use 5.36.0;
use lib '.';

use DDP;

use Part1;

package Part2;

use Math::Vector::Real;
use List::AllUtils qw/ uniq /;

my @directions = map { V(@$_) } [ -1, 0 ], [ 0, 1 ], [ 1, 0 ], [ 0, -1 ];

sub copy_grid ($grid) {
    return [ map { [@$_] } @$grid ];
}

sub add_vectors($x,$y) {
    return [ $x->[0]+$y->[0],$x->[1]+$y->[1]];
}

sub do_the_round ($grid) {
    my $guard             = Part1::find_guard($grid);
    my $current_direction = 0;

    my %seen;

    my $loop = 0;

    while () {
        my $ahead = $guard + $directions[$current_direction];
        last unless Part1::inside_grid( $grid, $ahead );
        if ( $grid->[ $ahead->[0] ][ $ahead->[1] ] eq '#' ) {
            $current_direction++;
            $current_direction %= @directions;
            redo;
        }
        $guard = $ahead;
        if ( $seen{"$guard"}{$current_direction} ) {
            $loop = 1;
            last;
        }
        $seen{"$guard"}{$current_direction}++;
    }

    return {
        loop => $loop,
        seen => [
              keys %seen
        ]
    };
}

sub solve ($grid) {
    my $guard             = Part1::find_guard($grid);
    my $current_direction = 0;

    my $r = do_the_round($grid);

    my $loops = 0;

    for my $loc ( grep { $grid->[ $_->[0] ][ $_->[1] ] ne '^' }
        map { [/(\d+)/g] } $r->{seen}->@* ) {
        my $copy = copy_grid($grid);
        $copy->[ $loc->[0] ][ $loc->[1] ] = '#';
        $loops++ if do_the_round($copy)->{loop};
    }

    return $loops;
}

1;