module Rack
  class Subdomain
    def initialize(app, domain, map_to = nil)
      @domain = domain
      @app = app
      @map_to = map_to
    end

    def call(env)
      @env = env
      subdomain = fetch_subdomain
      set_params(subdomain)

      @app.call(env)
    end

    def fetch_subdomain
      subdomain = @env['SERVER_NAME'].sub(/\.?#{@domain}$/,'')

      ['', 'www'].include?(subdomain) ? nil : subdomain
    end

    def set_params(subdomain)
      request = Rack::Request.new(@env)
      if subdomain
        request[:subdomain] = subdomain
        map_to(subdomain)
      end
    end

    def map_to(subdomain)
      if @map_to
        @map_to.gsub!(":subdomain", subdomain)
        path_info = @env["PATH_INFO"]
        @env["PATH_INFO"] = "#{@map_to}#{path_info}"
      end
    end
  end
end