import logging
import features

from collections import namedtuple

from data import model
from util.validation import generate_valid_usernames

logger = logging.getLogger(__name__)

UserInformation = namedtuple('UserInformation', ['username', 'email', 'id'])

DISABLED_MESSAGE = 'User creation is disabled. Please contact your adminstrator to gain access.'

class FederatedUsers(object):
  """ Base class for all federated users systems. """

  def __init__(self, federated_service, requires_email):
    self._federated_service = federated_service
    self._requires_email = requires_email

  @property
  def federated_service(self):
    return self._federated_service

  def get_user(self, username_or_email):
    """ Retrieves the user with the given username or email, returning a tuple containing
        a UserInformation (if success) and the error message (on failure).
    """
    raise NotImplementedError

  def verify_credentials(self, username_or_email, password):
    """ Verifies the given credentials against the backing federated service, returning
        a tuple containing a UserInformation (on success) and the error message (on failure).
    """
    raise NotImplementedError

  def query_users(self, query, limit=20):
    """ If implemented, get_user must be implemented as well. """
    return (None, 'Not supported')

  def link_user(self, username_or_email):
    (user_info, err_msg) = self.get_user(username_or_email)
    if user_info is None:
      return (None, err_msg)

    return self.get_and_link_federated_user_info(user_info)

  def get_and_link_federated_user_info(self, user_info):
    return self._get_and_link_federated_user_info(user_info.username, user_info.email)

  def verify_and_link_user(self, username_or_email, password):
    """ Verifies the given credentials and, if valid, creates/links a database user to the
        associated federated service.
    """
    (credentials, err_msg) = self.verify_credentials(username_or_email, password)
    if credentials is None:
      return (None, err_msg)

    return self._get_and_link_federated_user_info(credentials.username, credentials.email)

  def confirm_existing_user(self, username, password):
    """ Confirms that the given *database* username and service password are valid for the linked
        service. This method is used when the federated service's username is not known.
    """
    db_user = model.user.get_user(username)
    if not db_user:
      return (None, 'Invalid user')

    federated_login = model.user.lookup_federated_login(db_user, self._federated_service)
    if not federated_login:
      return (None, 'Invalid user')

    (credentials, err_msg) = self.verify_credentials(federated_login.service_ident, password)
    if credentials is None:
      return (None, err_msg)

    return (db_user, None)

  def service_metadata(self):
    """ Returns a dictionary of extra metadata to present to *superusers* about this auth engine.
        For example, LDAP returns the base DN so we can display to the user during sync setup.
    """
    return {}

  def check_group_lookup_args(self, group_lookup_args):
    """ Verifies that the given group lookup args point to a valid group. Returns a tuple consisting
        of a boolean status and an error message (if any).
    """
    return (False, 'Not supported')

  def iterate_group_members(self, group_lookup_args, page_size=None, disable_pagination=False):
    """ Returns an iterator over all the members of the group matching the given lookup args
        dictionary. The format of the lookup args dictionary is specific to the implementation.
    """
    return (None, 'Not supported')

  def _get_and_link_federated_user_info(self, username, email):
    db_user = model.user.verify_federated_login(self._federated_service, username)
    if not db_user:
      # We must create the user in our db. Check to see if this is allowed.
      if not features.USER_CREATION:
        return (None, DISABLED_MESSAGE)

      valid_username = None
      for valid_username in generate_valid_usernames(username):
        if model.user.is_username_unique(valid_username):
          break

      if not valid_username:
        logger.error('Unable to pick a username for user: %s', username)
        return (None, 'Unable to pick a username. Please report this to your administrator.')

      prompts = model.user.get_default_user_prompts(features)
      try:
        db_user = model.user.create_federated_user(valid_username, email, self._federated_service,
                                                   username,
                                                   set_password_notification=False,
                                                   email_required=self._requires_email,
                                                   prompts=prompts)
      except model.InvalidEmailAddressException as iae:
        return (None, iae.message)

    else:
      # Update the db attributes from the federated service.
      if email and db_user.email != email:
        db_user.email = email
        db_user.save()

    return (db_user, None)