1:- module(ag_preferences, []).    2
    3:- use_module(library(http/http_session)).    4:- use_module(library(semweb/rdf_db)).    5:- use_module(library(settings)).    6:- use_module(cliopatria(hooks)).    7:- use_module(user(user_db)).    8
    9:- rdf_meta
   10	cliopatria:user_preference_db(r,o),
   11	cliopatria:user_preference_default(r,o),
   12	set_user_preferences(r,o).   13
   14:- if(current_setting(user:lang)).   15% do nothing
   16:- else.   17:- setting(user:lang, atom, en, 'Preferred language').   18:- endif.   19
   20                 /*******************************
   21                 *   USER/SESSION PREFERENCES   *
   22                 *******************************/
   23
   24%%      cliopatria:user_preference_db(?Property:atom, ?Value:rdf_object) is nondet.
   25%
   26%       Query properties for the current   user/session.  This mechanism
   27%       allows code to access information about the user/session without
   28%       committing to a particular  implementation.   The  predicate and
   29%       values are compatible with RDF to   allow  implementing the user
   30%       database in RDF, typically using the OpenID as subject.
   31
   32cliopatria:user_preference_db(Property, Value) :-
   33	http_in_session(_),
   34	logged_on(User, anonymous),
   35	http_session_data(rdf(User, Property, Value)).
   36
   37%%      cliopatria:user_preference_default(?Property:atom, ?Value:rdf_object) is nondet.
   38%
   39%       Provides defaults for the user_preference/2.
   40%
   41%       @see user_preference_db/2
   42
   43cliopatria:user_preference_default(Prop, literal(Value)) :-
   44	rdf_equal(Prop, user:lang),
   45	setting(user:lang, Value)