it3s/meppit

module GeoJSON
  module_function

  # encode a geometry field to GeoJSON
  def encode(field, id=nil, properties={})
    return nil if field.nil?

    feature = build_feature field, id, properties
    encode_feature_collection([feature])
  end

  # convert a GeoJSON string or hash to a RGeo geometry object (or WKT string)
  def parse(geojson, opts={})
    return nil if geojson.nil? || geojson.try(:empty?)
    geojson_hash = geojson.is_a?(Hash) ? geojson : JSON.parse(geojson)
    decoded_geojson = RGeo::GeoJSON.decode(geojson_hash)
    decoded_geojson = decoded_geojson.first if decoded_geojson.is_a? Enumerable
    opts.fetch(:to, :geometry) == :wkt ? decoded_geojson.try(:geometry).try(:as_text) : decoded_geojson.try(:geometry)
  end

  def rgeo_factory
    RGeo::GeoJSON::EntityFactory.instance
  end

  def build_feature(field, id, properties)
    rgeo_factory.feature field, id, properties
  end

  # buid a geometry feature for a activerecord model
  def feature_from_model(model, field=:location)
    geometry = model.respond_to?("#{field}_geometry") ?
      model.send("#{field}_geometry") : # get geometry geojson from database
      model.send(field)                 # get geometry from rgeo object
    build_feature geometry, model.id, model.geojson_properties
  end

  def encode_feature_collection(features)
    features_with_geom, features_without_geom = features.partition &:geometry

    collection = RGeo::GeoJSON.encode rgeo_factory.feature_collection(features_with_geom)
    collection["features"].concat features_without_geom.map { |f| encode_feature(f) }
    collection
  end

  def encode_feature(feature)
    if feature.geometry
      if feature.geometry.kind_of? String
        # got the geometry as geojson directly from database
        {"type"=>"Feature", "geometry"=>JSON::parse(feature.geometry),"properties"=>feature.properties, "id"=>feature.properties["id"]}
      else
        RGeo::GeoJSON.encode feature
      end
    else
      {"type"=>"Feature", "geometry"=>nil,"properties"=>feature.properties, "id"=>feature.properties["id"]}
    end
  end
end