#!perl

my $err_stacked = "Stacked repetition is not supported.";
my $err_multi = "Repetition not supported in multi-user transactions.";
my $err_pfand = "Plugins 'pfand' and 'repeat' cannot be combined.";

my $limit = 24;
my $err_limit = "Repetition is limited at $limit items.";

sub _do_repeat {
    my ($cart, $item, $num) = @_;

    my $data = $item->{data};
    $data->{_repeated} = 1;

    $cart->add( @{ $item }{qw/user amount description/}, $data ) for 2..$num;
}

sub command {
    my ($self, $cart, $command) = @_;

    my @items = $cart->select_items;
    my $last = $items[-1];

    return ABORT, $err_pfand if grep $_->{is_pfand}, @items;

    my ($pre, $post) = $command =~ /^(\d+)?[x*](\d+)?$/
        or return NEXT;

    return NEXT if $pre and $post;  # 123x123 -> invalid syntax

    return REJECT, $err_multi if $cart->is_multi_user;

    if ($post) {
        return REJECT, $err_limit if $post > $limit;
        return ABORT, "Can't repeat an empty transaction." if not $cart->size;
        return REJECT, $err_stacked if $last->{_repeated};

        _do_repeat($cart, $last, $post);
        return ACCEPT;
    }

    my $item_replaced;

    if (not $pre and not $post) {
        # Lone operator. Convert withdrawal into repetition.

        if ($last->{is_withdrawal}) {
            $pre = abs $last->{amount};
            $pre == int $pre or return REJECT, "Repeat only works on integers.";
            $cart->delete($last->{user}, -1);
            $item_replaced = 1;
        } elsif (not $cart->size) {
            return ABORT, "Can't repeat an empty transaction.";
        }
    }

    if ($pre) {
        $pre = abs $pre;  # withdrawal is negative

        return REJECT, $err_limit if $pre > $limit;
        $cart->add(undef, 0, "Next product repeated $pre times", { _repeat => abs $pre });
        return ACCEPT;
    }

    return REJECT, $err_stacked if $last->{_repeated};
    return "Multiply previous product by", \&repeat;
}

sub repeat {
    my ($self, $cart, $arg) = @_;

    $arg =~ /^\d+$/ and $arg > 0
        or return REJECT, "Invalid value.";

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

    my @items = $cart->select_items;
    my $last = $items[-1];

    _do_repeat($cart, $last, $arg);
    return ACCEPT;
}

sub hook_added {
    my ($self, $cart, $user, $item) = @_;
    $cart->size >= 2 or return;

    my @planned = $cart->select_items('_repeat');
    my @repeated = $cart->select_items('_repeated');
    return ABORT, $err_multi if $cart->is_multi_user and @planned || @repeated;
    return ABORT, "Multiple repeats queued; I'm confused." if @planned > 1;
    return if not @planned;

    my @items = $cart->select_items;
    return ABORT, $err_pfand if grep $_->{is_pfand}, @items;

    for my $i (0 .. $#items - 1) {
        my $item = $items[$i];
        $item->{_repeat} or next;

        my $next = $items[$i + 1];

        return ABORT, $err_stacked if $next->{_repeat};

        my $num = $item->{_repeat};
        $cart->delete($item->{user}, $i);

        _do_repeat($cart, $next, $num);

        return;
    }
}