/**
         
 * Prolog code for the tic-tac-toe game.
         
 * Min-max search via negation.
         
 * Game board via Prolog term.
         
 *
         
 * Warranty & Liability
         
 * To the extent permitted by applicable law and unless explicitly
         
 * otherwise agreed upon, XLOG Technologies AG makes no warranties
         
 * regarding the provided information. XLOG Technologies AG assumes
         
 * no liability that any problems might be solved with the information
         
 * provided by XLOG Technologies AG.
         
 *
         
 * Rights & License
         
 * All industrial property rights regarding the information - copyright
         
 * and patent rights in particular - are the sole property of XLOG
         
 * Technologies AG. If the company was not the originator of some
         
 * excerpts, XLOG Technologies AG has at least obtained the right to
         
 * reproduce, change and translate the information.
         
 *
         
 * Reproduction is restricted to the whole unaltered document. Reproduction
         
 * of the information is only allowed for non-commercial uses. Selling,
         
 * giving away or letting of the execution of the library is prohibited.
         
 * The library can be distributed as part of your applications and libraries
         
 * for execution provided this comment remains unchanged.
         
 *
         
 * Restrictions
         
 * Only to be distributed with programs that add significant and primary
         
 * functionality to the library. Not to be distributed with additional
         
 * software intended to replace any components of the library.
         
 *
         
 * Trademarks
         
 * Jekejeke is a registered trademark of XLOG Technologies AG.
         
 */
         

         
% :- use_module(library(standard/lists)).
         
:- ensure_loaded(library(lists)).
         

         
/*************************************************************/
         
/* Console Play                                              */
         
/*************************************************************/
         

         
% play(+Board)
         
play :- init(X), show_board(X), prompt_board(X, Y), looser(Y).
         

         
% looser(+Board)
         
looser(X) :- win(X, x), !, write('You win.'), nl.
         
looser(X) :- tie(X, o), !, write('Nobody won.'), nl.
         
looser(X) :- best(X, o, Y), !, write('Computer move:'), nl, show_board(Y), winner(Y).
         
looser(_) :- write('I give up.'), nl.
         

         
% winner(+Board)
         
winner(X) :- win(X, o), !, write('I win.'), nl.
         
winner(X) :- prompt_board(X, Y), looser(Y).
         

         
% prompt_board(+Board, -Board)
         
prompt_board(X, Y) :-
         
   prompt_position(R, C),
         
   nth0(R, X, A, Z),
         
   nth0(C, A, _, H),
         
   nth0(C, B, 'x', H),
         
   nth0(R, Y, B, Z),
         
   show_board(Y).
         

         
% prompt_position(-Integer, -Integer)
         
prompt_position(R, C) :-
         
   write('Your move: '), flush_output,
         
   read(M), atom_codes(M, [P, Q]),
         
   R is P-0'a, C is Q-0'1.
         

         
% show_board(+Board)
         
show_board([P,Q,R]) :-
         
   write('  1 2 3'), nl,
         
   write(' +-+-+-+'), nl,
         
   write('a'), show_row(P),
         
   write(' +-+-+-+'), nl,
         
   write('b'), show_row(Q),
         
   write(' +-+-+-+'), nl,
         
   write('c'), show_row(R),
         
   write(' +-+-+-+'), nl.
         

         
% show_row(+Row)
         
show_row([A,B,C]) :-
         
   write('|'), write(A),
         
   write('|'), write(B),
         
   write('|'), write(C),
         
   write('|'), nl.