1/*  Part of ClioPatria SeRQL and SPARQL server
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2018, University of Amsterdam,
    7                              VU University Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(user_preferences,
   37          [ user_preference/2           % ?Preference, ?Value
   38          ]).   39:- use_module(library(semweb/rdf_db)).   40:- use_module(cliopatria(hooks)).   41
   42:- rdf_register_ns(user, 'http://www.swi-prolog.org/cliopatria/user/').   43
   44/** <module> User preference handling
   45
   46This module defines _access_  to  user-preferences.   The  API  for  the
   47preference system is based on RDF. This   allows for using the RDF-store
   48for storing preferences, typically using the  OpenID URI as subject. The
   49actual storage infrastructure must be  implemented   using  hooks in the
   50=cliopatria=      module:      cliopatria:user_preference_db/2       and
   51cliopatria:user_preference_default/2.
   52
   53Preferences are defines in the RDF   namespace with prefix =user=, which
   54expands to:
   55
   56        ==
   57        http://www.swi-prolog.org/cliopatria/user/
   58        ==
   59*/
   60
   61:- rdf_meta
   62    user_preference(r,o),
   63    builtin_default(r,o).   64
   65%!  user_preference(?Preference:resource, ?Value:object) is nondet.
   66%
   67%   True if Preference has Value.  Preference and Value use the RDF
   68%   data-representation.  E.g.,
   69%
   70%       ==
   71%       ?- user_preference(user:lang, literal(Lang))
   72%
   73%       Lang = en
   74%       ==
   75%
   76%   @see cliopatria:user_preference_db/2 provides the storage hook
   77%   @see cliopatria:user_preference_default/2 provides a hook for
   78%   defaults
   79%   @see builtin_default/2 provides built-in defaults
   80
   81user_preference(Pref, Value) :-
   82    nonvar(Pref),
   83    !,
   84    (   cliopatria:user_preference_db(Pref, Value)
   85    *-> true
   86    ;   cliopatria:user_preference_default(Pref, Value)
   87    *-> true
   88    ;   builtin_default(Pref, Value)
   89    ).
   90user_preference(Pref, Value) :-
   91    current_preference(Pref),
   92    user_preference(Pref, Value).
   93
   94current_preference(Pref) :-
   95    setof(P, current_pref(P), Prefs),
   96    member(Pref, Prefs).
   97
   98current_pref(P) :- cliopatria:user_preference_db(P, _).
   99current_pref(P) :- cliopatria:user_preference_default(P, _).
  100current_pref(P) :- builtin_default(P, _).
  101
  102%!  builtin_default(?Preference, ?Value) is nondet.
  103%
  104%   Provide defaults for commonly used preferences.
  105
  106builtin_default(user:lang, literal(en))