# Copyright 2015 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""OAuth 2.0 utitilies for Google Developer Shell environment."""

import json
import os

from . import client


DEVSHELL_ENV = 'DEVSHELL_CLIENT_PORT'


class Error(Exception):
  """Errors for this module."""
  pass


class CommunicationError(Error):
  """Errors for communication with the Developer Shell server."""


class NoDevshellServer(Error):
  """Error when no Developer Shell server can be contacted."""


# The request for credential information to the Developer Shell client socket is
# always an empty PBLite-formatted JSON object, so just define it as a constant.
CREDENTIAL_INFO_REQUEST_JSON = '[]'


class CredentialInfoResponse(object):
  """Credential information response from Developer Shell server.

  The credential information response from Developer Shell socket is a
  PBLite-formatted JSON array with fields encoded by their index in the array:
  * Index 0 - user email
  * Index 1 - default project ID. None if the project context is not known.
  * Index 2 - OAuth2 access token. None if there is no valid auth context.
  """

  def __init__(self, json_string):
    """Initialize the response data from JSON PBLite array."""
    pbl = json.loads(json_string)
    if not isinstance(pbl, list):
      raise ValueError('Not a list: ' + str(pbl))
    pbl_len = len(pbl)
    self.user_email = pbl[0] if pbl_len > 0 else None
    self.project_id = pbl[1] if pbl_len > 1 else None
    self.access_token = pbl[2] if pbl_len > 2 else None


def _SendRecv():
  """Communicate with the Developer Shell server socket."""

  port = int(os.getenv(DEVSHELL_ENV, 0))
  if port == 0:
    raise NoDevshellServer()

  import socket

  sock = socket.socket()
  sock.connect(('localhost', port))

  data = CREDENTIAL_INFO_REQUEST_JSON
  msg = '%s\n%s' % (len(data), data)
  sock.sendall(msg.encode())

  header = sock.recv(6).decode()
  if '\n' not in header:
    raise CommunicationError('saw no newline in the first 6 bytes')
  len_str, json_str = header.split('\n', 1)
  to_read = int(len_str) - len(json_str)
  if to_read > 0:
    json_str += sock.recv(to_read, socket.MSG_WAITALL).decode()

  return CredentialInfoResponse(json_str)


class DevshellCredentials(client.GoogleCredentials):
  """Credentials object for Google Developer Shell environment.

  This object will allow a Google Developer Shell session to identify its user
  to Google and other OAuth 2.0 servers that can verify assertions. It can be
  used for the purpose of accessing data stored under the user account.

  This credential does not require a flow to instantiate because it represents
  a two legged flow, and therefore has all of the required information to
  generate and refresh its own access tokens.
  """

  def __init__(self, user_agent=None):
    super(DevshellCredentials, self).__init__(
        None,  # access_token, initialized below
        None,  # client_id
        None,  # client_secret
        None,  # refresh_token
        None,  # token_expiry
        None,  # token_uri
        user_agent)
    self._refresh(None)

  def _refresh(self, http_request):
    self.devshell_response = _SendRecv()
    self.access_token = self.devshell_response.access_token

  @property
  def user_email(self):
    return self.devshell_response.user_email

  @property
  def project_id(self):
    return self.devshell_response.project_id

  @classmethod
  def from_json(cls, json_data):
    raise NotImplementedError(
        'Cannot load Developer Shell credentials from JSON.')

  @property
  def serialization_data(self):
    raise NotImplementedError(
        'Cannot serialize Developer Shell credentials.')