sub GetFacets {

    my $rs = shift;

    my $facets;

    my $index_mode = C4::Context->config('zebra_auth_index_mode') // 'dom';

    if ( $index_mode eq 'dom' ) {

        $facets = _get_facets_from_zebra( $rs );

    } else {

        $facets = _get_facets_from_records( $rs );

    }

    return $facets;

}

sub _get_facets_from_records {

    my $rs = shift;

    my $facets_maxrecs = C4::Context->preference('maxRecordsForFacets') // 20;

    my $facets_config  = getFacets();

    my $facets         = {};

    my $size           = $rs->size();

    my $jmax           = $size > $facets_maxrecs

                            ? $facets_maxrecs

                            : $size;

    for ( my $j = 0 ; $j < $jmax ; $j++ ) {

        my $marc_record = new_record_from_zebra (

                'biblioserver',

                $rs->record( $j )->raw()

        );

        if ( ! defined $marc_record ) {

            warn "ERROR DECODING RECORD - $@: " .

                $rs->record( $j )->raw();

            next;

        }

        _get_facets_data_from_record( $marc_record, $facets_config, $facets );

    }

    return $facets;

}

=head2 _get_facets_from_zebra

    my $facets = _get_facets_from_zebra( $result_set )

Retrieves facets for a specified result set. It loops through the facets defined

in C4::Koha::getFacets and returns a hash with the following structure:

   {  facet_idx => {

            facet_value => count

      },

      ...

   }

=cut

sub _get_facets_from_zebra {

    my $rs = shift;

    # save current elementSetName

    my $elementSetName = $rs->option( 'elementSetName' );

    my $facets_loop = getFacets();

    my $facets_data  = {};

    # loop through defined facets and fill the facets hashref

    foreach my $facet ( @$facets_loop ) {

        my $idx = $facet->{ idx };

        my $sep = $facet->{ sep };

        my $facet_values = _get_facet_from_result_set( $idx, $rs, $sep );

        if ( $facet_values ) {

            # we've actually got a result

            $facets_data->{ $idx } = $facet_values;

        }

    }

    # set elementSetName to its previous value to avoid side effects

    $rs->option( elementSetName => $elementSetName );

    return $facets_data;

}

=head2 _get_facet_from_result_set

    my $facet_values =

        C4::Search::_get_facet_from_result_set( $facet_idx, $result_set, $sep )

Internal function that extracts facet information for a specific index ($facet_idx) and

returns a hash containing facet values and count:

    {

        $facet_value => $count ,

        ...

    }

Warning: this function has the side effect of changing the elementSetName for the result

set. It is a helper function for the main loop, which takes care of backing it up for

restoring.

=cut

sub _get_facet_from_result_set {

    my $facet_idx = shift;

    my $rs        = shift;

    my $sep       = shift;

    my $internal_sep = '<*>';

    return if ( ! defined $facet_idx || ! defined $rs );

    # zebra's facet element, untokenized index

    my $facet_element = 'zebra::facet::' . $facet_idx . ':0:100';

    # configure zebra results for retrieving the desired facet

    $rs->option( elementSetName => $facet_element );

    # get the facet record from result set

    my $facet = $rs->record( 0 )->raw;

    # if the facet has no restuls...

    return if !defined $facet;

    # TODO: benchmark DOM vs. SAX performance

    my $facet_dom = XML::LibXML->load_xml(

      string => ($facet)

    );

    my @terms = $facet_dom->getElementsByTagName('term');

    return if ! @terms;

    my $facets = {};

    foreach my $term ( @terms ) {

        my $facet_value = $term->textContent;

        $facet_value =~ s/\Q$internal_sep\E/$sep/ if defined $sep;

        $facets->{ $facet_value } = $term->getAttribute( 'occur' );

    }

    return $facets;

}