_file_system_provider.GetTrunk()
 
     while has_greater_app_version(next_file_system):
       found = get_app_yaml_revision(next_file_system)
       # Back up a revision then find when app.yaml was last updated before then.
       if found == 0:
         logging.warning('All revisions are greater than %s' % app_version)
         return 0
-      next_file_system = self._host_file_system_creator.Create(
+      next_file_system = self._host_file_system_provider.GetTrunk(
           revision=found - 1)
 
     if found is None:
       raise ValueError('All revisions are less than %s' % app_version)
     return found