# Copyright 2014 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.cloudstorage import cloudstorage_api
from third_party.cloudstorage import common
from third_party.cloudstorage import errors

from docs_server_utils import StringIdentity
from file_system import FileSystem, FileNotFoundError, StatInfo
from future import Future
from path_util import (
    AssertIsDirectory, AssertIsFile, AssertIsValid, IsDirectory, Join)

import logging
import traceback


# See gcs_file_system_provider.py for documentation on using Google Cloud
# Storage as a filesystem.
#
# Note that the path requirements for GCS are different for the docserver;
# GCS requires that paths start with a /, we require that they don't.


# Name of the file containing the Git hash of the latest commit sync'ed
# to Cloud Storage. This file is generated by the Github->GCS sync script
LAST_COMMIT_HASH_FILENAME = '.__lastcommit.txt'

def _ReadFile(filename):
  AssertIsFile(filename)
  try:
    with cloudstorage_api.open('/' + filename, 'r') as f:
      return f.read()
  except errors.Error:
    raise FileNotFoundError('Read failed for %s: %s' % (filename,
        traceback.format_exc()))

def _ListDir(dir_name, recursive=False):
  AssertIsDirectory(dir_name)
  try:
    # The listbucket method uses a prefix approach to simulate hierarchy.
    # Calling it with the "delimiter" argument set to '/' gets only files
    # directly inside the directory, not all recursive content.
    delimiter = None if recursive else '/'
    files = cloudstorage_api.listbucket('/' + dir_name, delimiter=delimiter)
    return [os_path.filename.lstrip('/')[len(dir_name):] for os_path in files]
  except errors.Error:
    raise FileNotFoundError('cloudstorage.listbucket failed for %s: %s' %
                            (dir_name, traceback.format_exc()))

def _CreateStatInfo(bucket, path):
  full_path = Join(bucket, path)
  last_commit_file = Join(bucket, LAST_COMMIT_HASH_FILENAME)
  try:
    last_commit = _ReadFile(last_commit_file)
    if IsDirectory(full_path):
      child_versions = dict((filename, last_commit) 
                            for filename in _ListDir(full_path)) 
    else:
      child_versions = None
    return StatInfo(last_commit, child_versions)
  except (TypeError, errors.Error):
    raise FileNotFoundError('cloudstorage.stat failed for %s: %s' % (path,
                            traceback.format_exc()))

class CloudStorageFileSystem(FileSystem):
  '''FileSystem implementation which fetches resources from Google Cloud
  Storage.
  '''
  def __init__(self, bucket, debug_access_token=None, debug_bucket_prefix=None):
    self._bucket = bucket
    if debug_access_token:
      logging.debug('gcs: using debug access token: %s' % debug_access_token)
      common.set_access_token(debug_access_token)
    if debug_bucket_prefix:
      logging.debug('gcs: prefixing all bucket names with %s' %
                    debug_bucket_prefix)
      self._bucket = debug_bucket_prefix + self._bucket
    AssertIsValid(self._bucket)

  def Read(self, paths, skip_not_found=False):
    def resolve():
      try:
        result = {}
        for path in paths:
          full_path = Join(self._bucket, path)
          logging.debug('gcs: requested path "%s", reading "%s"' %
                        (path, full_path))
          if IsDirectory(path):
            result[path] = _ListDir(full_path)
          else:
            result[path] = _ReadFile(full_path)
        return result
      except errors.AuthorizationError:
        self._warnAboutAuthError()
        raise

    return Future(callback=resolve)

  def Refresh(self):
    return Future(value=())

  def Stat(self, path):
    AssertIsValid(path)
    try:
      return _CreateStatInfo(self._bucket, path)
    except errors.AuthorizationError:
      self._warnAboutAuthError()
      raise

  def GetIdentity(self):
    return '@'.join((self.__class__.__name__, StringIdentity(self._bucket)))

  def __repr__(self):
    return 'CloudStorageFileSystem(%s)' % self._bucket

  def _warnAboutAuthError(self):
    logging.warn(('Authentication error on Cloud Storage. Check if your'
                  ' appengine project has permissions to Read the GCS'
                  ' buckets. If you are running a local appengine server,'
                  ' you need to set an access_token in'
                  ' local_debug/gcs_debug.conf.'
                  ' Remember that this token expires in less than 10'
                  ' minutes, so keep it updated. See'
                  ' gcs_file_system_provider.py for instructions.'));
    logging.debug(traceback.format_exc())