demo_diagrammer.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker, Anne Ogborn
    E-mail:        aogborn@uh.edu
    WWW:           http://www.swi-prolog.org
    Copyright (C): 2014, VU University Amsterdam

    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation; either version 2
    of the License, or (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

    As a special exception, if you link this library with other files,
    compiled with a Free Software compiler, to produce an executable, this
    library does not by itself cause the resulting executable to be covered
    by the GNU General Public License. This exception does not however
    invalidate any other reasons why the executable file might be covered by
    the GNU General Public License.
*/

:- module(demo_diagrammer,[start_hubs/0]).

:- use_module(library(http/thread_httpd)).
:- use_module(library(http/http_dispatch)).
:- use_module(library(http/websocket)).
:- use_module(library(http/html_write)).
:- use_module(library(debug)).


:- use_module(library(http/hub)).
:- use_module(diagrammer).

:- debug(websocket).

/** <module> Demo of scalable websocket based diagrammer server in SWI-Prolog

Logic languages have a natural affinity to problems best expressed
by 'ball and circle' graphs or 'arrows between boxes' diagrams.

This is a small shared diagrammer application for collaboratively
drawing digraph diagrams. It's based on Jan Wielemaker's =|chatroom.pl|=
demo available at https://github.com/JanWielemaker/swi-chat  .

 @tbd  Write this up after you know where the API is going

  - Create a diagrammerroom using chatroom_create/3 and a thread that
    listens to diagrammer events and broadcasts the changes.

  - Serve a web page that provides the diagrammer frontend.  The frontend
    contains JavaScript that establishes a websocket on /chat.  If
    a websocket is obtained, hand it to to the room using
    chatroom_add/2
*/

% be a bit chatty.  Comment for silent operation.
:- debug(chat).
:- debug(diagrammer).

:-
   current_prolog_flag(version, X),
   (   X >= 70135
   ->  true
   ;   writeln('You must use SWI-Prolog version >= 7.1.35')
   ).

%%	start_hubs is det
%
%        starts up the hubs
%
% The server must be running

start_hubs :-
	(   debugging(chat)
	->  prolog_ide(thread_monitor)
	;   true
	),
	create_chat_room.

http:location(hub, root(hub), []).

% setup the HTTP location. The  first   (/)  loads  the application. The
% loaded application will create  a   websocket  using  /chat. Normally,
% http_upgrade_to_websocket/3 runs call(Goal, WebSocket)  and closes the
% connection if Goal terminates. Here, we use guarded(false) to tell the
% server we will take responsibility for the websocket.

:- http_handler(hub(.),	diagrammer_page, []).
:- http_handler(hub(chat),
		http_upgrade_to_websocket(
		    accept_chat,
		    [ guarded(false),
		      subprotocols([echo])
		    ]),
		[ id(chat_websocket)
		]).


diagrammer_page(_Request) :-
	reply_html_page(
	    title('Collaborative Diagram Editor'),
	    \diagrammer_body).

%%	diagrammer_body//
%
%	Generate the web page. To  keep   everything  compact  we do the
%	styling inline.

diagrammer_body -->
	html(h1('A Collaborative Diagram Editor')),
	diagrammer.

%%	accept_chat(+WebSocket) is det.
%
%	Normally,  the  goal  called    by   http_upgrade_to_websocket/3
%	processes all communication with the   websocket in a read/write
%	loop. In this case however,  we tell http_upgrade_to_websocket/3
%	that we will take responsibility for   the websocket and we hand
%	it to the chat room.
%
%	diagram_hub_room is the name of the chatroom

accept_chat(WebSocket) :-
	hub_add(diagram_hub_room, WebSocket, _Id).

%%	create_chat_room
%
%	Create our actual chat room.

create_chat_room :-
	hub_create(diagram_hub_room, Room, _{}),
	thread_create(diagrammer:chatroom_loop(Room), _, [alias(chatroom)]).