#! perl -sw
use strict;

sub roundRobin {
	my @q;
	my $next = -1;

	my %self = (
		values	=> sub {
			return @q[@_];
		},
		size	=> sub {
			return scalar @q;
		},
		pos		=> sub {
			return 0+$next;
		},
		add		=> sub {
			return push @q, @_;
		},
		del		=> sub {
			my ($i, %del) = (0);
			@del{@_} = undef;
			@q = grep { exists $del{$_} ? ($next -= $i <= $next) && 0 : ++$i } @q;
			return 1;
		},
		next	=> sub {
			return undef if not @q;
			++$next;
			$next %= @q;
			return $q[$next];
		},
		shuffle => sub {
			my $t;
			$t = $_ + rand @q - $_ and @q[$_, $t] = @q[$t, $_] for (0..$#q);
		},
	);
	return %self;
}

my %rr = roundRobin();

$rr{add}( 'a' .. 'z' );
print $rr{size}(), $rr{values}(0..$rr{size}()-1), $/;
$rr{add}( 'k' .. 'q' );
print $rr{size}(), $rr{values}(0..$rr{size}()-1), $/;
$rr{shuffle}();

while ( my $item = $rr{next}() ) {
	my $pos = $rr{pos}();
	print " @{[$rr{values}( 0 .. $pos -1 )]}".
		"<@{[$rr{values}($pos)]}>".
		"@{[$rr{values}($pos+1..$rr{size}()-1 )]}";
	if (rand(8) < 1) {
		my $new = chr(95+rand 26);
		$rr{add}( $new );
		print "\t --added ", $new;
	}
	if (rand(8) < 1) {
		my $toDelete = $item;
		$toDelete = do {
			$rr{values}( rand( $rr{size}()) )
		} until $toDelete ne $item;
		print "\t--deleting: '", $toDelete;
		$rr{del}( $toDelete );
	}
	print $/;
	select undef, undef, undef, .5;
}