DOCUMENT();

loadMacros('PGstandard.pl', 'MathObjects.pl', 'PGML.pl', 'parserMultiAnswer.pl', 'PGcourse.pl');

@letters = ('A' .. 'Z');
Context()->strings->add(map { $_ => {} } @letters);

$num_letters = 6;

@my_letters        = (map { splice(@letters, random(0, $#letters), 1) } 1 .. $num_letters);
$my_letters_string = join '', @my_letters;

@tmp         = (0 .. $num_letters - 1);
@derangement = @my_letters[ map { splice(@tmp, random(0, $#tmp, 1), 1) } @tmp ];
for my $i (0 .. $num_letters - 2) {
	if ($derangement[$i] eq $my_letters[$i]) {    # swap with letter on the right
		$derangement[$i] = $derangement[ $i + 1 ];
		$derangement[ $i + 1 ] = $my_letters[$i];
	}
}
if ($derangement[-1] eq $my_letters[-1]) {
	$derangement[-1] = $derangement[0];
	$derangement[0]  = $my_letters[-1];
}

$der_string = join '', @derangement;

$multi_ans = MultiAnswer(@derangement)->with(
	singleResult  => 1,
	separator     => ' ',
	tex_separator => '\hbox{ }',
	checker       => sub {
		my ($correct, $student) = @_;

		my $stu_der_string = join '', @$student;
		Value::Error('Repeated letters detected') if ($stu_der_string =~ /([a-zA-Z])~~1/);
		Value::Error('Invalid letters entered') if ($stu_der_string !~ /^[$der_string]*$/);

		for my $i (0 .. $num_letters - 1) {
			if ($my_letters[$i] eq $student->[$i]) {
				$multi_ans->setMessage($i + 1, "$student->[$i] in original spot");
				return 0;
			}
		}

		return 1;
	}
);

BEGIN_PGML
All questions are about the following ordering of letters:[:quad :] [$my_letters_string]

a. Give a derangement of the original ordering. Enter one letter in each of the blanks.

[_]{$multi_ans} [_]{$multi_ans} [_]{$multi_ans} [_]{$multi_ans} [_]{$multi_ans} [_]{$multi_ans}
END_PGML

ENDDOCUMENT();