import logging

import features

from oauth.base import OAuthService, OAuthExchangeCodeException, OAuthGetUserInfoException

logger = logging.getLogger(__name__)

class OAuthLoginException(Exception):
  """ Exception raised if a login operation fails. """
  pass

class OAuthLoginService(OAuthService):
  """ A base class for defining an OAuth-compliant service that can be used for, amongst other
      things, login and authentication. """

  def login_enabled(self):
    """ Returns true if the login service is enabled. """
    raise NotImplementedError

  def get_login_service_id(self, user_info):
    """ Returns the internal ID for the given user under this login service. """
    raise NotImplementedError

  def get_login_service_username(self, user_info):
    """ Returns the username for the given user under this login service. """
    raise NotImplementedError

  def get_verified_user_email(self, app_config, http_client, token, user_info):
    """ Returns the verified email address for the given user, if any or None if none. """
    raise NotImplementedError

  def get_icon(self):
    """ Returns the icon to display for this login service. """
    raise NotImplementedError

  def get_login_scopes(self):
    """ Returns the list of scopes for login for this service. """
    raise NotImplementedError

  def service_verify_user_info_for_login(self, app_config, http_client, token, user_info):
    """ Performs service-specific verification of user information for login. On failure, a service
        should raise a OAuthLoginService.
    """
    # By default, does nothing.
    pass

  def exchange_code_for_login(self, app_config, http_client, code, redirect_suffix):
    """ Exchanges the given OAuth access code for user information on behalf of a user trying to
        login or attach their account. Raises a OAuthLoginService exception on failure. Returns
        a tuple consisting of (service_id, service_username, email)
    """

    # Retrieve the token for the OAuth code.
    try:
      token = self.exchange_code_for_token(app_config, http_client, code,
                                           redirect_suffix=redirect_suffix,
                                           form_encode=self.requires_form_encoding())
    except OAuthExchangeCodeException as oce:
      raise OAuthLoginException(oce.message)

    # Retrieve the user's information with the token.
    try:
      user_info = self.get_user_info(http_client, token)
    except OAuthGetUserInfoException as oge:
      raise OAuthLoginException(oge.message)

    if user_info.get('id', None) is None:
      logger.debug('Got user info response %s', user_info)
      raise OAuthLoginException('Missing `id` column in returned user information')

    # Perform any custom verification for this login service.
    self.service_verify_user_info_for_login(app_config, http_client, token, user_info)

    # Retrieve the user's email address (if necessary).
    email_address = self.get_verified_user_email(app_config, http_client, token, user_info)
    if features.MAILING and email_address is None:
      raise OAuthLoginException('A verified email address is required to login with this service')

    service_user_id = self.get_login_service_id(user_info)
    service_username = self.get_login_service_username(user_info)

    logger.debug('Completed successful exchange for service %s: %s, %s, %s',
                 self.service_id(), service_user_id, service_username, email_address)
    return (service_user_id, service_username, email_address)