#!/usr/bin/perl
 
use strict;
use warnings;
 
srand;
 
my @board = (1 .. 8, '');
 
print "\n" x 100;
draw(\@board);
 
print "Your goal is to match this pattern.\n";
print "You may move any square that is next to the blank spot.\n";
print "Press enter when ready. ";
<>;
randomize(\@board);
 
while (1)
{
        draw(\@board);
        check_win(\@board);
        {
                print "Which square will you move? ";
                chomp(my $move = <>);
                exit if $move =~ /^q($|\D)/i;
 
                my ($from) = move_is_ok(\@board, $move);
                redo unless $from;
 
                make_move(\@board, $from, $move);
        }
}
 
sub move_to_index
{
        my $move = shift;
        my ($x, $y) = $move =~ /^([a-c])([1-3])$/;
        (ord($x) - ord('a')) * 3 + $y - 1;
}
 
#checks to make sure a proper piece is selected
sub move_is_ok {
        my $board = shift;
        my ($move) = @_;
 
        my ($x, $y) = $move =~ /^([a-c])([1-3])$/;
        return undef unless $x && $y;
 
        my @neighbors_1 = grep { /[a-c]/ } (chr(ord($x) - 1), chr(ord($x) + 1));
        my @neighbors_2 = grep { /[1-3]/ } ($y - 1, $y + 1);
 
        my @neighbors;
        push @neighbors, map { "${x}${_}" } @neighbors_2;
        push @neighbors, map { "${_}${y}" } @neighbors_1;
 
        grep { !$board->[$_] } map { move_to_index($_) } @neighbors;
}
 
# randomizes order of pieces for initial game play
sub randomize {
        my $board = shift;
 
        $board->[4] = '';
 
        my @squares = (0..3,5..8);
        my @values = (1 .. 8);
 
        while (@squares) {
                my $spot = splice @squares, rand $#squares, 1;
                $board->[$spot] = splice @values, rand $#values, 1;
        }
} 
 
sub make_move
{
        my $board = shift;
        my $from = shift;
        my $to = move_to_index(shift);
 
        @{$board}[$to, $from] = @{$board}[$from, $to];
}
 
# checks for winning sequence
sub check_win {
        my $board = shift;
 
        unless (grep { $_ + 1 != $board->[$_]} grep { length $board->[$_] } 0 .. $#$board) {
                print "YOU WIN!\n";
                exit;
        }
}
 
# draws board
sub draw {
        print "\n" x 100;
 
        print "    1   2   3\n";
        print "  +---+---+---+\n";
        printf " a| %1s | %1s | %1s |\n", @{$_[0]}[0..2];
        print "  +---+---+---+\n";
        printf " b| %1s | %1s | %1s |\n", @{$_[0]}[3..5];
        print "  +---+---+---+\n";
        printf " c| %1s | %1s | %1s |\n", @{$_[0]}[6..8];
        print "  +---+---+---+\n";
        print "\n" x13;
}