''' User Authentication and Authorization '''

from passlib.context import CryptContext
from pyramid.authentication import AuthTktAuthenticationPolicy
from pyramid.authorization import ACLAuthorizationPolicy
from pyramid.security import Authenticated, Everyone
from pyramid.settings import aslist

from ordr.models.account import User

#:  passlib context for hashing passwords
# at least one scheme must be set in advance, will be overridden by the
# settings in the .ini file.
password_context = CryptContext(schemes=['argon2'])


class AuthenticationPolicy(AuthTktAuthenticationPolicy):
    ''' How to authenticate users '''

    def authenticated_userid(self, request):
        ''' returns the id of an authenticated user

        heavy lifting done in get_user() attached to request
        '''
        user = request.user
        if user is not None:
            return user.id

    def effective_principals(self, request):
        ''' returns a list of principals for the user '''
        principals = [Everyone]
        user = request.user
        if user is not None:
            principals.append(Authenticated)
            principals.extend(user.principals)
        return principals


def get_user(request):
    ''' retrieves the user object by the unauthenticated user id

    :param pyramid.request.Request request:
        the current request object
    :rtype: :class:`ordr.models.account.User` or None
    '''
    user_id = request.unauthenticated_userid
    if user_id is not None:
        user = request.dbsession.query(User).filter_by(id=user_id).first()
        if user and user.is_active:
            return user
    return None
     

def crypt_context_settings_to_string(settings, prefix='passlib.'):
    ''' returns a passlib context setting as a INI-formatted content
    
    :param dict settings: settings for the crypt context
    :param str prefix: prefix of the settings keys
    :rtype: (str) config string in INI format for CryptContext.load()
    
    This looks at first like a dump hack, but the parsing of all possible
    context settings is quite a task. Since passlib has a context parser
    included, this seems the most reliable way to do it.
    '''
    config_lines = ['[passlib]']
    for ini_key, value in settings.items():
        if ini_key.startswith(prefix):
            context_key = ini_key.replace(prefix, '')
            # the pyramid .ini format is different on lists
            # than the .ini format used by passlib.
            if context_key in {'schemes', 'deprecated'} and ',' not in value:
                value = ','.join(aslist(value))
            config_lines.append(f'{context_key} = {value}')
    return '\n'.join(config_lines)
    

def includeme(config):  # pragma: no cover
    ''' initializing authentication, authorization and password hash settings

    Activate this setup using ``config.include('ordr.security')``.
    '''
    settings = config.get_settings()

    # configure the passlib context manager for hashing user passwords
    config_str = crypt_context_settings_to_string(settings, prefix='passlib.')
    password_context.load(config_str)

    # config for authentication and authorization
    authn_policy = AuthenticationPolicy(
        settings.get('auth.secret', ''),
        hashalg='sha512',
        )
    config.set_authentication_policy(authn_policy)
    config.set_authorization_policy(ACLAuthorizationPolicy())

    # attach the get_user function returned by get_user_closure()
    config.add_request_method(get_user, 'user', reify=True)