Dynamically generate a heading for Extension Docs API pages

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

+# Copyright (c) 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 file_system import FileNotFoundError
+import object_store
+
+class AvailabilityDataSource:
+  """Uses API data sources generated by a ChromeVersionDataSource in order to
+  search the filesystem for the earliest existence of a specified API throughout
+  the different versions of Chrome; this constitutes an API's availability.
+  """
+
+  def __init__(self, version_data_source, version, object_store):
+    self._version_data_source = version_data_source
+    self._version = version
+    self._object_store = object_store
+
+  def _CheckExistence(self, api_name, version):
+    """Tries to 'get' an api from the filesystem, and reports whether or not it
+    was successful.
+    """
+    api_data_source = self._version_data_source.GetDataSourceForVersion(
+        str(version))
+    try:
+      api_data_source.TryGet(api_name)
+    except FileNotFoundError:
+      try:
+        api_data_source.TryGet(api_name, try_non_unix=True)
+      except FileNotFoundError:
+        return False
+    return True
+
+  def FindEarliestAvailability(self, api_name):
+    """Searches in descending order through filesystem caches tied to specific
+    chrome version numbers and looks for the existence of a specified api,
+    |api_name|. When an api is not found, returns the previous version number
+    (the last known version where the api was found).
+    """
+    availability = self._object_store.Get(
+        api_name,
+        object_store.AVAILABILITY_DATA_SOURCE).Get()
+
+    if availability is not None:
+      return availability
+    elif availability is False:
+      return None
+
+    if self._version == 'trunk':
+      if not self._CheckExistence(api_name, 'trunk'):
+        # If the API wasn't found in trunk, then it isn't currently available.
+        self._object_store.Set(api_name,
+                               False,
+                               object_store.AVAILABILITY_DATA_SOURCE)
+        return None
+
+    if self._version == 'trunk':
+      latest_version = self._version_data_source.GetLatestVersionNumber()
+      version_int = latest_version
+    else:
+      version_int = int(self._version)
+
+    # Extension APIs are not present in the filesystem before version 18.
+    while version_int >= 18:
+      if not self._CheckExistence(api_name, version_int):
+        break
+      version_int -= 1
+
+    version_int += 1
+    # If the version number is greater than the current version of Chrome, then
+    # the API was not found in the current version.
+    if self._version == 'trunk':
+      if version_int > latest_version:
+        availability = 'trunk'
+      else:
+        availability = str(version_int)
+    elif version_int <= int(self._version):
+      availability = str(version_int)
+
+    self._object_store.Set(api_name,
+                           availability,
+                           object_store.AVAILABILITY_DATA_SOURCE)
+    return availability