| # 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 third_party.json_schema_compiler.memoize import memoize |
| |
| |
| class HostFileSystemIterator(object): |
| '''Provides methods for iterating through host file systems, in both |
| ascending (oldest to newest version) and descending order. |
| ''' |
| |
| def __init__(self, file_system_creator, host_file_system, branch_utility): |
| self._file_system_creator = file_system_creator |
| self._host_file_system = host_file_system |
| self._branch_utility = branch_utility |
| |
| @memoize |
| def _GetFileSystem(self, branch): |
| '''To avoid overwriting the persistent data store entry for the 'trunk' |
| host file system, hold on to a reference of this file system and return it |
| instead of creating a file system for 'trunk'. |
| Also of note: File systems are going to be iterated over multiple times |
| at each call of ForEach, but the data isn't going to change between calls. |
| Use |branch| to memoize the created file systems. |
| ''' |
| if branch == 'trunk': |
| # Don't create a new file system for trunk, since there is a bug with the |
| # current architecture and design of HostFileSystemCreator, where |
| # creating 'trunk' ignores the pinned revision (in fact, it bypasses |
| # every difference including whether the file system is patched). |
| # TODO(kalman): Fix HostFileSystemCreator and update this comment. |
| return self._host_file_system |
| return self._file_system_creator.Create(branch) |
| |
| def _ForEach(self, channel_info, callback, get_next): |
| '''Iterates through a sequence of file systems defined by |get_next| until |
| |callback| returns False, or until the end of the sequence of file systems |
| is reached. Returns the BranchUtility.ChannelInfo of the last file system |
| for which |callback| returned True. |
| ''' |
| last_true = None |
| while channel_info is not None: |
| file_system = self._GetFileSystem(channel_info.branch) |
| if not callback(file_system, channel_info): |
| return last_true |
| last_true = channel_info |
| channel_info = get_next(channel_info) |
| return last_true |
| |
| def Ascending(self, channel_info, callback): |
| return self._ForEach(channel_info, callback, self._branch_utility.Newer) |
| |
| def Descending(self, channel_info, callback): |
| return self._ForEach(channel_info, callback, self._branch_utility.Older) |
