module Krikri
  ##
  # Adds ability to generate a DPLA MAPv3.1 compliant JSON-LD
  # representation to `DPLA::MAP::Aggregation`.
  module MapCrosswalk
    ##
    # @return [Hash] a DPLA MAP 3.1 (APIv2) object
    def to_3_1_json
      CrosswalkHashBuilder.build(self)
    end

    ##
    # Generates a MAPv3.1 (APIv2) hash for the given parent Aggregation
    #
    # @example
    #   builder = CrosswalkHashBuilder.new(agg)
    #   builder.build # => {...}
    #
    # @example
    #   CrosswalkHashBuilder.build(agg) # => {...}
    #
    class CrosswalkHashBuilder
      attr_accessor :hash

      ##
      # @param parent [DPLA::MAP::Aggregation]
      def initialize(parent)
        @parent = parent
        @hash = {}
      end

      class << self
        def build(parent)
          new(parent).build
        end
      end

      def build
        @hash = {}
        build_aggregation
      end

      private

      ##
      # @todo: FIXME! The legacy system increments `ingestionSequence` for each
      #   subsequent harvest. Figure out how to do that, or what we want to do
      #   instead.
      def build_aggregation
        raise 'Tried to index a blank node!' if @parent.node?
        hash.merge!({ :ingestType => 'item',
                     :ingestionSequence => 999999,
                     :ingestDate => Date.today.as_json,
                     :@context => "http://dp.la/api/items/context",
                     :aggregatedCHO => '#sourceResource',
                     :@id => make_id,
                     :id => local_name
                   })

        set_value(hash, :dataProvider, @parent.dataProvider, true) do |d|
          get_label(d)
        end

        set_value(hash, :originalRecord, @parent.originalRecord, true) do |o|
          o.respond_to?(:rdf_subject) ? o.rdf_subject.to_s : nil
        end

        set_value(hash, :intermediateProvider,
                  @parent.intermediateProvider,
                  true) do |ip|
          ip.label.any? ? ip.label : ip.providedLabel
        end

        hash[:sourceResource] = build_source_resource

        set_value(hash, :provider, @parent.provider, true) do |provider|
          build_provider(provider)
        end

        set_value(hash, :hasView, @parent.hasView, true) do |view|
          view.respond_to?(:rdf_subject) ? view.rdf_subject.to_s : nil
        end

        set_value(hash, :isShownAt, @parent.isShownAt, true) do |view|
          view.respond_to?(:rdf_subject) ? view.rdf_subject.to_s : nil
        end

        set_value(hash, :object, @parent.preview, true) do |view|
          view.respond_to?(:rdf_subject) ? view.rdf_subject.to_s : nil
        end

        # This doesn't work, because we have no good way of implementing
        #`#get_provider_id`.
        #
        # p = @parent.provider.first || DPLA::MAP::Agent.new
        # p_id = p.node? ? p.rdf_subject.to_s.split('/').last : p.rdf_label
        # hash[:_id] = "#{p_id}-#{get_provider_id}"
        #
        # instead... do:
        hash[:_id] = hash[:id]

        hash
      end

      def build_source_resource
        return nil if @parent.sourceResource.empty?
        parent_sr = @parent.sourceResource.first
        sr = { :@id => "#{make_id}#sourceResource" }

        set_value(sr, :contributor, parent_sr.contributor) do |contrib|
          get_label(contrib)
        end

        set_value(sr, :creator, parent_sr.creator) do |creator|
          get_label(creator)
        end

        set_value(sr, :description, parent_sr.description, true)
        set_value(sr, :format, parent_sr.dcformat)
        set_value(sr, :identifier, parent_sr.identifier)

        set_value(sr, :language, parent_sr.language) do |lang|
          get_label(lang)
        end

        set_value(sr, :publisher, parent_sr.publisher) do |pub|
          get_label(pub)
        end
        set_value(sr, :relation, parent_sr.relation)

        set_value(sr, :genre, parent_sr.genre) do |genre|
          get_label(genre)
        end

        set_value(sr, :relation, parent_sr.relation)
        set_value(sr, :rights, parent_sr.rights, true)
        set_value(sr, :temporal, parent_sr.temporal)
        set_value(sr, :title, parent_sr.title)

        set_value(sr, :collection, parent_sr.collection) do |coll|
          build_collection(coll)
        end

        set_value(sr, :type, parent_sr.dctype, true) do |type|
          build_dc_type(type)
        end

        set_value(sr, :date, parent_sr.date) do |date|
          build_time_span(date)
        end

        set_value(sr, :spatial, parent_sr.spatial) do |place|
          build_place(place)
        end

        set_value(sr, :subject, parent_sr.subject) do |subj|
          build_subject(subj)
        end

        sr
      end

      def build_collection(source)
        return unless source.is_a? DPLA::MAP::Collection
        coll = {}
        set_value(coll, :title, source.title)
        coll[:@id] = source.rdf_subject.to_s
        coll[:id] = source.rdf_subject.to_s.split('/').last

        coll.any? ? coll : nil
      end

      def build_time_span(source)
        return unless source.is_a? DPLA::MAP::TimeSpan
        date = {}
        date[:displayDate]
        set_value(date, :begin, source.begin, true, &:as_json)
        set_value(date, :end, source.end, true, &:as_json)

        date.any? ? date : nil
      end

      def build_provider(source)
        return unless source.is_a? DPLA::MAP::Agent
        provider = {}
        provider[:name] = source.label.first if source.label.any?
        provider[:name] ||= source.providedLabel.first if
          source.providedLabel.any?
        provider[:@id] = source.rdf_subject.to_s
        provider.any? ? provider : nil
      end

      def build_dc_type(source)
        return unless source.is_a? DPLA::MAP::Controlled::DCMIType
        return if source.node?
        vocab_sym = source.rdf_subject.pname.split(':').last.to_sym
        RDF::DCMITYPE[vocab_sym].label.downcase
      end

      def build_place(source)
        return unless source.is_a? DPLA::MAP::Place
        place = {}
        place[:name] = source.label.first if source.label.any?
        place[:name] ||= source.providedLabel.first if source.providedLabel.any?
        place[:coordinates] = "#{source.lat}, #{source.long}" if
          source.lat.any? && source.long.any?
        place.any? ? place : nil
      end

      def build_subject(source)
        return unless source.is_a? DPLA::MAP::Concept
        subject = {}
        subject[:name] = source.prefLabel.first if
          source.prefLabel.any?
        subject[:name] = source.providedLabel.first if
          source.providedLabel.any?

        subject.any? ? subject : nil
      end

      def set_value(target_hash, key, value, first = false, &block)
        value = Array(value).map(&block) if block_given?
        return if Array(value).empty?
        value = Array(value).flatten.compact
        return if value.empty?
        target_hash[key] = first ? value.first : value
      end

      def local_name
        @parent.rdf_subject.to_s.split('/').last
      end

      def get_label(resource)
        return resource if resource.is_a? String
        return resource.prefLabel if resource.respond_to?(:prefLabel) &&
                                 resource.prefLabel.any?
        return resource.label if resource.respond_to?(:label) &&
                                 resource.label.any?
        return resource.providedLabel if resource.respond_to?(:providedLabel) &&
                                 resource.providedLabel.any?
        return resource.rdf_label if resource.respond_to?(:rdf_label) &&
                                 resource.rdf_label.any?
        return nil
      end

      def make_id(uri = nil)
        uri ||= "http://dp.la/api/items/#{local_name}"
        uri.to_s
      end
    end
  end
end