module RackHttpPreload

# File lib/rack_http_preload.rb, line 5
def http_preload path = nil, crossorigin: false, push: false, as: nil, type: nil
  as, type = guess_http_preload_opts(path) if (as.nil? && type.nil?)

  header = ["<#{path}>", "rel=preload"]
  header << "as=#{as}" if as
  header << "crossorigin" if crossorigin
  header << "nopush" if push
  header << "type='#{type}'" if type

  add_to_link_header header.join("; ")
end

# File lib/rack_http_preload.rb, line 19
def add_to_link_header link
  links = (response.headers['Link'] || "").split(',').map(&:strip)
  links << link
  response.headers["Link"] = links.join(', ') unless links.empty?
end

# File lib/rack_http_preload.rb, line 25
def guess_http_preload_opts path
  return nil unless defined? MIME::Types

  resource = URI(path).path.split('/').last
  mimetypes = MIME::Types.type_for(resource).map(&:content_type).join(" ")

  as = case mimetypes
  when /javascript/
    :script
  when /css/
    :style
  when /image/
    :image
  when /font/
    :font
  when /audio/
    :audio
  when /video/
    :video
  end

  type = if %i[font audio video].include?(as)
    MIME::Types.type_for(resource).first.content_type
  end

  [as, type]
end