package MusicBrainz::Server::Data::Role::Merge;
use Moose::Role;

use Carp qw( croak );

requires '_merge_impl';

# XXX HACK
# This is a bit ugly as Data::Entity already provides sub merge { }
# and roles will not overwrite methods that already exist (it assumes
# the method has already been provided). Here we ensure sub merge { }
# exists in some form, and then immeidately replace all the behaviour
# with an 'around' modifier.
#
# This will be solved by MBS-2618

sub merge { }
around merge => sub {
    my ($orig, $self, $new_id, @old_ids) = @_;

    $new_id && $new_id > 0
        or croak("new_id must be a positive integer");

    my @to_merge = grep { $_ != $new_id } @old_ids
        or croak("Attempted to merge empty list of IDs into target");

    @to_merge == @old_ids
        or croak("Attempted to merge an object into itself");

    $self->_merge_impl($new_id, @to_merge);
};

1;