use strict;
use warnings;

my $tape = bless {
    desc  => "5-state machine, theoretical max steps: >47,176,870",
    step  => 630,
    delta => 54,
    pos   => 224,
    cells => [],
};

push @{$tape->{cells}}, int rand (1.7) || ' ' for 1 .. 500;
$tape->show (82);

print <<ORG;

              5-state machine, theoretical max steps: >47,176,870
Step: 630
Current delta: 54
--------------------------------------------------------------------------------­-
1               2                                                                2
8     9         0         1         2         3          4         5         6   6
4567890123456789012345678901234567890123456789001234567890123456789012345678901234
----------------------------------------v---------------------------------------­-
1    11     1     1          1         11     111              1           11
ORG

sub show {
    my ($tape, $width) = @_;
    my $first   = int ($tape->{pos} - $width / 2);
    my $last    = $first + $width - 1;
    my $mag     = int (log ($last) / log (10)) + 1;
    my $divider = '-' x $width;

    $first = sprintf '%0*d', $mag, $first;
    $last  = sprintf '%0*d', $mag, $last;
    printf "%66s\n", $tape->{desc};
    print "Step: $tape->{step}\n";
    print "Current delta: $tape->{delta}\n";
    print $divider, "\n";

    for my $digit (0 .. $mag - 1) {
        my $lastDigit = -1;
        my $row;

        for my $num ($first .. $last) {
            my $newDigit = substr sprintf ("%${mag}d", $num), $digit, 1;
            $row .= $num != $last && $newDigit eq $lastDigit ? ' ' : $newDigit;
            $lastDigit = $newDigit;
        }

        print "$row\n";
    }

    substr $divider, $width / 2, 1, 'v';
    print $divider, "\n";
    print @{$tape->{cells}}[$first .. $last], "\n";
}