''' Provide a hook for supplying authorization mechanisms to a Bokeh server.

'''

#-----------------------------------------------------------------------------
# Boilerplate
#-----------------------------------------------------------------------------
import logging # isort:skip
log = logging.getLogger(__name__)

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------

# Standard library imports
import importlib.util
from os.path import isfile

# External imports
from tornado.web import RequestHandler

# Bokeh imports
from ..util.serialization import make_globally_unique_id

#-----------------------------------------------------------------------------
# Globals and constants
#-----------------------------------------------------------------------------

__all__ = (
    'AuthModule',
    'AuthProvider',
    'NullAuth'
)

#-----------------------------------------------------------------------------
# General API
#-----------------------------------------------------------------------------

class AuthProvider(object):
    ''' Abstract base class for implementing authorization hooks.

    Subclasses must supply one of: ``get_user`` or ``get_user_async``.

    Subclasses must also supply one of ``login_url`` or ``get_login_url``.

    Optionally, if ``login_url`` provides a relative URL, then ``login_handler``
    may also be supplied.

    The properties ``logout_url`` and ``get_logout_handler`` are analogous to
    the corresponding login properties, and are optional.

    '''

    def __init__(self):
        self._validate()

    @property
    def endpoints(self):
        ''' URL patterns for login/logout endpoints.

        '''
        endpoints = []
        if self.login_handler:
            endpoints.append((self.login_url, self.login_handler))
        if self.logout_handler:
            endpoints.append((self.logout_url, self.logout_handler))
        return endpoints

    @property
    def get_login_url(self):
        ''' A function that computes a URL to redirect unathenticated users
        to for login.

        This property may return None, if a ``login_url`` is supplied
        instead.

        If a function is returned, it should accept a ``RequestHandler``
        and return a login URL for unathenticated users.

        '''
        pass

    @property
    def get_user(self):
        ''' A function to get the current authenticated user.

        This property may return None, if a ``get_user_async`` function is
        supplied instead.

        If a function is returned, it should accept a ``RequestHandler``
        and return the current authenticated user.

        '''
        pass

    @property
    def get_user_async(self):
        ''' An async function to get the current authenticated user.

        This property may return None, if a ``get_user`` function is supplied
        instead.

        If a function is returned, it should accept a ``RequestHandler``
        and return the current authenticated user.

        '''
        pass

    @property
    def login_handler(self):
        ''' A request handler class for a login page.

        This property may return None, if ``login_url`` is supplied
        instead.

        If a class is returned, it must be a subclass of RequestHandler,
        which will used for the endpoint specified by ``logout_url``

        '''
        pass

    @property
    def login_url(self):
        ''' A URL to redirect unauthenticated users to for login.

        This proprty may return None, if a ``get_login_url`` function is
        supplied instead.

        '''
        pass

    @property
    def logout_handler(self):
        ''' A request handler class for a logout page.

        This property may return None.

        If a class is returned, it must be a subclass of RequestHandler,
        which will used for the endpoint specified by ``logout_url``

        '''
        pass

    @property
    def logout_url(self):
        ''' A URL to redirect unathenticated users to for logout.

        This proprty may return None.

        '''
        pass

    def _validate(self):
        if self.get_user and self.get_user_async:
            raise ValueError("Only one of get_user or get_user_async should be supplied")

        if (self.get_user or self.get_user_async) and not (self.login_url or self.get_login_url):
            raise ValueError("When user authentication is enabled, one of login_url or get_login_url must be supplied")

        if self.login_url and self.get_login_url:
            raise ValueError("At most one of login_url or get_login_url should be supplied")
        if self.login_handler and self.get_login_url:
            raise ValueError("LoginHandler cannot be used with a get_login_url() function")
        if self.login_handler and not issubclass(self.login_handler, RequestHandler):
            raise ValueError("LoginHandler must be a Tornado RequestHandler")
        if self.login_url and not probably_relative_url(self.login_url):
            raise ValueError("LoginHandler can only be used with a relative login_url")

        if self.logout_handler and not issubclass(self.logout_handler, RequestHandler):
            raise ValueError("LogoutHandler must be a Tornado RequestHandler")
        if self.logout_url and not probably_relative_url(self.logout_url):
            raise ValueError("LogoutHandler can only be used with a relative login_url")

class AuthModule(AuthProvider):
    ''' An AuthProvider configured from a Python module.

    The following properties return the corresponding values from the module if
    they exist, or None otherwise:

    * ``get_login_url``,
    * ``get_user``
    * ``get_user_async``
    * ``login_url``
    * ``logout_url``

    The ``login_handler`` property will return a ``LoginHandler`` class from the
    module, or None otherwise.

    The ``logout_handler`` property will return a ``LogoutHandler`` class from
    the module, or None otherwise.

    '''

    def __init__(self, module_path):
        if not isfile(module_path):
            raise ValueError("no file exists at module_path: %r" % module_path)

        self._module = load_auth_module(module_path)

        super(AuthModule, self).__init__()

    @property
    def get_user(self):
        return getattr(self._module, 'get_user', None)

    @property
    def get_user_async(self):
        return getattr(self._module, 'get_user_async', None)

    @property
    def login_url(self):
        return getattr(self._module, 'login_url', None)

    @property
    def get_login_url(self):
        return getattr(self._module, 'get_login_url', None)

    @property
    def login_handler(self):
        return getattr(self._module, 'LoginHandler', None)

    @property
    def logout_url(self):
        return getattr(self._module, 'logout_url', None)

    @property
    def logout_handler(self):
        return getattr(self._module, 'LogoutHandler', None)

class NullAuth(AuthProvider):
    ''' A default no-auth AuthProvider.

    All of the properties of this provider return None.

    '''
    @property
    def get_user(self):
        return None

    @property
    def get_user_async(self):
        return None

    @property
    def login_url(self):
        return None

    @property
    def get_login_url(self):
        return None

    @property
    def login_handler(self):
        return None

    @property
    def logout_url(self):
        return None

    @property
    def logout_handler(self):
        return None

#-----------------------------------------------------------------------------
# Dev API
#-----------------------------------------------------------------------------

def load_auth_module(module_path):
    ''' Load a Python source file at a given path as a module.

    Arguments:
        module_path (str): path to a Python source file

    Returns
        module

    '''
    module_name ="bokeh.auth_" + make_globally_unique_id().replace('-', '')
    spec = importlib.util.spec_from_file_location(module_name, module_path)
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    return module

def probably_relative_url(url):
    ''' Return True if a URL is not one of the common absolute URL formats.

    Arguments:
        url (str): a URL string

    Returns
        bool

    '''
    return not url.startswith(("http://", "https://", "//"))

#-----------------------------------------------------------------------------
# Private API
#-----------------------------------------------------------------------------

#-----------------------------------------------------------------------------
# Code
#-----------------------------------------------------------------------------
