#!perl

HELP "undo <transactionID>" => "Undo a transaction";

my $filename = ".revbank.undo";

sub command :Tab(undo) ($self, $cart, $command,  @) {
    $command eq 'undo' or return NEXT;

    $cart->size and return ABORT, "Undo is not available mid-transaction.";

    return "Transaction ID", \&undo;
}

sub undo($self, $cart, $tid, @) {
    open my $in,  '<', $filename or die "$filename: $!";
    open my $out, '>', "$filename.$$" or die "$filename.$$: $!";
    my $description = "Undo $tid";

    my $entry;

    while (defined(my $line = readline $in)) {
        if ($line =~ /^\Q$tid\E\s/) {
            my (undef, $user, $delta) = split " ", $line;

            $entry ||= $cart->add(0, $description);
            $entry->{FORCE} = 1;

            $entry->add_contra($user, $delta, "Undo $tid");
        } else {
            print {$out} $line;
        }
    }
    close $in;
    close $out or die $!;
    if ($cart->size) {
        rename "$filename.$$", $filename or die $!;
        $cart->checkout('**UNDO**');
    } else {
        return ABORT, "Transaction ID '$tid' not found in undo log.";
    }

    return ACCEPT;
}

sub hook_user_balance($class, $username, $old, $delta, $new, $transaction_id, @) {
    open my $fh, '>>', $filename or die "$filename: $!";
    print {$fh} join " ", $transaction_id, $username, -$delta, now(), "\n";
    close $fh or die "$filename: $!";
}