:- module(ann_preferences, []).

:- use_module(library(http/http_session)).
:- use_module(library(semweb/rdf_db)).
:- use_module(library(settings)).
:- use_module(cliopatria(hooks)).
:- use_module(user(user_db)).

:- rdf_meta
	cliopatria:user_preference_db(r,o),
	cliopatria:user_preference_default(r,o).

:- if(current_setting(user:lang)).
% do nothing
:- else.
:- setting(user:lang, atom, en, 'Preferred language').
:- endif.

                 /*******************************
                 *   USER/SESSION PREFERENCES   *
                 *******************************/

%%      cliopatria:user_preference_db(?Property:atom, ?Value:rdf_object) is nondet.
%
%       Query properties for the current   user/session.  This mechanism
%       allows code to access information about the user/session without
%       committing to a particular  implementation.   The  predicate and
%       values are compatible with RDF to   allow  implementing the user
%       database in RDF, typically using the OpenID as subject.

cliopatria:user_preference_db(Property, Value) :-
	http_in_session(_),
	logged_on(User, anonymous),
	http_session_data(rdf(User, Property, Value)).

%%      cliopatria:user_preference_default(?Property:atom, ?Value:rdf_object) is nondet.
%
%       Provides defaults for the user_preference/2.
%
%       @see user_preference_db/2

cliopatria:user_preference_default(Prop, literal(Value)) :-
	rdf_equal(Prop, user:lang),
	setting(user:lang, Value).