% sokoban\board.pl: board layout for Sokoban puzzle
%     ... learning Prolog with SWI-Prolog
% Author: Javier G. Sogo

/***************************************************************************/
/* Sokoban board: layout and relation rules                                */
/***************************************************************************/
/* The board is built based on adjacent squares using vertical (up|down)   */
/* and horizontal (right|left) directions. This set of rules defines the   */
/* relation between these concepts and the neighbourhoods for any square   */
/***************************************************************************/

/* Available directions                                                    */
direction(up).
direction(down).
direction(left).
direction(right).
direction(cenit).

/* Opposite directions                                                     */
opposite_dir(up, down).
opposite_dir(down, up).
opposite_dir(left, right).
opposite_dir(right, left).

/* Adjacent positions given a direction                                    */
:- table neib/3.
neib(P1, P2, up) :- top(P1, P2).
neib(P1, P2, down) :- top(P2, P1).
neib(P1, P2, right) :- right(P1, P2).
neib(P1, P2, left) :- right(P2, P1).

/* A corner is a square which has at most one neighbour square in vertical */
/* and one in horizontal. It is defined using the counter-rule noncorner.  */
:- table corner/1.
corner(X) :- \+ noncorner(X).
noncorner(X) :- top(_,X),top(X,_).
noncorner(X) :- right(_,X),right(X,_).


%%%%%%%%%%%%%%%%%%%%%%
% Unit tests
%%%%%%%%%%%%%%%%%%%%%%
:- begin_tests(board).                         
              %test(bottom) :- top(x1y3, x1y2), bottom(x1y2, x1y3).
:- end_tests(board).

%:- run_tests.