module NSWTopo

def add(archive, *layers, after: nil, before: nil, replace: nil, overwrite: false, strict: false, **options)
  create_options = {
    after: Layer.sanitise(after),
    before: Layer.sanitise(before),
    replace: Layer.sanitise(replace),
    overwrite: overwrite,
    strict: strict
  }
  map = Map.load archive
  Enumerator.new do |yielder|
    while layers.any?
      layer, basedir = layers.shift
      path = Pathname(layer).expand_path(*basedir)
      case layer
      when /^controls\.(gpx|kml)$/i
        yielder << [path.basename(path.extname).to_s, "type" => "Control", "path" => path]
      when /\.(gpx|kml)$/i
        yielder << [path.basename(path.extname).to_s, "type" => "Overlay", "path" => path]
      when /\.(tiff?|png|jpg)$/i
        yielder << [path.basename(path.extname).to_s, "type" => "Import", "path" => path]
      when "contours"
        yielder << [layer, "type" => "Contour"]
      when "spot-heights"
        yielder << [layer, "type" => "Spot"]
      when "relief"
        yielder << [layer, "type" => "Relief"]
      when "grid"
        yielder << [layer, "type" => "Grid"]
      when "declination"
        yielder << [layer, "type" => "Declination"]
      when "controls"
        yielder << [layer, "type" => "Control"]
      when /\.yml$/i
        basedir ||= path.parent
        raise "couldn't find '#{layer}'" unless path.file?
        case contents = YAML.load(path.read)
        when Array
          contents.reverse.map do |item|
            Pathname(item.to_s)
          end.each do |relative_path|
            raise "#{relative_path} is not a relative path" unless relative_path.relative?
            layers.prepend [Pathname(relative_path).expand_path(path.parent).relative_path_from(basedir).to_s, basedir]
          end
        when Hash
          name = path.sub_ext("").relative_path_from(basedir).descend.map(&:basename).join(?.)
          yielder << [name, contents.merge("source" => path)]
        else
          raise "couldn't parse #{path}"
        end
      else
        path = Pathname("#{layer}.yml")
        raise "#{layer} is not a relative path" unless path.relative?
        basedir ||= layer_dirs.find do |root|
          path.expand_path(root).file?
        end
        layers.prepend [path.to_s, basedir]
      end
    end
  rescue YAML::Exception
    raise "couldn't parse #{path}"
  end.map do |name, params|
    params.merge! options.transform_keys(&:to_s)
    params.merge! Config[name] if Config[name]
    Layer.new(name, map, params)
  end.tap do |layers|
    raise OptionParser::MissingArgument, "no layers specified" unless layers.any?
    unless layers.one?
      raise OptionParser::InvalidArgument, "can't specify opacity when adding multiple layers" if options[:opacity]
      raise OptionParser::InvalidArgument, "can't specify data path when adding multiple layers" if options[:path]
    end
    map.add *layers, **create_options
  end
end