Bug 20434: Add missing authority types

[koha.git] / Koha / SearchEngine / Elasticsearch.pm

package Koha::SearchEngine::Elasticsearch;

# Copyright 2015 Catalyst IT
#
# This file is part of Koha.
#
# Koha is free software; you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the Free Software
# Foundation; either version 3 of the License, or (at your option) any later
# version.
#
# Koha is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with Koha; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

use base qw(Class::Accessor);

use C4::Context;

use Koha::Database;
use Koha::Exceptions::Config;
use Koha::Exceptions::Elasticsearch;
use Koha::SearchFields;
use Koha::SearchMarcMaps;

use Carp;
use Clone qw(clone);
use JSON;
use Modern::Perl;
use Readonly;
use Search::Elasticsearch;
use Try::Tiny;
use YAML::Syck;

use List::Util qw( sum0 reduce );
use MARC::File::XML;
use MIME::Base64;
use Encode qw(encode);
use Business::ISBN;

__PACKAGE__->mk_ro_accessors(qw( index ));
__PACKAGE__->mk_accessors(qw( sort_fields ));

# Constants to refer to the standard index names
Readonly our $BIBLIOS_INDEX     => 'biblios';
Readonly our $AUTHORITIES_INDEX => 'authorities';

=head1 NAME

Koha::SearchEngine::Elasticsearch - Base module for things using elasticsearch

=head1 ACCESSORS

=over 4

=item index

The name of the index to use, generally 'biblios' or 'authorities'.

=back

=head1 FUNCTIONS

=cut

sub new {
    my $class = shift @_;
    my $self = $class->SUPER::new(@_);
    # Check for a valid index
    Koha::Exceptions::MissingParameter->throw('No index name provided') unless $self->index;
    return $self;
}

=head2 get_elasticsearch

    my $elasticsearch_client = $self->get_elasticsearch();

Returns a C<Search::Elasticsearch> client. The client is cached on a C<Koha::SearchEngine::ElasticSearch>
instance level and will be reused if method is called multiple times.

=cut

sub get_elasticsearch {
    my $self = shift @_;
    unless (defined $self->{elasticsearch}) {
        my $conf = $self->get_elasticsearch_params();
        $self->{elasticsearch} = Search::Elasticsearch->new($conf);
    }
    return $self->{elasticsearch};
}

=head2 get_elasticsearch_params

    my $params = $self->get_elasticsearch_params();

This provides a hashref that contains the parameters for connecting to the
ElasicSearch servers, in the form:

    {
        'nodes' => ['127.0.0.1:9200', 'anotherserver:9200'],
        'index_name' => 'koha_instance_index',
    }

This is configured by the following in the C<config> block in koha-conf.xml:

    <elasticsearch>
        <server>127.0.0.1:9200</server>
        <server>anotherserver:9200</server>
        <index_name>koha_instance</index_name>
    </elasticsearch>

=cut

sub get_elasticsearch_params {
    my ($self) = @_;

    # Copy the hash so that we're not modifying the original
    my $conf = C4::Context->config('elasticsearch');
    die "No 'elasticsearch' block is defined in koha-conf.xml.\n" if ( !$conf );
    my $es = { %{ $conf } };

    # Helpfully, the multiple server lines end up in an array for us anyway
    # if there are multiple ones, but not if there's only one.
    my $server = $es->{server};
    delete $es->{server};
    if ( ref($server) eq 'ARRAY' ) {

        # store it called 'nodes' (which is used by newer Search::Elasticsearch)
        $es->{nodes} = $server;
    }
    elsif ($server) {
        $es->{nodes} = [$server];
    }
    else {
        die "No elasticsearch servers were specified in koha-conf.xml.\n";
    }
    die "No elasticsearch index_name was specified in koha-conf.xml.\n"
      if ( !$es->{index_name} );
    # Append the name of this particular index to our namespace
    $es->{index_name} .= '_' . $self->index;

    $es->{key_prefix} = 'es_';
    $es->{client} //= '5_0::Direct';
    $es->{cxn_pool} //= 'Static';
    $es->{request_timeout} //= 60;

    return $es;
}

=head2 get_elasticsearch_settings

    my $settings = $self->get_elasticsearch_settings();

This provides the settings provided to Elasticsearch when an index is created.
These can do things like define tokenization methods.

A hashref containing the settings is returned.

=cut

sub get_elasticsearch_settings {
    my ($self) = @_;

    # Use state to speed up repeated calls
    state $settings = undef;
    if (!defined $settings) {
        my $config_file = C4::Context->config('elasticsearch_index_config');
        $config_file ||= C4::Context->config('intranetdir') . '/admin/searchengine/elasticsearch/index_config.yaml';
        $settings = LoadFile( $config_file );
    }

    return $settings;
}

=head2 get_elasticsearch_mappings

    my $mappings = $self->get_elasticsearch_mappings();

This provides the mappings that get passed to Elasticsearch when an index is
created.

=cut

sub get_elasticsearch_mappings {
    my ($self) = @_;

    # Use state to speed up repeated calls
    state %all_mappings;
    state %sort_fields;

    if (!defined $all_mappings{$self->index}) {
        $sort_fields{$self->index} = {};
        # Clone the general mapping to break ties with the original hash
        my $mappings = {
            data => clone(_get_elasticsearch_field_config('general', ''))
        };
        my $marcflavour = lc C4::Context->preference('marcflavour');
        $self->_foreach_mapping(
            sub {
                my ( $name, $type, $facet, $suggestible, $sort, $search, $marc_type ) = @_;
                return if $marc_type ne $marcflavour;
                # TODO if this gets any sort of complexity to it, it should
                # be broken out into its own function.

                # TODO be aware of date formats, but this requires pre-parsing
                # as ES will simply reject anything with an invalid date.
                my $es_type = 'text';
                if ($type eq 'boolean') {
                    $es_type = 'boolean';
                } elsif ($type eq 'number' || $type eq 'sum') {
                    $es_type = 'integer';
                } elsif ($type eq 'isbn' || $type eq 'stdno') {
                    $es_type = 'stdno';
                }

                if ($search) {
                    $mappings->{data}{properties}{$name} = _get_elasticsearch_field_config('search', $es_type);
                }

                if ($facet) {
                    $mappings->{data}{properties}{ $name . '__facet' } = _get_elasticsearch_field_config('facet', $es_type);
                }
                if ($suggestible) {
                    $mappings->{data}{properties}{ $name . '__suggestion' } = _get_elasticsearch_field_config('suggestible', $es_type);
                }
                # Sort is a bit special as it can be true, false, undef.
                # We care about "true" or "undef",
                # "undef" means to do the default thing, which is make it sortable.
                if (!defined $sort || $sort) {
                    $mappings->{data}{properties}{ $name . '__sort' } = _get_elasticsearch_field_config('sort', $es_type);
                    $sort_fields{$self->index}{$name} = 1;
                }
            }
        );
        $all_mappings{$self->index} = $mappings;
    }
    $self->sort_fields(\%{$sort_fields{$self->index}});

    return $all_mappings{$self->index};
}

=head2 _get_elasticsearch_field_config

Get the Elasticsearch field config for the given purpose and data type.

$mapping = _get_elasticsearch_field_config('search', 'text');

=cut

sub _get_elasticsearch_field_config {

    my ( $purpose, $type ) = @_;

    # Use state to speed up repeated calls
    state $settings = undef;
    if (!defined $settings) {
        my $config_file = C4::Context->config('elasticsearch_field_config');
        $config_file ||= C4::Context->config('intranetdir') . '/admin/searchengine/elasticsearch/field_config.yaml';
        $settings = LoadFile( $config_file );
    }

    if (!defined $settings->{$purpose}) {
        die "Field purpose $purpose not defined in field config";
    }
    if ($type eq '') {
        return $settings->{$purpose};
    }
    if (defined $settings->{$purpose}{$type}) {
        return $settings->{$purpose}{$type};
    }
    if (defined $settings->{$purpose}{'default'}) {
        return $settings->{$purpose}{'default'};
    }
    return;
}

=head2 _load_elasticsearch_mappings

Load Elasticsearch mappings in the format of mappings.yaml.

$indexes = _load_elasticsearch_mappings();

=cut

sub _load_elasticsearch_mappings {
    my $mappings_yaml = C4::Context->config('elasticsearch_index_mappings');
    $mappings_yaml ||= C4::Context->config('intranetdir') . '/admin/searchengine/elasticsearch/mappings.yaml';
    return LoadFile( $mappings_yaml );
}

sub reset_elasticsearch_mappings {
    my ( $self ) = @_;
    my $indexes = $self->_load_elasticsearch_mappings();

    while ( my ( $index_name, $fields ) = each %$indexes ) {
        while ( my ( $field_name, $data ) = each %$fields ) {

            my %sf_params = map { $_ => $data->{$_} } grep { exists $data->{$_} } qw/ type label weight staff_client opac facet_order /;

            # Set default values
            $sf_params{staff_client} //= 1;
            $sf_params{opac} //= 1;

            $sf_params{name} = $field_name;

            my $search_field = Koha::SearchFields->find_or_create( \%sf_params, { key => 'name' } );

            my $mappings = $data->{mappings};
            for my $mapping ( @$mappings ) {
                my $marc_field = Koha::SearchMarcMaps->find_or_create({
                    index_name => $index_name,
                    marc_type => $mapping->{marc_type},
                    marc_field => $mapping->{marc_field}
                });
                $search_field->add_to_search_marc_maps($marc_field, {
                    facet => $mapping->{facet} || 0,
                    suggestible => $mapping->{suggestible} || 0,
                    sort => $mapping->{sort},
                    search => $mapping->{search} // 1
                });
            }
        }
    }
}

# This overrides the accessor provided by Class::Accessor so that if
# sort_fields isn't set, then it'll generate it.
sub sort_fields {
    my $self = shift;
    if (@_) {
        $self->_sort_fields_accessor(@_);
        return;
    }
    my $val = $self->_sort_fields_accessor();
    return $val if $val;

    # This will populate the accessor as a side effect
    $self->get_elasticsearch_mappings();
    return $self->_sort_fields_accessor();
}

=head2 _process_mappings($mappings, $data, $record_document, $altscript)

    $self->_process_mappings($mappings, $marc_field_data, $record_document, 0)

Process all C<$mappings> targets operating on a specific MARC field C<$data>.
Since we group all mappings by MARC field targets C<$mappings> will contain
all targets for C<$data> and thus we need to fetch the MARC field only once.
C<$mappings> will be applied to C<$record_document> and new field values added.
The method has no return value.

=over 4

=item C<$mappings>

Arrayref of mappings containing arrayrefs in the format
[C<$target>, C<$options>] where C<$target> is the name of the target field and
C<$options> is a hashref containing processing directives for this particular
mapping.

=item C<$data>

The source data from a MARC record field.

=item C<$record_document>

Hashref representing the Elasticsearch document on which mappings should be
applied.

=item C<$altscript>

A boolean value indicating whether an alternate script presentation is being
processed.

=back

=cut

sub _process_mappings {
    my ($_self, $mappings, $data, $record_document, $altscript) = @_;
    foreach my $mapping (@{$mappings}) {
        my ($target, $options) = @{$mapping};

        # Don't process sort fields for alternate scripts
        my $sort = $target =~ /__sort$/;
        if ($sort && $altscript) {
            next;
        }

        # Copy (scalar) data since can have multiple targets
        # with differing options for (possibly) mutating data
        # so need a different copy for each
        my $_data = $data;
        $record_document->{$target} //= [];
        if (defined $options->{substr}) {
            my ($start, $length) = @{$options->{substr}};
            $_data = length($data) > $start ? substr $data, $start, $length : '';
        }
        if (defined $options->{value_callbacks}) {
            $_data = reduce { $b->($a) } ($_data, @{$options->{value_callbacks}});
        }
        if (defined $options->{property}) {
            $_data = {
                $options->{property} => $_data
            }
        }
        push @{$record_document->{$target}}, $_data;
    }
}

=head2 marc_records_to_documents($marc_records)

    my @record_documents = $self->marc_records_to_documents($marc_records);

Using mappings stored in database convert C<$marc_records> to Elasticsearch documents.

Returns array of hash references, representing Elasticsearch documents,
acceptable as body payload in C<Search::Elasticsearch> requests.

=over 4

=item C<$marc_documents>

Reference to array of C<MARC::Record> objects to be converted to Elasticsearch documents.

=back

=cut

sub marc_records_to_documents {
    my ($self, $records) = @_;
    my $rules = $self->_get_marc_mapping_rules();
    my $control_fields_rules = $rules->{control_fields};
    my $data_fields_rules = $rules->{data_fields};
    my $marcflavour = lc C4::Context->preference('marcflavour');
    my $use_array = C4::Context->preference('ElasticsearchMARCFormat') eq 'ARRAY';

    my @record_documents;

    foreach my $record (@{$records}) {
        my $record_document = {};
        my $mappings = $rules->{leader};
        if ($mappings) {
            $self->_process_mappings($mappings, $record->leader(), $record_document, 0);
        }
        foreach my $field ($record->fields()) {
            if ($field->is_control_field()) {
                my $mappings = $control_fields_rules->{$field->tag()};
                if ($mappings) {
                    $self->_process_mappings($mappings, $field->data(), $record_document, 0);
                }
            }
            else {
                my $tag = $field->tag();
                # Handle alternate scripts in MARC 21
                my $altscript = 0;
                if ($marcflavour eq 'marc21' && $tag eq '880') {
                    my $sub6 = $field->subfield('6');
                    if ($sub6 =~ /^(...)-\d+/) {
                        $tag = $1;
                        $altscript = 1;
                    }
                }

                my $data_field_rules = $data_fields_rules->{$tag};

                if ($data_field_rules) {
                    my $subfields_mappings = $data_field_rules->{subfields};
                    my $wildcard_mappings = $subfields_mappings->{'*'};
                    foreach my $subfield ($field->subfields()) {
                        my ($code, $data) = @{$subfield};
                        my $mappings = $subfields_mappings->{$code} // [];
                        if ($wildcard_mappings) {
                            $mappings = [@{$mappings}, @{$wildcard_mappings}];
                        }
                        if (@{$mappings}) {
                            $self->_process_mappings($mappings, $data, $record_document, $altscript);
                        }
                    }

                    my $subfields_join_mappings = $data_field_rules->{subfields_join};
                    if ($subfields_join_mappings) {
                        foreach my $subfields_group (keys %{$subfields_join_mappings}) {
                            # Map each subfield to values, remove empty values, join with space
                            my $data = join(
                                ' ',
                                grep(
                                    $_,
                                    map { join(' ', $field->subfield($_)) } split(//, $subfields_group)
                                )
                            );
                            if ($data) {
                                $self->_process_mappings($subfields_join_mappings->{$subfields_group}, $data, $record_document, $altscript);
                            }
                        }
                    }
                }
            }
        }
        foreach my $field (keys %{$rules->{defaults}}) {
            unless (defined $record_document->{$field}) {
                $record_document->{$field} = $rules->{defaults}->{$field};
            }
        }
        foreach my $field (@{$rules->{sum}}) {
            if (defined $record_document->{$field}) {
                # TODO: validate numeric? filter?
                # TODO: Or should only accept fields without nested values?
                # TODO: Quick and dirty, improve if needed
                $record_document->{$field} = sum0(grep { !ref($_) && m/\d+(\.\d+)?/} @{$record_document->{$field}});
            }
        }
        # Index all applicable ISBN forms (ISBN-10 and ISBN-13 with and without dashes)
        foreach my $field (@{$rules->{isbn}}) {
            if (defined $record_document->{$field}) {
                my @isbns = ();
                foreach my $input_isbn (@{$record_document->{$field}}) {
                    my $isbn = Business::ISBN->new($input_isbn);
                    if (defined $isbn && $isbn->is_valid) {
                        my $isbn13 = $isbn->as_isbn13->as_string;
                        push @isbns, $isbn13;
                        $isbn13 =~ s/\-//g;
                        push @isbns, $isbn13;

                        my $isbn10 = $isbn->as_isbn10;
                        if ($isbn10) {
                            $isbn10 = $isbn10->as_string;
                            push @isbns, $isbn10;
                            $isbn10 =~ s/\-//g;
                            push @isbns, $isbn10;
                        }
                    } else {
                        push @isbns, $input_isbn;
                    }
                }
                $record_document->{$field} = \@isbns;
            }
        }

        # Remove duplicate values and collapse sort fields
        foreach my $field (keys %{$record_document}) {
            if (ref($record_document->{$field}) eq 'ARRAY') {
                @{$record_document->{$field}} = do {
                    my %seen;
                    grep { !$seen{ref($_) eq 'HASH' && defined $_->{input} ? $_->{input} : $_}++ } @{$record_document->{$field}};
                };
                if ($field =~ /__sort$/) {
                    # Make sure to keep the sort field length sensible. 255 was chosen as a nice round value.
                    $record_document->{$field} = [substr(join(' ', @{$record_document->{$field}}), 0, 255)];
                }
            }
        }

        # TODO: Perhaps should check if $records_document non empty, but really should never be the case
        $record->encoding('UTF-8');
        if ($use_array) {
            $record_document->{'marc_data_array'} = $self->_marc_to_array($record);
            $record_document->{'marc_format'} = 'ARRAY';
        } else {
            my @warnings;
            {
                # Temporarily intercept all warn signals (MARC::Record carps when record length > 99999)
                local $SIG{__WARN__} = sub {
                    push @warnings, $_[0];
                };
                $record_document->{'marc_data'} = encode_base64(encode('UTF-8', $record->as_usmarc()));
            }
            if (@warnings) {
                # Suppress warnings if record length exceeded
                unless (substr($record->leader(), 0, 5) eq '99999') {
                    foreach my $warning (@warnings) {
                        carp $warning;
                    }
                }
                $record_document->{'marc_data'} = $record->as_xml_record($marcflavour);
                $record_document->{'marc_format'} = 'MARCXML';
            }
            else {
                $record_document->{'marc_format'} = 'base64ISO2709';
            }
        }
        my $id = $record->subfield('999', 'c');
        push @record_documents, [$id, $record_document];
    }
    return \@record_documents;
}

=head2 _marc_to_array($record)

    my @fields = _marc_to_array($record)

Convert a MARC::Record to an array modeled after MARC-in-JSON
(see https://github.com/marc4j/marc4j/wiki/MARC-in-JSON-Description)

=over 4

=item C<$record>

A MARC::Record object

=back

=cut

sub _marc_to_array {
    my ($self, $record) = @_;

    my $data = {
        leader => $record->leader(),
        fields => []
    };
    for my $field ($record->fields()) {
        my $tag = $field->tag();
        if ($field->is_control_field()) {
            push @{$data->{fields}}, {$tag => $field->data()};
        } else {
            my $subfields = ();
            foreach my $subfield ($field->subfields()) {
                my ($code, $contents) = @{$subfield};
                push @{$subfields}, {$code => $contents};
            }
            push @{$data->{fields}}, {
                $tag => {
                    ind1 => $field->indicator(1),
                    ind2 => $field->indicator(2),
                    subfields => $subfields
                }
            };
        }
    }
    return $data;
}

=head2 _array_to_marc($data)

    my $record = _array_to_marc($data)

Convert an array modeled after MARC-in-JSON to a MARC::Record

=over 4

=item C<$data>

An array modeled after MARC-in-JSON
(see https://github.com/marc4j/marc4j/wiki/MARC-in-JSON-Description)

=back

=cut

sub _array_to_marc {
    my ($self, $data) = @_;

    my $record = MARC::Record->new();

    $record->leader($data->{leader});
    for my $field (@{$data->{fields}}) {
        my $tag = (keys %{$field})[0];
        $field = $field->{$tag};
        my $marc_field;
        if (ref($field) eq 'HASH') {
            my @subfields;
            foreach my $subfield (@{$field->{subfields}}) {
                my $code = (keys %{$subfield})[0];
                push @subfields, $code;
                push @subfields, $subfield->{$code};
            }
            $marc_field = MARC::Field->new($tag, $field->{ind1}, $field->{ind2}, @subfields);
        } else {
            $marc_field = MARC::Field->new($tag, $field)
        }
        $record->append_fields($marc_field);
    }
;
    return $record;
}

=head2 _field_mappings($facet, $suggestible, $sort, $search, $target_name, $target_type, $range)

    my @mappings = _field_mappings($facet, $suggestible, $sort, $search, $target_name, $target_type, $range)

Get mappings, an internal data structure later used by
L<_process_mappings($mappings, $data, $record_document, $altscript)> to process MARC target
data for a MARC mapping.

The returned C<$mappings> is not to to be confused with mappings provided by
C<_foreach_mapping>, rather this sub accepts properties from a mapping as
provided by C<_foreach_mapping> and expands it to this internal data structure.
In the caller context (C<_get_marc_mapping_rules>) the returned C<@mappings>
is then applied to each MARC target (leader, control field data, subfield or
joined subfields) and integrated into the mapping rules data structure used in
C<marc_records_to_documents> to transform MARC records into Elasticsearch
documents.

=over 4

=item C<$facet>

Boolean indicating whether to create a facet field for this mapping.

=item C<$suggestible>

Boolean indicating whether to create a suggestion field for this mapping.

=item C<$sort>

Boolean indicating whether to create a sort field for this mapping.

=item C<$search>

Boolean indicating whether to create a search field for this mapping.

=item C<$target_name>

Elasticsearch document target field name.

=item C<$target_type>

Elasticsearch document target field type.

=item C<$range>

An optional range as a string in the format "<START>-<END>" or "<START>",
where "<START>" and "<END>" are integers specifying a range that will be used
for extracting a substring from MARC data as Elasticsearch field target value.

The first character position is "0", and the range is inclusive,
so "0-2" means the first three characters of MARC data.

If only "<START>" is provided only one character at position "<START>" will
be extracted.

=back

=cut

sub _field_mappings {
    my ($_self, $facet, $suggestible, $sort, $search, $target_name, $target_type, $range) = @_;
    my %mapping_defaults = ();
    my @mappings;

    my $substr_args = undef;
    if (defined $range) {
        # TODO: use value_callback instead?
        my ($start, $end) = map(int, split /-/, $range, 2);
        $substr_args = [$start];
        push @{$substr_args}, (defined $end ? $end - $start + 1 : 1);
    }
    my $default_options = {};
    if ($substr_args) {
        $default_options->{substr} = $substr_args;
    }

    # TODO: Should probably have per type value callback/hook
    # but hard code for now
    if ($target_type eq 'boolean') {
        $default_options->{value_callbacks} //= [];
        push @{$default_options->{value_callbacks}}, sub {
            my ($value) = @_;
            # Trim whitespace at both ends
            $value =~ s/^\s+|\s+$//g;
            return $value ? 'true' : 'false';
        };
    }

    if ($search) {
        my $mapping = [$target_name, $default_options];
        push @mappings, $mapping;
    }

    my @suffixes = ();
    push @suffixes, 'facet' if $facet;
    push @suffixes, 'suggestion' if $suggestible;
    push @suffixes, 'sort' if !defined $sort || $sort;

    foreach my $suffix (@suffixes) {
        my $mapping = ["${target_name}__$suffix"];
        # TODO: Hack, fix later in less hideous manner
        if ($suffix eq 'suggestion') {
            push @{$mapping}, {%{$default_options}, property => 'input'};
        }
        else {
            push @{$mapping}, $default_options;
        }
        push @mappings, $mapping;
    }
    return @mappings;
};

=head2 _get_marc_mapping_rules

    my $mapping_rules = $self->_get_marc_mapping_rules()

Generates rules from mappings stored in database for MARC records to Elasticsearch JSON document conversion.

Since field retrieval is slow in C<MARC::Records> (all fields are itereted through for
each call to C<MARC::Record>->field) we create an optimized structure of mapping
rules keyed by MARC field tags holding all the mapping rules for that particular tag.

We can then iterate through all MARC fields for each record and apply all relevant
rules once per fields instead of retreiving fields multiple times for each mapping rule
which is terribly slow.

=cut

# TODO: This structure can be used for processing multiple MARC::Records so is currently
# rebuilt for each batch. Since it is cacheable it could also be stored in an in
# memory cache which it is currently not. The performance gain of caching
# would probably be marginal, but to do this could be a further improvement.

sub _get_marc_mapping_rules {
    my ($self) = @_;
    my $marcflavour = lc C4::Context->preference('marcflavour');
    my $field_spec_regexp = qr/^([0-9]{3})([()0-9a-zA-Z]+)?(?:_\/(\d+(?:-\d+)?))?$/;
    my $leader_regexp = qr/^leader(?:_\/(\d+(?:-\d+)?))?$/;
    my $rules = {
        'leader' => [],
        'control_fields' => {},
        'data_fields' => {},
        'sum' => [],
        'isbn' => [],
        'defaults' => {}
    };

    $self->_foreach_mapping(sub {
        my ($name, $type, $facet, $suggestible, $sort, $search, $marc_type, $marc_field) = @_;
        return if $marc_type ne $marcflavour;

        if ($type eq 'sum') {
            push @{$rules->{sum}}, $name;
        }
        elsif ($type eq 'isbn') {
            push @{$rules->{isbn}}, $name;
        }
        elsif ($type eq 'boolean') {
            # boolean gets special handling, if value doesn't exist for a field,
            # it is set to false
            $rules->{defaults}->{$name} = 'false';
        }

        if ($marc_field =~ $field_spec_regexp) {
            my $field_tag = $1;

            my @subfields;
            my @subfield_groups;
            # Parse and separate subfields form subfield groups
            if (defined $2) {
                my $subfield_group = '';
                my $open_group = 0;

                foreach my $token (split //, $2) {
                    if ($token eq "(") {
                        if ($open_group) {
                            Koha::Exceptions::Elasticsearch::MARCFieldExprParseError->throw(
                                "Unmatched opening parenthesis for $marc_field"
                            );
                        }
                        else {
                            $open_group = 1;
                        }
                    }
                    elsif ($token eq ")") {
                        if ($open_group) {
                            if ($subfield_group) {
                                push @subfield_groups, $subfield_group;
                                $subfield_group = '';
                            }
                            $open_group = 0;
                        }
                        else {
                            Koha::Exceptions::Elasticsearch::MARCFieldExprParseError->throw(
                                "Unmatched closing parenthesis for $marc_field"
                            );
                        }
                    }
                    elsif ($open_group) {
                        $subfield_group .= $token;
                    }
                    else {
                        push @subfields, $token;
                    }
                }
            }
            else {
                push @subfields, '*';
            }

            my $range = defined $3 ? $3 : undef;
            my @mappings = $self->_field_mappings($facet, $suggestible, $sort, $search, $name, $type, $range);
            if ($field_tag < 10) {
                $rules->{control_fields}->{$field_tag} //= [];
                push @{$rules->{control_fields}->{$field_tag}}, @mappings;
            }
            else {
                $rules->{data_fields}->{$field_tag} //= {};
                foreach my $subfield (@subfields) {
                    $rules->{data_fields}->{$field_tag}->{subfields}->{$subfield} //= [];
                    push @{$rules->{data_fields}->{$field_tag}->{subfields}->{$subfield}}, @mappings;
                }
                foreach my $subfield_group (@subfield_groups) {
                    $rules->{data_fields}->{$field_tag}->{subfields_join}->{$subfield_group} //= [];
                    push @{$rules->{data_fields}->{$field_tag}->{subfields_join}->{$subfield_group}}, @mappings;
                }
            }
        }
        elsif ($marc_field =~ $leader_regexp) {
            my $range = defined $1 ? $1 : undef;
            my @mappings = $self->_field_mappings($facet, $suggestible, $sort, $search, $name, $type, $range);
            push @{$rules->{leader}}, @mappings;
        }
        else {
            Koha::Exceptions::Elasticsearch::MARCFieldExprParseError->throw(
                "Invalid MARC field expression: $marc_field"
            );
        }
    });
    return $rules;
}

=head2 _foreach_mapping

    $self->_foreach_mapping(
        sub {
            my ( $name, $type, $facet, $suggestible, $sort, $marc_type,
                $marc_field )
              = @_;
            return unless $marc_type eq 'marc21';
            print "Data comes from: " . $marc_field . "\n";
        }
    );

This allows you to apply a function to each entry in the elasticsearch mappings
table, in order to build the mappings for whatever is needed.

In the provided function, the files are:

=over 4

=item C<$name>

The field name for elasticsearch (corresponds to the 'mapping' column in the
database.

=item C<$type>

The type for this value, e.g. 'string'.

=item C<$facet>

True if this value should be facetised. This only really makes sense if the
field is understood by the facet processing code anyway.

=item C<$sort>

True if this is a field that a) needs special sort handling, and b) if it
should be sorted on. False if a) but not b). Undef if not a). This allows,
for example, author to be sorted on but not everything marked with "author"
to be included in that sort.

=item C<$marc_type>

A string that indicates the MARC type that this mapping is for, e.g. 'marc21',
'unimarc', 'normarc'.

=item C<$marc_field>

A string that describes the MARC field that contains the data to extract.
These are of a form suited to Catmandu's MARC fixers.

=back

=cut

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

    # TODO use a caching framework here
    my $search_fields = Koha::Database->schema->resultset('SearchField')->search(
        {
            'search_marc_map.index_name' => $self->index,
        },
        {   join => { search_marc_to_fields => 'search_marc_map' },
            '+select' => [
                'search_marc_to_fields.facet',
                'search_marc_to_fields.suggestible',
                'search_marc_to_fields.sort',
                'search_marc_to_fields.search',
                'search_marc_map.marc_type',
                'search_marc_map.marc_field',
            ],
            '+as'     => [
                'facet',
                'suggestible',
                'sort',
                'search',
                'marc_type',
                'marc_field',
            ],
        }
    );

    while ( my $search_field = $search_fields->next ) {
        $sub->(
            # Force lower case on indexed field names for case insensitive
            # field name searches
            lc($search_field->name),
            $search_field->type,
            $search_field->get_column('facet'),
            $search_field->get_column('suggestible'),
            $search_field->get_column('sort'),
            $search_field->get_column('search'),
            $search_field->get_column('marc_type'),
            $search_field->get_column('marc_field'),
        );
    }
}

=head2 process_error

    die process_error($@);

This parses an Elasticsearch error message and produces a human-readable
result from it. This result is probably missing all the useful information
that you might want in diagnosing an issue, so the warning is also logged.

Note that currently the resulting message is not internationalised. This
will happen eventually by some method or other.

=cut

sub process_error {
    my ($self, $msg) = @_;

    warn $msg; # simple logging

    # This is super-primitive
    return "Unable to understand your search query, please rephrase and try again.\n" if $msg =~ /ParseException/;

    return "Unable to perform your search. Please try again.\n";
}

=head2 _read_configuration

    my $conf = _read_configuration();

Reads the I<configuration file> and returns a hash structure with the
configuration information. It raises an exception if mandatory entries
are missing.

The hashref structure has the following form:

    {
        'nodes' => ['127.0.0.1:9200', 'anotherserver:9200'],
        'index_name' => 'koha_instance',
    }

This is configured by the following in the C<config> block in koha-conf.xml:

    <elasticsearch>
        <server>127.0.0.1:9200</server>
        <server>anotherserver:9200</server>
        <index_name>koha_instance</index_name>
    </elasticsearch>

=cut

sub _read_configuration {

    my $configuration;

    my $conf = C4::Context->config('elasticsearch');
    Koha::Exceptions::Config::MissingEntry->throw(
        "Missing 'elasticsearch' block in config file")
      unless defined $conf;

    if ( $conf && $conf->{server} ) {
        my $nodes = $conf->{server};
        if ( ref($nodes) eq 'ARRAY' ) {
            $configuration->{nodes} = $nodes;
        }
        else {
            $configuration->{nodes} = [$nodes];
        }
    }
    else {
        Koha::Exceptions::Config::MissingEntry->throw(
            "Missing 'server' entry in config file for elasticsearch");
    }

    if ( defined $conf->{index_name} ) {
        $configuration->{index_name} = $conf->{index_name};
    }
    else {
        Koha::Exceptions::Config::MissingEntry->throw(
            "Missing 'index_name' entry in config file for elasticsearch");
    }

    return $configuration;
}

=head2 get_facetable_fields

my @facetable_fields = Koha::SearchEngine::Elasticsearch->get_facetable_fields();

Returns the list of Koha::SearchFields marked to be faceted in the ES configuration

=cut

sub get_facetable_fields {
    my ($self) = @_;

    # These should correspond to the ES field names, as opposed to the CCL
    # things that zebra uses.
    my @search_field_names = qw( author itype location su-geo title-series subject ccode holdingbranch homebranch ln );
    my @faceted_fields = Koha::SearchFields->search(
        { name => { -in => \@search_field_names }, facet_order => { '!=' => undef } }, { order_by => ['facet_order'] }
    );
    my @not_faceted_fields = Koha::SearchFields->search(
        { name => { -in => \@search_field_names }, facet_order => undef }, { order_by => ['facet_order'] }
    );
    # This could certainly be improved
    return ( @faceted_fields, @not_faceted_fields );
}

1;

__END__

=head1 AUTHOR

=over 4

=item Chris Cormack C<< <chrisc@catalyst.net.nz> >>

=item Robin Sheat C<< <robin@catalyst.net.nz> >>

=item Jonathan Druart C<< <jonathan.druart@bugs.koha-community.org> >>

=back

=cut