use 5.20.0;

use List::AllUtils qw/ first_index indexes /;

my @code = split '', 'abcdefgh'; #fgh';  # agcebfdh

my @instructions = <>;

use Algorithm::Combinatorics qw(permutations);

my $comb = permutations(\@code);

while( my $c = $comb->next ) {
    my @code = @$c;
    my $o = "@code";

    for( @instructions ) {
        if( /swap position (\d+) with position (\d+)/ ) {
            @code[ $1, $2 ] = @code[$2, $1];
        }
        elsif( /swap letter (.) with letter (.)/ ) {
            my @x = indexes { $_ eq $1  or $_ eq $2 } @code;
            @code[ @x ] = @code[ reverse @x ];
        }
        elsif( /reverse positions (\d+) through (\d+)/ ) {
            @code[ $1..$2 ] = reverse @code[ $1..$2 ];
        }
        elsif( /rotate left (\d+)/ ) {
            push @code, shift @code for 1..$1;
        }
        elsif( /rotate right (\d+)/ ) {
            unshift @code, pop @code for 1..$1;
        }
        elsif( /move position (\d+) to position (\d+)/ ) {
            my($x) = splice @code, $1, 1;
            splice @code, $2, 0, $x;
        }
        elsif( /rotate based on position of letter (.)/ ) {
            my $i = first_index { $_ eq $1 } @code;
            $i++ if $i >= 4;
            $i++;
            unshift @code, pop @code for 1..$i;
        }
        else {
            die $_;
        }
    }

    say "@code";

    die $o if "@code" eq 'f b g d c e a h';

}