/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@uva.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 2009, 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 General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  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(portray_text,
	  [ portray_text/1,		% +Bool
	    set_portray_text/2		% +Name, +Value
	  ]).
:- use_module(library(error)).

/** <module> Portray text

A Prolog string is a list of character-codes: (small) integers, which
results in output like this:

    ==
    ?- writeln("hello").
    [104, 101, 108, 108, 111]
    ==

Unless you know the Unicode tables by   heart, this is pretty unpleasant
for debugging. Loading this library  makes   the  toplevel  and debugger
print strings with at least 3 characters  as "text ...". Of course, this
is an ambigious operation because nobody can know whether [65,66] should
be written as "AB" or a list: to  Prolog they are the same. Therefore it
is imported that the user  is  aware   of  the  fact that this heuristic
conversion  is  enabled.  This  is  why  this  library  must  be  loaded
explicitely to enable this conversion.

@tbd	Allow setting the character-codes we try to convert
*/

:- dynamic
	do_portray_text/1,
	portray_text_option/2.

do_portray_text(true).

portray_text_option(min_length, 3).
portray_text_option(ellipsis,  30).

%%	portray_text(+Boolean) is det.
%
%	If =true=, write lists of character   codes as "..." to simplify
%	debugging.

portray_text(OnOff) :-
	must_be(boolean, OnOff),
	retractall(do_portray_text(_)),
	assert(do_portray_text(OnOff)).

%%	set_portray_text(+Name, +Value) is det.
%
%	Set options for writing lists as strings.  Options are
%
%	    * min_length
%	    Only consider lists that are at least this long
%	    * ellipsis
%	    Write strings that are longer as "start...end"

set_portray_text(min_length, N) :-
	must_be(nonneg, N),
	retractall(portray_text_option(min_length, _)),
	assert(portray_text_option(min_length, N)).
set_portray_text(ellipsis, N) :-
	must_be(nonneg, N),
	retractall(portray_text_option(ellipsis, _)),
	assert(portray_text_option(ellipsis, N)).


:- multifile
	user:portray/1.
:- dynamic
	user:portray/1.

user:portray(Codes) :-
	do_portray_text(true),
	'$skip_list'(Length, Codes, Tail),
	portray_text_option(min_length, MinLen),
	Length >= MinLen,
	all_ascii(Codes),
	portray_text_option(ellipsis, IfLonger),
	put_char('"'),
	(   Length > IfLonger
	->  First is IfLonger - 5,
	    Skip is Length - 5,
	    skip_first(Skip, Codes, Rest),
	    put_n_codes(First, Codes),
	    format('...', [])
	;   Rest = Codes
	),
	(   var_or_numbered(Tail)
	->  put_var_codes(Rest)
	;   format('~s', [Rest])
	),
	put_char('"').

put_n_codes(N, [H|T]) :-
	N > 0, !,
	emit_code(H),
	N2 is N - 1,
	put_n_codes(N2, T).
put_n_codes(_, _).

skip_first(N, [_|T0], T) :-
	succ(N2, N), !,
	skip_first(N2, T0, T).
skip_first(_, L, L).

put_var_codes(Var) :-
	var_or_numbered(Var), !,
	format('|~p', [Var]).
put_var_codes([]).
put_var_codes([H|T]) :-
	emit_code(H),
	put_var_codes(T).

emit_code(0'\b) :- !, format('\\b').
emit_code(0'\r) :- !, format('\\r').
emit_code(0'\n) :- !, format('\\n').
emit_code(0'\t) :- !, format('\\t').
emit_code(C) :- put_code(C).

all_ascii(Var) :-
	var_or_numbered(Var), !.
all_ascii([]).
all_ascii([H|T]) :-
	isascii(H),
	all_ascii(T).

isascii(Term) :-
	integer(Term),
	ascii_code(Term), !.

ascii_code(9).
ascii_code(10).
ascii_code(13).				% ok ...
ascii_code(C) :-
	between(32, 126, C).

var_or_numbered(Var) :-
	var(Var), !.
var_or_numbered('$VAR'(_)).
