/*  $Id$

    Part of SWI-Prolog

    Author:        Markus Triska
    E-mail:        triska@gmx.at
    WWW:           http://www.swi-prolog.org
    Copyright (C): 2005, Markus Triska

    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., 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.
*/

%%%%%%% clp_distinct.pl - Weak arc consistent all_distinct/1 constraint %%%%%

% For details, see Neng-Fa Zhou, 2005:
%      "Programming Finite-Domain Constraint Propagators in Action Rules"

:- module(clp_distinct,
	[
		vars_in/2,
		vars_in/3,
		all_distinct/1
	]).
:- use_module(library(lists)).

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This library uses the following arribute value:

	dom_neq(Domain, Left, Right)

Domain is an unbounded  (GMP)  integer   representing  the  domain  as a
bit-vector, meaning N is in the domain iff 0 =\= Domain /\ (1<<N).

Left and Right are both lists of lists of variables. Each of those lists
corresponds to one all_distinct constraint the  variable is involved in,
and "left" and "right" means literally which  variables are to the left,
and which to the right in the first, second etc. of those constraints.

all_distinct([A,B,C,D]), all_distinct([X,Y,C,F,E]) causes the following 
attributes for "C":

	Left:  [[A,B],[X,Y]]
	Right: [[D],[F,E]]
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */


vars_in(Xs, From, To) :-
	Bitvec is (1<<(To+1)) - (1<<From),
	vars_in_(Xs, Bitvec).

vars_in(Xs, Dom) :-
	domain_bitvector(Dom, 0, Bitvec),
	vars_in_(Xs, Bitvec).

vars_in_([], _).
vars_in_([V|Vs], Bitvec) :-
	( var(V) ->
		( get_attr(V, clp_distinct, dom_neq(VBV,VLeft,VRight)) ->
			Bitvec1 is VBV /\ Bitvec,
		  	Bitvec1 =\= 0,
		        ( popcount(Bitvec1) =:= 1 ->
				V is msb(Bitvec1)
			;
				put_attr(V, clp_distinct, dom_neq(Bitvec1,VLeft,VRight))
			)
		;
			( popcount(Bitvec) =:= 1 ->
				V is msb(Bitvec)
			;
				put_attr(V, clp_distinct, dom_neq(Bitvec, [], []))
			)
		)
	;
		0 =\= Bitvec /\ (1<<V)
	),
	vars_in_(Vs, Bitvec).

domain_bitvector([], Bitvec, Bitvec).
domain_bitvector([D|Ds], Bitvec0, Bitvec) :-
	Bitvec1 is Bitvec0 \/ (1 << D),
	domain_bitvector(Ds, Bitvec1, Bitvec).
	

all_distinct(Ls) :-
	all_distinct(Ls, []),
	outof_reducer(Ls).

outof_reducer([]).
outof_reducer([X|Xs]) :-
	( var(X) ->
		get_attr(X, clp_distinct, dom_neq(Dom,Lefts,Rights)),
		outof_reducer(Lefts, Rights, X, Dom)
	;
		true
	),
	outof_reducer(Xs).

all_distinct([], _).
all_distinct([X|Right], Left) :-
	\+ list_contains(Right, X),
	outof(X, Left, Right),
	all_distinct(Right, [X|Left]).


outof(X, Left, Right) :-
	( var(X) ->
		get_attr(X, clp_distinct, dom_neq(Dom, XLefts, XRights)),
		put_attr(X, clp_distinct, dom_neq(Dom, [Left|XLefts], [Right|XRights]))
	;
		exclude_fire([Left], [Right], X)
	).


exclude_fire(Lefts, Rights, E) :-
	Mask is \ ( 1 << E),
	exclude_fire(Lefts, Rights, E, Mask).

exclude_fire([], [], _, _).
exclude_fire([Left|Ls], [Right|Rs], E, Mask) :-
	exclude_list(Left, E, Mask),
	exclude_list(Right, E, Mask),
	exclude_fire(Ls, Rs, E, Mask).


exclude_list([], _, _).
exclude_list([V|Vs], Val, Mask) :-
	( var(V) ->
		get_attr(V, clp_distinct, dom_neq(VDom0,VLefts,VRights)),
		VDom1 is VDom0 /\ Mask,
		VDom1 =\= 0,
		( popcount(VDom1) =:= 1 ->
			V is msb(VDom1)
		;
			put_attr(V, clp_distinct, dom_neq(VDom1,VLefts,VRights))
		)
	;
		V =\= Val
	),
	exclude_list(Vs, Val, Mask).

attr_unify_hook(dom_neq(Dom,Lefts,Rights), Y) :-
	( ground(Y) ->
		Dom /\ (1 << Y) =\= 0,
		exclude_fire(Lefts, Rights, Y)
	;
		
		\+ lists_contain(Lefts, Y),
		\+ lists_contain(Rights, Y),
		( get_attr(Y, clp_distinct, dom_neq(YDom0,YLefts0,YRights0)) ->
			YDom1 is YDom0 /\ Dom,
			YDom1 =\= 0,
			( popcount(YDom1) =:= 1 ->
				Y is msb(YDom1)
			;
				append(YLefts0, Lefts, YLefts1),
				append(YRights0, Rights, YRights1),
				put_attr(Y, clp_distinct, dom_neq(YDom1,YLefts1,YRights1))
			)
		;
			put_attr(Y, clp_distinct, dom_neq(Dom,Lefts,Rights))
		)
	).

lists_contain([X|Xs], Y) :-
	( list_contains(X, Y) ->
		true
	;
		lists_contain(Xs, Y)
	).

list_contains([X|Xs], Y) :-
	( X == Y ->
		true
	;
		list_contains(Xs, Y)
	).


outof_reducer([], [], _, _).
outof_reducer([L|Ls], [R|Rs], Var, Dom) :-
	append(L, R, Others),
	N is popcount(Dom),
	num_subsets(Others, Dom, 0, Num),
	( Num >= N ->
		fail
	; Num =:= (N - 1) ->
		reduce_from_others(Others, Dom)
	;
		true
	),
	outof_reducer(Ls, Rs, Var, Dom).


reduce_from_others([], _).
reduce_from_others([X|Xs], Dom) :-
	( var(X) ->
		get_attr(X, clp_distinct, dom_neq(XDom,XLeft,XRight)),
		( is_subset(Dom, XDom) ->
			true
		;
			NXDom is XDom /\ \Dom,
			NXDom =\= 0,
			( popcount(NXDom) =:= 1 ->
				X is msb(NXDom)
			;
				put_attr(X, clp_distinct, dom_neq(NXDom,XLeft,XRight))
			)
		)
	;
		true
	),
	reduce_from_others(Xs, Dom).

num_subsets([], _Dom, Num, Num).
num_subsets([S|Ss], Dom, Num0, Num) :-
	( var(S) ->
		get_attr(S, clp_distinct, dom_neq(SDom,_,_)),
		( is_subset(Dom, SDom) ->
			Num1 is Num0 + 1
		;
			Num1 = Num0
		)
	;
		Num1 = Num0
	),
	num_subsets(Ss, Dom, Num1, Num).


   % true iff S is a subset of Dom - should be a GMP binding (subsumption)

is_subset(Dom, S) :-
	S \/ Dom =:= Dom.

attr_portray_hook(dom_neq(Dom,_,_), _) :-
	Max is msb(Dom),
	Min is lsb(Dom),
	write(Min-Max).
