#!perl

HELP "<N>x, <N>*" => "Set quantity of previous/next product";
HELP "-<N>, +<N>, *<N>, x<N>" => "Change quantity of previous product";

my $err_stacked = "Stacked repetition is not supported.";
my $err_pfand = "Plugins 'pfand' and 'repeat' cannot be combined.";
my $err_nope = "Entry does not support repetition.";
my $err_postfix = "Addition/substraction is only supported the other way around.";

my $limit = 200;
my $err_limit = "Repetition is limited at $limit items.";

sub command($self, $cart, $command, @) {
    my ($lhs, $op, $rhs) = $command =~ /^(\d+)?([x*+-])(\d+)?$/
        or return NEXT;

    return ABORT, $err_pfand if $cart->entries('is_pfand');

    my $last = $cart->selected;

    return NEXT if $lhs and $rhs;  # 123x123 -> invalid, likely user or product

    if ($lhs) {
        return REJECT, $err_postfix if $op eq '+' or $op eq '-';

        $lhs = abs $lhs;  # withdrawal is negative

        return REJECT, $err_limit if $lhs > $limit;
        $cart
            ->add(0, "?  (The next thing you add will be multiplied.)", { _repeat => 1, refuse_checkout => 1 })
            ->quantity($lhs);
        return ACCEPT;
    }

    return ABORT, "Can't modify an empty transaction." if not $cart->size;
    return REJECT, $err_nope if $last->attribute('no_repeat');

    if ($rhs) {
        return REJECT, $err_limit if $rhs > $limit;

        if ($op eq '+') {
            my $new = $last->quantity + $rhs;
            return REJECT, $err_limit if $new > $limit;

            $last->quantity($new);
            return ACCEPT;
        }
        if ($op eq '-') {
            my $new = $last->quantity - $rhs;
            if ($new > 0) {
                $last->quantity($new);
            } else {
                $cart->delete($last);
                print "Deleted.\n";
            }
            return ACCEPT;
        }

        # $op is not + or -, so it must be * (or x).
        return REJECT, $err_stacked if $last->multiplied;
        $last->quantity($rhs);
        return ACCEPT;
    }

    if ($op eq '+' or $op eq '-') {
        $self->{op} = $op;
        return "$op how many?", \&plusminus;
    }

    # $op is not + or -, so it must be * (or x).
    return REJECT, $err_stacked if $last->multiplied;
    return "Multiply previous product by", \&repeat;
}

sub repeat($self, $cart, $arg, @) {
    $arg =~ /^\d+$/ and $arg > 0
        or return REJECT, "Invalid value.";

    return REJECT, $err_limit if $arg > $limit;

    $cart->selected->quantity($arg);
    return ACCEPT;
}

sub plusminus($self, $cart, $arg, @) {
    $arg =~ /^\d+$/ and $arg > 0
        or return REJECT, "Invalid value.";

    my $last = $cart->selected;
    my $new = $last->quantity;
    $new += $arg if $self->{op} eq '+';
    $new -= $arg if $self->{op} eq '-';

    return REJECT, $err_limit if $new > $limit;
    if ($new < 0) {
        $cart->delete($last);
        print "Deleted.\n";
    } else {
        $cart->selected->quantity($new);
    }
    return ACCEPT;
}

sub hook_added_entry($class, $cart, $entry, @) {
    $cart->size >= 2 or return;

    my @entries = $cart->entries;
    my @planned = $cart->entries('_repeat');


    return if not @planned;
    return ABORT, "Multiple repeats queued; I'm confused." if @planned > 1;
    return ABORT, $err_pfand if $cart->entries('is_pfand');
    return if $planned[0] == $entries[-1];
    return ABORT, "Queued repeat is not the penultimate item; I'm confused"
        if $entries[-2] != $planned[0];

    my $num = $planned[0]->quantity;
    if ($entries[-1]->attribute('no_repeat')) {
        print $err_nope, "\n";
        $num = 1;
    }

    $cart->delete($planned[0]);
    $entries[-1]->quantity($num);
}