module GeoConcerns
  module Extractors
    class FgdcMetadataExtractor
      attr_reader :doc
      def initialize(doc)
        @doc = doc
      end

      def to_hash
        metadata_required.merge(metadata_optional)
      end

      def metadata_required
        {
          coverage: coverage,
          creator: creators,
          description: [doc.at_xpath('//idinfo/descript/abstract').text],
          title: [doc.at_xpath('//idinfo/citation/citeinfo/title').text]
        }.compact
      end

      def metadata_optional
        {
          issued: issued,
          publisher: publishers,
          spatial: placenames,
          subject: keywords,
          temporal: timeperiods
        }.compact
      end

      def coverage
        doc.at_xpath('//idinfo/spdom/bounding').tap do |node|
          return GeoConcerns::Coverage.new(
            coverage_coordinate(node, 'north'),
            coverage_coordinate(node, 'east'),
            coverage_coordinate(node, 'south'),
            coverage_coordinate(node, 'west')
          ).to_s
        end
        nil
      end

      def coverage_coordinate(node, direction)
        node.at_xpath("#{direction}bc").text.to_f
      end

      def issued
        doc.at_xpath('//idinfo/citation/citeinfo/pubdate').tap do |node|
          return node.text[0..3].to_i unless node.nil? # extract year only
        end
        nil
      end

      def timeperiods
        ::GeoConcerns::TimePeriod.new(
          extract_multivalued('//idinfo/keywords/temporal/tempkey'), doc
        ).value
      end

      def publishers
        extract_multivalued('//idinfo/citation/citeinfo/pubinfo/publish')
      end

      def creators
        extract_multivalued('//idinfo/citation/citeinfo/origin')
      end

      def placenames
        extract_multivalued('//idinfo/keywords/place/placekey')
      end

      def keywords
        keywords = extract_multivalued('//idinfo/keywords/theme/themekey')
        keywords.map! { |k| TOPIC_CATEGORIES[k.to_sym].present? ? TOPIC_CATEGORIES[k.to_sym] : k }
        keywords.uniq!
        keywords.present? ? keywords : nil
      end

      # ISO 19115 Topic Category
      TOPIC_CATEGORIES = {
        farming: 'Farming',
        biota: 'Biology and Ecology',
        climatologyMeteorologyAtmosphere: 'Climatology, Meteorology and Atmosphere',
        boundaries: 'Boundaries',
        elevation: 'Elevation',
        environment: 'Environment',
        geoscientificinformation: 'Geoscientific Information',
        health: 'Health',
        imageryBaseMapsEarthCover: 'Imagery and Base Maps',
        intelligenceMilitary: 'Military',
        inlandWaters: 'Inland Waters',
        location: 'Location',
        oceans: 'Oceans',
        planningCadastre: 'Planning and Cadastral',
        structure: 'Structures',
        transportation: 'Transportation',
        utilitiesCommunication: 'Utilities and Communication',
        society: 'Society'
      }.freeze

      private

        def extract_multivalued(xpath)
          values = []
          doc.xpath(xpath).each do |node|
            values << node.text.strip
          end
          values.uniq!
          values.present? ? values : nil
        end
    end
  end
end