# Provide service for mapping graph to json limited to configured fields and context.
module Qa
  module LinkedData
    module Mapper
      class SearchResultsMapperService
        class_attribute :graph_mapper_service, :deep_sort_service, :context_mapper_service
        self.graph_mapper_service = Qa::LinkedData::Mapper::GraphMapperService
        self.deep_sort_service = Qa::LinkedData::DeepSortService
        self.context_mapper_service = Qa::LinkedData::Mapper::ContextMapperService

        class << self
          # Extract predicates specified in the predicate_map from the graph and return as an array of value maps for each search result subject URI.
          # If a sort key is present, a subject will only be included in the results if it has a statement with the sort predicate.
          # @param graph [RDF::Graph] the graph from which to extract result values
          # @param predicate_map [Hash<Symbol><String||Symbol>] value either maps to a predicate in the graph or is :subject_uri indicating to use the subject uri as the value
          # @example predicate map
          #   {
          #     uri: :subject_uri,
          #     id: 'http://id.loc.gov/vocabulary/identifiers/lccn',
          #     label: 'http://www.w3.org/2004/02/skos/core#prefLabel',
          #     altlabel: 'http://www.w3.org/2004/02/skos/core#altLabel',
          #     sort: 'http://vivoweb.org/ontology/core#rank'
          #   }
          # @param sort_key [Symbol] the key in the predicate map for the value on which to sort
          # @param context_map [Qa::LinkedData::Config::ContextMap] map of additional context to include in the results
          # @return [Array<Hash<Symbol><Array<Object>>>] mapped result values with each result as an element in the array
          #    with hash of map key = array of object values for predicates identified in map parameter.
          # @example value map for a single result
          #   [
          #     {:uri=>[#<RDF::URI:0x3fcff54a829c URI:http://id.loc.gov/authorities/names/n2010043281>],
          #      :id=>[#<RDF::Literal:0x3fcff4a367b4("n 2010043281")>],
          #      :label=>[#<RDF::Literal:0x3fcff54a9a98("Valli, Sabrina"@en)>],
          #      :altlabel=>[],
          #      :sort=>[#<RDF::Literal:0x3fcff54b4c18("2")>]}
          #   ]
          def map_values(graph:, predicate_map:, sort_key:, preferred_language: nil, context_map: nil)
            search_matches = []
            graph.subjects.each do |subject|
              next if subject.anonymous? # skip blank nodes
              values = graph_mapper_service.map_values(graph: graph, predicate_map: predicate_map, subject_uri: subject) do |value_map|
                map_context(graph, sort_key, context_map, value_map, subject)
              end
              search_matches << values if result_subject? values, sort_key
            end
            search_matches = deep_sort_service.new(search_matches, sort_key, preferred_language).sort
            search_matches
          end

          private

            # The graph mapper creates the basic value_map for all subject URIs, but we only want the ones that represent search results.
            def result_subject?(value_map, sort_key)
              return true unless sort_key.present?        # if sort_key is not defined, then all subjects are considered matches
              return false unless value_map.key? sort_key # otherwise, sort_key must be in the basic value_map
              value_map[sort_key].present?                # AND have a value for this to be a search result
            end

            def map_context(graph, sort_key, context_map, value_map, subject)
              return value_map if context_map.blank?
              return value_map unless result_subject? value_map, sort_key
              context = {}
              context = context_mapper_service.map_context(graph: graph, context_map: context_map, subject_uri: subject) if context_map.present?
              value_map[:context] = context
              value_map
            end
        end
      end
    end
  end
end