nofxx/georuby

require 'rexml/parsers/pullparser'
module GeoRuby
  class KmlParser
    ELEMENT_MAP = {
      # "Point" => SimpleFeatures::Point, # we don't need to map points.  they are done automatically by the coordinate parsing
      'LineString' => SimpleFeatures::LineString,
      'LinearRing' => SimpleFeatures::LinearRing,
      'Polygon' => SimpleFeatures::Polygon,
      'MultiGeometry' => SimpleFeatures::GeometryCollection
    }

    def initialize(factory)
      @factory = factory
      @buffer = ''
      @with_z = false
    end

    # argument should be a valid kml geometry fragment ie. <Point> .... </Point>
    # returns the GeoRuby geometry object back
    def parse(kml)
      @factory.reset
      @with_z = false
      @parser = REXML::Parsers::PullParser.new(kml)
      while @parser.has_next?
        e = @parser.pull
        if e.start_element?
          if (type = ELEMENT_MAP[e[0]])
            @factory.begin_geometry(type)
          else
            @buffer = '' if (e[0] == 'coordinates') # clear the buffer
            accumulate_start(e)
          end
        elsif e.end_element?
          if ELEMENT_MAP[e[0]]
            @factory.end_geometry(@with_z)
            @buffer = '' # clear the buffer
          else
            accumulate_end(e)
            if (e[0] == 'coordinates')
              parse_coordinates(@buffer)
              @buffer = '' # clear the buffer
            end
          end
        elsif e.text?
          accumulate_text(e)
        elsif e.cdata?
          accumulate_cdata(e)
        end
      end
      @factory.geometry.dup
    end

    private

    def accumulate_text(e)
      @buffer << e[0]
    end

    def accumulate_cdata(e)
      @buffer << "<![CDATA[#{e[0]}]]>"
    end

    def accumulate_start(e)
      @buffer << "<#{e[0]}"
      if (e[1].class == Hash)
        e[1].each_pair { |k, v| @buffer << " #{k}='#{v}'" }
      end
      @buffer << '>'
    end

    def accumulate_end(e)
      @buffer << "</#{e[0]}>"
    end

    def parse_coordinates(buffer)
      if buffer =~ /<coordinates>(.+)<\/coordinates>/m
        Regexp.last_match[1].gsub(/\n/, ' ').strip.split(/\s+/).each do |coord|
          x, y, z = coord.split(',')
          if x.nil? || y.nil?
            fail StandardError, 'coordinates must have at least x and y elements'
          end
          @factory.begin_geometry(SimpleFeatures::Point)
          if z.nil?
            @factory.add_point_x_y(x, y)
          else
            @factory.add_point_x_y_z(x, y, z)
            @with_z = true unless @with_z # is the conditional even necessary
          end
          @factory.end_geometry(@with_z)
        end
      end
    rescue
      raise StandardError, 'error parsing coordinates: check your kml for errors'
    end
  end
end