class Fastly::Invoice

def self.get_path(*args)
  opts = args.size>0 ? args[0] : {}
  url  = "/billing"
  if opts.has_key?(:service_id)
    url += "/service/#{opts[:service_id]}"
  end
  if opts.has_key?(:year) && opts.has_key?(:month)
    url += "/year/#{opts[:year]}/month/#{opts[:month]}"
  end
  url
end