/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2010-2015, University of Amsterdam
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

:- module(rdf,
          [ load_rdf/2,                 % +File, -Triples
            load_rdf/3,                 % +File, -Triples, :Options
            xml_to_rdf/3,               % +XML, -Triples, +Options
            process_rdf/3               % +File, :OnTriples, :Options
          ]).

:- meta_predicate
    load_rdf(+, -, :),
    process_rdf(+, :, :).

:- use_module(library(sgml)).           % Basic XML loading
:- use_module(library(option)).         % option/3
:- use_module(library(lists)).
:- use_module(rdf_parser).              % Basic parser
:- use_module(rdf_triple).              % Generate triples

%!  load_rdf(+File, -Triples) is det.
%!  load_rdf(+File, -Triples, :Options) is det.
%
%   Parse an XML file holding an RDF term into a list of RDF triples.
%   see rdf_triple.pl for a definition of the output format. Options:
%
%           * base_uri(+URI)
%           URI to use as base
%
%           * expand_foreach(+Bool)
%           Apply each(Container, Pred, Object) on the members of
%           Container
%
%           * namespaces(-Namespaces:list(NS=URL))
%           Return list of namespaces declared using xmlns:NS=URL in
%           the document.  This can be used to update the namespace
%           list with rdf_register_ns/2.
%
%   @see    Use process_rdf/3 for processing large documents in
%           _|call-back|_ style.

load_rdf(File, Triples) :-
    load_rdf(File, Triples, []).

load_rdf(File, Triples, M:Options0) :-
    entity_options(Options0, EntOptions, Options1),
    meta_options(load_meta_option, M:Options1, Options),
    init_ns_collect(Options, NSList),
    load_structure(File,
                   [ RDFElement
                   ],
                   [ dialect(xmlns),
                     space(sgml),
                     call(xmlns, rdf:on_xmlns)
                   | EntOptions
                   ]),
    rdf_start_file(Options, Cleanup),
    call_cleanup(xml_to_rdf(RDFElement, Triples0, Options),
                 rdf_end_file(Cleanup)),
    exit_ns_collect(NSList),
    post_process(Options, Triples0, Triples).

entity_options([], [], []).
entity_options([H|T0], Entities, Rest) :-
    (   H = entity(_,_)
    ->  Entities = [H|ET],
        entity_options(T0, ET, Rest)
    ;   Rest = [H|RT],
        entity_options(T0, Entities, RT)
    ).

load_meta_option(convert_typed_literal).

%!  xml_to_rdf(+XML, -Triples, +Options)

xml_to_rdf(XML, Triples, Options) :-
    is_list(Options),
    !,
    make_rdf_state(Options, State, _),
    xml_to_plrdf(XML, RDF, State),
    rdf_triples(RDF, Triples).
xml_to_rdf(XML, BaseURI, Triples) :-
    atom(BaseURI),
    !,
    xml_to_rdf(XML, Triples, [base_uri(BaseURI)]).


                 /*******************************
                 *       POST-PROCESSING        *
                 *******************************/

post_process([], Triples, Triples).
post_process([expand_foreach(true)|T], Triples0, Triples) :-
    !,
    expand_each(Triples0, Triples1),
    post_process(T, Triples1, Triples).
post_process([_|T], Triples0, Triples) :-
    !,
    post_process(T, Triples0, Triples).


                 /*******************************
                 *            EXPAND            *
                 *******************************/

expand_each(Triples0, Triples) :-
    select(rdf(each(Container), Pred, Object),
           Triples0, Triples1),
    !,
    each_triples(Triples1, Container, Pred, Object, Triples2),
    expand_each(Triples2, Triples).
expand_each(Triples, Triples).

each_triples([], _, _, _, []).
each_triples([H0|T0], Container, P, O,
             [H0, rdf(S,P,O)|T]) :-
    H0 = rdf(Container, rdf:A, S),
    member_attribute(A),
    !,
    each_triples(T0, Container, P, O, T).
each_triples([H|T0], Container, P, O, [H|T]) :-
    each_triples(T0, Container, P, O, T).

member_attribute(A) :-
    sub_atom(A, 0, _, _, '_').      % must check number?


                 /*******************************
                 *           BIG FILES          *
                 *******************************/

%!  process_rdf(+Input, :OnObject, :Options)
%
%   Process RDF from Input. Input is either an atom or a term of the
%   format stream(Handle). For each   encountered  description, call
%   OnObject(+Triples) to handle the  triples   resulting  from  the
%   description. Defined Options are:
%
%           * base_uri(+URI)
%           Determines the reference URI.
%
%           * db(DB)
%           When loading from a stream, the source is taken from
%           this option or -if non-existent- from base_uri.
%
%           * lang(LanguageID)
%           Set initial language (as xml:lang)
%
%           * convert_typed_literal(:Convertor)
%           Call Convertor(+Type, +Content, -RDFObject) to create
%           a triple rdf(S, P, RDFObject) instead of rdf(S, P,
%           literal(type(Type, Content)).
%
%           *  namespaces(-Namespaces:list(NS=URL))
%           Return list of namespaces declared using xmlns:NS=URL in
%           the document.  This can be used to update the namespace
%           list with rdf_register_ns/2.
%
%           * entity(Name, Value)
%           Overrule entity values found in the file
%
%           * embedded(Boolean)
%           If =true=, do not give warnings if rdf:RDF is embedded
%           in other XML data.

process_rdf(File, OnObject, M:Options0) :-
    is_list(Options0),
    !,
    entity_options(Options0, EntOptions, Options1),
    meta_options(load_meta_option, M:Options1, Options2),
    option(base_uri(BaseURI), Options2, ''),
    rdf_start_file(Options2, Cleanup),
    strip_module(OnObject, Module, Pred),
    b_setval(rdf_object_handler, Module:Pred),
    nb_setval(rdf_options, Options2),
    nb_setval(rdf_state, -),
    init_ns_collect(Options2, NSList),
    (   File = stream(In)
    ->  Source = BaseURI
    ;   is_stream(File)
    ->  In = File,
        option(graph(Source), Options2, BaseURI)
    ;   open(File, read, In, [type(binary)]),
        Close = In,
        Source = File
    ),
    new_sgml_parser(Parser, [dtd(DTD)]),
    def_entities(EntOptions, DTD),
    (   Source \== []
    ->  set_sgml_parser(Parser, file(Source))
    ;   true
    ),
    set_sgml_parser(Parser, dialect(xmlns)),
    set_sgml_parser(Parser, space(sgml)),
    do_process_rdf(Parser, In, NSList, Close, Cleanup, Options2).
process_rdf(File, BaseURI, OnObject) :-
    process_rdf(File, OnObject, [base_uri(BaseURI)]).

def_entities([], _).
def_entities([entity(Name, Value)|T], DTD) :-
    !,
    def_entity(DTD, Name, Value),
    def_entities(T, DTD).
def_entities([_|T0], DTD) :-
    def_entities(T0, DTD).

def_entity(DTD, Name, Value) :-
    open_dtd(DTD, [], Stream),
    xml_quote_attribute(Value, QValue),
    format(Stream, '<!ENTITY ~w "~w">~n', [Name, QValue]),
    close(Stream).


do_process_rdf(Parser, In, NSList, Close, Cleanup, Options) :-
    call_cleanup((   sgml_parse(Parser,
                                [ source(In),
                                  call(begin, on_begin),
                                  call(xmlns, on_xmlns)
                                | Options
                                ]),
                     exit_ns_collect(NSList)
                 ),
                 cleanup_process(Close, Cleanup, Parser)).

cleanup_process(In, Cleanup, Parser) :-
    (   var(In)
    ->  true
    ;   close(In)
    ),
    free_sgml_parser(Parser),
    nb_delete(rdf_options),
    nb_delete(rdf_object_handler),
    nb_delete(rdf_state),
    nb_delete(rdf_nslist),
    rdf_end_file(Cleanup).

on_begin(NS:'RDF', Attr, _) :-
    rdf_name_space(NS),
    !,
    nb_getval(rdf_options, Options),
    make_rdf_state(Options, State0, _),
    rdf_modify_state(Attr, State0, State),
    nb_setval(rdf_state, State).
on_begin(Tag, Attr, Parser) :-
    nb_getval(rdf_state, State),
    (   State == (-)
    ->  nb_getval(rdf_options, RdfOptions),
        (   memberchk(embedded(true), RdfOptions)
        ->  true
        ;   print_message(warning, rdf(unexpected(Tag, Parser)))
        )
    ;   get_sgml_parser(Parser, line(Start)),
        get_sgml_parser(Parser, file(File)),
        sgml_parse(Parser,
                   [ document(Content),
                     parse(content)
                   ]),
        b_getval(rdf_object_handler, OnTriples),
        element_to_plrdf(element(Tag, Attr, Content), Objects, State),
        rdf_triples(Objects, Triples),
        call(OnTriples, Triples, File:Start)
    ).

%!  on_xmlns(+NS, +URL, +Parser)
%
%   Build up the list of   encountered xmlns:NS=URL declarations. We
%   use  destructive  assignment  here   as    an   alternative   to
%   assert/retract, ensuring thread-safety and better performance.

on_xmlns(NS, URL, _Parser) :-
    (   nb_getval(rdf_nslist, List),
        List = list(L0)
    ->  nb_linkarg(1, List, [NS=URL|L0])
    ;   true
    ).

init_ns_collect(Options, NSList) :-
    (   option(namespaces(NSList), Options, -),
        NSList \== (-)
    ->  nb_setval(rdf_nslist, list([]))
    ;   nb_setval(rdf_nslist, -),
        NSList = (-)
    ).

exit_ns_collect(NSList) :-
    (   NSList == (-)
    ->  true
    ;   nb_getval(rdf_nslist, list(NSList))
    ).



                 /*******************************
                 *            MESSAGES          *
                 *******************************/

:- multifile
    prolog:message/3.

%       Catch messages.  sgml/4 is generated by the SGML2PL binding.

prolog:message(rdf(unparsed(Data))) -->
    { phrase(unparse_xml(Data), XML)
    },
    [ 'RDF: Failed to interpret "~s"'-[XML] ].
prolog:message(rdf(shared_blank_nodes(N))) -->
    [ 'RDF: Shared ~D blank nodes'-[N] ].
prolog:message(rdf(not_a_name(Name))) -->
    [ 'RDF: argument to rdf:ID is not an XML name: ~p'-[Name] ].
prolog:message(rdf(redefined_id(Id))) -->
    [ 'RDF: rdf:ID ~p: multiple definitions'-[Id] ].
prolog:message(rdf(unexpected(Tag, Parser))) -->
    { get_sgml_parser(Parser, file(File)),
      get_sgml_parser(Parser, line(Line))
    },
    [ 'RDF: ~w:~d: Unexpected element ~w'-[File, Line, Tag] ].


                 /*******************************
                 *          XML-TO-TEXT         *
                 *******************************/

unparse_xml([]) -->
    !,
    [].
unparse_xml([H|T]) -->
    !,
    unparse_xml(H),
    unparse_xml(T).
unparse_xml(Atom) -->
    { atom(Atom)
    },
    !,
    atom(Atom).
unparse_xml(element(Name, Attr, Content)) -->
    "<",
    identifier(Name),
    attributes(Attr),
    (   { Content == []
        }
    ->  "/>"
    ;   ">",
        unparse_xml(Content)
    ).

attributes([]) -->
    [].
attributes([H|T]) -->
    attribute(H),
    attributes(T).

attribute(Name=Value) -->
    " ",
    identifier(Name),
    "=",
    value(Value).

identifier(NS:Local) -->
    !,
    "{", atom(NS), "}",
    atom(Local).
identifier(Local) -->
    atom(Local).

atom(Atom, Text, Rest) :-
    atom_codes(Atom, Chars),
    append(Chars, Rest, Text).

value(Value) -->
    { atom_codes(Value, Chars)
    },
    "\"",
    quoted(Chars),
    "\"".

quoted([]) -->
    [].
quoted([H|T]) -->
    quote(H),
    !,
    quoted(T).

quote(0'<) --> "&lt;".
quote(0'>) --> "&gt;".
quote(0'") --> "&quot;".
quote(0'&) --> "&amp;".
quote(X)   --> [X].


                 /*******************************
                 *             XREF             *
                 *******************************/

:- multifile prolog:meta_goal/2.
prolog:meta_goal(process_rdf(_,G,_), [G+2]).
