import logging
import urllib

from abc import ABCMeta, abstractmethod
from six import add_metaclass

from util import get_app_url

logger = logging.getLogger(__name__)

class OAuthExchangeCodeException(Exception):
  """ Exception raised if a code exchange fails. """
  pass

class OAuthGetUserInfoException(Exception):
  """ Exception raised if a call to get user information fails. """
  pass

@add_metaclass(ABCMeta)
class OAuthService(object):
  """ A base class for defining an external service, exposed via OAuth. """
  def __init__(self, config, key_name):
    self.key_name = key_name
    self.config = config.get(key_name) or {}

  @abstractmethod
  def service_id(self):
    """ The internal ID for this service. Must match the URL portion for the service, e.g. `github`
    """
    pass

  @abstractmethod
  def service_name(self):
    """ The user-readable name for the service, e.g. `GitHub`"""
    pass

  @abstractmethod
  def token_endpoint(self):
    """ The endpoint at which the OAuth code can be exchanged for a token. """
    pass

  @abstractmethod
  def user_endpoint(self):
    """ The endpoint at which user information can be looked up. """
    pass

  @abstractmethod
  def validate_client_id_and_secret(self, http_client, app_config):
    """ Performs validation of the client ID and secret, raising an exception on failure. """
    pass

  @abstractmethod
  def authorize_endpoint(self):
    """ Endpoint for authorization. """
    pass

  def requires_form_encoding(self):
    """ Returns True if form encoding is necessary for the exchange_code_for_token call. """
    return False

  def client_id(self):
    return self.config.get('CLIENT_ID')

  def client_secret(self):
    return self.config.get('CLIENT_SECRET')

  def login_binding_field(self):
    """ Returns the name of the field (`username` or `email`) used for auto binding an external
        login service account to an *internal* login service account. For example, if the external
        login service is GitHub and the internal login service is LDAP, a value of `email` here
        will cause login-with-Github to conduct a search (via email) in LDAP for a user, an auto
        bind the external and internal users together. May return None, in which case no binding
        is performing, and login with this external account will simply create a new account in the
        database.
    """
    return self.config.get('LOGIN_BINDING_FIELD', None)

  def get_auth_url(self, app_config, redirect_suffix, csrf_token, scopes):
    """ Retrieves the authorization URL for this login service. """
    redirect_uri = '%s/oauth2/%s/callback%s' % (get_app_url(app_config), self.service_id(),
                                                redirect_suffix)
    params = {
      'client_id': self.client_id(),
      'redirect_uri': redirect_uri,
      'scope': ' '.join(scopes),
      'state': csrf_token,
    }

    authorize_url = '%s%s' % (self.authorize_endpoint(), urllib.urlencode(params))
    return authorize_url

  def get_redirect_uri(self, app_config, redirect_suffix=''):
    return '%s://%s/oauth2/%s/callback%s' % (app_config['PREFERRED_URL_SCHEME'],
                                             app_config['SERVER_HOSTNAME'],
                                             self.service_id(),
                                             redirect_suffix)

  def get_user_info(self, http_client, token):
    token_param = {
      'access_token': token,
      'alt': 'json',
    }

    got_user = http_client.get(self.user_endpoint(), params=token_param)
    if got_user.status_code // 100 != 2:
      raise OAuthGetUserInfoException('Non-2XX response code for user_info call: %s' %
                                      got_user.status_code)

    user_info = got_user.json()
    if user_info is None:
      raise OAuthGetUserInfoException()

    return user_info

  def exchange_code_for_token(self, app_config, http_client, code, form_encode=False,
                              redirect_suffix='', client_auth=False):
    """ Exchanges an OAuth access code for the associated OAuth token. """
    json_data = self.exchange_code(app_config, http_client, code, form_encode, redirect_suffix,
                                   client_auth)

    access_token = json_data.get('access_token', None)
    if access_token is None:
      logger.debug('Got successful get_access_token response with missing token: %s', json_data)
      raise OAuthExchangeCodeException('Missing `access_token` in OAuth response')

    return access_token

  def exchange_code(self, app_config, http_client, code, form_encode=False, redirect_suffix='',
                    client_auth=False):
    """ Exchanges an OAuth access code for associated OAuth token and other data. """
    payload = {
      'code': code,
      'grant_type': 'authorization_code',
      'redirect_uri': self.get_redirect_uri(app_config, redirect_suffix)
    }

    headers = {
      'Accept': 'application/json'
    }

    auth = None
    if client_auth:
      auth = (self.client_id(), self.client_secret())
    else:
      payload['client_id'] = self.client_id()
      payload['client_secret'] = self.client_secret()

    token_url = self.token_endpoint()
    if form_encode:
      get_access_token = http_client.post(token_url, data=payload, headers=headers, auth=auth)
    else:
      get_access_token = http_client.post(token_url, params=payload, headers=headers, auth=auth)

    if get_access_token.status_code // 100 != 2:
      logger.debug('Got get_access_token response %s', get_access_token.text)
      raise OAuthExchangeCodeException('Got non-2XX response for code exchange: %s' %
                                       get_access_token.status_code)

    json_data = get_access_token.json()
    if not json_data:
      raise OAuthExchangeCodeException('Got non-JSON response for code exchange')

    if 'error' in json_data:
      raise OAuthExchangeCodeException(json_data.get('error_description', json_data['error']))

    return json_data