#-----------------------------------------------------------------------------
# Copyright (c) 2012 - 2021, Anaconda, Inc., and Bokeh Contributors.
# All rights reserved.
#
# The full license is in the file LICENSE.txt, distributed with this software.
#-----------------------------------------------------------------------------
''' Bokeh Application Handler to look for Bokeh server lifecycle callbacks
in a specified Python module.

'''

#-----------------------------------------------------------------------------
# Boilerplate
#-----------------------------------------------------------------------------
from __future__ import annotations

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

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

# Standard library imports
from typing import Any, Callable

# Bokeh imports
from ...document import Document
from ..application import ServerContext, SessionContext
from .handler import Handler

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

__all__ = (
    'LifecycleHandler',
)

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

class LifecycleHandler(Handler):
    ''' Load a script which contains server lifecycle callbacks.

    .. autoclasstoc::

    '''

    _on_server_loaded: Callable[[ServerContext], None]
    _on_server_unloaded: Callable[[ServerContext], None]
    _on_session_created: Callable[[SessionContext], None]
    _on_session_destroyed: Callable[[SessionContext], None]

    def __init__(self) -> None:
        super().__init__()
        self._on_server_loaded = _do_nothing
        self._on_server_unloaded = _do_nothing
        self._on_session_created = _do_nothing
        self._on_session_destroyed = _do_nothing

    @property
    def safe_to_fork(self) -> bool:
        return True

    # Public methods ----------------------------------------------------------

    def modify_document(self, doc: Document) -> None:
        ''' This handler does not make any modifications to the Document.

        Args:
            doc (Document) : A Bokeh Document to update in-place

                *This handler does not modify the document*

        Returns:
            None

        '''
        # we could support a modify_document function, might be weird though.
        pass

    def on_server_loaded(self, server_context: ServerContext) -> None:
        ''' Execute `on_server_unloaded`` from the configured module (if
        it is defined) when the server is first started.

        Args:
            server_context (ServerContext) :

        '''
        return self._on_server_loaded(server_context)

    def on_server_unloaded(self, server_context: ServerContext) -> None:
        ''' Execute ``on_server_unloaded`` from the configured module (if
        it is defined) when the server cleanly exits. (Before stopping the
        server's ``IOLoop``.)

        Args:
            server_context (ServerContext) :

        .. warning::
            In practice this code may not run, since servers are often killed
            by a signal.

        '''
        return self._on_server_unloaded(server_context)

    async def on_session_created(self, session_context: SessionContext) -> None:
        ''' Execute ``on_session_created`` from the configured module (if
        it is defined) when a new session is created.

        Args:
            session_context (SessionContext) :

        '''
        return self._on_session_created(session_context)

    async def on_session_destroyed(self, session_context: SessionContext) -> None:
        ''' Execute ``on_session_destroyed`` from the configured module (if
        it is defined) when a new session is destroyed.

        Args:
            session_context (SessionContext) :

        '''
        return self._on_session_destroyed(session_context)

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

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

def _do_nothing(ignored: Any) -> None:
    pass

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