/*  $Id$

    Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        jan@swi.psy.uva.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 1985-2002, University of 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 Lesser 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(online_help,
	  [ help/1,
	    help/0,
	    apropos/1
	  ]).
:- use_module(lists, [append/3, member/2]).

:- if(exists_source(library(helpidx))).
:- use_module(library(helpidx)).
no_help :-
	fail.
:- else.
no_help :-
	print_message(warning, no_help_files).
function(_,_,_).			% make check silent
predicate(_,_,_,_,_).
section(_,_,_,_).
:- endif.

:- multifile
	prolog:help_hook/1,		% Generic help hook.
	prolog:show_help_hook/2.	% +Title, +TmpFile

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This module  defines the  online  help  facility of   SWI-Prolog.   It
assumes  (Prolog) index file  at library(help_index)   and  the actual
manual  at library(online_manual).   Output  is piped through  a  user
defined pager, which defaults to `more'.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

%	help/0

help :-
	no_help, !.
help :-
	prolog:help_hook(help), !.
help :-
	help(help/1).

%%	help(+Subject)
%
%	Display online help on specified subject.

help(_) :-
	no_help, !.
help(What) :-
	prolog:help_hook(help(What)), !.
help(What) :-
	give_help(What).

%%	apropos(Pattern)
%	Give a list of subjects that might be appropriate.

apropos(_) :-
	no_help, !.
apropos(What) :-
	prolog:help_hook(apropos(What)), !.
apropos(What) :-
	give_apropos(What).

give_help(Name/Arity) :- !,
	predicate(Name, Arity, _, From, To), !,
	show_help(Name/Arity, [From-To]).
give_help(Section) :-
	user_index(Index, Section), !,
	section(Index, _, From, To),
	show_help(Section, [From-To]).
give_help(Function) :-
	atom(Function),
	atom_concat('PL_', _, Function),
	function(Function, From, To), !,
	show_help(Function, [From-To]).
give_help(Name) :-
	findall(From-To, predicate(Name, _, _, From, To), Ranges),
	Ranges \== [], !,
	show_help(Name, Ranges).
give_help(What) :-
	format('No help available for ~w~n', [What]).

%%	show_help(+ListOfRanges)
%	Pipe specified ranges of the manual through the user defined pager

:- dynamic asserted_help_tmp_file/1.

help_tmp_file(X) :-
	asserted_help_tmp_file(X), !.
help_tmp_file(X) :-
	tmp_file(manual, X),
	asserta(asserted_help_tmp_file(X)).

write_ranges_to_file(Ranges, Outfile) :-
	online_manual_stream(Manual),
	help_tmp_file(Outfile),
	open(Outfile, write, Output),
	show_ranges(Ranges, Manual, Output),
	close(Manual),
	close(Output).

show_help(Title, Ranges) :-
	predicate_property(prolog:show_help_hook(_,_), number_of_clauses(N)),
	N > 0,
	write_ranges_to_file(Ranges, TmpFile),
	prolog:show_help_hook(Title, TmpFile).
show_help(_, Ranges) :-
	current_prolog_flag(pipe, true), !,
	online_manual_stream(Manual),
	pager_stream(Pager),
	catch(show_ranges(Ranges, Manual, Pager), _, true),
	close(Manual),
	catch(close(Pager), _, true).
show_help(_, Ranges) :-
	online_manual_stream(Manual),
	show_ranges(Ranges, Manual, user_output).

show_ranges([], _, _) :- !.
show_ranges([FromLine-ToLine|Rest], Manual, Pager) :-
	line_start(FromLine, From),
	line_start(ToLine, To),
	seek(Manual, From, bof, _),
	Range is To - From,
	copy_chars(Range, Manual, Pager),
	nl(Pager),
	show_ranges(Rest, Manual, Pager).

%%	copy_chars(+Count, +FromStream, +ToStream)
%
%	Note: stream is binary to deal with byte offsets. As the data is
%	ISO Latin-1 anyway, this is fine.

copy_chars(N, From, To) :-
	get0(From, C0),
	copy_chars(N, From, To, C0).

copy_chars(N, _, _, _) :-
	N =< 0, !.
copy_chars(N, _, To, _) :-
	0 =:= N mod 4096,
	flush_output(To),
	fail.
copy_chars(N, From, To, C) :-
	get_byte(From, C1),
	(   C1 == 8,			% backspace
	    \+ current_prolog_flag(write_help_with_overstrike, true)
	->  get_byte(From, C2),
	    NN is N - 2,
	    copy_chars(NN, From, To, C2)
	;   put_printable(To, C),
	    NN is N - 1,
	    copy_chars(NN, From, To, C1)
	).

put_printable(_, 12) :- !.
put_printable(_, 13) :- !.
put_printable(_, -1) :- !.
put_printable(To, C) :-
	put_code(To, C).

online_manual_stream(Stream) :-
	find_manual(Manual),
	open(Manual, read, Stream, [type(binary)]).

pager_stream(Stream) :-
	find_pager(Pager),
	open(pipe(Pager), write, Stream).

find_manual(Path) :-
	absolute_file_name(library('MANUAL'), Path, [access(read)]).

find_pager(Pager) :-
	getenv('PAGER', Pager), !.
find_pager(more).

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Set the write_help_with_overstrike feature.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

set_overstrike_feature :-
	current_prolog_flag(write_help_with_overstrike, _), !.
set_overstrike_feature :-
	(   getenv('TERM', xterm)
	->  Flag = true
	;   Flag = false
	),
	create_prolog_flag(write_help_with_overstrike, Flag, []).

:- initialization set_overstrike_feature.

%%	line_start(Line, Start) is det.
%
%	True if Start is the byte position at which Line starts.

:- dynamic
	start_of_line/2.

line_start(Line, Start) :-
	start_of_line(Line, Start), !.
line_start(Line, Start) :-
	line_index,
	start_of_line(Line, Start).


%%	line_index
%
%	Create index holding the byte positions for the line starts

line_index :-
	start_of_line(_,_), !.
line_index :-
	online_manual_stream(Stream),
	set_stream(Stream, encoding(octet)),
	call_cleanup(line_index(Stream, 1), close(Stream)).

line_index(Stream, LineNo) :-
	byte_count(Stream, ByteNo),
	assert(start_of_line(LineNo, ByteNo)),
	(   at_end_of_stream(Stream)
	->  true
	;   LineNo2 is LineNo+1,
	    skip(Stream, 10),
	    line_index(Stream, LineNo2)
	).


		 /*******************************
		 *	       APROPOS		*
		 *******************************/

give_apropos(Atom) :-
	ignore(predicate_apropos(Atom)),
	ignore(function_apropos(Atom)),
	ignore(section_apropos(Atom)).

apropos_predicate(Pattern, Name, Arity, Summary) :-
	predicate(Name, Arity, Summary, _, _),
	(   apropos_match(Pattern, Name)
	->  true
	;   apropos_match(Pattern, Summary)
	).

predicate_apropos(Pattern) :-
	findall(Name-Arity-Summary,
		apropos_predicate(Pattern, Name, Arity, Summary),
		Names),
	forall(member(Name-Arity-Summary, Names),
	       format('~w/~w~t~30|~w~n', [Name, Arity, Summary])).

function_apropos(Pattern) :-
	findall(Name, (function(Name, _, _),
		       apropos_match(Pattern, Name)), Names),
	forall(member(Name, Names),
	       format('Interface Function~t~30|~w()~n', Name)).

section_apropos(Pattern) :-
	findall(Index-Name, (section(Index, Name, _, _),
		       apropos_match(Pattern, Name)), Names),
	forall(member(Index-Name, Names),
	       (user_index(Index, UserIndex),
		format('Section ~w~t~30|"~w"~n', [UserIndex, Name]))).

apropos_match(Needle, Haystack) :-
	sub_atom_icasechk(Haystack, _, Needle).

user_index(List, Index) :-
	is_list(List), !,
	to_user_index(List, S),
	name(Index, S).
user_index(List, Index) :-
	to_system_index(Index, List).

to_user_index([], []).
to_user_index([A], S) :- !,
	name(A, S).
to_user_index([A|B], S) :-
	name(A, S0),
	append(S0, [0'-], S1),
	append(S1, Rest, S),
	to_user_index(B, Rest).

to_system_index(A-B, I) :- !,
	to_system_index(A, C),
	integer(B),
	append(C, [B], I).
to_system_index(A, [A]) :-
	integer(A).

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

:- multifile
        prolog:message/3.

prolog:message(no_help_files) -->
        [ 'The online help files (helpidx.pl, MANUAL) are not installed.', nl,
	  'If you installed SWI-Prolog from GIT/CVS, please consult', nl,
	  'README.doc and README.git in the toplevel of the sources.'
	].


