package Tie::ScalarIter;

sub TIESCALAR {
  my ($class, $init, $start) = @_;
  bless [ $init, $start, length($init) ], $class;
}

sub FETCH {
  my $s = shift;

  my $ret = $s->[0];
  my $p = $s->[2] - 1;

  while (1) {
    substr($s->[0], $p, 1) =~ tr/acgnt/cgnta/;
    last if substr($s->[0], $p--, 1) ne $s->[1];
    $s->[0] = "$s->[1]$s->[0]", $s->[2]++, last if $p < 0;
  }

  return $ret;
}

sub STORE {
  my $s = shift;
  my $rep = shift;

  if (ref $rep) { @$s = (@$rep, length $rep->[0]) }
  else { (@$s[0,2] = ($rep, length $rep) }
}

1;